Anticlockwise pressure–temperature paths record Variscan upper-plate exhumation: Example from micaschists of the Porto Vecchio region, Corsica

Hans Joachim, Massonne

First

;CRUCIANI, GABRIELE

Second

;FRANCESCHELLI, MARCELLO

Penultimate

;Giovanni, Musumeci

Last

2018-01-01

---

Abstract

To better understand the evolution of deep-seated crust of the Variscan orogen inthe Sardinia-Corsica region, we studied garnet-bearing micaschists which weresampled 3 km east and 15 km northeast of Porto Vecchio, south-eastern Corsica.After a careful investigation of the textural relations and compositions of miner-als, especially of zoned garnet, a P–T path was reconstructed using contoured P–T pseudosections. U–Th–Pb dating of monazite in the micaschists was undertakenwith the electron microprobe. The micaschists from both localities were formedalong similar anticlockwise P–T paths. The prograde branch of these paths startsat 3 kbar close to 600°C in the P–T field of sillimanite and reaches peak condi-tions at 7 kbar and 600 (15 km NE of Porto Vecchio) to 630°C (3 km E of PortoVecchio). The metamor phism at peak P–T conditions happened c. 340 Ma basedon low-Y (<0.65 wt% Y2O3) monazite. Ages of monazite with high-Y contents(>2 wt% Y2O3), which probably have formed before garnet, scatter around362 Ma. The retrograde branch of the P–T paths passes through 4 kbar at~550°C. We conclude that the micaschists belong to a common metasedimentarysequence, which extends over the Porto Vecchio region and is separated fromother metamorphic rock sequences in the north and the south by major tectonicboundaries. This sequence had experienced peak pressures which are lower thanthose determined for metamorphic rocks, such as micaschist and gneiss, fromnorth-eastern Sardinia. At presen t, we favour a continent – continent collisional sce-nario with the studied metasedimentary sequence buried during the collisionalevent as part of the upper plate. The contemporaneous high-P metamorphic rocksfrom NE Sardinia were part of the upper portion of the lower plate. Theaddressed rocks from both plates were exhumed in an exhumation channel.