Lajishan Ayishan Formation Rhyolites: Implications for the Closure Time of the Proto-Tethys Ocean

作     者：SUN Yi NIU Manlan LI Xiucai 

作者机构：Hefei University of TechnologyHefeiAnhui230009China 

出 版 物：《Acta Geologica Sinica(English Edition)》 (地质学报（英文版）)

年 卷 期：2020年第94卷第S01期

页      面：55-56页

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：granted by the National Natural Science Foundation of China(Grant Nos.41272221,41772228,41702239) the Geological Survey Program of China(Grant Nos.1212011120159,DD20160201-04) 

主　　题：Lajishan rhyolite Proto-Tethys Ocean South Qilian 

摘      要：The Qilian orogenic belt,as an important component of the central orogenic system,can be divided into three tectonic units from north to south:the North Qilian tectonic belt,the Central Qilian tectonic belt and the South Qilian tectonic *** Lajishan ophiolitic mélange zone is an important part of the South Qilian tectonic *** study of the formation age and tectonic attributes of the different rock units in the Lajishan is of great significance for reconstructing the tectonic evolution of the south Qilian tectonics belt and the Proto-Tethys *** Ayishan formation is an important unit of the Lajishan mélange belt,but its stratigraphic age and formation environment are still not constrained,which limits the reconstruction of the early Palaeozoic tectonic evolution of the South Qilian tectonic belt and the closure time of the Proto-Tethys *** recent years,a set of rock assemblages consisting of andesite,rhyolite,sandstone and pebbly sandstone have been identified in the Ayishan formation exposed in the Lajishan through detailed geological mapping in the *** are in fault contact with the underlying ophiolite mé***,a volcano-sedimentary succession consisting of andesite,rhyolite,volcanic breccia,and volcaniclastic sandstone nonconformably overlies the Cambrian arc-accretionarycomplex system in the Ayishan *** rocks were originally assigned to the Ayishan formation and attributed an Early Ordovician age(BGMRQP,1964,1991).Our rhyolite samples from the Ayishan formation yielded a weighted mean 206Pb/238U age of 447 Ma using zircon U-Pb dating,which can be interpreted as the eruption age of the volcanic *** volcanic rock assemblages are distributed in sandstone,pebbled sandstone and conglomerate in the form of ***,the zircon UPb age of the volcanic rocks can constrain the age of Ayishan formation that it should belong to the late Ordovician rather than early ***,we propose that the Ay