La mobilisation des REE et de l’Hf par un fluide aqueux durant les processus métamorphiques HP-BT peut entraîner des perturbations dans la signature des protolithes et/ou dans les datations obtenues par les systèmes isotopiques Sm-Nd et Lu-Hf. L’étude couplée de la transition éclogite - amphibolite de la localité de Vårdalsneset (WGR, Norvège) et des coefficients de partage des REE et de l’Hf entre un fluide aqueux à NaCl ou à CO2 et le grenat pyrope (P = 3 GPa, T = 800°C) déterminés expérimentalement conduit à deux résultats majeurs. Tout d’abord, une différence d’échelle de mobilité entre les REE (mobiles à l’échelle décimétrique) et l’Hf (mobile à l’échelle du grain) est démontrée. Les signatures des protolithes restent cependant identifiables et les âges modèles Sm-Nd et Lu-Hf des métabasites ne sont pas perturbés, arguant d’une mobilité restreinte des REE. Ensuite; cette étude montre l’influence du CO2 dissous dans le fluide aqueux sur le partage fluide-roche des HREE. L'étude expérimentale indique que les HREE sont incompatibles dans le pyrope en présence d'un fluide à CO2. Ces résultats permettent d’expliquer l’appauvrissement en HREE sous l'effet de fluides à H2O-CO2 ou à CO2 des métabasites de Vårdalsneset. / REE and Hf mobility in aqueous fluids during HP-BT metamorphism can disturb magmatic signatures of protoliths and Sm-Nd and Lu-Hf dating. This study performed on both natural samples from Vårdalsneset (WGR, Norway) and experimental estimates of REE and Hf partition coefficients between aqueous fluid with NaCl or CO2 and pyrope (P = 3 GPa, T = 800°C) highlights two main results. Firstly, REE can be mobilized at the sample scale (tens of centimetres) whereas Hf is only mobilized at the grain scale. Magmatic signatures of protoliths are nevertheless recognizable and Nd and Hf model ages are not disturbed, that suggests slight mobility of REE. Secondly, an aqueous fluid with CO2 induces an incompatible behaviour of HREE in pyrope, which can explain the depletion in HREE of the metabasites of Vårdalsneset in presence of a H2O-CO2 or CO2 fluid.

As sub-bacias Rincón Blanco e Cerro Puntudo são depocentros pertencente à parte norte da Bacia de Cuyo, que está exposta em um terreno alóctone da Pre- Cordilheira, Andes Centrais, Argentina. Este terreno é descrito como parte do Supercontinente Laurentia, que foi adicionado ao protomargin Gondwana durante o Oroviciano. A bacia, que é um rifte Triássico, foi preenchida predominantemente de sedimentos clásticos e material vulcânico, vulcanclástico e piroclástico em ambiente continental, e é composta de vários meio-grabens assimétricos conectados por zonas de acomodação. Análises isotópicas de UPb e Lu-Hf em zircão foram realizadas nas unidades do embasamento, rochas vulcanoclásticas rochas e tufos de ambas as sub-bacias triássicas. O embasamento, representado por rochas vulcânicas andesíticas, foi datado em 269,9 ± 2,9 Ma com idades modelo de Hf de 1,34 a 1,60 bilhões de anos (Ga). As rochas vulcanoclásticas são compostas por zircões com idades de 238 a 1433 milhões de anos (Ma), com moda principal no Permiano-Triássico e Esteniano (1,0 a 1,2 Ga). Riolito e tufos triássicos formaram-se entre 246 e 230 Ma e têm idades modelo Hf variando de 1,02 a 1,50 Ga. Assim, as rochas vulcanoclásticas presentes apresentam dominantemente idades mesoproterozóicas, as quais são correlacionados ao Evento Grenviliano. Alguns grãos de zircão mostram