Geology and Geochemistry of Ophiolitic Extrusive Sequence in Forumad Area, Northeast Iran

The Forumadophiolitic rocks as a part of Iran marginal microcontinentophiolites have been situated in the western part of Sabzevarophiolite. Field study shows extrusive sequence in this area with Late Cretaceous in age. This sequence has included basaltic pillow lavas with radiolarian chert related to Late Turonian-Santonian، in contrast to Coniacian- Late Campanian age، when this sequence has composed of basaltic pillow lavas in lower - middle part and various tuffs in upper part. Sheet flows، hyaloclasticbreccias and pelagic limestone are intercalations between lavas and tuffs. Abundantly، pillow lavas with phyric texture are most predominant feature contrast with sheet flows. Whereas enrichment of LILE and depletion of some HFSE (Nb، Ta) exhibit subduction environment (island arcs) for pillow lavas of Forumad، and different enrichment in LREE to HREE displays unhomogenous mantle in the generation of them; the presence of two magmatic nature in lavas (tholeiitic and calc-alkaline)، their positions in tectonomagmatic diagrams and clear enrichment of Th element in Late Turonian –Santonian lavas which are generally exhibition of ophiolitic extrusive sequence in Forumad area have been generated in a supra-subduction environment and back-arc basin.