First discovery of Late Triassic tuffs in the South Qilian Basin: geochemical characteristics， zircon LA-ICP-MS U-Pb ages and potential source regions

作     者：Fangpeng Du Furong Tan Shiming Liu Xiaochen Zhao Yingtao Chen Junwei Qiao 

作者机构：College of Geology and Environment， Xi'an University of Science and Technology Shaanxi Provincial Key Laboratory of Geological Support for Coal Green Exploitation China National Administration of Coal Geology Shaanxi Institute of Geological Survey School of Energy Resource， China University of Geosciences 

出 版 物：《Journal of Earth Science》 (地球科学学刊(英文版))

年 卷 期：2021年

核心收录：

学科分类：0709[理学-地质学] 070901[理学-矿物学、岩石学、矿床学] 07[理学] 

基　　金：support of National Natural Science Foundation of China (No. 41702144 42002194) Natural Science Basic Research Plan in Shaanxi Province of China (No. 2019JQ-991 2020JQ-746) 

摘      要：This investigation reports the first discovery of more than 70 tuff intervals in the Upper Triassic， South Qilian Basin. Petrographic and geochemical analyses were carried out on ten tuffs and zircon U-Pb dating were on three. Thin section and X-ray diffraction （XRD） results indicate that the tuffs were composed of crystal shards and altered glass shards; crystal shards include plagioclase and quartz. Most of the tuffs had been transformed into illite/smectite mixed-layers （I/S）. In addition， calcite， pyrite， dolomite and siderite were also identified in some tuffs. Analysis of major elements suggests that the tuffs are a peraluminous high-K calcalkaline series. Trace elements results indicate that the tuffs were enriched in high field strength elements （HFSE）， including Th， U， Ta， Zr and Hf. Geochemical characteristics suggest that the tuffs originated from comendite pantellerite and rhyolite from within plate settings. Zircon U-Pb dating （236.0 ± 1.7 Ma， 231.4 ± 1.6 Ma and 223.1 ± 3.9 Ma） indicate that the tuffs were erupted in the Late Triassic. Comparative chronology and geochemical analyses suggest that the West Qinling Belt and the East Kunlun Belt are the potential source regions of these tuffs， and they originating from the within plate magma during a post-collisional period.