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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

By Samuele Papeschi, Giovanni Musumeci, Hans&#8208 Massonne, Francesco Mazzarini, Eric James Ryan and Giulio Viola

Abstract

The Acquadolce Subunit on the Island of Elba, Italy, records blueschist facies met- amorphism related to the Oligocene\u2013early 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 calcs- chist. These rock types occur as lenses in a schistose complex representing fore- deep deposits of early Oligocene age. Detailed petrological analyses on metabasic and metapelitic protoliths, involving mineral and bulk-rock chemistry coupled with P\u2013T and P\u2013T\u2013X(Fe 2 O 3 ) pseudosection modelling using PERPLE_X, show that the Acquadolce Subunit recorded nearly isothermal exhumation from peak pressure\u2013 temperature conditions of 1.5\u20131.8\ue01eGPa and 320\u2013370\ub0C. 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 tec- tonic 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 \u2018cold\u2019 and nearly isothermal paths, compatible with syn-orogenic extrusion

Topics: blueschist, continental underthrusting, glaucophane, lawsonite, syn-orogenic extrusion
Publisher: 'Wiley'
Year: 2020
DOI identifier: 10.1111/jmg.12530
OAI identifier: oai:cris.unibo.it:11585/759134
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