Mineralogy, petrology and geochemistry of mafic dikes in the southeast Jebal-E-Barez Granitoids (Bam, Kerman province, Iran): Studies from mafic dikes formed in a volcanic arc-setting

Authors: SHIRIN BEHPOUR, ABBAS MORADIAN, HAMID AHMADIPOUR, KAZUO NAKASHIMA

Abstract: In the southeastern part of the Jebal-E-Barez Oligocene granitoids (Kerman province, Iran), there are numerous mafic dikes and this work attempts to investigate the petrological, geochemical and mineral chemistry of these dikes. The dikes clearly follow faults which trend mainly N50-70W and N20-40W. Their thicknesses vary from 1 cm to 3 m and their contacts with the host granitic rocks are sharp without any extensive contact metamorphism which may be due to the lack of magmatic fluids. The Jebal-E-Barez mafic dikes contain plagioclase, clinopyroxene and amphibole as major minerals and overall show porphyritic texture, but intergranular, ophitic and subophitic textures are also visible. The amphiboles are classified mainly as paragasite and tschermakite. These are magmatic, as indicated by Si content of the studied mafic dikes. Based on Al-in-hornblende geothermobarometry, average crystallization pressures are estimated from 5.25 to 7.07 kbar and temperatures from 867 to 872 °C. Thermobarometric estimations show temperatures of 1000 ± 200 °C and depth of 30?40 km for crystallization of the clinopyroxenes. Chemical composition of the amphiboles suggests the parent magmas of the mafic dikes derived from a mantle source. Whole rock geochemistry data reveal that the studied dikes belong to the calc-alkaline magma series. They are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE) such as Cs, Rb, Ba, and Sr, with negative anomalies for high-field-strength elements (HFSE) such as Nb and Ta. The weak negative Eu anomaly is evidence of a slightly earlier separation of a mineral phase such as plagioclase. According to trace element abundances, Ba/Nb, Ce/Yb, and Zr/Y ratios, and tectono-magmatic discrimination diagrams, the primitive magma derived from an enriched garnet-free mantle source, contaminated by the crust and emplaced in continental arc environment.

Keywords: Mafic dikes, mineral chemistry, petrology, calc-alkaline, geothermobarometer, continental arc, Central Iran

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