Geochemistry of Dras volcanics and the evolution of the Indus Suture ophiolites

Abstract

The Indus Suture Zone, with many ophiolite occurrences, represents the northern limit of the Tethyan Himalaya. The volcanic rocks of the Dras ophiolite zone exhibit low TiO₂, K₂O, P₂O₅, SiO₂, Pb, Rb, Ba, Sr and Zr concentrations and lower La/Yb ratios than the intraplate tholeiites. Intercalation of marine sediments, presence of pillow lavas, low K₂O, low to moderate TiO₂, high MgO, CaO/TiO₂ and Al₂O₃, flat REE patterns with lower La_N/Sm_N ratios and increase of SiO₂, FeO(T) and TiO₂ with the fractionation indicate that they are island-arc tholeiites similar to lavas of late Cretaceous age in Cyprus and Oman. These volcanics are postulated to have been derived from a tholeiitic magma generated by a high degree of partial melting and fractionation of mafic phases prior to the crystallization of plagioclase. The island-arc tholeiitic volcanism, the lack of major CA volcanic activity and the reported blueschist metamorphism of the Indus ophiolites suggest a palaeo-island arc development along the Indus Suture Zone along which the Tethys oceanic crust was consumed.