Magmatic systems beneath Ashikule volcanic cluster (Western Kunlun, China): insights from compositional and textural features of lavas

Abstract

This study considered the petrology, chemical composition, texture, and magma temperature and pressure of the volcanic rocks in the Ashikule volcanic cluster (AVC), Western Kunlun, China, to investigate the magmatic systems prior to eruption. The whole rock geochemistry of AVC lavas revealed a wide compositional range that included phonotephrite, basaltic trachyandesite, trachyandesite, trachyte, and acid rhyolite but mainly trachyandesite. The K2O/Na2O ratios were greater than 1, falling into the shoshonite series in a K2O vs. SiO2 diagram. Oxide diagrams showed that intermediate and acidic volcanic rocks have similar magmatic evolutions, mainly related to the fractional crystallization of pyroxene, plagioclase, apatite, and ilmenite. Acidic magma was found as the product of magmatic crystallization in the final stage. Trace element contents indicated that the magma underwent mixing with crustal components in the process of crystallization before eruption. Xishan phonotephrite revealed a different evolutionary series compared with the intermediate and acidic volcanic rocks, highlighting the differences of their magmatic sources. The equilibrium temperature and pressure of phonotephrite were 1146–1316 °C and 0.38–1.70 GPa, respectively, which correspond to a depth of 14–62 km. The equivalent values for intermediate rocks were 1062–1215 °C and 0.22–1.18 GPa, respectively, corresponding to a depth of 8–43 km. Acidic rocks had lower magmatic temperatures (778–889 °C). Active tectonics led to multiple events of magma upwelling, and the magma in each event underwent its own evolution. There were many different components of magma beneath the study area contemporaneously, i.e., multiple magma capsules with different compositions.