Thermobarometric and structural constraints on multistage emplacement mechanism of the Garagheh pluton, Sistan Suture Zone (SE Iran)

Journal of Asian Earth Sciences(2023)

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Mineral compositions and U-Pb ages, combined with microstructural observations, decipher the emplacement mechanism of the Garagheh pluton. The pluton is part of the Zahedan-Saravan magmatic belt, which intrudes flysch sediments of the Sistan Suture Zone in eastern Iran. The pluton consists of granodiorite (center) and biotite granite (margin). The rocks of the Garagheh pluton show a mylonitic foliation defined by biotite and S-C ' structures of feldspar. Asymmetric folds are recorded by aplite dykes with apparent vergence within the deformed biotite granite. Aligned and sigma-type enclaves are observed in the biotite granite. The quartz crystals show chess-board patterns and bulging recrystallization. These microstructures suggest solid-state deformation at moderate-temperature (400-500 degrees C). There is also evidence of solid-state fabrics at low temperature, such as kinks structures in biotite. Thus, moderate temperature fabrics were gradually overprinted by solid-state fabrics during the syntectonic cooling of the pluton. Thermo-barometry and geochronology, combined with lithological observations, establish the following sequence of events: (i) At 44.5 +/- 0.7 Ma the granitic magma crystallized at 1.1-1.5 +/- 0.3 kbar. (ii) This stage was tectonically controlled and the pluton was exhumed to shallower crustal levels corresponding to -0.6 kbar, imparting a mylonitic fabric on the granite. (iii) At 44.3 +/- 0.6 Ma granodiorite was emplaced in the center of the pluton at 0.5-0.7 +/- 0.3 kbar. (iv) -42 Ma ago the level of tectonic activity had diminished, since the granodiorite of the Gapdan pluton, located -12 km away from the Garagheh, does not show deformation texture.
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