idades modelo Hf paleoproterozóicas, que são interpretadas como sugestiva proveniência do Supercontinente Gondwana. A presença de idades mesoproterozoica dominante sugere que o magmatismo ácido associado a Bacia do Cuyo e o próprio Terreno Alóctono Cuyano tenha um embasamente Grenviliano. / The sub-basins Rincón Blanco and Cerro Puntudo are depocenter belonging to the northern part of the Cuyo Basin, exposed in an allochthonous terrane of Laurentia that was added to the Gondwana protomargin and now exposed in the Precordillera Argentina. The rift basin was filled predominantly of pyroclastic and continental clastic sediments, and is composed of many asymmetric grabens half-linked by accommodation zones. U-Pb and Lu-Hf zircon isotope analyses were carried out in the basement units and volcanoclastic rocks and tuffs of both Triassic sub-basins. Basement rocks were dated at 269.9±2.9 Ma with Hf model ages 1.34 to 1.60 Ga. The volcanoclastic rocks contain zircons crystallized from 238 Ma to 1433 Ma with main peak at Permian-Triassic and Stenian (1.0 to 1.2 Ga). The Triassic rhyolite and tuffs formed between 246 and 230 Ma and have Hf model ages ranging from 1.02 to 1.50 Ga. Indeed, the volcanoclastic rocks present dominant Mesoproterozoic ages, mostly correlated to the Grenvillian. Some zircon grains show Hf Paleoproterozoic model ages which are interpreted to be part of Gondwana cratonic areas. The presence of dominant Mesoproteorzoic favored the hypotheses of a Grevillian basement for the related acid magmatism of the Cuyo Basin and allocthonous Cuyan Terrane.

Le présent travail regroupe un ensemble de quatre parties distinctes, qui ont pour point commun l'analyse géochimique. La première partie présente, sous la forme d'un recueil d'articles, la méthode de dilution isotopique et ses applications. En particulier, il y est traité de la théorie de la dilution isotopique, avec le détail des calculs impliqués, des avantages de cette méthode "absolue" sur les mesures comparatives, et de la puissance de la combinaison séparation chimique – dilution isotopique pour le dosage très précis des éléments en trace dans les échantillons géologiques. La seconde partie est consacrée à la séparation chimique des Lanthanides et du Hf en vue des analyses isotopiques des deux systèmes élément radioactif – élément radiogénique Sm-Nd et Lu-Hf. Trois méthodes nouvelles de séparations sont décrites et comparées. Les protocoles analytiques utilisés dans le cas de mesures par MC-ICP-MS sont détaillés, et les différents pièges analytiques rencontrés ont été clairement identifiés, et une solution a été proposée à chaque fois. La troisième partie décrit et caractérise divers dispositifs d'introduction de l'échantillon pour les appareils à source plasma, essentiellement axés sur la désolvatation cryogénique et l'introduction à micro-débit, et montre un exemple d'application avec un appareil MC-ICP-MS. La quatrième et dernière partie présente quelques unes des données géochronologiques Sm-Nd et Lu-Hf obtenues sur différents environnement métamorphiques de haut grade (granulites hercynienne en xénolites du Maroc, granulites hercynienne d'Europe Centrale (Autriche, Pologne), et éclogites de la zone de Sesia (Alpes)). Nous y montrons que la géochronologie comparée fait face, dans le cas des roches crustales, à une complexité du comportement des géochronomètres beaucoup plus importante que ce qui est généralement admis.

