GEOCHEMICAL INVESTIGATION OF THE IGNEOUS ROCKS FROM THE NURALI OPHIOLITE MELANGE ZONE, SOUTHERN URALS

The Nurali massif is a small ophiolite located along the Main Uralian Fault in the Southern Urals. It includes a mantle sequence, a transiti on zone and a melange zone, with an intrusive, gabbro to oxide-diorite , unit interposed between the transition zone and the melange. Various igneous rocks occur as exotic blocks within the Nurali melange, inclu ding tholeiitic (gabbro to diorite) and calc-alkaline (diorite, tonali te, granodiorite and granite) intrusives, tholeiitic basalt and calc-a lkaline basaltic andesite to dacite. The Poljakovka Complex basalts of Silurian age are similar to the tholeiitic effusives and are also int ruded by gabbros similar to those in the melange zone calc-alkaline in trusives. The rocks of tholeiitic affinity in the tectonic mClange are the remnants of an oceanic stage. Both intrusive and effusive calc-al kaline products can likely represent a subduction-related magmatism de veloped in an are environment (intra-oceanic are or continental margin ). They are analogous to those from the Kraka massif which occur west of the Main Uralian Fault.