New detections of feldspar-bearing volcanic rocks in the walls of Valles Marineris, Mars

Data is a collection of Tiff files of the different series bundled into zip files.Eight new detections of plagioclase-like signatures are reported in their original geologic context in the walls of Valles Marineris. At one location, the feldspar signatures are clearly associated with a 200 m thick sub-horizontal layer, hinting at an eruptive origin. DTM and image were calculated using the NASA Ames Stereopipeline.Detection of plagioclase feldspar minerals from remote sensing instruments onboard Mars missions is difficult, and only a handful of occurrences have been reported so far. We present here new detections of such minerals in the giant martian canyon of Valles Marineris, exposed in their original context, and associated at least in one location, to a 200 m thick sub-horizontal layer within the walls. Analyses were performed using visible near-infrared spectral data, which are commonly compared to reference spectra of known terrestrial minerals, or mineral powders, acquired in the laboratory. Whereas previous detections were interpreted as evidence for plagioclase-dominated, or at least, nearly mafic-free, plutonic rocks, we argue here that the Valles Marineris outcrops correspond to erupted, volcanic products. The signature of plagioclase could originate from large crystals hosted in mafic, intermediate, or felsic volcanic rocks; from a lava flow, or from welded ashes. Our new observations confirm that plagioclase detections on Mars can correspond to multiple types of rocks and bring more clues to ongoing debates regarding the extent of Mars' magmatic processes and the nature of its crust.We are grateful to the Mars Reconnaissance Orbiter team for the availability of the data. This study was supported by the CNRS Momentum, LUE future leader programs, and the French “Program National de Planétologie”. The authors acknowledge the support of the French Agence Nationale de la Recherche (ANR), under grant ANR-21-CE49-0003 (MARS-Spec). CRISM data have been processed with the MarsSI (marssi.univ-lyon1.fr) application founded by the European Union’s Seventh Framework Program (FP7/2007-2013) (ERC Grant Agreement No. 280168). The component of the work by Frank Fueten was funded by an NSERC discovery grant

Tectono-Thermal History of the Neoarchean Balehonnur Shear Zone, Western Dharwar Craton (Southern India)

AbstractA widely spaced Neoarchean shear zone network traverses the granite-greenstone terrains of the Western Dharwar craton (WDC). The NNW-SSE trending Balehonnur shear zone traverses the largest part of the preserved tilted Archean crustal ensemble in the Western Dharwar craton (WDC) from the amphibolite-granulite transition in the south to greenschist facies in the north and eventually concealed under Deccan lava flows. Published tectonic fabrics data and kinematic analysis, with our data reveal a sinistral sense of shearing that effectuate greenstone sequences, Tonalite-Trondhjemite-Granodiorite Gneisses (TTG), and Koppa granite as reflected in variable deformation and strain localization. A profound increase of strain towards the core of the shear zone in the ca. 2610 Ma Koppa granite is marked by a transition from weak foliation outside the shear zone through the development of C-S structures and C-prime fabrics, mylonite to ultramylonite. The mineral assemblages in the Koppa granite and adjoining greenstone indicate near peak P-T conditions of 1.2 Gpa, 775-800°C following a slow cooling path of 1.0 GPa and 650°C. Field-based tectonic fabrics data together with U-Pb zircon ages reveal that the Koppa granite emplaced along the contact zone of Shimoga-Bababudan basin ca. 2610 Ma, coinciding with the emplacement of ca. 2600 Ma Arsikere-Banavara, Pandavpura, and Chitradurga granites further east which mark the stabilization of WDC. Significant variation in major element oxide (SiO2 = 56-69 wt.%) together with high content of incompatible elements (REE, Nb, Zr, and Y) and high zircon crystallization temperatures (~1000°C) of Koppa granite suggests derivation by partial melting of composite sources involving enriched uppermost mantle and lower crust. The development of widely spaced shear zones is probably linked to the assembly of eastern and western blocks through westward convergence of hot oceanic lithosphere against already cratonized thick colder western block leading to the development of strain heterogeneities between greenstone and TTGs due to their different mineral assemblages leading to rheological contrast in the cratonic lithologies

