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

Authors: SEYED JAVAD YOUSEFI, ABBAS MORADIAN, HAMID AHMADIPOUR

Abstract: In the Gandom Beryan area, basanitic lava flows erupted from fractures in the Nayband fault zone and formed an area of about 300 km² of basanitic rocks in the western part of the Lut Block. Olivine and clinopyroxene are the major phenocrysts in a microlitic groundmass for these basanitic rocks. The geochemical data show that Gandom Beryan rocks are basanite in composition and belong to intercontinental rifts related to alkali basanites. These rocks have low Fe/Mg ratios (Fe₂O_3t/MgO = 1.07-1.43) with low silica content (SiO₂ = 44.89-48.26 wt.%) and are high-Ti basanites. The investigated rocks are characterized by a significant enrichment of 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 residual garnet in the partially melted mantle. The ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁶Pb/²⁰⁴Pb 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 a left-step, pull-apart basin in the Nayband N-S trending strike-slip fault system. Although the fault system is older than Gandom Beryan volcanism, it seems that it has been reactivated during and after the volcanism.

Keywords: Lut Block, Gandom Beryan area, basanite, Geochemistry, Nd-Sr-Pb isotopes

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