GEOLOGICAL AND PETROGRAPHICAL CHARACTERISTICS OF SORAP MASSIF GABBROS, RAS-KOH OPHIOLITE, BALOCHISTAN, WESTERN PAKISTAN

This study discussed the Sorap Massif which is the ophiolitic fragment composed of the upper mantle and lower crustal section of an ophiolitic sequence. An ophiolitic sequence in Sorap Massif consists of harzburgite, dunite, large distant units of serpentinized wehrlite intrusion and outcrop of confined layered gabbro covered by the Quaternary sand dunes. The basal part of gabbroic intrusion is in contact with mantle rocks and the upper part is juxtaposed with the Kuchakki Volcanic Group. On outcrop-level and in hand specimen, the gabbros exhibit needle-like ferromagnesian minerals including hornblende associated with plagioclase and pyroxene. Petrographically the gabbros are classified into norite, gabbro norite and gabbro. The mineral constituents of norite are plagioclase, orthopyroxene and amphibole, gabbro norite is consists of equal constituents of orthopyroxene and clinopyroxene, plagioclase and amphibole and the gabbro is composed of clinopyroxene, plagioclase and amphibole. The high constituents of minerals such as pyroxene, amphibole and low constituents of olivine in the Sorap gabbros indicates that these gabbros are formed by the immature part of the oceanic plate with dehydration of the oceanic plate subduction