Geochemistry and Geodynamic setting of Crustal sequence in Shahini ophiolitic complex, NW of Kamyaran

Abstract

The Shahini ophiolitic complex is located west of Kamyaran as a ring connection between the Kermanshah and Kurdistan ophiolites, outcropped along the Zagros and Neotethys suture zone, in western Iran. This complex include the mantle peridotites and crustal sequence. The peridotites are highly serpentinized mantle peridotites consist of cpx-bearing harzburgite and lherzolite that cross cut by isolated diabasic dikes. The crustal sequence include pegmatic gabbros, Isotropic gabbro, microgabbroic dykes, basalt and pyroclastic andesite. The sedimentary-volcanic sequence consist of shale, limestone, sandstone and tuff horizons covered the extrusive sequence. Based on chemical analyses the crustal sequence shows the various composition with tholeiitic to calcalkaline affinity. In the tectonomagmatic diagrams, these rocks are often plotted in the MORB regions and in some occasions, they are plotted in volcanic arcs regions. The enrichment in LILE, slightly depletion of HFSE, different enrichment in LREE and linear trends of HREE suggested the magma source originated in the arc environment from the heterogeneous mantle with varying degrees of partial melting. However, the low ratios of Th/Yb, La/Nb, Ce/Nb and Ce/Th inclined the tendency between the IAB and MORB environments. The depth of partial melting estimate between 50 to 60 km correlating and show the partial melting happens in the spinel lherzolite zone. Field relationships and geochemical evidence indicate that Kamyaran ophiolites formed in the oceanic basin in the ocean-continent borders zone in the northwest margin of Neotethys Ocean.

Keywords

• geochemistry
• ophiolitic crustal sequence
• supra-subduction
• nw of kamyaran
• zagros