ASSOCIATION OF MORB AND SSZ OPHIOLITES ALONG THE SHEAR ZONE BETWEEN COLOURED MÉLANGE AND BAJGAN COMPLEXES (NORTH MAKRAN, IRAN): EVIDENCE FROM THE SORKHBAND AREA

Abstract

One of the largest worldwide accretionary wedges is exposed in the Makran region (SE Iran). The backstop of this accretionary wedge consists of an imbricate stack of continental and oceanic units, referred as North Makran domain. This domain is characterized by a km-thick shear zone, along which the metamorphic Bajgan Complex is thrust onto the Coloured Mélange Complex. Along this shear zone two slices of ophiolites have been identified in the Sorkhband area. The upper tectonic slice consists of gabbros, whereas the lower tectonic one consists of mantle peridotites associated with dunites and chromitite ore deposits. Petrography and geochemistry of gabbros clearly indicate an N-MORB-type affinity, suggesting that they were generated at mid-ocean ridge setting. In contrast, mantle peridotites consist of harzburgites and depleted harzburgites, both showing geochemical features suggesting their genesis in a SSZ setting. The new data presented in this paper indicate that the slices of ophiolites from Sorkhband area derived from two different oceanic domains representing two different geodynamic settings. This occurrence provide new evidence that the boundary between the Coloured Mélange and the Bajgan Complexes represents a first-order tectonic structure that played an important role in the geodynamic evolution of the Makran area.