Damien Cividini

@article{Pasava_etal2021,

title = {Elemental and isotopic compositions of trench-slope black shales, Bohemian Massif, with implications for oceanic and atmospheric oxygenation in early Cambrian},

author = {J. Pasava and L. Ackerman and J. Zak and F. Veselovsky and R. A. Creaser and M. Svojtka and B. Luais and O. Pour and O. Sebek and J. Trubac and E. Vosahlova and D. Cividini},

doi = {10.1016/j.palaeo.2020.110195},

year  = {2021},

date = {2021-01-01},

journal = {Palaeogeography, Palaeoclimatology, Palaeoecology},

volume = {564},

pages = {110195},

abstract = {This study examines a lower Cambrian pyrite-bearing black shale--graywacke succession in the Czech Republic interpreted as infill of a deep-marine, extensional trench-slope basin on top of an accretionary wedge that developed during subduction of an oceanic plate beneath the northern margin of Gondwana. The new U--Pb detrital zircon geochronology of the graywacke constrains the maximum age of deposition to 533 +5/−6 Ma, whereas the Re--Os dating of pyrite yielded a younger age of 507 textpm 16 Ma. Distribution of major and trace elements and calculated enrichment factors (EF) indicate that this succession was deposited under changing redox conditions over a short time span and that the basin was presumably controlled by tectonic subsidence and varying supply of terrigenous arc-derived material. This depositional setting is reflected by largely variable EFs and $delta$98Mo and $delta$53Cr values. Euxinic conditions detected at the base of the sampled black shale interval are documented by the highest values of EFs of redox-sensitive metals (e.g., Mo, U, V, Ni, Co, As) and also the Corg/P (\>1000) and DOPT (\>0.7) values. Black shales show lower $delta$56Fe values due to the excess of authigenic pyrite-Fe with a mean $delta$56Fe value of −0.02texttenthousand over detrital Fe in graywacke with a mean $delta$56Fe value of +0.25texttenthousand. However, the Fe isotopic signatures of the black shales are not consistent with iron shuttling, mixing of authigenic and detrital sources, or hydrothermal metal enrichment. Instead, they most likely resulted from partial oxidation of pyrite through the syndepositional oxidizing hydrothermal fluids (Si--Ba enrichment), which resulted in precipitation of isotopically heavy Fe-oxyhydroxides. We propose that our maximal recorded $delta$98Mo value (+ 0.98texttenthousand) might represent the best estimate for the ancient local seawater Mo composition at around 533 Ma and argues against deep-ocean oxygenation in the early Cambrian. On the other hand, the Se/Co ratios of synsedimentary pyrite indicate a mean atmosphere O2 value of textasciitilde27%.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ElKorh_etal2017,

title = {Investigation of Ge and Ga exchange behaviour and Ge isotopic fractionation during subduction zone metamorphism},

author = {A. El Korh and B. Luais and M. C. Boiron and E. Deloule and D. Cividini},