Les isotopes de l'hafnium dans les TTG et leurs zircons : témoins de la croissance des premiers continents

This PhD thesis presents combined whole-rock and single zircon MC-ICP-MS Lu-Hf isotope data for a large collection of Archean granitoids belonging to typical Tonalite-Trondhjemite-Granodiorite (TTG) suites. The data were collected in an attempt to shed new light on early crustal growth. Our data display overall good agreement between Hf isotope compositions of igneous zircons, measured by both laser-ablation and solution chemistry, and their host-rocks. It is shown that the time-integrated Lu/Hf of the mantle source of TTGs is near-chronditic and has not significantly changed over the last 4 Gy. Continents therefore most likely grew from nearly primordial unfractionated material extracted from the deep mantle via rising plumes that left a depleted melt residue in the upper mantle. Zircons extracted from the analyzed TTGs have Hf isotopic compositions broadly consistent within populations, whereas the U-Pb system in the same grains is often disturbed, causing spurious initial εHf values. This problem is endemic to the Archean detrital zircon record and consistent with experimental results bearing on the relative retentivity of Hf vs. U and Pb in zircon. We argue that this behavior biases the Archean zircon record towards negative εHf values, which are at odds with the present TTG data set but can be explained by zircons having non-magmatic 207Pb/206Pb ages. If the Hadean Jack Hills zircons are considered in light of these results, the mantle source of continents has remained unchanged for the last 4.3 Gy.Ce travail de thèse présente des analyses isotopiques Lu-Hf par MC-ICP-MS combinées de zircons ignés et de roches totales d’une importante collection de granitoïdes archéens appartenant à la suite des Tonalite-Trondhjémite-Granodiorite (TTG) afin d’apporter un regard nouveau sur la croissance de la croûte continentale et tout particulièrement dans le début de l’histoire de la Terre. Nos données indiquent un bon accord général entre les zircons ignés, mesurés par ablation-laser et par solution, avec leurs roche-hôtes. Nous démontrons que le rapport Lu/Hf intégré dans le temps de la source mantellique des TTG est près de la valeur chondritique et n’a pas significativement changée au cours des 4 derniers milliards d’années. Par conséquent, les continents se sont formés à partir d’un matériel primitif non fractionné extrait du manteau profond par l’intermédiaire de panaches qui après fusion partielle ont laissés un résidu appauvri dans le manteau supérieur. Les cristaux de zircon extraits des TTG ont des compositions isotopiques en Hf cohérentes au sein d’une même population alors que le système U-Pb, dans les mêmes grains, est souvent perturbé résultant ainsi en l’obtention de valeurs d’εHf initial erronées. Ce problème est endémique aux cristaux de zircon détritiques archéens et en accord avec des résultats expérimentaux sur la mobilité préférentielle de l’Hf en fonction de celle de l’U et du Pb au sein du zircon. Nous suggérons que ce problème biaise l’enregistrement détritique archéen en faveur de valeurs d’εHf initial négatives qui contrastent avec les valeurs obtenues pour les TTG mais peuvent être expliquées par l’utilisation d’âges 207Pb/206Pb non-magmatiques. Si l’on considère les cristaux de zircon de Jack Hills au vu de ces résultats, la source des continents serait restée inchangée depuis 4,3 Ga

Hafnium isotopes in TTGs and their zircons : witnesses of the growth of first continents

