Lydéric France

@article{Boulanger+France2023,

title = {Cumulate formation and melt extraction from mush-dominated magma reservoirs: The melt flush process exemplified at mid-ocean ridges},

author = {M. Boulanger and L. France},

doi = {ht10.1093/petrology/egad005},

year  = {2023},

date = {2023-01-01},

journal = {Journal of Petrology},

volume = {64},

number = {2},

pages = {1--20},

abstract = {Volcanism is the surface expression of extensive magmatic systems, with their intrusive counterpart representing textasciitilde80% of the total magma budget. Our knowledge of igneous processes therefore largely relies on our understanding of deep plutonic processes. In continental or oceanic environments, most of the intrusive igneous rocks bear geochemical cumulate signatures (e.g. depletion in incompatible elements and enrichment in compatible ones) that are commonly explained by mineral-melt segregation during differentiation. Deformation-assisted compaction aided by melt buoyancy is usually referred to as the main process involved in melt extraction. However, buoyancy alone is not sufficient, and a number of cumulative rocks are lacking any compaction evidence, opening the potential for the involvement of other processes. In addition, our view of magmatic systems has shifted in the last decades from large melt-rich bodies to crystal-rich magma reservoirs. This paradigm shift challenges some of the long-established first-order igneous concepts like the idea that melt differentiation at depth is mainly governed by (fractional) crystallization; alternatively, the presence of mush potentially favors additional processes such as melt-mush reactions. We propose a novel igneous process for the formation of igneous cumulates, consistent with the mushy nature of oceanic igneous reservoirs, their continuous/cyclic replenishment by primitive melts, and the widespread occurrence of reactive porous flow (RPF) during magma differentiation identified in a growing number of magmatic systems. The melt flush process relies on melt-mush reactions between the primitive recharge melt(s) and crystal mush. Replacement of the more evolved interstitial melt by the primitive recharge melt leading to reactions (dissolution+crystallization) and concomitant extraction of the more evolved melt from the cumulate by buoyancy participate in the acquisition of the final cumulate signature. This process relying on oceanic igneous systems considers for the first time melt inputs and not only melt extraction and matches the petrographic (e.g. mineral dissolution evidence) and geochemical constraints (trace element signatures) brought by natural oceanic samples. We tested various melt-mush reactions likely involved in the early stages of the melt flush process during RPF to investigate their thermodynamic feasibility with the Magma Chamber Simulator. First-order results show that one-step equilibration of primitive melts with primitive to moderately differentiated mush crystals triggers mineral assimilation. Together with the constraints established from the natural rock record, it strengthens the idea that RPF is a potential key process for magma differentiation in magma reservoirs at different evolution stages. The proposed melt flush process eventually adds to other processes involved in cumulate formation like magma compaction or crystal settling and is likely to apply to any other magmatic system from various settings sharing similar reservoir characteristics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Neukampf_etal2022,

title = {Degassing from magma reservoir to eruption in silicic systems : The Li elemental and isotopic record from rhyolitic melt inclusions and host quartz in a Yellowstone rhyolite},

author = {J. Neukampf and O. Laurent and P. Tollan and A. S. Bouvier and T. Magna and P. Ulmer and L. France and B. S. Ellis and O. Bachmann},

doi = {10.1016/j.gca.2022.03.037},

year  = {2022},

date = {2022-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {326},

pages = {56--76},

abstract = {Lithium and hydrogen are volatile elements which diffuse rapidly in crystals and melt, making them powerful geochemical tools to reconstruct geological processes that take place on short time scales, such as syn- and post-eruptive degassing. Although the dynamics of hydrogen are fairly well understood to better constrain such processes, the assessment of Li behaviour within the magma reservoir relevant for ascent-related degassing still lacks detailed evaluation. Here, the first in situ Li concentrations and isotopic compositions (using SIMS analysis) of rhyolitic quartz-hosted, naturally glassy and crystallised melt inclusions (MIs) and groundmass glass (Mesa Falls Tuff, Yellowstone) are used to reconstruct Li elemental and isotopic evolution in the magma reservoir. Lithium concentrations in quartz-hosted glassy MIs (10--61 ppm) from a fallout deposit overlap with their groundmass glass (32--46 ppm) and their host quartz (8--15 ppm). Crystallised MIs from a later erupted flow pumice clast sample have higher Li concentrations (8--190 ppm) compared to the groundmass glass (32--51 ppm) and their host quartz (15--24 ppm). Lithium content in quartz from the early erupted sample is relatively homogenous, whereas it is up to a factor of two higher and heterogeneous in the later erupted sample, with a simultaneous increase in Li versus a decrease in H towards crystal rims. The d7Li difference (expressed as D7LiMI--glass) between MIs (-8.0texttenthousand to + 12.3texttenthousand) and groundmass glass (+9.0texttenthousand to + 20.5texttenthousand) of two pyroclastic deposits reaches up to 29texttenthousand. Glassy MIs are internally heterogeneous in d7Li and Li abundance. The cores of the glassy MIs record the d7Li of the least modified melt during entrapment and the data distribution can be modelled by equilibrium fractionation between the melt and vapour phase during early opensystem degassing in the magma reservoir. Late degassing during eruption triggers Li--H diffusional exchange between quartz and melt, as the degassing of H2O and the accompanying pressure change trigger H diffusion out of the host quartz and the MIs, which is charge balanced by inward Li diffusion. This results in the modification of Li contents in quartz and d7Li values in the rims of the glassy MIs. Crystallised MIs reflect the loss of H2O from the MIs and the resulting enrichment of Li during the crystallisation. Additionally, the variations of d7Li in the groundmass glass can be explained through modelling by kinetic fractionation between the melt and vapour during late stage open-system degassing linked with magma ascent.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Pieterek_etal2022,

title = {Sulfide enrichment along igneous layer boundaries in the lower oceanic crust : IODP Hole U1473A, Atlantis Bank, Southwest Indian Ridge},

author = {B. Pieterek and J. Ciazela and M. Boulanger and M. Lazarov and A. V. Wegorzewski and M. Panczyk and H. Strauss and H. J. B. Dick and A. Muszynski and J. Koepke and T. Kuhn and Z. Czupyt and L. France},

doi = {10.1016/j.gca.2022.01.004},

year  = {2022},

date = {2022-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {320},

pages = {179--206},

abstract = {Reactive porous or focused melt flows are common in crystal mushes of mid-ocean ridge magma reservoirs. Although they exert significant control on mid-ocean ridge magmatic differentiation, their role in metal transport between the mantle and the ocean floor remains poorly constrained. Here we aim to improve such knowledge for oceanic crust formed at slow-spreading centers (approximately half of present-day oceanic crust), by focusing on specific igneous features where sulfides are concentrated. International Ocean Discovery Program (IODP) Expedition 360 drilled Hole U1473A 789 m into the lower crust of the Atlantis Bank oceanic core complex, located at the Southwest Indian Ridge. Coarse-grained (5--30 mm) olivine gabbro prevailed throughout the hole, ranging locally from fine- (\<1 mm), to very coarse-grained (\>30 mm). We studied three distinct intervals of igneous grain size layering at 109.5--110.8, 158.0--158.3, and 593.0--594.4 meters below seafloor to understand the distribution of sulfides. We found that the layer boundaries between the fine- and coarse-grained gabbro were enriched in sulfides and chalcophile elements. On average, sulfide grains throughout the layering were composed of pyrrhotite (81 vol. % ; Fe1-xS), chalcopyrite (16 vol.% ; CuFeS2), and pentlandite (3 vol.% ; [Ni,Fe,Co]9S8), which reflect paragenesis of magmatic origin. The sulfides were most commonly associated with Fe-Ti oxides (titanomagnetites and ilmenites), amphiboles, and apatites located at the interstitial positions between clinopyroxene, plagioclase, and olivine. Pentlandite exsolution textures in pyrrhotite indicate that the sulfides formed from high-temperature sulfide liquid separated from mafic magma that exsolved upon cooling. The relatively homogenous phase proportion within sulfides along with their chemical and isotopic compositions throughout the studied intervals further support the magmatic origin of sulfide enrichment at the layer boundaries. The studied magmatic layers were likely formed as a result of intrusion of more primitive magma (fine-grained gabbro) into the former crystal mush (coarse-grained gabbro). Sulfides from the coarse-grained gabbros are Ir-Platinum Group Element-rich (PGE ;i.e., Ir, Os, Ru) but those from the fine-grained gabbros are Pd-PGE-rich (i.e., Pd, Pt, Rh). Notably, the sulfides from the layer boundaries are also enriched in Pd-PGEs, and therefore elevated sulfide contents at the boundaries were likely related to the new intruding melt. Because S concentration at sulfide saturation level is dependent on the Fe content of the melt, sulfide crystallization may have been caused by FeO loss, both via crystallization of late-precipitating oxides at the boundaries, and by exchange of Fe and Mg between melt and Fe-bearing silicates (olivine and clinopyroxene). The increased precipitation of sulfide grains at the layer boundaries might be widespread in the lower oceanic crust, as also observed in the Semail ophiolite and along the Mid-Atlantic Ridge. Therefore, this process might affect the metal budget of the global lower oceanic crust. We estimate that up to \"{E}œ20% of the Cu, \"{E}œ8% of the S, and \"{E}œ84% of the Pb of the oceanic crust inventory is accumulated at the layer boundaries only from the interaction between crystal mush and new magma.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lang_etal2022,

title = {Partitioning of Ti, Al, P, and Cr between olivine and a tholeiitic basaltic melt: Insights on olivine zoning patterns and cation substitution reactions under variable cooling rate conditions},

author = {S. Lang and S. Mollo and L. France and V. Misiti and M. Nazzari},

doi = {10.1016/j.chemgeo.2022.120870},

year  = {2022},

date = {2022-01-01},

journal = {Chemical Geology},

volume = {601},

pages = {120870},

abstract = {The mechanism governing the kinetic growth of olivine in dynamic volcanic settings has been the subject of considerable attention in recent years. Under variable cooling rate (CR) and undercooling (−$Delta$T) regimes, the textual maturation of olivine proceeds from skeletal/dendritic crystals to polyhedral morphologies by infilling of the crystal framework. Owing to the establishment of a diffusion-controlled growth regime, a sharp diffusive boundary layer develops in the melt next to the advancing olivine surface. In this context, we have quantified the apparent partitioning of Ti, Al, P, and Cr between olivine and a Hawaiian tholeiitic basaltic melt at P = 1 at},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Pin_etal2022,

title = {Thermodynamic modeling of melt addition to peridotite: Implications for the refertilization of the non-cratonic continental mantle lithosphere},

