Petrology, geochemistry and mineral chemistry of the subvolcanic rocks and enclaves in the Shirmazdtapeh area (SW Arak)


1 Department of Geology, Faculty of Sciences, Lorestan University, Khorramabad, Iran

2 دانشگاه لرستان، دانشکده علوم پایه، گروه زمین شناسی


The sub volcanic rocks in Shazand area (the Markazi province) which formed a part of the Sanandaj-Sirjan zone are composed of dacitic rocks with major minerals such as plagioclase, quartz, alkali feldspar and minor minerals such as biotite, zircon and apatite. One of the characteristic features of these rocks is the existence of two types of enclaves with dacitic and andesitic compositions. The former, share similar mineralogical composition with the host dacitic rocks and the latter is characterized by the presence of amphibole phenocryst (pargasite), orthopyroxene (enstatite) and plagioclases (labrador-bytownite). Thermometry on biotite and feldspar from the host dacite rocks showed temperature range of 675 and 600 ºC, respectively. The calculated temperature formation for biotite, feldspar and pargasite from the andesitic enclaves are 620, 650 and 810 ºC, respectively. LREE enrichment in comparison with HREE, high LILE relative to HFSE, negative anomalies of Nb, Ti, P, and positive anomalies of Pb, K indicate that these rocks formed in subduction zones. Also, the geochemical characteristics of these rocks reveal that the nature of magma is calc-alkaline enriched in potassium derived from partial melting of continental crust units related to normal active continental margin volcanic arc.