Tectonic Evolution of the Metamorphic Core Complex Around the Kotah and Loe Sar Domes, Swat, North Pakistan

Abstract

The Swat Valley rocks encompass at least four tectonic and three metamorphic events since the initial collision between the Indian Plate and Kohistan Island Arc (KIA). The early S₁ preserved in garnets and microlithon of the S₂ are obscured at the outcrop scale by D₂. S₂ foliations are preserved in garnet porphyroblasts and the main matrix foliations. Post D₂ domes exhumed S₂ tectonic fabric and the metamorphic core complex of the Indian Plate in the Kotah and Loe Sar Domes. These domes are wrapped by the Swat Tourmaline Granite (STG) that was developed by anatectic processes. S₂ parallel kyanites indicate that the D₂ tectonic event developed under upper amphibolite facies metamorphic conditions before the Kotah and Loe Sar Domes culmination. D₃ resulted in S₂ crenulations, L₃ intersection lineations and syn–S₃ growth of biotite, garnet, staurolite, kyanite and weakly developed sillimanite. The upper amphibolite facies metamorphic conditions around the domes and greenschist facies conditions along the Main Mantle Thrust (MMT) indicate that the high grade metamorphic rocks are exhumed by the Indian Plate basement rocks protrusion in the cores of the domes. Episodic reaction textures preserved in porphyroblasts and index minerals growth yielded a clockwise P–T path for the Alpurai Group Metasediments (AGM).