As sub-bacias Rincón Blanco e Cerro Puntudo são depocentros pertencente à parte norte da Bacia de Cuyo, que está exposta em um terreno alóctone da Pre- Cordilheira, Andes Centrais, Argentina. Este terreno é descrito como parte do Supercontinente Laurentia, que foi adicionado ao protomargin Gondwana durante o Oroviciano. A bacia, que é um rifte Triássico, foi preenchida predominantemente de sedimentos clásticos e material vulcânico, vulcanclástico e piroclástico em ambiente continental, e é composta de vários meio-grabens assimétricos conectados por zonas de acomodação. Análises isotópicas de UPb e Lu-Hf em zircão foram realizadas nas unidades do embasamento, rochas vulcanoclásticas rochas e tufos de ambas as sub-bacias triássicas. O embasamento, representado por rochas vulcânicas andesíticas, foi datado em 269,9 ± 2,9 Ma com idades modelo de Hf de 1,34 a 1,60 bilhões de anos (Ga). As rochas vulcanoclásticas são compostas por zircões com idades de 238 a 1433 milhões de anos (Ma), com moda principal no Permiano-Triássico e Esteniano (1,0 a 1,2 Ga). Riolito e tufos triássicos formaram-se entre 246 e 230 Ma e têm idades modelo Hf variando de 1,02 a 1,50 Ga. Assim, as rochas vulcanoclásticas presentes apresentam dominantemente idades mesoproterozóicas, as quais são correlacionados ao Evento Grenviliano. Alguns grãos de zircão mostram idades modelo Hf paleoproterozóicas, que são interpretadas como sugestiva proveniência do Supercontinente Gondwana. A presença de idades mesoproterozoica dominante sugere que o magmatismo ácido associado a Bacia do Cuyo e o próprio Terreno Alóctono Cuyano tenha um embasamente Grenviliano. / The sub-basins Rincón Blanco and Cerro Puntudo are depocenter belonging to the northern part of the Cuyo Basin, exposed in an allochthonous terrane of Laurentia that was added to the Gondwana protomargin and now exposed in the Precordillera Argentina. The rift basin was filled predominantly of pyroclastic and continental clastic sediments, and is composed of many asymmetric grabens half-linked by accommodation zones. U-Pb and Lu-Hf zircon isotope analyses were carried out in the basement units and volcanoclastic rocks and tuffs of both Triassic sub-basins. Basement rocks were dated at 269.9±2.9 Ma with Hf model ages 1.34 to 1.60 Ga. The volcanoclastic rocks contain zircons crystallized from 238 Ma to 1433 Ma with main peak at Permian-Triassic and Stenian (1.0 to 1.2 Ga). The Triassic rhyolite and tuffs formed between 246 and 230 Ma and have Hf model ages ranging from 1.02 to 1.50 Ga. Indeed, the volcanoclastic rocks present dominant Mesoproterozoic ages, mostly correlated to the Grenvillian. Some zircon grains show Hf Paleoproterozoic model ages which are interpreted to be part of Gondwana cratonic areas. The presence of dominant Mesoproteorzoic favored the hypotheses of a Grevillian basement for the related acid magmatism of the Cuyo Basin and allocthonous Cuyan Terrane.

As sub-bacias Rincón Blanco e Cerro Puntudo são depocentros pertencente à parte norte da Bacia de Cuyo, que está exposta em um terreno alóctone da Pre- Cordilheira, Andes Centrais, Argentina. Este terreno é descrito como parte do Supercontinente Laurentia, que foi adicionado ao protomargin Gondwana durante o Oroviciano. A bacia, que é um rifte Triássico, foi preenchida predominantemente de sedimentos clásticos e material vulcânico, vulcanclástico e piroclástico em ambiente continental, e é composta de vários meio-grabens assimétricos conectados por zonas de acomodação. Análises isotópicas de UPb e Lu-Hf em zircão foram realizadas nas unidades do embasamento, rochas vulcanoclásticas rochas e tufos de ambas as sub-bacias triássicas. O embasamento, representado por rochas vulcânicas andesíticas, foi datado em 269,9 ± 2,9 Ma com idades modelo de Hf de 1,34 a 1,60 bilhões de anos (Ga). As rochas vulcanoclásticas são compostas por zircões com idades de 238 a 1433 milhões de anos (Ma), com moda principal no Permiano-Triássico e Esteniano (1,0 a 1,2 Ga). Riolito e tufos triássicos formaram-se entre 246 e 230 Ma e têm idades modelo Hf variando de 1,02 a 1,50 Ga. Assim, as rochas vulcanoclásticas presentes apresentam dominantemente idades mesoproterozóicas, as quais são correlacionados ao Evento Grenviliano. Alguns grãos de zircão mostram idades modelo Hf paleoproterozóicas, que são interpretadas como sugestiva proveniência do Supercontinente Gondwana. A presença de idades mesoproterozoica dominante sugere que o magmatismo ácido associado a Bacia do Cuyo e o próprio Terreno Alóctono Cuyano tenha um embasamente Grenviliano. / The sub-basins Rincón Blanco and Cerro Puntudo are depocenter belonging to the northern part of the Cuyo Basin, exposed in an allochthonous terrane of Laurentia that was added to the Gondwana protomargin and now exposed in the Precordillera Argentina. The rift basin was filled predominantly of pyroclastic and continental clastic sediments, and is composed of many asymmetric grabens half-linked by accommodation zones. U-Pb and Lu-Hf zircon isotope analyses were carried out in the basement units and volcanoclastic rocks and tuffs of both Triassic sub-basins. Basement rocks were dated at 269.9±2.9 Ma with Hf model ages 1.34 to 1.60 Ga. The volcanoclastic rocks contain zircons crystallized from 238 Ma to 1433 Ma with main peak at Permian-Triassic and Stenian (1.0 to 1.2 Ga). The Triassic rhyolite and tuffs formed between 246 and 230 Ma and have Hf model ages ranging from 1.02 to 1.50 Ga. Indeed, the volcanoclastic rocks present dominant Mesoproterozoic ages, mostly correlated to the Grenvillian. Some zircon grains show Hf Paleoproterozoic model ages which are interpreted to be part of Gondwana cratonic areas. The presence of dominant Mesoproteorzoic favored the hypotheses of a Grevillian basement for the related acid magmatism of the Cuyo Basin and allocthonous Cuyan Terrane.

