YI Shan-xin1, LI Yong-jun1, JIAO Guang-lei1, SUN Yu1, YANG Gao-xue1, WANG Jun-nian2, YANG Feng-zhu2
1. Earth Science & Resources College of Chang'an University; Key laboratory of Western China, Mineral Resources and Geological Engineering, Ministry of Education, Xi'an, Shaanxi 710054, China;
2. No.7 Geological Survey Team, Xinjiang Bureau of Geology and Mineral Resource Exploration, Wusu, Xinjiang 833000, China
Abstract: The Lower Carboniferous Heishantou Formation in the west Xiemisitai Mountain, northwest of Junggar, consists pyroclastic rocks and neutral-acidic volcanic lava. Geochemical studies of the neutral-acidic volcanic rocks in the Heishantou Formation improve understandings of the Boshchekul-Chingiz volcanic arc and magmatic and tectonic evolutions of the northern West Junggar. The geochemical characteristics study showed that the dacites are Alkaline-subalkaline series and the andesites are Calcium alkaline. Their SiO2 contents are higher (60.52%-71.58%), their P2O5 and TiO2contents are lower (0.03%-0.27% and 0.07%-1.89%, respectively), their total alkaline (Na2O+K2O) is about 6.88%-10.31% and their Al2O3 contents are about 13.37%-16.31%. They have high ΣREE of 62.7×10-6~274×10-6, enrich LREE with (La/Yb)N=2.75~12.7, and have a significant Eu anomalies of δEu=0.247~0.501, they also enrich LILE (Rb, Ba, Th) and slightly deplete HFSE (Nb, Ta, Ti), showing the similarities to island-arc volcano rocks. It can be concluded that the Boshchekul-Chingiz volcanic arc was formed by the former subduction of the island-arc zone and mixed with melted subduction sediment during the formation.
Keywords: geochemistry island-arc Heishantou Formation Boshchekul-Chingiz volcanic arc West Junggar
