GEOCHEMISTRY AND TECTONIC SETTINGS OF PERMIAN VOLCANIC ROCKS IN SANTANGHU BASIN, XINJIANG

Abstract

The study on the Permian dynamic background of northeast Xinjiang has gained more consideration. Based on analyses of major and trace elements of Permian volcanic rocks in Santanghu basin, this paper attempts to clarify the palaeo-tectonic setting more objectively and also provides independent evidence for understanding the nature of the basin. The volcanic rocks are dominated by basalts, diabases, andesite-basalts and with minor dacites and rhyolites, which are fallen into sub-alkaline series. Major elements show the characteristics with higher titanium (Ti = 1.54 - 2.68). LREE/HREE ratio are varying range from 3.8 to 10.40. Different volcanic rocks are all enriched in LREE without obviously Eu anomaly (δEu = 0.92 - 1.13). LILE are enriched in the basalts. Nb and Ta relative to La deplete strongly and show "TNT" negative anomaly. This type of volcanic rocks shows not only the signature of within-plate setting, but also that of subduction zone, which are similar to the some characteristics of "lagged are volcanic rocks", but lack CFB element. Combining with the regional geological data, we conclude that the Permian magmatic activity of the study area generated in an extensional setting of the late stage of orogenesis.