Nature of the Shyok (Northern) Suture Zone between India and Asia: petrology, geochemistry and origin of the Tirit granitoids and associated dykes (Nubra Valley Ladakh Himalaya, NW India)

Abstract The Shyok Suture Zone is an oceanic remnant of the Neo-Tethyan ocean sandwiched between the Ladakh Batholiths to the south and Karakoram Batholith to the north. The Tirit granitoids in this suture are dark-coloured, relatively rich in ferromagnesian minerals and range from granodiorite–tonalite to gabbro–diorite in composition. Mafic igneous enclaves are quite common and they are intruded by NW–SE parallel doleritic and aplitic dykes. The Tirit granitoids have a wide range of major oxide compositions (SiO2 = 52.1–72.11 wt %, TiO2 = 0.21–1.23 wt %, Al2O3 = 11.42–13.52 wt %, MgO = 1.69–10.69 wt % and CaO = 3.24–9.31 wt %) and show calc-alkaline, metaluminous, I-type characteristics, transitional between primitive and mature arc continental plutons. Rare earth elements (REE) show considerable enrichment in light REE (LREE) as compared to the heavy REE (HREE). Late Cretaceous U/Pb dates (74–68 Ma) show that they formed during the pre-collision northward movement of India. The Tirit dykes are only slightly younger and probably part of the same episode.