Petrology, geochemistry and geochronology of granites and granite gneisses in the SE Karakoram, India: Record of subduction-related and pre- to syn-kinematic magmatism in the Karakoram Fault Zone

Abstract

The granites and granite gneisses from a tectono-metamorphic complex exposed along the Shyok Valley in the Karakoram region, India, forms the southern margin of Asian plate in the India-Asia collision zone. These rocks have been subjected to mineralogical, geochemical, and U-Pb zircon geochronological investigations to constrain the petrogenetic and geodynamic evolution of the Karakoram terrane. Outcrop-scale observations reveal the presence of pre- and syn-kinematic leucogranite bodies intruded within the granites and granite gneisses. The foliation-parallel deformed leucogranite sill shows the dextral shear sense in an extensive metamorphic complex that is in concordance with the Karakoram Fault (KF) in the Ladakh region, NW India. Whole-rock elemental and biotite chemistry equivocally suggest subduction-related metaluminous (I-type) calc-alkaline nature for most of the host granites and gneisses, and generation of syn-collisional peraluminous (S-type) leucogranites through crustal anatexis of pre-existing rocks. The obtained U-Pb zircon ages for the granites, granite gneisses, deformed and undeformed leucogranites vary widely from ca. 160 Ma to 15 Ma and reveal: (a) the initiation of subduction of the Neo-Tethyan oceanic crust beneath the southern Asian Plate at least ~160 Ma ago, and (b) existence of continuous or intermittent deformation along ~1000 km long lithospheric scale dextral KF during ~27−15 Ma.