author = {J. Pin and L. France and S. Lambart and L. Reisberg},

doi = {10.1016/j.chemgeo.2022.121050},

year  = {2022},

date = {2022-01-01},

journal = {Chemical Geology},

volume = {609},

pages = {121050},

abstract = {In a classic model of evolution of the non-cratonic continental mantle lithosphere, harzburgites represent the refractory (\<5% clinopyroxene) residues of high degrees of partial melting of fertile mantle, while lherzolites (\>5% clinopyroxene) represent residues of lesser degrees of partial melting. However, partial melting is not the only process that could explain the peridotite compositional variability that ranges from fertile (\>2 wt% Al2O3, \<45 wt% MgO) to refractory (\<2 wt% Al2O3, \>45 wt% MgO). In the refertilization process, harzburgite is a refractory protolith (potentially previously formed by partial melting of a fertile mantle) that undergoes reactive percolation of silicate melts derived from the underlying asthenosphere, resulting in the crystallization of a new generation of minerals (mostly clinopyroxene). A simple but critical first step towards understanding therefertilization process is to examine how modal and major element compositions evolve as melts are added to peridotites. Here we use a thermodynamically-constrained two-component mixing model to independently evaluate the roles of five different parameters: pressure, temperature, redox conditions, and compositions of the initial peridotite and the added basaltic melt (hereafter referred to P-T-fO2-X$pi$-Xmelt), during melt addition. We compare the results with observed suites of peridotites. The main observations are as follows: (1) the produced model is consistent with the global peridotite database, and (2) T, fO2 and small variations of pressure have almost no impact on the evolution of the system. In contrast, the mineralogy of the percolated harzburgite has a substantial effect on the variation of the modal proportions. The parameter with the most significant impact is Xmelt, which is directly linked to the geodynamic context and melting conditions. This parameter directly controls the refertilization reaction and so, the phase proportions and the bulk-rock composition. Elements that partition preferentially in the melt phase (e.g., Na) display depletions in natural assemblages that are stronger than those predicted from the simple mixing model, consistent with the fact that the natural process occurs in an open system, and that reactive percolation likely results in incompatible element enrichment in the associated melt. Our results corroborate the suggestion that most of the spectrum of compositional variability observed in lithospheric mantle peridotites can be explained by the impregnation of primitive silicate melt in refractory harzburgites.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ferrando_etal2022,

title = {Brown amphibole as tracer of tectono-magmatic evolution of the Atlantis Bank Oceanic Core Complex (IODP Hole U1473A)},

author = {C. Ferrando and R. Tribuzio and C. J. Lissenberg and L. France and C. J. MacLeod and V. Basch and J. Villeneuve and E. Deloule and A. Sanfilippo},

doi = {10.1093/petrology/egac089},

year  = {2022},

date = {2022-01-01},

journal = {Journal of Petrology},

volume = {63},

pages = {1--27},

abstract = {Brown amphibole is a minor but common mineral component in lower oceanic crust. It is generally interpreted as products of migrating SiO2 and H2O-rich fluids or melts, which can be either residual melts from advanced magmatic differentiation of Mid-Ocean Ridge Basalt (MORB), or hydrothermal fluids including a seawater component. Within the lower oceanic crust exhumed at the Atlantis Bank Oceanic Core Complex, along the ultraslow Southwest Indian Ridge, brown amphibole is ubiquitous in all lithologies from olivine- to oxide-gabbros and diorites, including both undeformed and plastically deformed varieties. We here show the results of a systematic petrological study conceived to unravel the nature of the H2O-rich component recorded in brown amphiboles and document: (i) the evolution of migrating melts during the magmatic stage and (ii) different extents of melt-bearing deformation events recorded throughout the entire crustal transect. The low Cl contents and the light over heavy rare earth elements (LREE/HREE) ratios and high Ti contents in brown amphiboles indicate they crystallized from melts with a magmatic hydrous component. Consistently, their $delta$18O values are in equilibrium with Mid-Ocean Ridge Basalt (MORB) composition, except for diorite amphiboles that possibly record the local assimilation of altered minerals. In undeformed olivine gabbros, interstitial pargasite crystallized at hypersolidus conditions (textasciitilde1000textdegreeC) from the melt residual after late stages of MORB differentiation. We speculate that before the olivine gabbro crystal mush reached fully solid state, some aliquots of residual melts were extracted and accumulated within discrete intervals. There, ferrobasaltic melts differentiated through the early crystallization of Fe-Ti oxides and clinopyroxene as liquidus phases, ultimately forming the oxide gabbros. This process promoted rapid Si enrichment and depletion in Fe, Ti, V in the residual melt, later extracted to form the crosscutting diorite veins. The mylonitic olivine gabbros record high-temperature plastic deformation (textasciitilde900textdegreeCthinspacetextpmthinspace50textdegreeC) under hypersolidus conditions, involving melts residual from previous crystallization of the gabbroic rock. Further solid-state plastic deformation led to substantial grain size reduction and, consequently, to an increase in porosity. This created pathways for subsequent melt focusing, which likely represent late-stage differentiated melts migrating throughout the lower crustal section. This study shows that brown amphibole in the Atlantis Bank lower oceanic crust is the crystallization product of melts residual from advanced magmatic differentiation, which are also locally involved in the plastic deformation events during crustal accretion.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Dhar_etal2022,

title = {The lower oceanic crust at ultraslow-spreading Southwest Indian Ridge: The inside story},

author = {A. Dhar and B. Ghosh and D. Bandyopadhyay and T. Morishita and A. Tamura and L. France and Du K. Nguyen and M. Boulanger and M. Koley and S. Roy and S. Chattopadhaya},

doi = {10.1016/j.gr.2022.08.008},

year  = {2022},

date = {2022-01-01},

journal = {Gondwana Research},

volume = {111},

pages = {223--248},

abstract = {Owing to the lack of persistent magma chamber and the complex interplay between magmatism and tectonism at slow- to ultraslow-spreading ridges, the likeliness of fractional crystallization being the predominant process of evolution of crustal magmas is weak. Here, we report a detailed petro-geochemical investigation from the lower crustal gabbroic rocks recovered from Hole U1473A in Atlantis Bank oceanic core complex, Southwest Indian Ridge that may potentially provide new insights on the dynamic accretion process at ultraslow-spreading ridge. Sampling the entire lithological spectrum encompassing a single geochemical cycle in this study permit us to probe the underlying magmatic processes in ultraslowspreading lower crust. Grain-size variation is ubiquitously recorded in the gabbroic lithologies of Hole U1473A, where fine-grained intervals represent relatively evolved chemistry than the coarser domains. This suggests that, they were crystallized from a common genetic melt during different degrees of evolution. The forward geochemical modelling approach have not only affirmed the long-established theory of assimilation (of early mushes’ crystals)-fractional crystallization to be the key mechanism in lower crust formation, but also provided explanation for the restricted whole rock geochemical cluster observed throughout all the rock types. We demonstrate for the first time the relationship between the progressive modal mineralogical evolution with respect to the different assimilation/fractionation ratios (r). The observed trend has been successfully replicated for the experiments with high r values = 0.8--0.9, previously predicted from this region. Integrating all results, our study supports the model of lower crustal formation via reactive porous flow of the squeezed-out melt percolating throughout the cumulate pile and segregated into different horizons.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Azevedo-Vannson_etal2021,

title = {Mantle metasomatic influence on water contents in continental lithosphere : New constraints from garnet pyroxenite xenoliths (France \& Cameroon volcanic provinces)},

author = {S. Azevedo-Vannson and L. France and J. Ingrin},

doi = {10.1016/j.chemgeo.2021.120257},

year  = {2021},

date = {2021-01-01},

journal = {Chemical Geology},

volume = {575},

pages = {120257},

abstract = {Quantifying water contents in the lithospheric mantle is key to our understanding of global geodynamics, mantle composition, and related physical properties. Most mantle lithologies (peridotite) contain little water ( 50 ppm), but petrological heterogeneities such as pyroxenites are more hydrous ( 300 ppm) relative to the mantle rocks. Pyroxenites also melt at lower temperatures than peridotites and are thus important to magma genesis. Thus, quantifying pyroxenite water contents provides new information on the distribution of water in the mantle. Here, we present phase-specific FTIR measurements of the water contents in pyroxenite mantle xenoliths from two continental lithospheric domains that experienced intense metasomatism : the French Massif Central (FMC, France) and the Adamawa Volcanic Plateau (AVP, Cameroon). The AVP garnet pyroxenites are more hydrated ([H2O]Clinopyroxene = 386--685 ppm ; [H2O]Orthopyroxene = 124--155 ppm ; [H2O]Garnet \< 0.5 ppm) than FMC ones ([H2O]Clinopyroxene = 112--465 ppm ; [H2O]Orthopyroxene = 61--104 ppm ; [H2O]Garnet \< 0.5 ppm). These water concentrations are homogenous at the grain and correlate with equilibrated major element concentrations, indicating that they are representative of lithospheric water, although the FMC pyroxenites were dehydrated during metasomatism by a carbonatitic fluid (based on the correlation between LaN/SmN and Ti/Eu ratios) ; the water contents of AVP pyroxenites were likely not affected by metasomatism. FMC pyroxenites show peculiar FTIR spectra that may reflect the preferential dehydration of specific sites in the pyroxene structure. In both regions, metasomatism modified the light rare Earth element contents (e.g., Ce) of the pyroxenites, resulting in highly variable H2O/Ce ratios. Therefore, we conclude that the utility of the H2O/Ce ratio to identify the involvement of pyroxenites in magmas genesis is limited.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Boulanger_etal2021,

title = {Magma-mush interactions in the lower oceanic crust : Insights From Atlantis bank layered series (Southwest Indian Ridge)},

author = {M. Boulanger and L. France and C. Ferrando and B. Ildefonse and B. Ghosh and A. Sanfilippo and C. Z. Liu and T. Morishita and J. Koepke and O. Bruguier},

doi = {10.1029/2021JB022331},

year  = {2021},

date = {2021-01-01},

journal = {JGR Solid Earth},

volume = {126},

number = {9},

pages = {e2021JB022331},

abstract = {Magma migration and differentiation processes are key to understanding the development and evolution of oceanic magma reservoirs. To provide new quantitative geochemical constraints on these processes, we applied a high-resolution approach to study an interlayered section of the lower oceanic crust sampled at Atlantis Bank, on the (ultra)slow-spreading Southwest Indian Ridge. The section is characterized by sharp grain-size layering between fine- and coarse-grained olivine gabbros that is representative of other layered structures described at the Atlantis Bank oceanic core complex. The textures and fabrics of the layers and the nature of their contacts indicate formation by intrusion of a magma (i.e., crystal-bearing) into an almost solidified coarse-grained mush. Petrographic observations and in situ incompatible trace element signatures indicate that the fine- and coarse-grained layers record reactive porous migration of melts. Widespread reactive porous flow occurred prior to intrusion within the coarse-grained gabbro, producing mineral compositions enriched in incompatible elements. The intrusive fine-grained lithology records a late stage event of localized reactive melt percolation in cm-scale structures, which lead to strong light rare earth elements depletion relative to heavy rare earth elements. In addition, we highlight the occurrence of interactions at the contacts between layers and partial modification in compositions of the intruded lithology. This layered section likely represents a contact between two larger magma bodies emplaced within the lower crust during accretion, where the type of melt migration (intrusion or porous flow) and the modalities of melt percolation (widespread or localized) strongly govern the composition of the crustal lithologies.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ferrando_etal2021,

