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 TiO 2, K 2O, P 2O 5, SiO 2, 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 K 2O, low to moderate TiO 2, high MgO, CaO TiO 2 and Al 2O 3 TiO 2 , flat REE patterns with lower La N Sm N ratios and increase of SiO 2, FeO (T) and TiO 2 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.