Geochemical Characteristics and Tectonic Setting of the Elashan Formation Volcanic Rocks in the Aksu River Region, East Kunlun, Xinjiang

Abstract The Aksu River region, located in East Kunlun, Xinjiang, is part of the Qin-Qi-Kun Orogenic System and the North Kunlun magmatic arc. The region hosts Late Triassic volcanic rocks of the Elashan Formation, primarily composed of andesite, dacite, and rhyolite. Geochemical analyses of these volcanic rocks are essential to deciphering the tectonic evolution of the region. This study investigates the geological characteristics, petrology, and geochemistry of the Elashan Formation to elucidate its tectonic setting and significance. The rocks display SiO 2 contents of 53.65–76.16%, total alkali contents of 4.77–6.05%, Rittmann index values of 0.86–3.2, and aluminum saturation indices (ASI) of 1.39–1.84, classifying them as predominantly calc-alkaline, ranging from metaluminous to peraluminous, and intermediate to acidic in composition. The total rare earth element (REE) content ranges from 101.05 to 215.77 ppm, with light-to-heavy REE ratios of 6.44–19.24, indicating significant REE fractionation and light REE enrichment (δEu = 0.53–1.05). The REE distribution patterns exhibit a rightward incline. Large-ion lithophile elements (LILEs) such as Rb, U, and K exhibit significant enrichment, while Nb, Ta, Sr, P, and Ti are relatively depleted, forming troughs in trace element distribution diagrams indicative of enrichment in strongly incompatible elements. Based on Rittmann, Pearce, and Harris diagrams, along with regional tectonic evolution and petrographic characteristics, the Elashan Formation volcanic rocks are interpreted to have formed in an active continental margin continental arc environment.