Abstract
With an east–west exposure trend, Peshtasar Complex, which is located in the sedimentary basin of Moghan, northwestern Iran, is lithologically varied. The main constituent minerals are plagioclase, clinopyroxene and iddingsitised olivine in basalts and plagioclase megacryst, clinopyroxene and leucite in tephrite. The studied rocks are plotted in the fields of basaltic trachy-andesite, trachy-andesite and tephri-phonolite in the total alkali-silica (TAS) diagram as well as high-K to calc-alkaline and shoshonite fields. The chondrite normalised pattern of rare earth elements indicates the enrichment of LILE and LREE as well as the depletion of HFSE and HREE. Nb and Ti have a negative anomaly in the spider diagram. Eu/Eu* represents a positive anomaly for Eu indicating the frequency of calcic plagioclase and low oxygen fugacity in rocks. Geochemical parameters and diagrams predict a magmatic evolution via assimilation – fractional crystallisation process. According to the Ce/Yb vs. Ce diagram, partial melting has happened within the garnet–lherzolite field in the depth of \({\sim }100\) km. Based on \(^{87}\)Sr/\(^{86}\)Sr, Shahyourdi samples have EM1 sources, whereas Germi and Tazehkand basalts have EM11 sources that are indicative of different mantle sources for basalts in the western Moghan of the central and eastern areas. Basalts are found in active continental margins associated with the post-collision arcs.
Highlights
Eocene volcanic activity is one of the most important magmatic phenomena in Iran
The results of chemical and isotopic analyses of Peshtasar basalts of the Moghan sedimentary basin are presented in tables 1 and 2
Based on the geochemical diagrams and rare elements these rocks are formed in an active continental margin and a post-collision arc system
Summary
Eocene volcanic activity is one of the most important magmatic phenomena in Iran. Basalts are recognised as basic volcanic rocks that are poor in silica (silica oxide < 53 wt%) and rich in MgO (>5 wt%) (Le Maitre et al 1989). 0123456789().,--: vol V magma is a primary magma produced by partial melting of a source region of peridotitic rocks (BVSP 1981). The study of geochemical characteristics of these rocks, as well as xenoliths entrained in them, provides a lot of information about the composition and mineralogy of their source regions. Basalts erupt in a wide range of tectonic environments. The basaltic magmas are known to be parental to most of the more evolved magmas in oceanic as well as continental environments (Gill 2010).
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