Magmatic evolution of the Karakoram Batholith, Trans-Himalaya, NW India: Geochemical insights for arc dynamics and crustal growth

Abstract

The Karakoram Terrane (KT), a continental block along the southern margin of the Asian Plate, originated within the peri-Gondwanan Cimmerian assemblage. It rifted from the Gondwana during the Permian, opened the Neo-Tethys Ocean, and accreted to southern Asia by the Early Jurassic. To constrain its tectono-magmatic evolution, we present whole-rock geochemical data from the Karakoram Batholith (KB), a major granitoid complex of the Trans-Himalaya, NW India. The KB is dominated by porphyritic granites containing abundant diorite enclaves, reflecting magma mingling between coeval mafic and felsic melts. Geochemically, KB granites and diorites exhibit calc-alkaline metaluminous characteristics typical of I-type granitoids, analogous to subduction-zone settings. KB granites have whole-rock ε_Nd(t = 110 Ma) values from -6.9 to -8.8 with Nd depleted mantle model ages (T_DM) from 1650 to 1857 Ma. Similarly, KB diorites have whole-rock ε_Nd(t = 110 Ma) values from -4.5 to -6.3 with T_DM from 1800 to 1953 Ma. These results are analogous to those of the Middle Cretaceous KB diorites (-8.2 to -7.3, and 1380 to 1650 Ma; respectively). These features indicate that during the Jurassic-Cretaceous, northward subduction of the Neo-Tethys oceanic plate beneath the southern margin of the KT established an Andean-type tectonic setting. This emplaced extensive KB magmatism derived from mixed sources, including the mantle wedge and upper crustal rocks of the KT.