科研之友
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摘要
To better understand the evolution of deep-seated crust of the Variscan orogen in the Sardinia-Corsica region, we studied garnet-bearing micaschists which were sampled 3km east and 15km northeast of Porto Vecchio, south-eastern Corsica. After a careful investigation of the textural relations and compositions of minerals, 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 undertaken with the electron microprobe. The micaschists from both localities were formed along similar anticlockwise P-T paths. The prograde branch of these paths starts at 3kbar close to 600 degrees C in the P-T field of sillimanite and reaches peak conditions at 7kbar and 600 (15km NE of Porto Vecchio) to 630 degrees C (3km E of Porto Vecchio). The metamorphism at peak P-T conditions happened c. 340Ma based on low-Y (<0.65wt% Y2O3) monazite. Ages of monazite with high-Y contents (>2wt% Y2O3), which probably have formed before garnet, scatter around 362Ma. The retrograde branch of the P-T paths passes through 4kbar at similar to 550 degrees C. We conclude that the micaschists belong to a common metasedimentary sequence, which extends over the Porto Vecchio region and is separated from other metamorphic rock sequences in the north and the south by major tectonic boundaries. This sequence had experienced peak pressures which are lower than those determined for metamorphic rocks, such as micaschist and gneiss, from north-eastern Sardinia. At present, we favour a continent-continent collisional scenario with the studied metasedimentary sequence buried during the collisional event as part of the upper plate. The contemporaneous high-P metamorphic rocks from NE Sardinia were part of the upper portion of the lower plate. The addressed rocks from both plates were exhumed in an exhumation channel.
- 出版日期2018-1