doi = {10.1016/j.chemgeo.2016.11.017},

year  = {2017},

date = {2017-01-01},

journal = {Chemical Geology},

volume = {449},

pages = {165--181},

abstract = {Germanium(Ge) and gallium(Ga) are slightly to moderately incompatible trace elements during magmatic processes and may be indicators of the nature of the mantle source. Because of their solubility in fluids, Ge and Ga are also geochemical tracers of various hydrothermal processes. Understanding high-pressure/low-temperature (HP--LT) recycling processes of Ge and Ga through fluid-mediated mass transfers in subduction zones can then allow discussing whether they can be source of geochemical heterogeneities in the mantle wedge. We have analysed Ge and Ga abundances and Ge isotope composition of a series of well-characterised HP--LT metabasites of mid-ocean ridge basalt (MORB) affinity and pelitic micaschists fromthe Ile de Groix (France), to determine Ge and Ga behaviour and Ge isotope fractionation during subduction zone metamorphism(SZM). Metabasites have Ge and Ga contents of 1.2--2.1 ppm and 17--22 ppm, respectively, typical of tholeiitic basalts. Garnet-bearing blueschists and eclogites have $delta$74Ge values (+0.42 to +0.65texttenthousand) similar within error to that of tholeiitic basalts (+0.55 to +0.57texttenthousand ; Luais, 2012). Our study shows that during the prograde metamorphism, Ge and Ga abundances and $delta$74Ge values do not vary from blueschists to eclogites, owing to the large stability field of Ge- and Ga-hosting minerals (epidote, garnet, titanite, amphiboles and omphacite) under varying P--T conditions. During the retrograde metamorphism, the slight decrease of the Ga content of c. 8% in greenschists (19 textpm 1 ppm ; 2$sigma$) compared to HP rocks (21 textpm 1 ppm ; 2$sigma$) suggests Ga loss during retrogression, whereas Ge abundances remain within the same range as blueschists and eclogites. In the garnet-bearing greenschists (early stages of retrogression), the $delta$74Ge values (+0.38 to +0.49texttenthousand) remain similar within error to HP rocks. However, albite- and calcite-bearing greenschists have higher $delta$74Ge values (+0.84 to +0.98texttenthousand), showing evidence of Ge fractionation under intensive fluidrock interactions (late stage of retrogression). Micaschists have Ge and Ga abundances within the same range as continental crust and schists. Their variations in $delta$74Ge (+0.29 to+0.70texttenthousand) reflect variations in the sedimentary source and protolith composition. The relatively small variation of $delta$74Ge values inmetabasites compared tomantle rocks implies that the subducted oceanic crust cannot trigger Ge isotopic heterogeneities in the mantle through fluid-induced metasomatism or recycling in the deep mantle. However, during the late stages of retrogression, migration of oxidising fluids along the crust-mantle wedge may be responsible for a resolvable increase of the $delta$74Ge value of the mantle wedge along the subduction channel. Besides, the larger range of Ge concentrations and $delta$74Ge values in the micaschists suggests that recycling of subducted sediments may generate mantle Ge elemental and isotopic heterogeneities.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ElKorh_etal2017_2,

title = {Iron isotope fractionation in subduction‑related high‑pressure metabasites (Ile de Groix, France)},

author = {A. El Korh and B. Luais and E. Deloule and D. Cividini},

doi = {10.1007/s00410-017-1357-x},

year  = {2017},

date = {2017-01-01},

journal = {Contributions to Mineralogy and Petrology},

volume = {172},

pages = {41},

abstract = {Characterisation of mass transfer during subduction is fundamental to understand the origin of compositional heterogeneities in the upper mantle. Fe isotopes weremeasured in high-pressure/low-temperature metabasites (blueschists, eclogites and retrograde greenschists) from the Ile de Groix (France), a Variscan high-pressure terrane, to determine if the subducted oceanic crust contributes to mantle Fe isotope heterogeneities. The metabasites have $delta$56Fe values of +0.16 to +0.33texttenthousand, which are heavier than typical values of MORB and OIB, indicating that theirbasaltic protolith derives from a heavy-Fe mantle source. The $delta$56Fe correlates well with Y/Nb and (La/Sm)PM ratios, which commonly fractionate during magmatic processes, highlighting variations in the magmatic protolith composition. In addition, the shift of $delta$56Fe by +0.06 to 0.10texttenthousand compared to basalts may reflect hydrothermal alteration prior to subduction. The $delta$56Fe decrease from blueschists(+0.19 textpm 0.03 to +0.33 textpm 0.01texttenthousand) to eclogites (+0.16 textpm 0.02 to +0.18 textpm 0.03texttenthousand) reflects small variations in the protolith composition, rather than Fe fractionation during metamorphism: newly-formed Fe-rich minerals allowed preserving bulk rock Fe compositions during metamorphic reactions and hampered any Fe isotope fractionation. Greenschists have $delta$56Fe values (+0.17 textpm 0.01 to+0.27 textpm 0.02texttenthousand) similar to high-pressure rocks. Hence, metasomatism related to fluids derived from the subducted hydrothermally altered metabasites might only have a limited effect on mantle Fe isotope composition under subsolidus conditions, owing to the large stability of Fe-rich minerals and low mobility of Fe. Subsequent melting of the heavy-Fe metabasites at deeper levels is expected to generate mantle Fe isotope heterogeneities.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Liu_etal2014,

title = {Disequilibrium iron isotopic fractionation during the high-temperature magmatic differentiation of the Baima Fe--Ti oxide-bearing mafic intrusion, SW China},

author = {P. P. Liu and M. F. Zhou and B. Luais and D. Cividini and C. Rollion-Bard},

doi = {10.1016/j.epsl.2014.05.002},

year  = {2014},

date = {2014-01-01},

journal = {Earth and Planetary Science Letters},

volume = {399},

pages = {21--29},

keywords = {},

pubstate = {published},

tppubtype = {article}

}