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Volume 16, Issue 41 (5-2015)
Abstract
The Almabulage complex is located in the Sanandaj-Sirjan structural zone, NW of Hamadan. This complex consists of low-grade metamorphic rocks, and two intrusions of felsic and mafic rocks. In this research, we have studied the mafic intrusion. The intrusion has ophitic, subophitic and inter-granular textures and is mainly composed of plagioclase, clinopyroxene, amphibole and minor amounts of K-feldspar, quartz and opaque minerals. Secondary minerals include epidote, chlorite and amphiboles formed in the rim of clinopyroxene. Clinopyroxene is of augite type, amphibole is tschermakite, plagioclase is in the range of andesine-labradorite, k-feldspar is anorthoclase and the opaque mineral is ilmenite. According to the bulk rock geochemistry and mineral chemistry of clinopyroxene, the mafic intrusion of the Almabulage complex has been crystallized from a calc-alkaline magma and is related to subduction area. The element Nb displays distinctive negative anomalies compared to the primitive mantle, which can suggest subduction-related magmatism. Emplacement temperatures and pressure of mafic rocks shown by pyroxene-amphibole thermometer and amphibole barometer indicate temperature and pressure ranges of 750 to 900 °C and 6 to 7 kbar, respectively.
Based on Sm/Yb and La/Sm rations, the parental melt of the mafic rocks of the Almabulage complex, derived from partial melting of garnet–spinel lherzolite. According to the bulk rock geochemistry and mineral chemistry of mafic rocks, the rocks formed in a subduction area during Late Jurassic-Early Cretaceous before the Neo-Tethys closure in Sanandaj- Sirjan zone.
