Clinopyroxene composition of Daralu gabbro-dioritic rocks in the southern of Urumieh-Dokhtar magmatic arc, Iran: constraints on tectono-magmatic setting and crystallization processes.

The Oligo-Miocene Daralu gabbro–dioritic rocks, structurally located in the southern part of Urumieh-Dokhtar magmatic arc (UDMA), are exposed as isolated outcrops in the Eocene volcanoclastic-sedimentary rocks. The gabbro–dioritic rocks are mainly consisting of plagioclase, clinopyroxene, amphibole, and biotite phenocrysts in a microlithic groundmass. Clinopyroxenes compositionally belong to Ca-Mg-Fe type and classified as diopside-augite (En_39.0-47.3Fs_9.3-17.5Wo_38.1-47.0). Their various thermobarometric calculations suggest that the clinopyroxenes were formed at 1.9–7 kbar, 930–1114 °C, and high oxygen fugacity. These thermodynamic parameters reveal a polybaric crystallization which is inline with their formation in a multi-level magmatic storage system. Moreover, composition of clinopyroxenes indicates that the Daralu gabbro-dioritic rocks have a calc-alkaline nature and formed in a volcanic arc tectonic environment. It seems that northward subduction of Neotethys oceanic lithosphere beneath the Central Iranian microcontinent during Tertiary triggered magmatism. This happened as a result of partial melting of subcontinental lithospheric mantle at depth over 23 Km that produced mafic magma and its crystallization during ascent in the magmatic reservoirs at different levels. The role of crustal contamination in the development of these rocks is relatively insignificant. [ABSTRACT FROM AUTHOR]