Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We present new Sr-Nd-Pb isotope data of the western Alpujárride metamorphic basement and the pre-Miocene Flysch sediments of the Betic Cordillera (southern Spain). Nd model ages are consistent with an increasing detrital input from the Alborán domain to the Flysch Trough in the western Mediterranean during the late Oligocene. The Alpujárride metamorphic crustal rocks derived from Archean-Paleoproterozoic terranes located along the northern margin of Gondwana in the Neoproterozoic. The heterogeneous isotopic signatures of the Alpujárride units indicate that they have different sedimentary protoliths and underwent contrasted Variscan and pre-Variscan tectono-magmatic evolutions. Melts/fluids derived from the western Alpujárride gneisses contaminated the mantle source of the Ronda high-Mg pyroxenite dykes, implying that the Alpujárride lower crust underthrusted the subcontinental lithospheric mantle of the Alborán domain generating subduction-like magmatism in the late Oligocene. The western Alpujárride upper crust is involved in the Neogene volcanism of the Alborán Sea basin, but only contaminated some LREE-enriched calc-alkaline lavas erupted along the continental margins. On the other hand, tholeiitic lavas in the center of the basin show no isotopic evidence of crustal assimilation. This indicates that most of the crust in the central Alborán Sea accreted by Miocene tholeiitic magmatism and that Alpujárride lower crust is absent and likely foundered close to the continental margins of the basin.
ISSN: 0024-4937

hal-01526912
https://hal.archives-ouvertes.fr/hal-01526912
DOI : 10.1016/j.lithos.2016.10.003

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Borborema Province of northeastern Brazil is divided into three main domains: northern, central, and southern. Several U-Pb zircon ages of plutons and orthogneisses became available in the recent years in the central and northern domains, but similar results are scarce in the southern domain. This study reports U-Pb dates for single zircon grains from one orthogneiss (Jupi orthogneiss) and two plutons (Cachoeirinha syenitic pluton and Cabanas granite) south of the East Pernambuco shear zone system (EPSZ). The results provide geochronological constraints on the timing of deformation and magmatism in this part of the southern domain and allow correlations with the central domain. The Jupi orthogneiss was emplaced and deformed during development of the regional flat-lying foliation. A Pb-206/U-238 weighted apparent mean age of 606 +/- 8 Ma is interpreted as the crystallization age of the protolith of the orthogneiss and consequently the age of high-grade Brasiliano metamorphism. The NNE-trending Cachoeirinha pluton is only locally affected by strike-slip deformation, whereas the ENE-trending Cabanas granite is intensely affected by deformation related to the EPSZ. The 587 8 Ma and 573 4 Ma ages of the Cachoeirinha pluton and Cabanas granite, respectively, bracket the main period of activity of the EPSZ. Tectonomagmatic activity in the study area is similar to the age of Brasiliano events in the central domain, north of the EPSZ. In addition, xenocrystic zircons in the Jupi orthogneiss and Cabanas granite are interpreted as inherited from Paleoproterozoic source rocks, suggesting the presence of widespread reworked old crust in the southern domain, similar to the central domain. These results support the idea that the central and southern domains belonged to the same crustal block before the onset of the Brasiliano orogeny.
ISSN: 0895-9811

hal-00411394
https://hal.archives-ouvertes.fr/hal-00411394
DOI : 10.1016/j.jsames.2007.06.003

