Guillaume Caro

@article{Grocolas_etal2022,

title = {Eoarchean subduction-like magmatism recorded in 3750 Ma mafic--ultramafic rocks of the Ukaliq supracrustal belt (Qu\'{e}bec)},

author = {T. Grocolas and P. Bouilhol and G. Caro and S. Mojzsis},

doi = {10.1007/s00410-022-01904-x},

year  = {2022},

date = {2022-01-01},

journal = {Contributions to Mineralogy and Petrology},

volume = {177},

number = {39},

abstract = {Our understanding of the nature of crustal formation in the Eoarchean is limited by the scarcity and poor preservation of the oldest rocks and variable and imperfect preservation of protolith magmatic signatures. These limitations hamper our ability to place quantitative constraints on thermomechanical models for early crustal genesis and hence on the operative geodynamic regimes at that time. The recently discovered ca. 3.75 Ga Ukaliq supracrustal enclave (northern Qu\'{e}bec) is mainly composed of variably deformed and compositionally diverse serpentinized ultramafic rocks and amphibolitized mafic schists whose metamorphic peak, inferred from phase equilibria modeling, was below 720 textdegreeC. Inferred protoliths to the Ukaliq ultramafic rocks include cumulative dunites, pyroxenites, and gabbros, whereas the mafic rocks were probably picrites, basalts, and basaltic andesites. The bulk-rock and mineral chemistry documents the partial preservation of cumulative pyroxenes and probably amphiboles and demonstrates the occurrence of a clinopyroxene-dominated, tholeiitic suite and an orthopyroxene-dominated, boninite-like suite. Together with the presence of negative $mu$142Nd anomalies in the boninitic basalts, two liquid lines of descent are inferred : (i) a damp tholeiitic sequence resulting from the fractionation of a basaltic liquid produced by mantle decompression ; and (ii) a boninitic suite documenting the evolution of an initially primitive basaltic andesite liquid produced by flux melting. Petrographic observations, thermodynamic modeling, bulk-rock and mineral chemistry, and 142Nd isotopic compositions identify the Ukaliq supracrustal belt as the remnant of an Eoarchean arc crust produced by the recycling of Hadean crust in a similar way as modern-style subduction.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Maltese_etal2022,

title = {Direct evidence for crust-mantle differentiation in the late Hadean},

author = {A. Maltese and G. Caro and O. P. Pandey and D. Upadhyay and K. Mezger},

doi = {10.1038/s43247-022-00341-9},

year  = {2022},

date = {2022-01-01},

journal = {Communications Earth \& Environment},

volume = {3},

number = {12},

abstract = {Constraints on the evolution of the silicate Earth between 4.5 and 3.8 billion years ago are limited by the scarcity of pristine geological material from that period. The geodynamic evolution of the early Earth, prior to the preserved rock record, is thus mainly inferred from numerical modelling. To evaluate the geological significance of these simulations, geochronological constraints pertaining to the evolution of the Hadean crust are required. Here we show using Neodymium isotope variations generated by decay of now-extinct 146-Samarium that Paleoarchean rocks from the Singhbhum Craton, India derived from a Hadean depleted mantle reservoir that differentiated 4.19+0.06\^{a}ˆ’0.12 billion years ago. The event postdates Neodymium model ages of mantle depletion inferred from other Archean rocks by 200 million years. This geochronological record is mirrored in the Hafnium isotope composition of the oldest zircon grains, suggesting that Hadean mantle differentiation proceeded via distinct pulses of large-scale magmatic activity and crustal rejuvenation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Davenport_etal2022,

title = {Decoupling of physical and chemical erosion in the Himalayas revealed by radiogenic Ca isotopes},

