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Alpine orogenic evolution from subduction to collisional thermal overprint: The 40 Ar/ 39 Ar age constraints from the Valaisan Ocean, central Alps
Author(s) -
Wiederkehr Michael,
Sudo Masafumi,
Bousquet Romain,
Berger Alfons,
Schmid Stefan M.
Publication year - 2009
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/2009tc002496
Subject(s) - metamorphism , geology , metamorphic rock , subduction , geochemistry , biotite , paleontology , tectonics , quartz
The investigated HP/LT metasedimentary units of the Valaisan and adjacent European domains occupy a key position in the Alpine belt for understanding the transition from early subduction‐related HP/LT metamorphism to collision‐related Barrovian overprint and the evolution of mountain belts in general. The timing of high‐pressure metamorphism, subsequent retrogression and following Barrow‐type overprint was studied by 40 Ar/ 39 Ar dating of biotite and several white mica generations that are well characterized in terms of mineral chemistry, texture and associated mineral assemblages. Four distinct age populations of white mica record peak pressure conditions (42–40 Ma) and several stages of subsequent retrograde metamorphic evolution (36–25 Ma). Biotite isotopic analyses yield consistent apparent ages that cluster around 18–16 Ma for the Barrow‐type thermal overprint. The recorded isotopic data reveal a significant time gap in the order of some 20 Ma between subduction‐related HP/LT metamorphism and collision‐related Barrovian overprint, supporting the notion of a polymetamorphic evolution associated with a bimodal P‐T path.