Éditeur(s) : HAL CCSD
Résumé : International audience
Hundreds of Paleoproterozoic gold occurrences are known in the Tapajós Gold Province, northern Brazil. However, few deposits have been analysed in detail to understand the genesis of these systems. In this study, we present data concerning the largest deposit presently known in this Province, the Tocantinzinho deposit. A strike-slip fault system controls the emplacement of the mineralized rocks and the development of the brittle fracturing that host the main gold mineralization. Hydrothermal activity played an important role in the mineralization processes.
Mineral Resources in a Sustainable World
Nancy, France

hal-01356009
https://hal.archives-ouvertes.fr/hal-01356009

Éditeur(s) : HAL CCSD
Résumé : aucun
Ce travail de thèse s'intéresse à l'événement transamazonien en Guyane Française. Le Transamazonien constitue l'événement géodynamique majeur structurant le bouclier des Guyanes entre 2.2 et 2.0 Ga. L'évolution de l'orogenèse transamazonienne est décrite en termes de croissance crustale, prenant en compte des processus de recyclage archéen ainsi que des processus d'accrétion juvénile et de réactivation thermotectonique au Paléoprotérozoïque. Notre travail axé sur une étude géochronologique (U-Pb et Ar/Ar) et une étude géochimique (éléments majeurs et éléments en trace) a permis de proposer un modèle d'évolution en quatre étapes : une première étape avec la formation d'une croûte océanique juvénile à 2.2 Ga, une seconde étape de croissance crustale, avec la formation de série TTG entre 2.18 et 2.1Ga. Cette seconde étape présente une évolution du contexte de subduction générant les TTG, le résultat est la formation de magmas type «sanukitoïdes». La troisième étape présente la formation de magmas calco-alcalins (2.1 à 2.08 Ga) résultant du «refroidissement» du contexte de subduction déjà initié lors de la seconde étape. Le stade final est caractérisé par la formation de granites d'anatexie crustale (2.1 à 2.06 Ga). Plus globalement, notre étude sur le Transamazonien s'intéresse à la question clé des domaines paléoprotérozoïques, qui est de définir quels types de processus étaient actifs à cette période ? Le Paléoprotérozoïque se situe à la transition entre la période archéenne dominée par des processus de croissance crustale dits «archaïques» et une période récente caractérisée par des processus de croissance crustale dits «modernes».
https://tel.archives-ouvertes.fr/tel-00441743

tel-00441743
https://tel.archives-ouvertes.fr/tel-00441743
https://tel.archives-ouvertes.fr/tel-00441743/document
https://tel.archives-ouvertes.fr/tel-00441743/file/thesenjolvy.pdf

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
In south China the Lushan massif forms a topographic high of the South China Block south of the Qinling-Dabie belt. The Lushan massif consists of two main lithotectonic units separated by a major tectonic contact: a Neoproterozoic (upper Sinian)-Paleozoic unit comprising primarily unmetamorphosed sandstones overlies a Paleoproterozoic unit mainly composed of low-pressure, high-temperature gneisses and micaschists. Both units are cut by Cretaceous granitic intrusions. Three primary tectono-metamorphic and magmatic events are recognized. The eastern part of the Lushan massif is cut by a NNE-SSW trending ductile normal fault (D3 deformation) coeval to the emplacement of a 100-110 Ma leucogranite dated by 40Ar/39Ar laserprobe on biotite and muscovite. D2 deformation is responsible for the formation of a decakilometer-scale NE-SW trending upright anticline characterized by NE-SW stretching and NW-SE shortening. The age of this folding event is defined by a 127±1 (2σ) Ma U/Pb titanite date obtained for a syntectonic granodiorite and 40Ar/39Ar ages of 133 Ma for amphibole. This Cretaceous age also corresponds to the 40Ar/39Ar ages of 126 Ma found on syntectonic muscovites at the base of the Sinian unit. An older deformation event, D1, characterized by a top-to-the-NW extensional decollement of the Sinian-Paleozoic series above Proterozoic metamorphic rocks is related to the Triassic tectonics of the Dabieshan. Lastly, in the lower part of Sinian rocks, the occurrence of kyanite cataclased during D1 documents an older, poorly preserved, late Paleozoic-early Mesozoic tectonometamorphic event (Dx) related to a blind thrust in the continental crust of the South China Block in the southern foreland of the Dabieshan.
ISSN: 0278-7407

insu-00717721
https://hal-insu.archives-ouvertes.fr/insu-00717721
https://hal-insu.archives-ouvertes.fr/insu-00717721/document
https://hal-insu.archives-ouvertes.fr/insu-00717721/file/Lin-Tectonics-2000.pdf
DOI : 10.1029/2000TC900009

