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The Study of Petrogenesis and Geochemistry of Alkaline Volcanic Rocks in Kojor Region, Central Alborz Mountain)

Abstract

The volcanic rocks comprises the extracted melt products of adiabatic decompression melting of the mantle that are represented by small-volume intra-continental plate volcanic rocks of alkaline basalts and their evaluated Rocks with compositions representative of mantle-derived, primary (or near-primary) melts. The Kojor region contains a number of intra-continental alkaline volcanic range situated on central Alborz Mountains, formed along the localized extensional basins developed in relation with the lithospheric thinning and Cretaceous compersional processes. Trace element patterns with significant enrichment in LILE, HFSE and REEs, relative to primordial mantle. Trace element variations of individual basaltic rocks are characterized by an increase in incompatible elements and MgO, with decreasing SiO2 as melt production proceeds. They are mainly alkaline basalt. Most of these rocks display overlapping primitive Mg-numbers, Cr and Ni contents, steep chondrite-normalized rare earth element patterns (La/Yb CN = 6.46–19.26) and an overall enrichment in incompatible elements. The existence of distinct primary magmas is also indicated by heterogeneity in highly incompatible element ratios (e.g. Zr/Nb,La/Nb). Trace element modelling indicates that the magmas were generated by comparably variable degrees of partial melting of different garnet lherzolite and a heterogeneous asthenospheric mantle source.

Keywords

Volcanic Rocks; Cretaceous; Garnet Lherzolite; Kojor; Primordial Mantle;

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