The structural lineament mapping of southern India along withgeological, geochronological datasets help in redefining the Precambrian crustal blocks.The newly proposed Kumta and Mercara suture zones welding Archean crustal blocks in western peninsular India offer critical insights into the crustal evolution of Gondwana. The Kumta suturemainly consists of schistose rocks including quartz-phengite, garnet-biotite, chlorite, fuchsite and marble, whereas the Mercara suture contains mylonitic quartzo-feldspathic gneiss, garnet-kyanite-sillimanite gneiss, calc-silicate granulite and metagabbro. Metamorphic pressure-temperature estimations (Kumta suture: 11-18 kbar at 790-550oC; Mercara suture: 13 kbar at 825oC) suggest that, the sediments have undergone subduction to greater depths. The K-Ar age of biotite, phengite and U-Pb dating of zircon yields consistent metamorphic age of 1100-1400 Ma. In situ zircon 176Lu/177Hf isotope analysis shows wide range of εHf (t) values indicating the protolith sediments were derived from Paleo-Neoarchean juvenile crust that mixed with recycled older crust. The Bondla ultramafic-gabbro complex, northwest of the Kumta suture contains basalt, dolerite, gabbro, serpentinite, chromitite, peridotite and chromian spinel chemistry suggests evolution in a supra-subduction zone arc tectonic setting.The Sirsi shelf towards east of the Kumta suture, contains weakly deformed sedimentary rocks (limestone, shale, banded iron formations, greywacke, sandstone and quartzite) unconformable on relatively high-grade ca. 2571 Ma gneisses of the Dharwar craton. The Karwar block to the west is composed of weakly metamorphosedca. 3200 Ma tonalite-trondhjemite-granodiorite (TTG) with enclaves of amphibolite. In situ zircon 176Lu/177Hf isotope analysis and whole-rock 143Nd/144Nd isotopic analysis of TTGs show positive εHf and εNd values indicating ca. 3200 Ma juvenile crust. The Coorg block consists of ca. 3200 Ma charnockite, mafic granulites, hornblende-biotite gneiss, garnet-hornblende gabbro and anorthosite.In situ zircon 176Lu/177Hf isotope analysis indicates source as mixture of juvenile crust and older recycled crustal materials. Synthesis of the above results with published data suggests that Kumta and Mercara suture zones incorporate Paleoarchean to Mesoproterozoic sedimentssubjected to high-pressure metamorphism in the late Mesoproterozoic. Metamorphic P-T estimations of mafic granulite and U-Pb zircon geochronology of pelitic gneisses from Betsimisaraka suture zone, Madagascar suggests the rocks were underwent metamorphism at c. 24 kbar and c. 780°C during Mesoproterozoic suturing of Antongil-Masora blocks with the Antananarivo block.From the integration of above results with the new geophysical results and published data Mesoproterozoic Kumta-Mercara suture is interpreted as eastern extension of the Mesoproterozoic Betsimisaraka suture of Madagascar into western India.