title = {Role of compaction in melt extraction and accumulation at a slow spreading center: Microstructures of olivine gabbros from the Atlantis Bank (IODP Hole U1473A, SWIR)},

author = {C. Ferrando and V. Basch and B. Ildefonse and J. Deans and A. Sanfilippo and F. Barou and L. France},

doi = {10.1016/j.tecto.2021.229001},

year  = {2021},

date = {2021-01-01},

journal = {Tectonophysics},

volume = {815},

pages = {229001},

abstract = {The exposure of gabbroic sequences at Oceanic Core Complexes (OCC) along ultraslow- to slow-spreading ridges permits the study of the processes forming the lower oceanic crust. On top of the Atlantis Bank OCC along the ultraslow-spreading Southwest Indian Ridge, IODP Expedition 360 drilled Hole U1473A, mainly composed of primitive olivine gabbros interspersed with more evolved Ti-Fe oxide-bearing gabbros and minor felsic veins. These rocks record a complex history of protracted magmatism during continuous uplift and deformation of the gabbroic sequence. Extensive crystal-plastic deformation is dominantly recorded in the shallower sections of the drillhole, whereas the deeper sections better preserve primary magmatic features. We focus on microstructures, including intra-crystalline deformation of rock-forming minerals, and plagioclase crystallographic preferred orientations of olivine gabbros lacking evidence for exhumation-related crystal plastic deformation, to gain insights on the relationship between compaction, melt migration and melt accumulation during the early magmatic history of this section of lower oceanic crust. Olivine gabbros are characterized by ubiquitous grain-size variations, from coarse- to fine-grained intervals. Minerals in coarse-grained intervals show intra-crystalline deformation, while fine-grained crystals lack internal strain. Bent coarse-grained plagioclase associated with weak magmatic foliation and lack of lineation suggest that the coarse-grained intervals were deformed under weak compaction. On the other hand, crystallographic preferred orientations of undeformed fine-grained plagioclase show weak lineations, likely indicative of non-coaxial strain. We thereby infer that the coarse-grained intervals underwent ongoing weak compaction from the stage of olivine + plagioclase textpm clinopyroxene crystal mush to the melt-poor stage, and that this process likely aided melt extraction and accumulation in discrete melt-rich zones where crystals orientated in the direction of magmatic flow. Crystallization of melts in the melt-rich zones ultimately formed the fine-grained intervals at different depths in Hole U1473A. This indicates that processes of compaction can lead to local chemical and grain-size heterogeneities in a lower crustal section, while had a minor role in the melt movement at larger scales (e.g., the whole crystal mush) within the oceanic crust.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ferrando_etal2021_2,

title = {Grain size variations record segregation of residual melts in slow-spreading oceanic crust (Atlantis Bank, 57textdegreeE Southwest Indian Ridge)},

author = {C. Ferrando and L. France and V. Basch and A. Sanfilippo and R. Tribuzio and M. Boulanger},

doi = {10.1029/2020JB020997},

year  = {2021},

date = {2021-01-01},

journal = {JGR Solid Earth},

volume = {106},

number = {4},

pages = {e2020JB020997},

abstract = {Beneath slow‐spreading ridges, melt bodies are generally considered to represent ephemeral magma reservoirs filled with crystal mushes. Formation of the oceanic crust requires at least partial extraction of melts from these crystal mushes. However, melts collection and extraction are processes yet to be fully constrained. We investigate olivine gabbros from the plutonic section recovered at the IODP Hole U1473A, in the Atlantis Bank Oceanic Core Complex (Southwest Indian Ridge), to unravel (i) the process of melt migration through lower crustal crystal mushes, and (ii) the collection and segregation of melts forming discrete microgabbro intervals. Throughout the Hole, fine‐ to coarse‐grained intervals are widespread in olivine gabbros. Along the contacts, coarse‐grained minerals display resorbed grain boundaries against the fine‐grained minerals, suggesting partial dissolution by the melt crystallizing the fine‐grained material. Coarse‐grained plagioclase and clinopyroxene are zoned, showing progressive chemical evolution from more primitive crystal cores to more evolved crystal rims. Fine‐grained minerals are unzoned and chemically similar to rims of coarse‐grained minerals, indicating a genetic relationship. We attribute significant enrichments in the most incompatible elements of plagioclase and clinopyroxene to a magma evolution process associated with reactive melt migration. As temperature decreased, melts residual from the reactive processes were segregated in magma pockets that ultimately crystallize the fine‐grained intervals (microgabbros). We document, for the first time, that these microgabbros are crystallization products of melts modified by reactive melt migration ; the melts were extracted from the crystal mush and accumulated into discrete melt‐rich zones. This process could have promoted partial extraction of those melts that in turn potentially contribute to Mid Ocean Ridge Basalts erupted at the seafloor.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lang_etal2021,

title = {Kinetic partitioning of major-minor cations between olivine and Hawaiian tholeiitic basalt under variable undercooling and cooling rate conditions},

author = {S. Lang and S. Mollo and L. France and V. Misiti and M. Nazzari},

doi = {10.1016/j.chemgeo.2021.120485},

year  = {2021},

date = {2021-01-01},

journal = {Chemical Geology},

volume = {584},

pages = {120485},

abstract = {In order to elucidate the kinetic partitioning of cations between olivine and basalt, we performed undercooling (−$Delta$T) and cooling rate (CR) experiments at atmospheric pressure and QFM-2 buffer. Starting from the superliquidus temperature of 1250 textdegreeC, a Hawaiian tholeiitic basalt was cooled at the rates of 4 (CR4), 20 (CR20), and 60 (CR60) textdegreeC/h to the final target temperatures of 1175 textdegreeC (−$Delta$T = 35 textdegreeC ; −$Delta$T35) and 1125 textdegreeC (−$Delta$T = 85 textdegreeC ; −$Delta$T85). Results show that polyhedral olivine morphologies are obtained at -$Delta$T35, whereas strong disequilibrium skeletal and/or dendritic textures form at -$Delta$T85. The amount of forsterite in olivine decreases from to 85% to 78% with increasing both -$Delta$T and CR. A diffusive boundary layer also develops in the melt next to the olivine surface and its composition becomes progressively enriched in Ca, owing to its incompatible behavior with the lattice site. Residual melts are progressively depleted in silica and enriched in alkali from CR4 to CR60, but silica-rich melts are observed with increasing -$Delta$T. In terms of Fe2+-Mg exchange, olivines obtained at -$Delta$T35 are always in equilibrium with the diffusive boundary layer, comprising both the interface melt next to the olivine surface and the far-field melt where all chemical gradients cease. At -$Delta$T85, however, the Fe2+-Mg exchange indicates two distinct equilibration stages between olivine core and far-field melt, and between olivine rim and interface melt. Partition coefficients (Kd) of Mg, Fe, Mn, Ca, and Cr calculated at the olivine-melt interface preferentially change as a function of -$Delta$T rather than CR. From -$Delta$T35 to -$Delta$T85, KdMg, KdFe, KdMn, and KdCr remarkably increase, whereas the opposite applies to KdCa. Through the application of equilibrium partitioning models, we found that Mg, Fe, Mn, and Ca are incorporated into the olivine lattice site at near-equilibrium proportions. This generally good agreement with modeling data demonstrates that diffusive mass transport of cations in our experiments occurred under the conditions of local equilibrium at the olivine surface. In contrast, marked deviations from the expected equilibrium are found for KCr in response to the major influence of crystal field stabilization energy on cation incorporation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rose-Koga_etal2021,

title = {Silicate melt inclusions in the new millennium: A review of recommended practices for preparation, analysis, and data presentation},

author = {E. F. Rose-Koga and A. S. Bouvier and G. A. Gaetani and P. J. Wallace and C. M. Allison and J. A. Andrys and A. Angeles de la Torre and A. Barth and R. J. Bodnar and A. J. J. Bracco Gartner and D. Butters and A. Castillejo and B. Chilson-Parks and B. R. Choudhary and N. Cluzel and M. Cole and E. Cottrel and A. Daly and L. V. Danyushevsky and C. L. DeVitre and M. J. Drignon and L. France and e},

doi = {10.1016/j.chemgeo.2021.120145},

year  = {2021},

date = {2021-01-01},

journal = {Chemical Geology},

volume = {570},

pages = {120145},

abstract = {Mineral-hosted melt inclusions have become an important source of information on magmatic processes. As the number of melt inclusion studies increases, so does the need to establish recommended practice guidelines for collecting and reporting melt inclusion data. These guidelines are intended to ensure certain quality criteria are met and to achieve consistency among published melt inclusion data in order to maximize their utility in the future. Indeed, with the improvement of analytical techniques, new processes affecting melt inclusions are identified. It is thus critical to be able to reprocess any previously published data, such that reporting the raw data is one of the first textquotelefttextquoteleftrecommended practicestextquoterighttextquoteright for authors and a publication-criteria that reviewers should be sensitive to. Our guidelines start with melt inclusion selection, which is a critical first step, and then continue onto melt inclusion preparation and analysis, covering the entire field of methods applicable to melt inclusions. Dedication: In March of 2000, a melt inclusion workshop was held at the Chateau de Sassenage in Grenoble and a companion issue of Chemical Geology entitled textquotelefttextquoteleftMelt Inclusions at the Millenniumtextquoterighttextquoteright was published. Erik Hauri was heavily involved with the meeting and contributed two landmark papers to the topical issue of Chemical Geology on the use of secondary ion mass spectrometry to analyze volatiles in melt inclusions. When the melt inclusion community re-convened at Woods Hole Oceanographic Institution (WHOI) in August of 2018, we were saddened that Erik was unable to join us due to his failing health. Less than a month later came the devastating news of his passing at only 52 years of age. In recognition of his incredible contributions to science in general and to the insitu analysis of melt inclusions in particular, the participants and organizers of the WHOI melt inclusion workshop dedicate this collegial paper to Erik Hauri, our colleague, mentor and friend. Thank you Erik.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{France_etal2021,

title = {Early carbonatite magmatism at Oldoinyo Lengai volcano (Tanzania) : carbonatite--silicate melt immiscibility in Lengai I melt inclusions},

