|
|||||
|
|
Thermobarometry and granite genesis: the Hercynian low-P, high-T Velay anatectic dome (French Massif Central) |
|
| Authors: | J M MONTEL C MARIGNAC P BARBEY M PICHAVANT |
| Institution: | Department de Géologie, U.A.-10, 5 rue Kessler, 63038 Clermont-Ferrand Cedex, France;Ecole Nationale Supérieure des Mines, Parc de Saurupt, 54042 Nancy Cedex, France;Laboratoire de Pétrologie, Universitéde Nancy I, BP 239, 54506 Vandoeuvre les Nancy Cedex, and CRPG-CNRS, BP 20, 54501 Vandoeuvre les Nancy Cedex, France;CNRS-CRSCM, 45071 Orléans Cedex 2, France |
| Abstract: | The Velay dome (French Massif Central) offers a quasi-continuous section across an anatectic domain comprising low- to high-grade schists, gneisses and granites. Two main tectonometamorphic events, and their related generation of granitic material, were recognized in addition to a major Barrrovian tangential event (D2) attributed to intracontinental collision tectonics: (i) a medium- to low- P , high- T event (D3) which gave rise to migmatites and syntectonic monzonitic granites and granodiorites, and (ii) a widespread melting event (D4) which led to the generation of migmatities, the Velay granite and post-anatectic granites. Thermobarometry on samples collected from both the metamorphic envelope and the granitic core distinguishes two distinct geotherms: (i) a first, associated with the D3 event, characterized by P > 5 kbar, T ≤ 750° C and water-present melting (biotite remains stable) which led to large-scale migmatization but minor amount of granites; (ii) a second, associated with the D4 event and characterized by vapour-absent melting ( P = 4–5 kbar, T = 760–850° C) which gave rise to the Velay granites and late-migmatitic granites. The temperature increase during the D4 event is attributed to the intrusion of hot mafic magmas within the crust. The time-integrated features of the different granitic rocks in the Velay dome can be directly related to a |
| Keywords: | granites Hercynian migmatites thermal anomaly thermobarometry |