Document Type : Final File

Authors

Department of Geology, Faculty of Sciences, University of Hormozgan, Hormozgan, Iran, Islamic Republic of Iran

Abstract

The Upper Cretaceous Arangue complex is located in the Makran structural zone at the SE of Iran. The complex consist of ultra-mafic rocks, microgabbro dykes, pillow lavas and lime stones that pillow lavas are mainly exposed to the northwest and southeast part of study area. The basaltic pillow lavas occur as oval and tubular shape with bread crust crack surface. They predominantly composed of plagioclase, clinopyroxene with minor olivine and opaque minerals in a fine-grained groundmass along with glass. Mineral chemistry data show that plagioclases and clinopyroxene composition varies from An68.27-81.73 Ab18.27-31.57 Or0-0.41 and Wo38.1- 47.8Fs8.2-19.3 En38.6-48.7 respectively. On Nb/Y versus Zr/TiO2 and SiO2 versus Nb/Y diagrams the pillow lavas plot in the field of basalt and sub-alkaline respectively. The relatively low immobile trace elements ratioare another sign of their tholeiitic affinity. The absence of Eu anomaly on REE patterns suggests insignificances of plagioclase fractionation, or magma was relatively oxidized. The Arangue complex pillow lavas are similar to transitional basalts that lie between enriched MORB and OIB and some back arc basin basalts. However enrichment in incompatible elements, depletion in Nb and low La/Nb ratios (0.8-2.1) are signature of BABB. They were formed by approximately 15-25% partial melting of plagioclase lherzolite where fractionation was controlled by removal of olivine, spinel, clinopyroxene. Petrogenetic study indicates that mantle lherzolite source underwent variable extent of enrichment in subduction derived component consisting of pure aqueous fluids for pillow lavas.

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