author = {L. France and F. Brouillet and S. Lang},

doi = {10.5802/crgeos.99r/geoscience/},

year  = {2021},

date = {2021-01-01},

journal = {Comptes Rendus. G\'{e}oscience ?\u{I} Sciences de la Plan`ete},

volume = {353},

number = {S2},

pages = {273--288},

abstract = {Carbonatites are unusual C-rich alkaline magmas that have been reported throughout the geological record. Nevertheless, there is only one currently active carbonatite system on Earth : Oldoinyo Lengai stratovolcano in northern Tanzania (God’s mountain in Maasai culture). Presentday Lengai carbonatites are natrocarbonatites, peculiar Na-rich carbonatites that, under atmospheric conditions, alter and leach to compositions similar to the more common Ca-carbonatites within weeks, preventing any long-term geological record of such Na-rich magmas. It follows that the oldest report of natrocarbonatites at Oldoinyo Lengai dates to the 19th century. Here, by using samples from the Lengai I cone (`E11 ka), we show that immiscible silicate--carbonatite melts were already present at reservoir conditions at that time. Measurements of three-phase (carbonatite + silicate + gas) melt inclusions from Lengai I highlight that their chemical compositions were similar to those of immiscible melts recently present in the reservoir. Alkaline carbonatites in melt inclusions from both Lengai I and historical explosive eruptions are enriched in Ca relative to those historically effused at the surface and likely record higher equilibrium temperatures (\>1100 textdegreeC). We also report chemical maps that qualitatively document elemental partitioning between immiscible silicate--carbonatite melts.We show that at the melt inclusions’ entrapment conditions Si, Fe, K, Na, and Cl are compatible with the silicate phase when C, Ca, P, Sr, Ba, and F are compatible with the carbonate phase.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Baudouin_etal2020,

title = {Trace element partitioning between clinopyroxene and alkaline magmas: parametrization and role of M1 site on HREE enrichment in clinopyroxenes},

author = {C. Baudouin and L. France and M. Boulanger and C. Dalou and J. L. Devidal},

doi = {10.1007/s00410-020-01680-6},

year  = {2020},

date = {2020-01-01},

journal = {Contributions to Mineralogy and Petrology},

volume = {175},

pages = {42},

abstract = {Trace element partitioning between minerals and liquids provides crucial constraints on igneous processes. We quantified trace element concentrations in clinopyroxene (Cpx) phenocrysts and their phonolite melt inclusions from the 2007--08 erup-tion of Oldoinyo Lengai (Tanzania), and report Cpx-melt partition coefficients (D) and corresponding partitioning equations for rare earth elements (REE) and high field strength elements (HFSE) in alkaline magmas. Heavy REE (HREE: Er, Tm, Yb, Lu) are enriched relative to middle REE in alkaline Cpx and display a specific partitioning behavior that is characteristic of alkaline systems. HFSE (Ti, Zr, Hf) and HREE have similar D values (DHf = 0.25; DLu = 0.4) that are significantly higher than MREE (DSm = 0.06). High DHREE/DMREE are strongly correlated with the high values of DZr and DHf relative to the low DMREE values. In this study, REE partitioning between phonolite melt and Cpx is not consistent with standard models assum-ing incorporation of all REE in the Cpx M2 site, but rather highlights HREE substitution in both the M1 and M2 sites. Here we highlight the preferential incorporation of HREE in the VI-coordinated M1 site, whereas light REE and MREE remain mostly distributed in the VIII-coordinated M2 site. REE partitioning is strongly dependent on Cpx chemistry: the ideal ionic radius and HREE incorporation in the M1 site increase with increasing Fe3+ content and decrease with increasing Mg2+ and AlVI content. In our study, we focus on alkaline evolved magmas, and update existing models to obtain adequate DHREE for alkaline evolved melts. We provide equations to quantify REE and HFSE partitioning, and HREE enrichment in Cpx that are based on Cpx major element composition and temperature. We propose a new model based on the lattice strain approach that predicts HREE partitioning between Cpx and alkaline magmas. The knowledge of the melt composition or of the trace element contents is not required to obtain DREE from the new model. An improved parameterization of HFSE partitioning between Cpx and phonolite and trachy--phonolite melts is also provided herein. We discuss the potential implications of the new data on our understanding of REE deposits that are commonly associated with igneous alkaline complexes.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Boulanger_etal2020,

title = {Magma reservoir formation and evolution at a slow-spreading center (Atlantis Bank, Southwest Indian Ridge)},

author = {M. Boulanger and L. France and J. R. Deans and C. Ferrando and C. J. Lissenberg},

doi = {10.3389/feart.2020.554598},

year  = {2020},

date = {2020-01-01},

journal = {Frontiers in Earth Science},

abstract = {Several ODP-IODP expeditions drilled oceanic core complexes interpreted as exhumed portions of lower crust close to the ridge axis, and provide the community with invaluable sampling opportunity for further constraining magmatic processes involved in the formation of the slow-spreading lower oceanic crust. ODP Hole 735B presents the most primitive lithologies sampled at Atlantis Bank oceanic core complex (Southwest Indian Ridge) in a �`u250 m thick section that was previously interpreted as a single crustal intrusion. We combined detailed structural and petrographic constraints with whole rock and in situ mineral analyses of this section in order to precisely determine the processes of emplacement, crystallization, and melt migration within the lower crust. The lower half of the unit is comprised of alternating olivine gabbros and troctolites showing intrusive contacts, magmatic fabrics, and crystal-plastic fabrics. Such structures and primitive lithologies are lacking in the upper half, rather uniform, gabbroic sequence. Whole rock compositions highlight the cumulative character of both lower and upper units and a great compositional variability in the lower sequence, whereas the upper sequence is homogeneous and differentiates up-section. In situ analyses of mineral phases document magma emplacement processes and provide evidence for ubiquitous reactive porous flow (RPF) during differentiation. We show that the whole section, and related geochemical unit, constitutes a single magmatic reservoir, in which the lower unit is formed by stacked primitive sills formed by repeated recharge of primitive melts and melt-present deformation. Recharge led to partial assimilation of the crystallizing primitive cumulates, and hybridization with their interstitial melts. Hybrid melts were progressively collected in the overlying mushy part of the reservoir (upper unit), whereas the sillstextquoteright residual hybrid melts differentiated by RPF processes under a predominantly crystallization regime. Similarly, hybrid meltstextquoteright evolution in the upper unit was governed by upward RPF, and progressive differentiation and accumulation of evolved melts at the top of the reservoir. Our results provide the community with the first integrated model for magma reservoir formation in the lower slow-spreading oceanic crust that can potentially be applied to other magmatic lower crust sections.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Casola_etal2020,

title = {No evidence for carbon enrichment in the mantle source of carbonatites in eastern Africa},

author = {V. Casola and L. France and A. Galy and N. Bouden and J. Villeneuve},

doi = {10.1130/G47629.1},

year  = {2020},

date = {2020-01-01},

journal = {Geology},

volume = {48},

pages = {971--975},

abstract = {Carbonatites are unusual, carbon-rich magmas thought to form either by the melting of a carbon-rich mantle source or by low-degree partial melting of a carbon-poor (\<80 ppm C) mantle followed by protracted differentiation and/or immiscibility. Carbonate-bearing mantle xenoliths from Oldoinyo Lengai (East African Rift), the only active volcano erupting carbonatites, have provided key support for a C-rich mantle source. Here, we report unique microscale O and C isotopic analyses of those carbonates, which are present as interstitial grains in the silicate host lava, veins in the xenoliths, and pseudo-inclusions in olivine xenoliths. The $delta$18O values vary little, from 19texttenthousand to 29texttenthousand, whereas $delta$13C values are more variable, ranging from --23texttenthousand to +0.5texttenthousand. We show that such carbonate $delta$18O values result from the low-temperature precipitation of carbonate in equilibrium with meteoric water, rather than under mantle conditions. In this framework, the observed $delta$13C values can be reproduced by Rayleigh distillation driven by carbonate precipitation and associated degassing. Together with petrological evidence of a physical connection between the three types of carbonates, our isotopic data support the pedogenic formation of carbonates in the studied xenoliths by soil-water percolation and protracted crystallization along xenolith cracks. Our results refute a mechanism of C enrichment in the form of mantle carbonates in the mantle beneath the Natron Lake magmatic province and instead support carbonatite formation by low-degree partial melting of a C-poor mantle and subsequent protracted differentiation of alkaline magmas.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{France2020,

title = {Can destabilization rims of hydrous minerals be used to constrain magma ascent kinetics at lava dome volcanoes ?},

author = {L. France},

doi = {10.1007/s00445-020-01405-4},

year  = {2020},

date = {2020-01-01},

journal = {Bulletin of Volcanology},

volume = {82},

pages = {66},

abstract = {Time constraints on igneous processes related to eruption triggering, e.g., magma mixing or ascent in the conduit, are needed in any risk mitigation attempt. In this context, magma ascent rate and kinetics are key parameters as they may correspond to the response time available to civil protection during volcanic unrest. Several tools available to quantify such durations include diffusion chronometry, isotopic geochemistry, and hydrous mineral destabilization related to magma degassing during ascent through the conduit. Here I discuss the possible limitations of the widely used hydrous mineral destabilization chronometry applied to minerals within large lava bodies that cool relatively slowly (over days or weeks) such as thick lava flows and lava domes. Based on the type case of the Sarcoui dome (Cha^ine des Puys, France) and its associated phreatomagmatic outbreak deposits, I suggest that hydrous mineral destabilization rims may, in some cases, develop at the surface during dome emplacement. From this perspective, preeruptive timescales calculated based on disequilibrium kinetics will be greatly underestimated, leading to a serious issue in the reconstruction of the eruption dynamics and its possible applications to emergency management for future eruptions. More generally, hydrous mineral destabilization chronometry should be used with great caution. Nevertheless, it remains a choice tool to quantify magma ascent rates for eruptions during which magmas quench upon arrival at the surface (e.g., Plinian, Vulcanian, or phreatomagmatic eruptions), with pumiceous textures being a good indicator of quenching. In the case of lava dome emplacement, I suggest that the minerals embedded in pumiceous clasts emitted during explosive phases are more reliable candidates for chronometry studies than crystals within the dome itself as those clasts might represent the fresh magma that triggered the explosion.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kelemen_etal2020,

title = {Proceedings of the Oman Drilling Project},

author = {P. Kelemen and J. M. Matter and D. A. H. Teagle and J. A. Coggon and Oman Drilling Project Science Team and L. France and M. Boulanger and D. Jousselin and D. Klaessens and L. Reisberg},

doi = {10.14379/OmanDP.proc.2020},

year  = {2020},

date = {2020-01-01},

journal = {College Station, TX (International Ocean Discovery Program},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Baudouin+France2019,

title = {Trace element partitioning between wollastonite and alkaline silicate magmas},

author = {C. Baudouin and L. France},

doi = {10.1016/j.chemgeo.2019.06.001},

year  = {2019},

date = {2019-01-01},

journal = {Chemical Geology},

volume = {523},

pages = {88--94},

abstract = {he partitioning of trace elements between wollastonite and melt provides a choice tool for understanding differentiation processes and trace element fractionation in alkaline-rich and silica-undersaturated magmatic systems at crustal conditions, but very few data are currently available. Here we provide the first partition coefficients and associated lattice strain parameters between wollastonite and silicate magmas of Oldoinyo Lengai (Tanzania). Trace element partitioning of isovalent cations shows a parabolic dependence between the partition coefficients and ionic radii explained by the lattice strain model with the site radius (r0) decreasing with increasing charge from r0 1+=1.2 r{A} to r0 5+=0.6 r{A}. Bivalent cations are moderately incompatible (DMg=0.12 and DSr=0.5) to compatible (DMn=1). High field strength elements such as Zr and Nb are strongly incompatible in wollastonite (D \< 0.01), and rare earth element (REE) partition coefficients increase with decreasing ionic radius from DLa=0.19 to DLu=2.8. The crystallization of wollastonite could eventually strongly influence REE fractionation (and more specifically the light-heavy REE ratios) during magmatic differentiation of alkali-rich foiditic melts and should therefore be considered to fully understand trace element evolution and partitioning in alkaline and silica-undersaturated magmas.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Dick_etal2019,