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Microstructures, U-Pb SHRIMP zircon ages and temperature estimates were used to constrain the fabric evolution and timing of mylonitisation in the Patos shear zone (NE Brazil). Melt-bearing HT-mylonitic orthogneiss displays solid-state fabrics with coarse quartz ribbons and sutured grain boundaries. K-feldspar is often fractured and shows peripheral myrmekite. The textures typically become magmatic at the contacts with the Espinho Branco anatexite. Zircon crystals from two samples of the leucosome show Paleoproterozoic (ca. 2.2 Ga) inherited cores that are enveloped by recrystallised Neoproterozoic rims. These zircon grains define a discordia with lower intercept ages of 558 and 562 Ma but with large analytical errors. A leucogranite with transitional contacts with host diatexites provides a well-constrained zircon mean age of 566 ± 6 Ma (n = 15, 95% conf.), which is considered the best estimate for the peak metamorphic conditions. The transition from HT-mylonites to fine-grained mylonites and ultramylonites is marked by a progressive grain size reduction assisted by recrystallisation. Quartz crystallographic fabrics display [0 0 0 1] concentrations between Z and Y. K-feldspar and plagioclase fabrics record the activity of the (0 1 0)[0 0 1] and (0 1 0)[1 0 0] slip systems and, in the lower-temperature tectonites, the (1 0 0)[0 1 0] slip system. These results suggest a diachronic evolution in which an initial HT northern domain was deformed by intracrystalline slip and melt-assisted granular flow, followed by medium- to low-temperature solid-state creep in the southern shear zone domain. The mylonites therefore record the rheological heterogeneities responsible for the formation of a late continental shear zone that nucleated under partially molten conditions and was later reactivated through melt-absent strain localization following exhumation.
ISSN: 0301-9268

hal-01053497
https://hal.archives-ouvertes.fr/hal-01053497
DOI : 10.1016/j.precamres.2013.12.020

Éditeur(s) : HAL CCSD Elsevier
Résumé : Detailed sedimentological investigations on numerous outcrops and drill-core sections in the 2.1-Ga-old Franceville basin, Gabon, provide evidence for a large-scale injectite network. The injectites were formed by the injection of sands through a thickness of about 150 m of the FB1 Member, and now cover a minimum area of 70 km2 corresponding to the Bangombé plateau, but are also recognized close to Franceville 35 km farther south-east. The injectite lithology corresponds to a mud- or carbonate-supported sandstone characterized by a loose and uncompacted fabric contrasting with the host-rock. Because the injectites are often parallel to subparallel to the stratification, they were misinterpreted as depositional beds by previous authors. At outcrop, the injectite bodies exhibit sill, dyke, wing and protrusive geometries emplaced during early burial within poorly compacted material, with partial wall erosion and dissociation. The source of the sand material is attributed to a channel-levee turbidite depositional system located in the lower part of the FB1 Member. These deposits were buried by a thick biochemical muddy cap deposited during a starvation phase, which increased the seal capacity of the system. This type of architecture has a high potential to develop compaction disequilibrium during burial. Moreover, in the case of the Francevillian injectites, the abundance of microbial organic matter favoured early methane degassing and lateral charging of the sand reservoir. The overpressure in the channels was periodically released during early burial, through the effect of rapid sedimentary and tectonic loading, and possible seismic activity. The fluidized sand was injected according to a symmetrical wing pattern. Thus, the injected masses caused a local decrease in the grade of the lateritic manganese ore deposit of the Bangombé plateau.
ISSN: 0301-9268

hal-01667217
https://hal.archives-ouvertes.fr/hal-01667217
DOI : 10.1016/j.precamres.2017.09.022