Geochronology and geochemistry of the Late Devonian–Early Carboniferous volcanic rocks in Aksu River area, western end of the East Kunlun Orogen

Abstract

We present LA‐ICP‐MS zircon U–Pb dating, geochemical data for the Late Devonian–Early Carboniferous volcanic rocks in the Aksu River area, western end of the East Kunlun Orogen, with an aim to constrain the ages, petrogenesis, and tectonic setting of volcanic rocks and to comprehend the Late Devonian–Early Carboniferous tectonic evolution of the north branch of the Paleo‐Tethys Ocean. The Late Devonian–Early Carboniferous volcanic rocks are mostly composed of andesite and rhyolite. The new U–Pb ages show that the volcanic rocks formed in the Late Devonian–Early Carboniferous with ages of ca. 364–343 Ma. The volcanic rocks are classified as calc‐alkaline series. All of the volcanic rocks are characterized by enrichment in large‐ion lithophile elements (e.g., Rb, Ba, U, Sr, and K) and light rare earth elements and depletion in some high‐field‐strength elements (e.g., Nb, Ta, P, and Ti). The andesite samples have relatively high La/Nb (1.66–3.63) but low La/Ba (0.05–0.23) ratios, indicating the mantle source could be depleted mantle, and it had been metasomatized before partial melting. The rhyolite samples have low Nb/Ta and Zr/Hf ratios and Cr, Ni, and Co contents, which indicate that the material source was mainly crust derived and has experienced fractional crystallization process. Combined with our zircon U–Pb dating, geochemical data and geological field investigation, the tectonic setting of the Late Devonian–Early Carboniferous volcanic rocks is possibly related to the subduction process. Furthermore, the Paleo‐Tethys oceanic crust between the Bayan Har and East Kunlun‐Qaidam terrane northward subducted beneath the East Kunlun‐Qaidam terrane in the Late Devonian–Early Carboniferous, and the north branch of the Paleo‐Tethys Ocean between the Bayan Har and East Kunlun‐Qaidam terrane opening event should be earlier than this time (~364 Ma).