Petrogenesis of Plio-Quaternary basanites in the Gandom Beryan area, Kerman, Iran: geochemical evidence for the low-degree partial melting of enriched mantle

Abstract

In the Gandom Beryan area, basanitic lava flows erupted from fractures in the Nayband fault zone and formed an areaof about 300 km 2of basanitic rocks in the western part of the Lut Block. Olivine and clinopyroxene are the major phenocrysts in amicrolitic groundmass for these basanitic rocks. The geochemical data show that Gandom Beryan rocks are basanite in compositionand belong to intercontinental rifts related to alkali basanites. These rocks have low Fe/Mg ratios (Fe 2 O 3t /MgO = 1.07 1.43) with lowsilica content (SiO 2= 44.89 48.26 wt.%) and are high-Ti basanites. The investigated rocks are characterized by a significant enrichmentof total REE and LREE relative to chondrite. Moreover, the REE patterns of these rocks are linear without any negative Eu anomalies.The low abundances of HREE in basanitic rocks and the REE modeling together reflect the relation between these elements and residualgarnet in the partially melted mantle. The207 Pb/ 204 Pb and206 Pb/ 204 Pb ratios of the basanitic rocks fall near the field of enriched mantle II(EM-II). The Gandom Beryan volcanism, which was related to partial melting of mantle within an extensional setting, resulted from aleft-step, pull-apart basin in the Nayband N S trending strike slip fault system. Although the fault system is older than Gandom Beryanvolcanism, it seems that it has been reactivated during and after the volcanism.