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Successive geotherms, Granitic production and evolution of the lower crust in a post collisional context

Abstract : Post-collisional context is commonly associated with production of large amount of peraluminous granitic magmas produced from the melting of crustal material. The variability of the produced granite commonly varies from leucogranitic to granodioritic and are mostly peraluminous. The South-Eastern French Massif Central (EFMC) region record several evidence for crustal melting revealed by migmatitic and granitic bodies providing ~30 Ma history of peraluminous granite production. Previous thermobarometric studies provides records for two successivves melting event: 1) a biotite stable event at ~314Ma (720°C and 5 kb) 2) a bitotite breakdown melting event constrained at ~301Ma (850°C 4kb) This suggests geotherms evolution from 45 °C/km to 70°C/km in 13Ma. A thermodynamic modelling approach considering a 20km thick pile of crustal material undergoing successive geotherm evolving from 25°C/km to 70°C/km with starting conditions between 3 and 10 kb. Along this evolution our approach allows successive melt extraction and the monitoring of melt compositional variability, residuum evolution and mineral phases modal and compositional variabities according to depth, geotherm and composition of the source. Over the 5 crustal sources used as starting composition for the model, 305 individual partial melting reactions are triggered. Melt and peritectic phases produced provide a variability that suggest the importance of source composition in matter of granite production for some element and ratios (K/Na, XMg). Compared to regional granites (EMCF). Most of the granites produced in the post collisional context of the EFMC can be reproduced by either melt only (leucogranite) or melt in addition to peritectic material produced along with melt (granite to granodiorite). In the same way, the relative-time constrain provided by the approach shows that it is possible to produce simultaneously heterogeneous granitic magmas in respect to source protolith and depth. Identically, the residual crust undergo an very variable evolution depending on protolith leading to an heterogeneous granulitic lower crust.
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https://hal-insu.archives-ouvertes.fr/insu-00877536
Contributor : Nathalie Pothier <>
Submitted on : Monday, October 28, 2013 - 5:17:11 PM
Last modification on : Wednesday, September 23, 2020 - 4:37:53 AM

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  • HAL Id : insu-00877536, version 1

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Arnaud Villaros, Jean-François Moyen, Michel Pichavant. Successive geotherms, Granitic production and evolution of the lower crust in a post collisional context. Goldschmidt, Aug 2013, Florence, Italy. ⟨insu-00877536⟩

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