Ce travail de thèse présente des analyses isotopiques Lu-Hf par MC-ICP-MS combinées de zircons ignés et de roches totales d’une importante collection de granitoïdes archéens appartenant à la suite des Tonalite-Trondhjémite-Granodiorite (TTG) afin d’apporter un regard nouveau sur la croissance de la croûte continentale et tout particulièrement dans le début de l’histoire de la Terre. Nos données indiquent un bon accord général entre les zircons ignés, mesurés par ablation-laser et par solution, avec leurs roche-hôtes. Nous démontrons que le rapport Lu/Hf intégré dans le temps de la source mantellique des TTG est près de la valeur chondritique et n’a pas significativement changée au cours des 4 derniers milliards d’années. Par conséquent, les continents se sont formés à partir d’un matériel primitif non fractionné extrait du manteau profond par l’intermédiaire de panaches qui après fusion partielle ont laissés un résidu appauvri dans le manteau supérieur. Les cristaux de zircon extraits des TTG ont des compositions isotopiques en Hf cohérentes au sein d’une même population alors que le système U-Pb, dans les mêmes grains, est souvent perturbé résultant ainsi en l’obtention de valeurs d’εHf initial erronées. Ce problème est endémique aux cristaux de zircon détritiques archéens et en accord avec des résultats expérimentaux sur la mobilité préférentielle de l’Hf en fonction de celle de l’U et du Pb au sein du zircon. Nous suggérons que ce problème biaise l’enregistrement détritique archéen en faveur de valeurs d’εHf initial négatives qui contrastent avec les valeurs obtenues pour les TTG mais peuvent être expliquées par l’utilisation d’âges 207Pb/206Pb non-magmatiques. Si l’on considère les cristaux de zircon de Jack Hills au vu de ces résultats, la source des continents serait restée inchangée depuis 4,3 Ga.This PhD thesis presents combined whole-rock and single zircon MC-ICP-MS Lu-Hf isotope data for a large collection of Archean granitoids belonging to typical Tonalite-Trondhjemite-Granodiorite (TTG) suites. The data were collected in an attempt to shed new light on early crustal growth. Our data display overall good agreement between Hf isotope compositions of igneous zircons, measured by both laser-ablation and solution chemistry, and their host-rocks. It is shown that the time-integrated Lu/Hf of the mantle source of TTGs is near-chronditic and has not significantly changed over the last 4 Gy. Continents therefore most likely grew from nearly primordial unfractionated material extracted from the deep mantle via rising plumes that left a depleted melt residue in the upper mantle. Zircons extracted from the analyzed TTGs have Hf isotopic compositions broadly consistent within populations, whereas the U-Pb system in the same grains is often disturbed, causing spurious initial εHf values. This problem is endemic to the Archean detrital zircon record and consistent with experimental results bearing on the relative retentivity of Hf vs. U and Pb in zircon. We argue that this behavior biases the Archean zircon record towards negative εHf values, which are at odds with the present TTG data set but can be explained by zircons having non-magmatic 207Pb/206Pb ages. If the Hadean Jack Hills zircons are considered in light of these results, the mantle source of continents has remained unchanged for the last 4.3 Gy

Les isotopes de l'hafnium dans les TTG et leurs zircons (témoins de la croissance des premiers continents)

