Petrography and Geochemistry of ophiolitic basalts from Marivan-Palangan region (Zagros, western Iran)

Abstract

Basaltic rocks from Marivan-Palangan ophiolite suite (MPO), Zagros suture zone, western Iran, are studied for magmatic evolution, and source rock partial melting processes. The basaltic rocks have remarkable outcrops in the crustal sequence of the MPO and show pillow structure. In terms of microscopic and chemical characteristics, two distinct rock groups are characterized. Based on chemical classification, both groups are basalt. CIPW norm calculations indicate that all basalts are olivine tholeiite (abyssal tholeiite). In terms of the magma series, they also show tholeiitic affinity, somehow close to transition series. Besides, based on the TiO2 content, they belong to high Ti-type ophiolite. Fractionation of varying amounts of olivine, plagioclase, and clinopyroxene has been inferred from Fenner's diagram, especially for group II samples. Although the samples from both groups are similar to E-MORB in multi-elemental diagrams, the show remarkable distinction in HREE and MREE. Melting models show the various degrees of partial melting from a spinel lherzolite source rock (5-25% for the group I and 15-25% for group II). Due to similarity of Sm/Nd, Ce/Sm, Sm/Yb and La/Yb ratios of both groups to enriched mantle type II (EMII) ratios, contribution of EMII-type components to the source of magma is thought to be responsible for the enriched nature of basalts. It is proposed here that variable degrees of partial melting of a spinel-facies peridotite source and contribution of EMII-type components to the source region controlled enriched nature of the ophiolitic basalts of this part of the Neo-Tethyan realm.

Keywords

• basalt
• morb
• ophiolite
• neo-tethys
• marivan-palangan
• zagros