Petrology, geochemistry and tectonic setting of intrusive rocks in the southwest of Sorkh-Kuh (Lut Block, eastern Iran)


Research Center for Ore Deposits of Eastern Iran, Ferdowsi University of Mashhad, Khorasan Razavi, Iran


The southwest of Sorkh-kuh area is located in 120 km SW of Birjand city and it is a portion of the Tertiary volcanic-plutonic rocks in the west of the Lut block. Geology of this area comprising andesitic and basaltic volcanic rocks, which have intruded by intrusive rocks, at different stage, such as hornblende diorite, hornblende microdiorite, hornblende diorite porphyry, hornblende quartz diorite porphyry and biotite quartz monzonite caused extensively alteration in volcanic rocks. The texture of intrusive rocks is porphyritic, granular and poikilitic. Hornblende and plagioclase are two common minerals in these intrusive rocks and biotite and quartz are common in biotite quartz monzonite. Composition of intrusive rocks show metaluminous to low peraluminous nature with calc-alkaline and sometimes tholeiitic affinities in diorites. These intrusive rocks belong to volcanic granite arc and magnetite (or I) series granitoids. Enrichment of LILE (Ba, K, Cs and Sr), depleted of HFSE (Nb, P, Ti) and enrichment of LREE versus HREE indicated that magma formed in subduction zone environment. The high ratios of Eu/Eu* (0.8-0.9 in all diorite rocks and 1.5 in biotite quartz monzonite) and also enrichment of Sr especially in biotite quartz monzonite (900 ppm) shows there were no plagioclase in the source of magma. Depletion of Nb and high amount of Zr/Nb show low contamination of crust in magma. The (LaN/YbN) is low between 5-9. The magmatic source of intrusive rocks had been generated from 1 to 5% of partial melting of garnet-spinel lherzolite (low garnet) and in 60 km asthenosphere depth.