author = {J. Davenport and G. Caro and C. France-Lanord},

doi = {10.1016/j.gca.2022.10.031},

year  = {2022},

date = {2022-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {338},

pages = {199--219},

abstract = {Determining the rate of CO2 consumption associated with the Himalayan uplift is an essential prerequisite to understanding climate evolution throughout the Cenozoic. The riverine fluxes of dissolved calcium can be used to quantify uptakes of atmospheric CO2 by chemical weathering, but this approach requires deciphering the silicate-derived Ca flux from the generally dominant carbonate-derived Ca flux. Here we present high-precision radiogenic calcium (40Ca) analyses of bank sediments and dissolved loads from a network of rivers in central Nepal Himalaya and Bangladesh, to constrain the sources and relative contributions of carbonate and silicate-derived calcium to the dissolved loads of Himalayan rivers. Calcium isotope analyses were performed in multidynamic mode by thermal ionization mass spectrometry, yielding an external precision of textpm0.4 $epsilon$-units (2 S.D.). Our results show that silicate catchments exposed in the Himalayan range have variably radiogenic $epsilon$40Ca compositions relative to seawater, ranging from +0.7 in the TSS to +14 in the LH. In contrast, sedimentary carbonates, including metamorphosed dolomites with variably radiogenic 87Sr/86Sr, exhibit uniform $epsilon$40Ca identical to modern seawater. The homogeneous $epsilon$40Ca composition of sedimentary carbonates confirms the relative resistance of radiogenic Ca signatures to post-depositional alteration and provides a robust baseline against which the contribution of silicate weathering to the riverine Ca flux can be evaluated. Dissolved load compositions of rivers draining LH catchments exhibit $epsilon$40Ca values ranging from 0 to +11, reflecting the relative contribution of unradiogenic carbonates and highly radiogenic metapelitic units of the LH sequence. HHC rivers show a more moderate range, from 0.5 to +2, reflecting the less radiogenic composition of HHC paragneisses. Himalayan front rivers draining all three lithotectonic units of the Himalayan range exhibit moderately radiogenic $epsilon$40Ca, ranging from +0.5 to +1.4 and overall similar to the average composition of the Ganga mainstream in Bangladesh. Using an approach combining conventional alkalinity budgets with isotopic mass balance calculations, we show that the dissolved silicate Ca flux of major Himalayan front rivers is primarily derived from the weathering of metapelitic rocks of the lesser Himalaya. In contrast, regions of the high range that generate the bulk of the detrital flux to the Gangetic floodplain represent a subordinate source of silicate-derived Ca. This result demonstrates that the chemical weathering of Ca-silicates in the Himalayan system is decoupled from physical erosion. The extensive erosional activity observed in the high range may thus play a limited role in promoting CO2 consumption and global cooling by silicate weathering.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Greer_etal2020,

title = {Widespread poly-metamorphosed Archean granitoid gneisses and supracrustal enclaves of the southern Inukjuak Domain, Qu\'{e}bec (Canada)},

author = {J. Greer and G. Caro and N. L. Cates and P. Tropper and W. Bleeker and N. M. Kelly and S. J. Mojzsis},

