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High pressure‐low temperature metamorphism in the Gran Paradiso basement, Western Alps
Author(s) -
VEARNCOMBE J. R.
Publication year - 1983
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.1525-1314.1983.tb00267.x
Subject(s) - geology , metamorphism , gneiss , geochemistry , basement , ophiolite , metamorphic rock , metamorphic facies , greenschist , nappe , amphibole , petrology , geomorphology , facies , paleontology , tectonics , civil engineering , quartz , structural basin , engineering
The Gran Paradiso basement complex of the French and Italian Alps is composed of metasediments, termed the gneiss minuti, and metabasic rocks, both of which are intruded by a late Hercynian granite. The Bonneval gneiss, which crops out at the western edge of the complex, is composed of highly deformed metasediments, volcanics and volcaniclastic rocks. Eclogites, now highly altered, occur in the metabasic rocks. Kyanite and blue‐green amphibole are locally present in the gneiss minuti and aegirine plus riebeckite occur in the Bonneval gneiss. A moderately high pressure ‐ low temperature metamorphic event of probable Alpine age occurred in the basement complex. This metamorphic event differs from that in the overlying Sesia unit and ophiolites of the Schistes lustrés nappe in being at lower pressures (below the ab = jd 100 + qz transition) and post‐dating the major (D2 A ) deformation. The origin of the metamorphism is discussed and interpreted as a probable consequence of the overlying nappe pile which was emplaced during the D2 A event. Subsequent greenschist facies metamorphism in the basement complex is a consequence of thermal relaxation during uplift.