Geochemistry and tectonic setting of the Chah-Bazargan sub-volcanic mafic dykes, south Sanandaj–Sirjan Zone (SSZ), Iran

Abdolnaser Fazlnia

Abstract


The Chah-Bazargan sub-volcanic mafic dykes (trachybasalt and basaltic trachyandesite) are located in the south of the Sanandaj–Sirjan Zone (SSZ), Iran. The dyke mineralogy mostly comprises amphibole, clinopyroxene, olivine, orthopyroxene, and plagioclase as phenocrysts and fine-grained plagioclase and some ferromagnesian minerals in the matrix. The rocks are alkaline and shoshonitic in composition. The mafic melts relate to Neotethys subduction activity beneath the southern SSZ in the ~Eocene–Miocene interval. Markedly positive Ba, U, K, Pb, and Sr and negative HFSE (high field strength elements: Nb, Ta, Zr, Hf, P, and Ti) anomalies demonstrate this subduction. The sub-volcanic mafic dykes were produced from a metasomatized upper lithospheric mantle wedge at a depth consistent with the stability field of phlogopite-spinel (or -spinel/garnet) lherzolite. Geochemical studies on the basis of the rare earth elements (REE) and HFSE, and large ion lithophile elements (LILE) display that the mantle wedge underwent degrees of partial melting averaging between 5 and 15% to form the Chah-Bazargan sub-volcanic mafic dykes. It is possible that the chemical composition of the rocks was changed due to fractional crystallization and crustal contamination during emplacement.


Keywords


alkali sub-volcanic mafic dykes; the Chah-Bazargan intrusions; phlogopite-spinel (or -spinel/garnet) lherzolite; subduction zone; Neotethys

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