doi = {10.1016/j.lithos.2020.105520},

year  = {2020},

date = {2020-01-01},

journal = {Lithos},

volume = {364-365},

pages = {105520},

abstract = {The textasciitilde12,000 km2 Inukjuak Domain in northern Qu\'{e}bec is part of the Archean Minto Block in the northwestern Superior Province of Canada. Eoarchean (ca. \>3800--3780 Ma) rocks of the Nuvvuagittuq supracrustal belt (NSB) are the best known occurrence of otherwise abundant \<1 m to km-scale supracrustal enclaves dispersed throughout the Innuksuac Complex. The supracrustals are dominantly amphibolites, with subordinate intermediate-, mafic- and ultramafic schists, quartzo-feldspathic (trondhjemitic and granodioritic) sills, dikes and sheets, banded iron-formations and quartz-pyroxenetextpmmagnetite rocks, and (detrital) fuchsitic quartzites. Supracrustal assemblages are in turn hosted by variably deformed granite-granitoid gneisses metamorphosed to amphibolite facies. Locally, retrogression is expressed as pervasive chloritization and development of jaspilite box veinings. This metamorphic history precludes preservation of original fragile microfossil shapes. Despite its importance as one of the few terranes to host Eoarchean supracrustal assemblages, limited geochronology was previously available for rocks beyond the textasciitilde8 km2 NSB. Here, we report new major-, minor-, and trace-element geochemistry and metamorphic petrology coupled with Usingle bondPb zircon geochronology, from rocks within and surrounding the NSB. These include the little-studied but volumetrically significant Voizel suite gneisses. Results show that intra-NSB fold belt rocks of the Central Tonalitic Gneiss (CTG) preserve mainly ca. 3650 Ma zircons. Beyond the NSB, the Voizel gneisses -- previously considered contemporaneous with the CTG -- are instead about 100 Myr younger (textasciitilde3550 Ma). Tonalitic (ortho)gneisses at the margin of the NSB were previously assigned a ca. 3650 Ma age, and the surrounding Boizard suite gneisses may be about 2700 Ma. We find the Boizard rocks contain inherited zircon cores up to ca. 3700 Ma, with younger overgrowths dated at ca. 2700 Ma. A tonalitic gneiss that transects another highly deformed supracrustal enclave north of the NSB -- dubbed the Ukaliq Supracrustal Belt -- yields maximum concordant zircon ages of 3653 textpm 16 Ma (2$sigma$). Detrital zircons from Ukaliq and Nuvvuagittuq quartzites and quartz-biotite schists define a maximum age of ca. 3780 Ma. No indication of Usingle bondPb zircon ages older than about 3800 Ma exist in this terrane from our geochronological surveys. New reconnaissance sampling of gneisses to the west of the NSB fold belt yielded more zircon-bearing rocks with ages of ca. 3760 Ma. This discovery of more pre-3700 Ma rocks beyond the NSB outcrops calls attention to the existence of hitherto unidentified but widespread scattered occurrences of Eoarchean and Paleoarchean rocks throughout the region.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Morino_etal2018,

title = {Differentiation mechanisms of the early Hadean mantle: Insights from combined 176 Hf- 142,143 Nd signatures of Archean rocks from the Saglek Block},

author = {P. Morino and G. Caro and L. Reisberg},

doi = {10.1016/j.gca.2018.08.026},

year  = {2018},

date = {2018-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {240},

pages = {43--63},

abstract = {Positive 142Nd anomalies in Eoarchean rocks provide evidence for early (4.40 textpm 0.03 Ga ; Morino et al., 2017) depletion of Earthtextquoterights mantle. This model age lies within errors of the Pb-Pb textquotelefttextquoteleftage of the Earthtextquoterighttextquoteright (Connelly and Bizzarro, 2016), and is similar to model ages inferred for crystallization of the lunar mantle (McLeod et al., 2014), implying that this large-scale event may reflect crystallization of a magma ocean following the Moon-forming impact. However, differentiation mechanisms responsible for the formation of this early depleted mantle reservoir and the depth at which it formed cannot be constrained from the Sm-Nd isotope system alone, because the magnitude of Sm/Nd fractionation during partial melting or fractional crystallization shows little dependence on pressure-controlled changes in mantle mineralogy. In contrast, the Lu-Hf isotope system is highly dependent on mineralogy, notably the presence or absence of garnet, an upper mantle phase, and thus may be used to constrain the pressure of fractionation. This study provides the first 176Lu-176Hf isotopic results on mafic and ultramafic rocks belonging to the Eoarchean (Nulliak) and Mesoarchean suites of the Saglek Block (northern Labrador, 3.2--3.9 Ga). The 176Lu-176Hf dating confirms the distinction between these two groups of rocks and provides ages consistent with those obtained from 147Sm-143Nd dating. The whole rock 176Lu-176Hf errorchrons yield ages and initial epsilon values of 3766 textpm 140 Ma, $epsilon$176Hfi = 6.0 textpm 2.5 and 3023 textpm 390 Ma, $epsilon$176Hfi = −0.3 textpm 2.5 for the Nulliak suite and the Mesoarchean suite respectively. The time-integrated 176Lu/177Hf for the sources of the Nulliak and the Mesoarchean suites considering a time of differentiation at 4.40 textpm 0.03 Ga are estimated to be 0.047 textpm 0.005 and 0.033 textpm 0.005, respectively. For the Mesoarchean samples, the combined 146,147Sm-142,143Nd and 176Lu-176Hf data are consistent with a near-chondritic mantle source. On the other hand, Nulliak ultramafic rocks were derived from a mantle reservoir with superchondritic Lu/Hf and Sm/Nd. The Nulliak parent reservoir, however, does not plot on the $epsilon$176Hf-$epsilon$143Nd mantle array defined by modern oceanic basalts. Instead, the Nulliak source more likely belongs to a distinct array defined by Eo- and Meso-Archean komatiites. These results are interpreted in the framework of a simple model of crystallization of a primordial magma ocean. It appears that the fractionation observed in the mantle source of Nulliak was most likely generated by crystallization of a garnet-bearing assemblage in the shallow mantle, above the transition zone rather than by perovskite fractionation in the lower mantle. To preserve this depleted reservoir from the rest of the hot and vigorously convecting mantle, the Nulliak mantle source may have been isolated either at the top of the mantle in a buoyant lithosphere or near the core-mantle boundary, with the latter setting being more consistent with the komatiitic nature of the erupted rocks. Given that the garnet signature argues for differentiation of the Nulliak source at relatively shallow depth (few hundred kilometers), its isolation in the deep mantle would require a cumulate overturn following crystallization of the magma ocean.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Caro_etal2017,