title = {Dynamic accretion beneath a slow‐spreading ridge segment : IODP Hole 1473A and the Atlantis Bank oceanic core complex},

author = {H. J. B. Dick and C. J. MacLeod and P. Blum and N. Abe and D. K. Blackman and J. A. Bowles and M. J. Cheadle and K. Cho and J. Ciazela and Deans and J.R. and V. P. Edgcomb and C. Ferrando and L. France and B. Ghosh and B. Ildefonse and B. John and M. A. Kendrick and J. Koepke and J. A. M. Leong and C. Liu and Q. Ma and T. Morishita and A. Morris and J. H. Natland and T. Nozaka and O. Pluemper and A. Sanfilippo and J. B. Sylvan and M. A Tivey and and R. Tribuzio and G. Viegas},

doi = {10.1029/2018JB016858},

year  = {2019},

date = {2019-01-01},

journal = {Journal of Geophysical Research ?\u{I} Solid Earth},

volume = {124},

pages = {12,631--12,659},

abstract = {809 deep IODP Hole U1473A at Atlantis Bank,SWIR,is2.2kmfrom1,508‐m Hole735B and 1.4 from 158‐m Hole 1105A. With mapping, it provides the �textordfemininerst3‐D view of the upper levels of a 660‐km2 lower crustal batholith. It is laterally and vertically zoned, representing a complex interplay of cyclic intrusion, and ongoing deformation, with kilometer‐scale upward and lateral migration of interstial melt. Transform wall dives over the gabbro‐peridotite contact found only evolved gabbro intruded directly into the mantle near the transform. There was no high‐level melt lens, rather the gabbros crystallized at depth, and then emplaced into the zone of diking by diapiric rise of a crystal mush followed by crystal‐plastic deformation and faulting. The residues to mass balance the crust to a parent melt composition lie at depth below the center of the massif---likely near the crust‐mantle boundary. Thus, basalts erupted to the sea�-oor from \>1,550 mbsf. By contrast, the Mid‐Atlantic Ridge lower crust drilled at 23textdegreeN and at Atlantis Massif experienced little high‐temperature deformation and limited late‐stage melt transport. They contain primitive cumulates and represent direct intrusion,storage,and crystallization of parental MORB in thinner crust be low the dike‐gabbro transition.The strong asymmetric spreading of the SWIR to the south was due to fault capture, with the northern rift valley wall faults cutoff by a detachment fault that extended across most of the zone of intrusion.This caused rapid migration of the plate boundary to the north,while the large majority of the lower crust to spread south unroo�textordfeminineng Atlantis Bank and uplifting it into the rift mountains.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ayalew_etal2019,

title = {Differential fractionation of rhyolites during the course of crustal extension, Western Afar (Ethiopian Rift)},

author = {D. Ayalew and R. Pik and N. Bellahsen and L. France and G. Yirgu},

doi = {10.1029/2018GC007446},

year  = {2019},

date = {2019-01-01},

urldate = {2018-01-01},

journal = {Geochemistry, Geophysics, Geosystems G3},

volume = {20},

number = {2},

pages = {571--593},

abstract = {We report field observation, age, chemical (major and trace elements), and isotope (Sr‐Nd‐Pb) data for felsic volcanic rocks from Central Afar and adjacent western margin. Investigated volcanic rocks are dominantly rhyolites with minor trachytes, and they are geochemically similar. Their ages range from textasciitilde30 Ma (prerift stage), textasciitilde20 Ma (early synrift), textasciitilde8--4 Ma (main thinning event) to textasciitilde2.5--0.1 Ma (late synrift/continental breakup), representing the entire volcanic‐tectonic events that occurred episodically. Major element variations are consistent with fractionation of gabbroic cumulates. Trace element and isotope data preclude an origin by crustal anatexis; the rhyolites are rather genetically linked to the associated basalts and variously contaminated by the crust during differentiation of magmas. Chemical and isotopic data of the rhyolites support an origin by open system differentiation at deep crustal levels (hot wall rock and high r = rate of assimilation/rate of crystallization) and shallow crustal levels (cold wall rock and low r) with a change in the composition of the assimilated material from lower crustal to upper crustal type. Assimilation appears to decrease in recent times with Quaternary rhyolites, emplaced nearby the active magmatic segments in Afar, which exhibit the isotopic compositions closest to original mantle signature. This is compatible with a crust below the active magmatic segments resulting from important addition of juvenile basic magmas. Such results and interpretations provide actual constrains to suggest that the present‐day stage is probably very close to continental breakup, which will be achieved once the continental crust will be entirely replaced by new magmatic crust.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Gu_etal2018,

title = {Metasomatism in the sub-continental lithospheric mantle beneath the south French Massif Central: Constraints from trace elements, Li and H in peridotite minerals},

author = {X. Gu and J. Ingrin and E. Deloule and L. France and Q. Xia},

doi = {10.1016/j.chemgeo.2017.08.006},

year  = {2018},

date = {2018-01-01},

journal = {Chemical Geology},

volume = {478},

pages = {2--17},

abstract = {Mantle metasomatism by percolating melts/fluids can significantly modify the geochemical and mineralogical compositions of the sub-continental lithospheric mantle (SCLM). We present a detailed study of water contents and Li concentrations and isotopic compositions in mantle minerals from a suite of peridotite xenoliths entrained by a Cenozoic Strombolian volcano in the southern French Massif Central (FMC). Wide ranging clinopyroxene trace element distributions (e.g., (La/Yb) N from 0.25 to 22.21 ; Ti/Eu ratios from 453 to 4892) suggest that the SCLM has undergone metasomatism by carbonatitic melts/fluids or melts/fluids related to subducted materials. Two amphibole-bearing samples exhibit depletion of light rare earth elements (LREE ; (La/Yb) N= 0.26 and 0.30, respectively) in amphiboles, similar to that in co-existing clinopyroxenes ; these samples indicate that amphiboles grew during a separate modally metasomatic event predating the cryptic metasomatism accounting for LREE enrichment and negative HFSE anomalies in other samples. Mineral Li concentrations are similar to those in the normal mantle, with inter-mineral Li partitioning nearly equilibrated and intragranular Li distributions nearly homogeneous. However, negative $delta$7 Li values of pyroxenes in some samples (as low as − 8.8 texttenthousand in clinopyroxene of sample MC38) can be attributed to diffusive exchange with a small-volume melt of moderate Li concentration and light Li isotopic composition, originally associated with a recycled component. Preservation of the currently observed large inter-mineral Li isotopic variations indicates that melt percolation occurred shortly before entrainment of the peridotite xenoliths by the host magma. Mineral water contents vary from 41 to 428 ppm in clinopyroxenes and from 28 to 152 ppm in orthopyroxenes, and their roughly negative co-variation with co-existing olivine Fo contents imply that partial melting was the main control over mineral water content variations in most samples. Varied water contents in LREE-enriched metasomatized samples indicate the involvement of metasomatic agents of different origins. The aqueous agent responsible for generation of amphiboles in two samples did not produce a notable increase in the water contents of coexisting nominally anhydrous minerals.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mollex_etal2018,

title = {Tracing helium isotope compositions from mantle source to fumaroles at Oldoinyo Lengai volcano, Tanzania},

author = {G. Mollex and E. F\"{u}ri and P. Burnard and L. Zimmermann and G. Chazot and E. O. Kazimoto and B. Marty and L. France},

doi = {10.1016/j.chemgeo.2017.08.015},

year  = {2018},

date = {2018-01-01},

journal = {Chemical Geology},

volume = {480},

pages = {66--74},

abstract = {Oldoinyo Lengai is the only volcano on Earth currently erupting natrocarbonatites, of which the source and genesis remain controversial. Cognate xenoliths and fumaroles were sampled at the summit of Oldoinyo Lengai, and deep crustal xenoliths from Oltatwa maar, in 2010 and 2014, after the 2007--2008 sub-Plinian eruption. Thesummit cognate xenoliths provide direct information on the isotopic composition of the mid-crustal magma chamber that was active during the 2007--2008 explosive eruption. Cognate xenolith-hosted pyroxenes from Oldoinyo Lengai have an average 3He/4He =6.58 textpm 0.46 RA, similar to values from nearby silicate volcanoes(4.95--7.30 RA), and reflecting a sub-continental lithospheric mantle (SCLM) signature. This similarity implies that Oldoinyo Lengai carbonatites form from a similar mantle reservoir as the nearby silicate volcanoes. We identify SCLM, metasomatized by fluids/melts derived from the depleted convective mantle, as the common source of magmas in the Arusha volcanic province. Fumarole measurements highlight that fumarolic 3He/4He values have been relatively constant since at least 1988, indicating that dramatic changes to the crater region morphology during the 2007--2008 eruption did not affect the architecture of the hydrothermal system, which is probably connected to the crustal magma chamber(s). Moreover, the similarity between 3He/4He values from the mid-crustal magma chamber (6.58 textpm 0.46 RA) and fumaroles (7.31 textpm 0.24 RA) of Oldoinyo Lengai attests that helium is not subjected to atmospheric contamination or crustal assimilation during transport to the surface.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nguyen_etal2018,

title = {Occurrence of felsic rocks in oceanic gabbros from IODP hole U1473A : Implications for evolved melt migration in the lower oceanic crust},

author = {D. C. Nguyen and T. Morishita and Y. Soda and A. Tamura and B. Ghosh and Y. Harigane and L. France and C. Liu and J. H. Natland and A. Sanfilippo and C. J. MacLeod and P. Blum and H. J. B. Dick},

doi = {10.3390/min8120583},

year  = {2018},

date = {2018-01-01},

journal = {Minerals},

volume = {8},

number = {583},

abstract = {Felsic rocks are minor in abundance but occur ubiquitously in International OceanDiscovery Program Hole U1473A, Southwest Indian Ridge. The trace element abundances of high-Ti brown amphibole, plagioclase, and zircon in veins, as well as the presence of myrmekitic texture in the studied felsic rocks support crystallization origin from highly-evolved melts, probably controlled by fractional crystallization. Based on geochemical criteria and texture of the mineral assemblagein felsic rocks and their relationship with host gabbros, they can be divided into three types: (1)Felsic rock with sharp boundaries is formed when felsic melt intrudes into fractures of host gabbros,resulting in minimal interaction between the melt and the wall minerals. (2) Replacive felsic rock,which is characterized by a pseudomorphic replacement of minerals in the host gabbro. This veintype is caused by the replacement of the host mineralogy by minerals in equilibrium with the felsicmelts. (3) Felsic rock with diffused boundaries is formed either by infiltration of felsic melt into thesolidifying gabbro body or crystallization of interstitial melts. Infiltration modes of felsic melts arelikely controlled by the temperature condition of the cooling host gabbros.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Erdmann_etal2017,

