The tectonic evolution of the Dras arc complex along the Indus Suture Zone, western Himalaya: Implications for the Neo-Tethys Ocean geodynamics

Abstract

In this study we present new whole-rock geochemical data on the Dras arc complex exposed along the Dras–Kargil National Highway, western Ladakh. This complex forms a part of the Indus Suture Zone, which is a major tectonic unit extending along the Himalaya from the Pakistan in the west to the Tibet in the east. The Dras arc complex is dominated by mafic volcanics, with subordinate gabbros at the base exposed near Kargil. The Dras volcanics have augite and plagioclase phenocrysts embedded in a groundmass of plagioclase and pyroxene with porphyritic, intergranular and ophitic textural relationships. Also chlorite and epidote are present as secondary mineral assemblage in these volcanics. Plagioclase and pyroxene are the dominant mineral assemblage in the Kargil gabbro, with minor amounts of oxides and relict olivine. These rock types are characterized by ophitic textures and are devoid of any secondary mineral assemblage when compared to the mafic volcanics, which have suffered greenschist metamorphism. Geochemically, the Dras volcanics and the Kargil gabbros are classified as sub-alkaline tholeiites and show a compositional variation from basalt to basaltic andesite. On a Nb/Yb vs. Th/Yb diagram, they fall within the compositional field of arc-related rocks. NMORB-normalized multi-element patterns shows enrichment in large ion lithophile elements (e.g., Rb, Ba, Th, U, K and Pb) and light rare earth elements (LREE), but a depletion in high field strength elements (e.g., Nb, P, Zr and Ti), which supports a subduction-related origin. Lower Ba/La and La/Yb ratios indicate contribution from fluid fluxing, rather than slab melts to the mantle wedge. The Dras volcanics show similar geochemical trends to volcanic arc rocks from the Nidar and the Spongtang ophiolite complex of the Ladakh Himalaya as well as the Hasanbag and Kata Rush arc rocks from the Iraqi Zagros Suture, having similar age relationships in the context of the Neo-Tethys Ocean.