title = {Sluggish Hadean geodynamics: Evidence from coupled 146,147Sm-142,143Nd systematics in Eoarchean supracrustal rocks of the Inukjuak domain (Qu\'{e}bec)},

author = {G. Caro and P. Morino and S. J. Mojzsis and N. L. Cates and W. Bleeker},

doi = {10.1016/j.epsl.2016.09.051},

year  = {2017},

date = {2017-01-01},

journal = {Earth and Planetary Science Letters},

volume = {457},

pages = {23--37},

abstract = {The discovery of deficits in 142Nd/144Nd in mafic rocks of the Nuvvuagittuq supracrustal belt (NSB) has triggered a debate about the possible preservation of Hadean (pre-3.85 Ga) crustal remnants in the little-known but areally extensive Innuksuac complex (3.6--3.8 Ga, Inukjuak domain, Northeast Superior Province, Canada). Geochronological investigations in the NSB, however, are hampered by the poor preservation and highly disturbed isotopic record of various mafic (amphibolite) lithologies that host the 142Nd anomalies. Here we present 146Sm--142Nd and 147Sm--143Nd data for rocks of extrusive magmatic and sedimentary protoliths from the Ukaliq supracrustal belt, a newly discovered volcano-sedimentary enclave enclosed in granitoid gneisses of the Inukjuak domain. Our study also includes the first 146Sm--142Nd data for quartz-magnetite rocks (banded iron-formation ; BIF) of the NSB and the Eoarchean Isua supracrustal belt (ISB) in southern West Greenland. We show that Ukaliq amphibolites carry variably negative 142Nd anomalies, ranging from 0 to −10 ppm, which are positively correlated with their Sm/Nd ratio. If considered as an isochron relationship, the 146Sm--142Nd array yields an apparent Hadean emplacement age of 4215−76+50 Ma. The negative 142Nd anomalies, however, appear to be mainly restricted to amphibolites with boninitic affinities, likely reflecting inheritance from an enriched mantle source. In contrast, tholeiitic and ultramafic lavas have normal $mu$142Nd regardless of their Sm/Nd ratio. Furthermore, BIF from Ukaliq and Nuvvuagittuq lack the negative 142Nd anomalies that should have been produced by in situ decay of 146Sm had these sediments been deposited prior to ca. 4.1 Ga. Instead, they exhibit $mu$142Nd identical to that measured in Isua BIF. Collectively, our results suggest that the 146Sm--142Nd array characterizing mafic lithologies of Ukaliq and Nuvvuagittuq is an inherited signature with doubtful chronological significance. We interpret the volcanic protoliths of the Innuksuac complex to have been produced by metasomatically triggered melting of a variably enriched Eoarchean mantle, following addition of felsic melts and/or fluids derived from a foundering Hadean mafic crust. Application of coupled 146,147Sm--142,143Nd chronometry to Ukaliq lavas yields a model age of differentiation of 4.36−0.06+0.05 Ga for this Hadean precursor. This is similar to late-stage crystallization ages inferred for the lunar and terrestrial magma oceans. The long-term preservation of Earthtextquoterights primordial crust points to subdued lithospheric recycling in the post-magma ocean Earth.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Morino_etal2017,

