Deformation Microstructures and Conditions in Muteh-Golpayegan Metamorphic Core Complexes

Two main metamorphic events have occurred within Muteh- Golpayegan metamorphic core complexes (including eastern and western complexes) in the Sanandaj-Sirjan zone. Some grain-scale deformations were also happened in relation to these metamorphisms which have produced various deformation microstructures. Microfaults are among the microstructures that were formed during brittle conditions. Bulging recrystallization of quartz and rarely feldspar grains, and bookshelf structure of fragmented feldspar porphyroclasts indicate various deformation and formation of shear zones under low-temperature conditions in the eastern complex. Polygonal granoblastic texture of polycrystalline quartz porphyroclasts documents post-mylonitization annealing at medium- grade conditions in shear zones of eastern complex. Chessboard pattern quartz subgrains propose high-grade metamorphic conditions during the first deformation. However, their undulatory extinction reveals low-grade conditions for the second deformation. Polygonal granoblastic texture of chevron folded feldspar grains also accurately supports these conditions during the two mentioned deformations. In general, considering deformation microstructures and conditions, three stages of recrystallization are respectively recognizable in the Muteh-Golpayegan metamorphic complexes including: 1- high-grade static recrystallization subsequent to early metamorphic event, 2- dynamic recrystallization and related mylonitization under low-grade to locally medium-grade conditions, 3-post-mylonitization static recrystallization in medium-grade conditions. The north Golpayegan intrusive bodies can be considered as the heat source for annealing in the western complex but the cause of annealing is not evident in the eastern complex.