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Thermobarometry and granite genesis: the Hercynian low‐ P , high‐ T Velay anatectic dome (French Massif Central)
Author(s) -
MONTEL J. M.,
MARIGNAC C.,
BARBEY P.,
PICHAVANT M.
Publication year - 1992
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/j.1525-1314.1992.tb00068.x
Subject(s) - geology , massif , migmatite , geochemistry , dome (geology) , mafic , gneiss , biotite , metamorphic rock , partial melting , crust , metamorphic facies , geomorphology , quartz , facies , paleontology , structural basin
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 H2O in the source region and illustrate the progressive dehydration of a middle to lower crustal segment over 60 Ma.