title = {Trace elements in anatectic products at the roof of mid-ocean ridge magma chambers: An experimental study},

author = {M. Erdmann and L. France and L. A. Fischer and E. Deloule and J. Koepke},

doi = {10.1016/j.chemgeo.2017.03.004},

year  = {2017},

date = {2017-01-01},

journal = {Chemical Geology},

volume = {456},

pages = {43--57},

abstract = {At fast-spreading mid-ocean ridges (MORs), the horizon between the axial melt lens (AML) and the overlying sheeted dikes is characterized by extensive anatectic processes. The heat flux of the AML in combination with hydrothermal fluids from above causes high-grade contact metamorphism,which may result in anatexis of the roof rocks above the AML. The products of this process are silica-rich anatectic melts that have the potential to contaminate MOR basalts and residual hornfels. Here, we simulate the complex igneous and metamorphic processes occurring at the AML roof by hydrous partial melting experiments and provide corresponding trace element partition coefficients between melt and residues, which are useful to quantify those processes. We present trace element patterns from experimental anatectic felsic melts and the related residue produced by hydrous partial meltingof various types of AML roof rocks. The starting materials used are sheeted dikes and hornfelses from Hole 1256D drilled by the Integrated Ocean Drilling Program. Results are compared with directly-related natural lithologies (i.e., felsic veins and granoblastic hornfels) from the same site. The trace element contents generally overlap with natural examples and experimental melts produced at low water activity (aH2O\<0.5) can be highly enriched in trace elements despite relatively low SiO2 contents (58.9 to 65.7 wt%). A low aH2O is required to reproduce the low Al2O3 contents observed in natural silica-rich rocks. However, low aH2O implies that the presence of residual amphibole is not required for anatectic processes Even though residual amphibole is often used as an importantphase for explaining trace element characteristics in relevant felsic rocks formed at MORs when modeling anatexis. Because amphibole is lacking in any experimental residue, which is in agreement with natural hornfelses from thedike/gabbro transition at Site 1256, we assume that partial melting within the AML roof rocks proceeds without the participation of amphibole as residual phase. We present a comprehensive set of trace element compositions as well as bulk and mineral/melt trace element partition coefficients obtained from our amphibole-free experimental results for different potential protoliths over a large range of temperature and at different aH2Os.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Zhang_etal2017,

title = {Felsic plutonic rocks from IODP hole 1256D, Eastern Pacific: Implications for the nature of the axial melt lens at fast-spreading mid-ocean ridges},

author = {C. Zhang and J. Koepke and L. France and M. Godard},

doi = {10.1093/petrology/egx064},

year  = {2017},

date = {2017-01-01},

journal = {Journal of Petrology},

volume = {58},

number = {8},

pages = {1535--1566},

abstract = {Although the axial melt lens (AML) beneath fast-spreading mid-ocean ridges has been detected by seismic reflection for decades, its nature and role in the accretion of lower oceanic crust and the evolution and eruption of mid-ocean ridge basalts (MORB) are still poorly constrained. Plutonic rocks consisting of quartz-bearing gabbros, diorites and tonalites, which might represent the upper part of a fossilized AML, have for the first time been recovered from an intact fast-spreading oceanic crust section by Integrated Ocean Drilling Program (IODP) Hole 1256D. Whole-rock major elements show a wide and continuous compositional range (e.g. Mg# 24--70) and apparent enrichments in Ti and Fe at intermediate MgO contents (4--6 wt %). Trace element characteristics are coherent for the different lithology groups defined by petrography and mineral modes; that is, gabbro, clinopyroxene-rich diorite, amphibole-rich or oxide-rich diorite and tonalite. The gabbros and diorites are consistent with modeled products of MORB fractional crystallization, composed of mixed melt and cumulate in varying ratios. Modeled trace elements (especially with respect to Eu) support a model in which the tonalites originated from low-degree partial melting of the sheeted dikes overlying the AML, rather than extreme fractional crystallization. Enrichments in rare earth elements (REE) in clinopyroxenes from the gabbroic and dioritic intrusive rocks suggest strong assimilation of REE-rich tonalitic components by evolved MORB magmas. Hydrothermal alteration was pervasive during cooling of the plutonic system, which can be traced by petrography, mineral compositions and bulk-rock geochemistry. The upper part of AML, largely composed of low-density and high-viscosity felsic magmas, may serve as a barrier to eruptible MORB melts in the lower part of AML.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Zhang_etal2017_2,

title = {Volatiles (CO2, S, F, Cl, Br) in the dike-gabbro transition zone at IODP Hole 1256D: Magmatic imprint versus hydrothermal influence at fast-spreading mid-ocean ridge},

author = {C. Zhang and L. X. Wang and M. A. W. Marks and L. France and J. Koepke},

year  = {2017},

date = {2017-01-01},

journal = {Chemical Geology},

volume = {459},

pages = {43--60},

abstract = {The dike-gabbro transition zone of mid-ocean ridges (MORs) is a critical site for the accretion of oceanic crusts as it is the main zone of interactions between the hydrothermal and magmatic systems. In this study, volatiles contents of CO2, S, F, Cl and Br for a variety of lithologies from the dike-gabbro transition zone of an intact oceanic crust were investigated in order to examine the magmatic imprint versus hydrothermal influence. The studied samples include plutonic rocks (gabbros, diorites and tonalites), hornfelses (i.e. granoblastic dikes), an amphibole-rich vein and albitites. These rocks were recently sampled by the IODP (Integrated Ocean Drilling Program) at Site 1256, representing parts of an oceanic crust that formed at the fast-spreading ridge of the East Pacific Rise. The bulk CO2 contents (500--10,000 ppm) show no lithological dependence and are similar to those of fresh lavas. Highly variable bulk S concentrations (3--900 ppm) show significant depletions compared to undegassed MORB melts, which might be caused by exsolution of magmatic fluids during crystallization. The plutonic samples have Cl concentrations of 500--1000 ppm, remarkably higher than the hornfelses (200--600 ppm Cl) and erupted lavas (average 200 ppm Cl). Except for the albitites that contain very low F (20--30 ppm) and the hydrothermal amphibole-rich vein that contains extremely high F ( 1000 ppm), the other lithologies have similar F concentrations within 100--350 ppm. The Br concentrations of different lithologies are largely overlapping within 0.5--3.5 ppm. Petrological and mineralogical evidence indicates that bulk F concentrations are dominated by the presence of amphibole and apatite, whereas Cl and Br are mainly hosted in fluid inclusions rather than in hydrous minerals. The variation of F/Cl and Br/Cl ratios may trace the mixing between MORB magmas and seawaterderived fluids, crystallization of apatite and amphibole, and/or extraction of magmatic fluids. Our data support the current S budget of oceanic crust, but indicate that the budgets of C and Cl may have been underestimated.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Dick_etal2016,

title = {Expedition 360 Preliminary Report: Southwest Indian Ridge lower crust and Moho. Internat. Ocean Discovery Program.},

author = {H. J. B. Dick and C. J. MacLeod and P. Blum and N. Abe and D. K. Blackman and J. A. Bowles and M. J. Cheadle and K. Cho and J. Ciazela and J. R. Deans and V. P. Edgcomb and C. Ferrando and L. France and B. Ghosh and B. Ildefonse and M. A. Kendrick and J. H. Koepke and J. A. M. Leong and C. Liu and Q. Ma and T. Morishita and A. Morris and J. H. Natland and T. Nozaka and O. Pluemper and A. Sanfilippo and J. B. Sylvan and M. A. Tivey and R. Tribuzio and L. G. F. Viegas},

doi = {10.14379/iodp.pr.360.2016},

year  = {2016},

date = {2016-01-01},

journal = {Expedition 360 Preliminary Report},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Fischer_etal2016,

title = {Trace element evidence for anatexis at oceanic magma chamber roofs and the role of partial melts for contamination of fresh MORB},

author = {LA. Fischer and M. Erdmann and L. France and P. E. Wolff and E. Deloule and C. Zhang and M. Godard and J. Koepke},

doi = {10.1016/j.lithos.2016.05.001},

year  = {2016},

date = {2016-01-01},

journal = {Lithos},

volume = {260},

pages = {1--8},

abstract = {At oceanic spreading centers, interactions between magma and hydrothermal convecting systems trigger major physical, thermal, and chemical exchanges. The two-pyroxene hornfels recovered from the base of the sheeted dike sequence at Integrated Ocean Drilling Program(IODP) Site 1256 (equatorial Eastern Pacific) are interpreted as a conducting boundary layer between the underlying axial melt lens and the hydrothermally cooled sheeted dikes. They are cut by numerous small, felsic veins, which were recently interpreted as a product of hydrous partial melting of sheeted dikes. Here, we present trace element compositions of products (melts and residues) of hydrous partial melting experiments using basalts and hornfels from IODP Site 1256 as starting material. The experimental products generated between 910 textdegreeC and 970 textdegreeC match the natural lithologies from Site 1256 interms of major and trace element compositions. The compositions of the anatectic melts correspond to the compositions of the felsic veins, while the residual minerals match the compositions of the two-pyroxene hornfels, evidencing that hydrous partial melting is an important magmatic process in the gabbro/dike transition of fast-spreading mid-oceanic ridges. Our results complement previous experimental studies on anatectic processes occurring at the roof of the magma chambers from fast-spreading mid-ocean ridges. Moreover, calculations of mixing and assimilation fractional crystallization using the experimental partial melts as contaminant/assimilant showed that anatectic melts can only be a minor contributor to the contamination process.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{France_etal2016,

title = {Oxygen isotopes reveal crustal contamination and a large, still partially molten magma chamber in Cha^ine des Puys (French Massif Central)},