title = {Chemical stratification in the post-magma ocean Earth inferred from coupled 146,147Sm--142,143Nd systematics in ultramafic rocks of the Saglek block (3.25--3.9 Ga; northern Labrador, Canada},

author = {P. Morino and G. Caro and L. Reisberg and A. Schumacher},

doi = {10.1016/j.epsl.2017.01.044},

year  = {2017},

date = {2017-01-01},

journal = {Earth and Planetary Science Letters},

volume = {463},

pages = {136--150},

abstract = {The coupled 146,147Sm--142,143Nd chronometer has the potential to provide precise constraints on both the age and the composition of silicate reservoirs generated by magma ocean processes on accreting planets. Application of this chronometer to early Earth differentiation, however, is made difficult by the poor preservation and complex geological history of Eoarchean rocks hosting 142Nd anomalies, which often prevents accurate determination of their initial 143Nd/144Nd ratios. In order to better constrain the chronological aspects of Earthtextquoterights formation, we investigated the 146,147Sm--142,143Nd systematics of well-preserved mafic/ultramafic enclaves of the Archean Saglek block of northern Labrador (3.25--3.9Ga). Our results show that two distinct ultramafic suites are present within the Hebron/Saglek fjords region. The first group of samples, with $mu$142Nd=1.6 textpm2.8 and $epsilon$143Ndi=0.4 textpm0.4, yields a whole-rock isochron age of 3365 textpm100 Ma and is tentatively suggested to be associated with the Mesoarchean Upernavik formation. The second group, with $mu$142Nd= 8.6 textpm3.3ppm and $epsilon$143Ndi=1.4 textpm0.6, yields an Eoarchean date of 3782 textpm93 Ma, and is assigned to the Nulliak assemblage. Application of coupled 146,147Sm--142,143Nd chronometry to the Nulliak suite yields a model age of differentiation of 4.40+0.05−0.06Ga, and a corresponding (147Sm/144Nd) source ratio of 0.211 textpm0.007 for the early depleted mantle. These estimates are remarkably similar to those obtained for a tholeiitic lava of the Abitibi greenstone belt (Theotextquoterights flow, 2.7Ga) based on the 142,143Nd dataset of Debaille et al.(2013). Viewed in conjunction with previous 142,143Nd data, our results provide a precise estimate of the age of primordial differentiation of Earthtextquoterights mantle, 160+30−20Myrafter formation of the solar system. This chronological constraint, combined with evidence for late solidification of the lunar magma ocean, strongly supports a young age for the giant impact and the Earth--Moon system. Further, the similarity of 146,147Sm--142,143Nd model ages and (Sm/Nd) source ratios inferred for Nulliak, Isua and Theotextquoterights flow suggests that their parent magmas were derived from a common mantle reservoir. This early depleted domain appears to have evolved as a closed-system on a multi-billion year timescale despite efficient mixing in the hot Hadean/Archean mantle. We thus propose that the occurrence of positive 142Nd anomalies in the Archean rock record reflects episodic melting of a depleted reservoir otherwise isolated from the convective system, rather than progressive homogenization of a highly depleted Hadean mantle.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Davenport_etal2014,