Ce travail de thèse présente des analyses isotopiques Lu-Hf par MC-ICP-MS combinées de zircons ignés et de roches totales d une importante collection de granitoïdes archéens appartenant à la suite des Tonalite-Trondhjémite-Granodiorite (TTG) afin d apporter un regard nouveau sur la croissance de la croûte continentale et tout particulièrement dans le début de l histoire de la Terre. Nos données indiquent un bon accord général entre les zircons ignés, mesurés par ablation-laser et par solution, avec leurs roche-hôtes. Nous démontrons que le rapport Lu/Hf intégré dans le temps de la source mantellique des TTG est près de la valeur chondritique et n a pas significativement changée au cours des 4 derniers milliards d années. Par conséquent, les continents se sont formés à partir d un matériel primitif non fractionné extrait du manteau profond par l intermédiaire de panaches qui après fusion partielle ont laissés un résidu appauvri dans le manteau supérieur. Les cristaux de zircon extraits des TTG ont des compositions isotopiques en Hf cohérentes au sein d une même population alors que le système U-Pb, dans les mêmes grains, est souvent perturbé résultant ainsi en l obtention de valeurs d Hf initial erronées. Ce problème est endémique aux cristaux de zircon détritiques archéens et en accord avec des résultats expérimentaux sur la mobilité préférentielle de l Hf en fonction de celle de l U et du Pb au sein du zircon. Nous suggérons que ce problème biaise l enregistrement détritique archéen en faveur de valeurs d Hf initial négatives qui contrastent avec les valeurs obtenues pour les TTG mais peuvent être expliquées par l utilisation d âges 207Pb/206Pb non-magmatiques. Si l on considère les cristaux de zircon de Jack Hills au vu de ces résultats, la source des continents serait restée inchangée depuis 4,3 Ga.This PhD thesis presents combined whole-rock and single zircon MC-ICP-MS Lu-Hf isotope data for a large collection of Archean granitoids belonging to typical Tonalite-Trondhjemite-Granodiorite (TTG) suites. The data were collected in an attempt to shed new light on early crustal growth. Our data display overall good agreement between Hf isotope compositions of igneous zircons, measured by both laser-ablation and solution chemistry, and their host-rocks. It is shown that the time-integrated Lu/Hf of the mantle source of TTGs is near-chronditic and has not significantly changed over the last 4 Gy. Continents therefore most likely grew from nearly primordial unfractionated material extracted from the deep mantle via rising plumes that left a depleted melt residue in the upper mantle. Zircons extracted from the analyzed TTGs have Hf isotopic compositions broadly consistent within populations, whereas the U-Pb system in the same grains is often disturbed, causing spurious initial Hf values. This problem is endemic to the Archean detrital zircon record and consistent with experimental results bearing on the relative retentivity of Hf vs. U and Pb in zircon. We argue that this behavior biases the Archean zircon record towards negative Hf values, which are at odds with the present TTG data set but can be explained by zircons having non-magmatic 207Pb/206Pb ages. If the Hadean Jack Hills zircons are considered in light of these results, the mantle source of continents has remained unchanged for the last 4.3 Gy.LYON-ENS Sciences (693872304) / SudocSudocFranceF

Record of low-temperature aqueous alteration of Martian zircon during the late Amazonian

International audienceSeveral lines of evidence support the presence of liquid water on Mars at different times.Among those, hydrated minerals testify to past aqueous weathering processes that can beprecisely studied in Martian meteorites such as NWA 7533/7034. Bringing constraints onthe timing of weathering of the Martian crust would help understand its evolution, theavailability of liquid water, and the habitability of Mars. Here we present a new method basedon U–Th–Pb isotope systems to assess if zircon crystals underwent low-temperature aqueousalteration, such as exemplified by Hadean-aged detrital crystals from Western Australia. Datafor NWA 7533 zircons show evidence for aqueous alteration and modeling of U–Th–Pbisotope system evolution indicates that the latest alteration event occurred during the lateAmazonian (227–56 Ma). This finding largely expands the time duration over which liquidwater was available near the Martian surface, thereby suggesting that Mars might still behabitable

Implications of discordant U–Pb ages on Hf isotope studies of detrital zircons

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Hafnium isotope evidence for early-Proterozoic volcanic arc reworking in the Skellefte district (northern Sweden) and implications for the Svecofennian orogen

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Editorial: The Early Earth Crust and Its Formation