author = {L. France and M. Demacon and A. A. Gurenko and D. Briot},

doi = {10.1016/j.lithos.2016.05.013},

year  = {2016},

date = {2016-01-01},

journal = {Lithos},

volume = {260},

pages = {328--338},

abstract = {The two main magmatic properties associated with explosive eruptions are high viscosity of silica-rich magmas and/or high volatile contents. Magmatic processes responsible for the genesis of such magmas are differentiation through crystallization, and crustal contamination (or assimilation) as this process has the potential to enhance crystallization and add volatiles to the initial budget. In the Cha^ine des Puy series (FrenchMassif Central), silica and H2O-rich magmas were only emitted during the most recent eruptions (ca. 6--15 ka). Here, we use in situ measurements of oxygen isotopes in zircons from two of the main trachytic eruptions from the Cha^ine des Puys to track the crustal contamination component in a sequence thatwas previously presented as an archetypal fractional crystallization series. Zircons from Sarcoui volcano and Puy de D^ome display homogeneous oxygen isotope compositions with $delta$18O = 5.6 textpm 0.25texttenthousand and 5.6 textpm 0.3texttenthousand, respectively, and have therefore crystallized from homogeneous melts with $delta$18Omelt = 7.1 textpm 0.3texttenthousand. Compared to mantle derived melts resulting from pure fractional crystallization ($delta$18Odif.mant. = 6.4 textpm 0.4texttenthousand), those $delta$18Omelt values are enriched in 18O and support a significant role of crustal contamination in the genesis of silica-rich melts in the Cha^ine des Puys. Assimilation--fractional--crystallization models highlight that the degree of contamination was probably restricted to 5.5--9.5% with Rcrystallization/Rassimilation varying between 8 and 14. The very strong intra-site homogeneity of the isotopic data highlights that magmas were well homogenized before eruption, and consequently that crustal contamination was not the trigger of silica-rich eruptions in the Cha^ine des Puys. The exceptionally strong inter-site homogeneity of the isotopic data brings to light that Sarcoui volcano and Puy de D^ome were fed by a single large magma chamber. Our results, together with recent thermo-kinetic models and an experimental simulation (Martel et al., 2013), support the existence of a large (textasciitilde6--15 km3), still partially molten mid-crustal reservoir (10--12 km deep) that is filled with silica-rich magma},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Gu_etal2016,

title = {Multi-stage metasomatism revealed by trace element and Li isotope distributions in minerals of peridotite xenoliths from All`egre volcano (French Massif Central)},

author = {X. Gu and E. Deloule and L. France and J. Ingrin},

doi = {10.1016/j.lithos.2016.07.019},

year  = {2016},

date = {2016-01-01},

journal = {Lithos},

volume = {264},

pages = {158--174},

abstract = {The modal, chemical, and isotopic compositions of mantle peridotite are largely modified by metasomatic processes, which may affect them repeatedly. Xenoliths are commonly used to characterize those metasomatic processes along with the structure, and chemical and isotopic compositions of mantle domains. Nevertheless, the original mantle signatures born by mantle xenoliths are potentially obscured by the interactions occurring between the hostmagma and the xenolith itself. Here we attempt to identify to which degree the original Li content and isotopic composition, as well as other trace element contents of mantle xenoliths, can be modified by interaction with the host magma. Peridotite xenoliths that have suffered extensive exchange with the entraining magma were sampled in the solidified lava lake of All`egre, Southern French Massif Central, in order to decipher the signature related to peridotite-melt interaction, and to further unravel the evolution of the sub-continental lithospheric mantle. In-situ trace element analyses of clinopyroxene (Cpx) were performed via LA--ICP-- MS, and the Li content and isotopic composition of pyroxene and olivine (Ol) via SIMS. Negative HFSE anomalies (Ti/Eu ratios as low as 437) and markedly high LREE/HREE ratios ((La/Yb) N as high as 79) are characteristic of mantle metasomatism at depth. Lithium isotope systematics indicates that at least two different metasomatic events affected the peridotite. Exceptionally high Li contents in Cpx (up to 50 ppm) and slight Li enrichment of Ol rims are ascribed to diffusive Li in flux with a positive $delta$7 Li value (+3.2texttenthousand) from the host magma after entrain- ment. Conversely, Ol cores preserve extremely light Li isotopic compositions ($delta$7 Li as low as − 25 texttenthousand )with high Li contents (up to 4.4 ppm) compared to normal mantle, indicating a metasomatic event that occurred before xenolith entrainment. The negative $delta$7 Li signature of this early metasomatism may be related to subduction-related fluids released during the Variscan orogeny. Trace element distributions in minerals reveal that the HFSE and REE composition of Cpx and the negative $delta$7 Li signature in Ol cores were not acquired simultaneously. Therefore at least three successive metasomatic events affected the Allegre peridotites, as revealed through the use of detailed in-situ Li isotopic analyses to trace melt-rock interactions},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Medynski_etal2016,

title = {Magmatic cycles pace tectonic and morphological expression of rifting (Afar depression, Ethiopia)},

author = {S. Medynski and R. Pik and P. Burnard and S. Dumont and R. Grandin and A. Williams and P. H. Blard and I. Schimmelpfennig and C. Vye-Brown and L. France and D. Ayalew and L. Benedetti and G. Yirgu and ASTER team},

doi = {10.1016/j.epsl.2016.04.014},

year  = {2016},

date = {2016-01-01},

journal = {Earth and Planetary Science Letters},

volume = {446},

pages = {77--88},

abstract = {The existence of narrow axial volcanic zones of mid-oceanic ridges testifies of the underlying concentration of both melt distribution and tectonic strain. As a result of repeated diking and faulting, axial volcanic zones therefore represent a spectacular topographic expression of plate divergence. However, the submarine location of oceanic ridges makes it difficult to constrain the interplay between tectonic and magmatic processes in time and space. In this study, we use the Dabbahu--Manda Hararo (DMH) magmatic rift segment (Afar, Ethiopia) to provide quantitative constraints on the response of tectonic processes to variations in magma supply at divergent plate boundaries. The DMH magmatic rift segment is considered an analogue of an oceanic ridge, exhibiting a fault pattern, extension rate and topographic relief comparable to intermediate- to slow-spreading ridges. Here, we focus on the northern and central parts of DMH rift, where we present quantitative slip rates for the past 40 kyr for major and minor normal fault scarps in the vicinity of a recent (September 2005) dike intrusion. The data obtained show that the axial valley topography has been created by enhanced slip rates that occurred during periods of limited volcanism, suggestive of reduced magmatic activity, probably in association with changes in strain distribution in the crust. Our results indicate that the development of the axial valley topography has been regulated by the lifetimes of the magma reservoirs and their spatial distribution along the segment, and thus to the magmatic cycles of replenishment/differentiation (\<100 kyr). Our findings are also consistent with magma-induced deformation in magma-rich rift segments. The record of two tectonic events of metric vertical amplitude on the fault that accommodated the most part of surface displacement during the 2005 dike intrusion suggests that the latter type of intrusion occurs roughly every 10 kyr in the northern part of the DMH segment.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Scheffer_etal2016,

title = {Syn- to post-orogenic exhumation of metamorphic nappes: Structure and thermobarometry of the western Attic-Cycladic metamorphic complex (Lavrion, Greece)},

author = {C. Scheffer and O. Vanderhaeghe and P. Lanari and A. Tarantola and L. Ponthus and A. Photiades and L. France},

doi = {10.1016/j.jog.2015.08.005},

year  = {2016},

date = {2016-01-01},

journal = {Journal of Geodynamics},

volume = {96},

pages = {174--1923},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Erdmann_etal2015,

title = {Anatexis at the roof of an oceanic magma chamber at IODP Site 1256 (equatorial Pacific): an experimental study},

author = {M. Erdmann and L. A. Fischer and L. France and C. Zhang and M. Godard and J. Koepke},

doi = {10.1007/s00410-015-1136-5},

year  = {2015},

date = {2015-01-01},

journal = {Contributions to Mineralogy and Petrology},

volume = {169},

number = {39},

abstract = {Replenished axial melt lenses at fast-spreading mid-oceanic ridges may move upward and intrude into the overlying hydrothermally altered sheeted dikes, resultingin high-grade contact metamorphism with the potential to trigger anatexis in the roof rocks. Assumed products of this process are anatectic melts of felsic composition and granoblastic, two-pyroxene hornfels, representing the residueafter partial melting. Integrated Ocean Drilling Program Expeditions 309, 312, and 335 at Site 1256 (eastern equatorial Pacific) sampled such a fossilized oceanicmagma chamber. In this study, we simulated magma chamber roof rock anatectic processes by performing partial melting experiments using six different protoliths from the Site 1256 sheeted dike complex, spanning a lithological range from poorly to strongly altered basalts to partially or fully recrystallized granoblastic hornfels. Results show that extensively altered starting material lacking primary magmatic minerals cannot reproduce the chemistry of natural felsic rocks recovered in ridge environments, especially elements sensitive to hydrothermal alteration (e.g., K, Cl). Natural geochemical trends are reproduced through partial melting of moderately altered basalts from the lower sheeted dikes. Two-pyroxene hornfels, the assumed residue, were reproduced only at low melting degrees (\<20 vol%).The overall amphibole absence in the experiments confirms the natural observation that amphibole is not produced during peak metamorphism. Comparing experimental products with the natural equivalents reveals that water activity (aH2O) was significantly reduced during anatectic processes, mainly based on lower melt aluminum oxide and lower plagioclase anorthite content at lower aH2O. Highsilica melt at the expected temperature (1000--1050 textdegreeC; peak thermal overprint of two-pyroxene hornfels) could only be reproduced in the experimental series performed at aH2O = 0.1.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{France_etal2015,

title = {Mantle refertilization and magmatism in old orogenic regions: The role of late-orogenic pyroxenites},

author = {L. France and G. Chazot and J. Kornprost and L. Dallai and R. Vannucci and M. Gr\'{e}goire and H. Bertrand and P. Boivin},

doi = {10.1016/j.lithos.2015.05.017},

year  = {2015},

date = {2015-01-01},

journal = {Lithos},

volume = {232},

pages = {49--75},

abstract = {Pyroxenites and garnet pyroxenites are mantle heterogeneities characterized by a lower solidus temperature than the enclosing peridotites; it follows that they are preferentially involved during magma genesis. Constraining their origin, composition, and the interactions they underwent during their subsequent evolutionis therefore essential to discuss the sources of magmatism in a given area. Pyroxenites could represent either recycling of crustal rocks in mantle domains or mantle originated rocks (formed either by olivine consuming melt-rock reactions or by crystal fractionation). Petrological and geochemical (major and trace elements, Sr--Nd and O isotopes) features of xenoliths from various occurrences (French Massif-Central, Jordan, Morocco and Cameroon) showthat these samples represent cumulates crystallized duringmelt percolation atmantle conditions.They formed in mantle domains at pressures of 1--2 GPa during post-collisional magmatism (possibly Hercynian for the French Massif-Central, and Panafrican for Morocco, Jordan and Cameroon). The thermal reequilibration of lithospheric domains, typical of the late orogenic exhumation stages, is also recorded by the samples. Most of the samples display a metasomatic overprint that may be either inherited or likely linked to the recent volcanic activity that occurred in the investigated regions. The crystallization of pyroxenites during late orogenic events has implications for the subsequent evolution of the mantle domains. The presence of largeamounts ofmantle pyroxenites in old orogenic regions indeed imparts peculiar physical and chemical characteristics to these domains. Among others, the global solidus temperature of the whole lithospheric domain will be lowered; in turn, this implies that old orogenic regions are refertilizedzones where magmatic activity would be enhanced.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Medynski_etal2015,

title = {Stability of rift axis magma reservoirs: Spatial and temporal evolution of magma supply in the Dabbahu rift segment (Afar, Ethiopia) over the past 30 kyr},

