Petrographic and Geochemical Investigation of Dasht-e-Nawur Volcanic Rocks, Ghazni Province, Afghanistan

Abstract

The Dasht-e-Nawur volcanic basin is one of the largest and best-known volcanic provinces in Afghanistan. This study investigates the petrographic characteristics, geochemical composition, and geotectonic setting of the volcanic rocks to clarify their magmatic evolution and tectonomagmatic origin. We systematically collected about ten representative rock samples. We performed petrographic analyses on thin sections using a polarizing microscope and determined major and trace geochemistry by X-ray. Petrographic observations indicate that the volcanic suite mainly comprises andesite, quartz andesite, trachy-andesite, and andesitic dacite, with predominantly porphyritic textures and massive structures. The main mineral assemblages include plagioclase, hornblende, biotite, and quartz. Geochemically, the rocks display intermediate to acidic compositions (SiO₂ = 63-79 wt.%) and belong to the calc-alkaline to alkaline magmatic series. Primitive mantle-normalized spider diagrams reveal enrichment in large-ion lithophile elements (LILE) together with marked negative Nb, Sr, P, and Ti anomalies, indicating a subduction-modified mantle source and extensive fractional crystallization of plagioclase, apatite, and Fe-Ti oxides. The volcanism of Dasht-e-Nawur is interpreted to be related to the Indian-Eurasian continental post-collision. Advanced fractional crystallization, accompanied by crustal assimilation and lithospheric thickening, primarily controlled magmatic evolution. Future research should therefore focus on high-resolution isotopic studies and accurate geochronological dating to enhance understanding of crust–mantle interactions and clarify the post-collisional magmatic and tectonic evolution of the south-central volcanic rocks.