Mineral chemistry and K-Ar ages of plutons across the Karakoram fault in the Shyok-Nubra confluence of northern Ladakh Himalaya, India

Abstract

Petrographic analyses of plutons across the Karakoram fault in the Shyok-Nubra confluence of northern Ladakh area revealed that the rocks consist of diorite, granodiorite, granite and leucogranite. Pyroxene and biotite chemistries by EPMA indicate that most of the diorite, granodiorite and granite are calc-alkaline and formed in an arc-related tectonic setting. These calc-alkaline plutons yield K-Ar biotite ages from 49.3 ± 1.1 to 51.2 ± 1.1 for Ladakh batholith in Khardung La and from 60.8 ± 1.3 to 65.8 ± 1.4 Ma for granites and diorites in Hundar area. The K-Ar ages of the Hundar igneous complex are within the age range of 46-70 Ma of the Ladakh batholith near Leh town and the neighbor sites, indicating the Hundar igneous complex as a part of the Ladakh arc. Their ages are also coincident with the Khardung volcanics (67.4 and 60.5 Ma). The calc-alkaline granites from Panamik of Karakoram block yield K-Ar biotite ages of 95.7 ± 2.1 and 96.7 ± 2.1 Ma, suggesting that the granites are member of the plutons (90-120 Ma) occurring in northern Pakistan, Tangtse in Ladakh and western Tibet that emplaced during subduction of the Neo-Tethyan oceanic plate under the Karakoram block. The leucogranite and granodiorite in the Panamik region yield K-Ar biotite and muscovite ages ranging from 9.18 ± 0.21 to 9.45 ± 0.21 Ma. The leucogranites are the S-type related to post-collision tectonic setting and are considered to have emplaced in relating to activation of the Karakoram fault.