author = {S. Medynski and R. Pik and P. Burnard and C. Vye-Brown and L. France and I. Schimmelpfennig and K. Whaler and N. Johnson and L. Benedetti and D. Ayelew and G. Yirgu},

doi = {10.1016/j.epsl.2014.11.002},

year  = {2015},

date = {2015-01-01},

journal = {Earth and Planetary Science Letters},

volume = {409},

pages = {278--289},

abstract = {Unravelling the volcanic history of the Dabbahu/Manda Hararo rift segment in the Afar depression (Ethiopia) using a combination of cosmogenic (36Cl and 3He) surface exposure dating of basaltic lava-flows, field observations, geological mapping and geochemistry, we show in this paper that magmatic activity in this rift segment alternates between two distinct magma chambers. Recent activity in the Dabbahu rift (notably the 2005--2010 dyking crises) has been fed by a seismically well-identified magma reservoir within the rift axis, and we show here that this magma body has been active over the last 30kyr. However, in addition to this axial magma reservoir, we highlight in this paper the importance of a second, distinct magma reservoir, located 15 km west of the current axis, which has been the principal focus of magma accumulation from 15 ka to the subrecent. Magma supply to the axial reservoir substantially decreased between 20 ka and the present day, while the flank reservoir appears to have been regularly supplied with magma since 15 ka ago, resulting in less variably differentiated lavas. The trace element characteristics of magmas from both reservoirs were generated by variable degrees of partial melting of a single homogeneous mantle source, but their respective magmas evolved separately in distinct crustal plumbing systems.Magmatism in the Dabbahu/Manda Hararo rift segment is not focussed within the current axial depression but instead is spread out over at least 15 kmon the western flank. This is consistent with magneto-telluric observations which show that two magma bodies are present below the segment, with the main accumulation of magma currently located below the western flank, precisely where the most voluminous recent (\<15 ka) flank volcanism is observed at the surface.Applying these observations to slow spreading mid-ocean ridges indicates that magma bodies likely have a lifetime of a least 20 ka, and that the continuity of magmatic activity is maintained by a system of separate relaying reservoirs, which could in return control the location of spreading. This long term (\>105yr) alternation between distinct crustal reservoirs located broadly at the same location relative to the segment appears to be a key feature for organizing and maintaining active spreading centres over stable soft points in the mantle.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Pezzali_etal2015,

title = {Analogues of exhumed pyroxenite layers in the Alboran domain sampled as xenoliths by Middle Atlas Cenozoic volcanism},

author = {I. Pezzali and L. France and G. Chazot and R. Vannucci},

doi = {10.1016/j.lithos.2015.02.024},

year  = {2015},

date = {2015-01-01},

journal = {Lithos},

volume = {230},

pages = {184--188},

abstract = {The evolutionary stages of lithosphericmantle in the Alboran domain are recorded by peridotites and associated pyroxenites outcropping in the Betic--Rifean orogenic belt.We showhere that the scale of lithosphericmantle interpretation can be extended up to at least 300 kmfarther south of Beni Bousera thanks to the occurrence inMiddle Atlas Cenozoic volcanics of rare pyroxenite mantle xenoliths, which unlike most peridotite xenoliths still preserve their pre-metasomatic geochemical signatures. These pyroxenites closely match mafic layers fromRonda and Beni Bousera occurrences and include, in addition tomore common Spl-facies pyroxenites and former Grt-bearing pyroxenites accreted to the lithosphere and equilibrated under Spl-facies condition, also former Plbearingcumulates that represent old sectors of delaminated lower crust. The close similarity ofMiddle Atlas pyroxenite xenoliths to mafic layers in the Alboran domain makes the region comprising the Betic-Rifean belt and Middle Atlas one of the fewoccurrences that allowpetrological and chemical information from exhumed mantle sectors to be combined with that from non-exhumed sectors, which only a few million years later were brought to the surface by volcanic activity.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{France_etal2014,

title = {Contamination of MORB by anatexis of magma chamber roof rocks: Constraints from a geochemical study of experimental melts and associated residues},

author = {L. France and J. Koepke and C. J. MacLeod and B. Ildefonse and M. Godard and E. Deloule},

doi = {10.1016/j.lithos.2014.05.018},

year  = {2014},

date = {2014-01-01},

journal = {Lithos},

volume = {202-203},

pages = {120--137},

abstract = {Mid-ocean ridge basalts (MORBs) are the most abundant magmas produced on Earth. They are widely studied to infer mantle compositions and melting processes. However, MORB liquids are also the complex end-product of a variety of intra-crustal processes such as partial or fractional crystallization, melt -- rock interaction, and contamination. Deciphering the relative contribution of these different processes is of first-order importance. Contamination at ocean crustal levels is likely, and may occur at magma chamber margins where fresh magmas can interact with previously hydrothermally altered rocks. Characterizing the composition of this crustal contaminant component is critical if we are to understand the relative importance of each component in the resulting MORB liquid. Here we present the results of experiments designed to reproduce the processes occurring at oceanic magma chamber roofs, where crustal contamination should be most extensive, by melting a representative sample of the sheeted dike complex. Anatectic melts thus produced are likely to represent the principal crustal contaminant in MORB. These melts were characterized for major and trace elements, showing B, Zr, Hf, and U enrichment, and Sr, Ti, and V depletion relative to original MORB liquids. In comparison to the starting material, relative element fractionations are observed in the anatectic melts, with enrichments of : U relative to Ba, Nb, and Th ; LREE and MREE relative to Sr ; and Zr -- Hf relative to LREE. Bulk partition coefficients for element partitioning during magma chamber roof anatexis are derived and proposed as valuable tools for tracking MORB contamination. Comparison with natural samples from the East Pacific Rise and the Oman ophiolite shows that anatectic melts can crystallize in situ to form oceanic plagiogranite intrusions, and that residual assemblages associated with the hydrous partial melting stage are represented by hornfelsic dikes and enclaves (also named granoblastic basalts). We now recognize these as commonplace at the root of the sheeted dike complex both at present-day and fossil oceanic spreading centers.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{France_etal2013,

title = {Hydrous magmatism triggered by assimilation of hydrothermally altered rocks in fossil oceanic crust (northern Oman ophiolite)},

author = {L. France and B. Ildefonse and J. Koepke},

doi = {10.1002/ ggge.20137.},

year  = {2013},

date = {2013-01-01},

journal = {Geochemistry, Geophysics, Geosystems G3},

volume = {14},

number = {8},

pages = {2598--2614},

abstract = {Mid-ocean ridges magmatism is, by and large, considered to be mostly dry. Nevertheless, numerous works in the last decade have shown that a hydrous component is likely to be involved in ocean ridges magmas genesis and/or evolution. The petrology and geochemistry of peculiar coarse grained gabbrossampled in the upper part of the gabbroic sequence from the northern Oman ophiolite (Wadi Rajmi) provide information on the origin and fate of hydrous melts in fast-spreading oceanic settings. Uncommon crystallization sequences for oceanic settings (clinopyroxene crystallizing before plagioclase), extreme mineral compositions (plagioclase An% up to 99, and clinopyroxene Mg # up to 96), and the presence of magmatic amphibole, imply the presence of a high water activity duringcrystallization. Various petrological and geochemical constraints point to hydration, resulting from the recycling of hydrothermal fluids. This recycling event may have occurred at the top of the axial magma chamber where assimilation of anatectic hydrous melts is recurrent along mid-ocean ridges or close tosegments ends where fresh magma intrudes previously hydrothermally altered crust. In ophiolitic settings, hydration and remelting of hydrothermally altered rocks producing hydrous melts may also occur during the obduction process. Although dry magmatism dominates oceanic magmatism, the dynamic behavior of fast-spreading ocean ridge magma chambers has the potential to produce the observed hydrous melts (either in ophiolites or at spreading centers), which are thus part of the generalmid-ocean ridges lineage},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Medynski_etal2013,

title = {Controls on magmatic cycles and development of rift topography of the Manda Hararo segment (Afar, Ethiopia):Insights from cosmogenic 3He investigation of landscape evolution},

author = {S. Medynski and R. Pik and P. Burnard and A. Williams and C. Vye-Brown and D. Ferguson and P. H. Blard and L. France and G. Yirgu and J. I. Seid and D. Ayalew and A. Calvert},

doi = {doi.org/10.1016/j.epsl.2013.02.006},

year  = {2013},

date = {2013-01-01},

journal = {Earth and Planetary Science Letters},

volume = {367},

pages = {133--145},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bolfan-Casanova_etal2012,

title = {Ferric iron and water incorporation in wadsleyite under hydrous and oxidizing conditions: A XANES, M\"{o}ssbauer, and SIMS study},

author = {N. Bolfan-Casanova and M. Munoz and C. McCammon and E. Deloule and A. F\'{e}rot and S. Demouchy and L. France and D. Andrault and S. Pascarelli},

doi = {10.2138/am.2012.3869},

year  = {2012},

date = {2012-01-01},

journal = {American Mineralogist},

volume = {97},

number = {8-9},

pages = {1483--1493},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Deschamps_etal2012,

title = {Behavior of fluid-mobile elements in serpentines from abyssal to subduction environments: Examples from Cuba and Dominican Republic},

author = {F. Deschamps and M. Godard and S. Guillot and C. Chauvel and M. Andreani and K. Hattori and B. Wunder and L. France},

doi = {10.1016/j.chemgeo.2012.04.009},

year  = {2012},

date = {2012-01-01},

journal = {Chemical Geology},

number = {312-313},

pages = {93--117},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Koepke_etal2011,

title = {Gabbos from IODP site 1256, equatorial Pacific: Insight into axial magma chamber processes at fast spreading ocean ridges},

author = {J. Koepke and L. France and T. M\"{u}ller and F. Faure and N. Goetze and W. Dziony and B. Ildefonse},

doi = {10.1029/2011GC003655},

year  = {2011},

date = {2011-01-01},

journal = {Geochemistry, Geophysics, Geosystems G3},

volume = {12},

number = {9},

pages = {Q09014},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Teagle_etal2011,

title = {Expedition 335 Scientists, 2011. Superfast spreading rate crust 4: drilling gabbro in intact ocean crust formed at a superfast spreading rate},

author = {D. Teagle and B. Ildefonse and P. Blum and G. Gu\'{e}rin and N. Zakharova and N. Abe and B. Abily and Y. Adachi and J. C. Alt and R. Anma and G. Baines and J. Deans and H. Dick and D. Endo and E. C. Ferre and L. France and M. M. Godard and M. Harris and Y. Kim and J. H. Koepke and M. D. Kurz and C. J. Lissenberg and S. Miyashita and A. Morris and R. Oizumi and B. D. Payot and M. Python and P. Roy and J. L. Till and M. Tominaga and D. S. Wilson},

doi = {10.2204/iodp.pr.335.2011},

year  = {2011},

date = {2011-01-01},

journal = {IODP Preliminary Report},

volume = {335},

keywords = {},

pubstate = {published},

tppubtype = {article}

}