International audienceEditorial on the Research Topic The Early Earth Crust and Its Formation The geochemical and petrological nature of the early Earth crust, and the processes involved in its formation and stabilization, are critical questions to understand the earliest evolution of our planet, and have yet to be resolved. The ancient rock archives in stable cratons provide the foundation for our understanding of the early formation and evolution of Earth's crust, but it is unlikely that these archives are representative of average early crustal composition or its evolution. Geodynamic modeling and isotope tracers provide key complementary constraints, as well as tests for hypotheses proposed based on the rock record. One of the most fundamental questions that is still unresolved is the timing of the onset of plate tectonics, which is a feature that is unique to the Earth among the known rocky planets. Subduction zones represent the geological environment in which crustal fractionation currently takes place, but it could be argued that this particular setting is not conducive to the long-term preservation of crust due to recycling. Moreover, the style of subduction, or horizontal tectonics more broadly, may have changed during early Earth history, and hence the nature of crusts generated over time. Additionally, the onset of subduction could well have pre-dated global plate tectonics, as the required assemblage of global plates may not have been a stable configuration on the hot young Earth. Interpretations of the ancient rock record are strongly debated and divided among those who support horizontal plate tectonic processes throughout the Archean Eon, and those who invoke a plume-dominated, stagnant lid scenario and infracrustal differentiation with a transition (gradual or abrupt) to modern-style plate tectonics, likely towards the end of the Archean. This Research Topic brings together articles that explore the earliest part of Earth's geological history; from mantle-derived magmas and their fractionation, all the way through partial melting and crustal differentiation to form stable continental crust. The invited review by Hawkesworth et al. comprehensively combines observations from metamorphism, tectonics, geochemistry, petrology and geophysics to infer the nature and secular evolution of the continental crust, and its implications for the onset of plate tectonics. They purposely provide a global picture, which advocates for a transition in the nature of the crust towards a more felsic flavor, coincidental with a proposed onset of plate tectonics at ∼3.0 Ga. The formation and evolution of the early Earth's crust is further evaluated by Garde et al. who reviewed the geological history of the North Atlantic craton of West Greenland and present their conclusions regarding the geodynamical context of its construction from the Eoarchean to Mesoarchean. The authors conclusions advocate for the existence of horizontal tectonics since the Eoarchean

New constraints on the early formation of the Western Dharwar Craton (India) from igneous zircon U-Pb and Lu-Hf isotopes

Co-auteur étrangerInternational audienceThe Western Dharwar Craton (WDC) is an Archean crustal segment for which the earliest stages of developmenthave remained poorly constrained because the oldest identified lithologies are chronologically indistinguishabledespite vastly different compositions and origins (i.e., 3352 ± 110 Ma Sargur-group komatiites and3342 ± 6 Ma Hassan-Gorur TTG gneiss). Indication for older crust come from ancient detrital zircons(3450–3610 Ma), although their genetic link to the WDC is purely conjectural. In order to bring new under-standing to early development of the WDC, we studied orthogneisses around the Holenarsipur Schist Belt (HSB)for their petrography, major-oxide concentrations, zircon U-Pb geochronology, and Lu-Hf isotope systematics.Our results reveal that the WDC igneous record contains crust older than 3350 Ma in the form of a3410.8 ± 3.6 Ma granitic gneiss and inherited zircons with ages ranging from 3295 ± 18 to 3607 ± 16 Mathat were found within a 3178 ± 10 Ma trondhjemitic gneiss and a biotite-rich enclave found within it. Thepresence of muscovite and the peraluminous signature of the granitic gneiss, in spite of mildly-depleted Hfisotopic signature (εHf= +2.2 ± 0.6 at 3410.8 Ma), suggest that this sample formed by reworking of a felsicprecursor with short crustal residence time, possibly marking the beginning of WDC formation. The oldest in-herited zircons display variableεHfranging from +10.4 at 3414 Ma to−2.3 at 3607 Ma that did not seem tohave influenced the Hf isotopic composition of granitoids of the WDC that formed between 3200 and 3410 Ma,except perhaps in the Sargur area. We suggest that the WDC formed remote from continental crust until a crustalblock containing > 3410 Ma zircons was accreted to it∼3200 My ago. This event resulted in the stabilization ofthe WDC which is marked by diapiric granitoids to which the 3178 Ma trondhjemitic gneiss belongs. After3200 Ma, the crustal block together with granitoids formed between 3410 and 3200 Ma buffered the Hf isotopicsignature of newly formed granitoids, hence, indicating that, by then, the WDC already was a stable continentalsegment