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High‐ P ( P = 1.5–1.8 GPa) blueschist from Elba: Implications for underthrusting and exhumation of continental units in the Northern Apennines
Author(s) -
Papeschi Samuele,
Musumeci Giovanni,
Massonne HansJoachim,
Mazzarini Francesco,
Ryan Eric James,
Viola Giulio
Publication year - 2020
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/jmg.12530
Subject(s) - blueschist , glaucophane , geology , lawsonite , metamorphism , greenschist , metamorphic rock , geochemistry , protolith , metamorphic facies , petrology , subduction , paleontology , facies , tectonics , eclogite , structural basin
The Acquadolce Subunit on the Island of Elba, Italy, records blueschist facies metamorphism related to the Oligocene–early Miocene stages of continental collision in the Northern Apennines. The blueschist facies metamorphism is represented by glaucophane‐ and lawsonite‐bearing metabasite associated with marble and calcschist. These rock types occur as lenses in a schistose complex representing foredeep deposits of early Oligocene age. Detailed petrological analyses on metabasic and metapelitic protoliths, involving mineral and bulk‐rock chemistry coupled with P – T and P – T – X (Fe 2 O 3 ) pseudosection modelling using PERPLE_X, show that the Acquadolce Subunit recorded nearly isothermal exhumation from peak pressure–temperature conditions of 1.5–1.8 GPa and 320–370°C. During exhumation, peak lawsonite‐ and possibly carpholite‐ or stilpnomelane‐bearing assemblages were overprinted and partially obliterated by epidote‐blueschist and, subsequently, albite‐greenschist facies metamorphic assemblages. This study sheds new light on the tectonic evolution of Adria‐derived metamorphic units in the Northern Apennines, by showing (a) the deep underthrusting of continental crust during continental collision and (b) rapid exhumation along ‘cold’ and nearly isothermal paths, compatible with syn‐orogenic extrusion.