科研之友
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摘要
Quartz-monzodioritic dykes have intruded the Hercynian continental lower crust of Calabria at 323 +/- 5 Ma. Pseudosection and average PT calculations have been performed using THERMOCALC. The obtained P (average PT) and T (pseudosection and average PT) values indicate that the quartz-monzodioritic dykes have intruded the 750 degrees C hot metapelitic-migmatitic country-rocks at a depth of about 32 km, with a temperature of ca. 850 degrees C. Microstructural analysis suggests that deformation of the dykes started at hypersolidus conditions during emplacement and continued after cooling at sub-solidus granulite facies conditions together with the country rocks. During this deformation event, which started not later than 323 +/- 5 Ma ago, the main Sn+1 schistosity evolved. Vorticity analysis of the quartz-metadioritic dykes and of the metapelitic country rocks shows that the Sn+1 schistosity evolved during a general shear deformation characterized by 60 to 70% of pure shear. This high percentage of pure shear suggests that the main Sn+1 schistosity evolved in the hot lower crust undergoing extension during vertical shortening. A horizontal attitude of this extensional schistosity is confirmed by retro-deformation of the today obliquely SE-ward dipping Sn+1 schistosity. Extension continued with time and propagated upwards within the crust, affecting the middle crust in a time interval of 306 +/- 1 to ca. 300 Ma when huge masses of granitoid rocks intruded it. The deepest batches of these granitoid bodies show a gneissic schistosity which developed under ductile conditions, while granitoids at higher levels became deformed in a brittle fashion. Our whole data set is consistent with a late Hercynian evolution in Calabria characterized by a progressively crust overlying a mantle that gradually rose during lithospheric extension. This extension was asynchronous, starting at 323 +/- 5 Ma in the lower crust and affecting higher crustal levels at progressively later times.
- 出版日期2012-1-20
