1- Payame Noor University (PNU)
Abstract: (458 Views)
Neogene magmatism in the west of Zavarian area has formed the Khastak volcanic mountain through two distinct magmatic phases. The units of the earlier phase include a series of basic to intermediate pyroclastics and basaltic andesite to Andesite lavas that lie atop the equivalent units of the Upper Red Formation. The later phase consists of small subvolcanic bodies with porphyritic gabbro–diorite lithology that cut through the previous units. The andesite – basaltic andesite rocks (earlier phase) and gabbro–diorite rocks (later phase) exhibit similar geochemical characteristics and thus can be genetically related. In the rare earth element (REE) patterns, the gabbro–diorite group rocks display relatively flat patterns. However, with an increase in silica content and towards the andesite group rocks, the slope of the patterns increases systematically, showing enrichment of LREE compared to HREE. On multi-element diagrams, the LILE elements show slight enrichment compared to the LREE elements. However, as with subduction zone igneous rocks, Nb-Ta depletion can be observed compared to adjacent REEs. Based on the geochemical study of trace elements, these rocks exhibit intermediate characteristics of magmatic rocks associated with active continental margins and island arcs. The intermediate geochemical characteristics of active continental margins and island arcs can be related to magmatism in an extensional Continental (ensialic) back-arc basin. The partial melting with relatively high degrees in a shallow lithospheric mantle in the spinel peridotite facies, which has previously undergone metasomatism due to subduction, can be considered the cause of magmatism in this region.
Keywords: Zavarian, Khastak mountain, geochemistry, Continental (ensialic) back-arc, Urumieh-Dokhtar magmatic belt
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