title = {Tracing silicate weathering in the Himalaya using the 40K-40Ca system: A reconnaissance study},

author = {J. Davenport and G. Caro and C. France-Lanord},

doi = {10.1016/j.proeps.2014.08.030},

year  = {2014},

date = {2014-01-01},

journal = {Procedia Earth and Planetary Science},

volume = {10},

pages = {238--242},

abstract = {Himalayan erosional system. To this end, we present high precision 40Ca data on river sediments, dissolved river loads and whole-rock carbonates representative of the main tectonic units of the Himalayas. Our results show that metamorphoseddolomites from the Lesser Himalaya (LH) exhibit no radiogenic 40Ca excess despite highly variable 87Sr/86Sr signatures (0.73-0.85). In contrast, silicate material is radiogenic, with $epsilon$40Ca ranging between +1 in the TSS to +4 $epsilon$-units in the LH. Preliminary results obtained from a series of 27 Himalayan rivers show that $epsilon$40Ca in the dissolved load is significantly influenced by silicate lithologies, with $epsilon$40Ca ranging from +0.1 to +1.6 $epsilon$-units. Our results suggest that the 40Ca signature of Himalayan rivers primarily reflects the lithological nature of their erosional source, and highlights the potential of the 40K-40Ca decay scheme as atracer of silicate weathering.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Caro2011,

title = {Early silicate earth differentiation},

author = {G. Caro},

year  = {2011},

date = {2011-01-01},

journal = {Annual Review of Earth and Planetary Science},

volume = {39},

pages = {31--58},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Caro+Bourdon2010,

title = {Non-chondritic Sm/Nd ratio in the terrestrial planets: Consequences for the geochemical evolution of the mantle-crust system},

author = {G. Caro and B. Bourdon},

doi = {10.1016/j.gca.2010.02.025},

year  = {2010},

date = {2010-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {74},

number = {11},

pages = {3333--3349},

abstract = {Super-chondritic 142Nd signatures are ubiquitous in terrestrial, Martian and lunar samples, and indicate that the terrestrial planets may have accreted from material with Sm/Nd ratio higher than chondritic. This contradicts the long-held view thatchondrites represent a reference composition for the 147Sm--143Nd system. Using coupled 146Sm--142Nd and 147Sm--143Nd systematics in planetary samples, we have proposed a new set of values for the 147Sm/144Nd and 143Nd/144Nd ratios of the bulksilicate Earth (Caro et al., 2008). Here, we revise the Bulk Silicate Earth estimates for the 87Rb--87Sr and 176Lu--176Hf systems using coupled Sr--Nd--Hf systematics in terrestrial rocks. These estimates are consistent with Hf--Nd systematics in lunar samples.The implications of a slightly non-chondritic silicate Earth with respect to the geochemical evolution of the mantle--crust system are then examined. We show that the Archean mantle has evolved with a composition indistinguishable from that ofthe primitive mantle until about 2 Gyr. Positive e143Nd and e176Hf values ubiquitous in the Archean mantle are thusaccounted for by the non-chondritic Sm/Nd and Lu/Hf composition of the primitive mantle rather than by massive early crustalformation, which solves the paradox that early Archean domains only have a limited extension in the present-day continents.The Sm--Nd and Lu--Hf evolution of the depleted mantle for the past 3.5 Gyr can be entirely explained by continuousextraction of the continents from a well-mixed mantle. Thus, in contrast to the chondritic Earth model, Sm--Nd mass balancerelationships can be satisfied without the need to call upon hidden reservoirs or layered mantle convection. This new Sm--Ndmass balance yields a scenario of mantle evolution consistent with trace element and noble gas systematics. The high 3He/4Hemantle component is associated with 143Nd/144Nd compositions indistinguishable from the bulk silicate Earth, suggesting thatthe less degassed mantle sources did not experience significant fractionation for moderately incompatible elements.},

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pubstate = {published},

tppubtype = {article}

}