%0 Journal Article
%T The relationship between the Alxa Block and the North China Plate during the Early Paleozoic: New information from the Middle Ordovician detrial zircon ages in the eastern Alxa Block<br>早古生代阿拉善地块与华北地块之间的关系:来自阿拉善东缘中奥陶统碎屑锆石的信息
%A ZHANG Jin
%A LI JinYi
%A LIU JianFeng
%A LI YanFeng
%A QU JunFeng
%A FENG QianWen
%A <br>张进
%A 李锦轶
%A 刘建峰
%A 李岩峰
%A 曲军峰
%A 冯乾文
%J 岩石学报
%D 2012
%I 
%X Located between the North China Plate to the east, and the North Qilian Orogenic Belt to the southeast, the eastern Alxa Block is the key region to answer many controversies surrounding the tectonic setting of this region in the Early Paleozoic; among them the debates on the basement composition of the Alxa Block, whether the Alxa Block connected to the North China Plate in the Early Paleozoic, when exactly this event did happen, where the Lower Paleozoic sedimentary rocks along the southwestern Ordos had their provenances, and whether the so-called Helan Aulacogen formed in the Ordovician are the key questions to be solved. Laser-ablation inductively coupled plasma mass spectroscopy U-Pb dating of detrital zircons in two samples from Middle Ordovician sandstones to the west of Helan Shan located in the eastern Alxa Block yields a majority of 206Pb/238U ages between 900Ma and 950Ma with peak ages at 916Ma in Sample Alxa-1 and 953Ma in Sample Alxa-2, respectively, a smaller group yields 206Pb/238U ages between 494Ma and 623Ma with peak ages at 505Ma and 588Ma in Sample Alxa-1 and 494Ma, 517Ma and 623Ma in Sample Alxa-2, respectively. Two samples all have a minor peak age at ca. 2500Ma with 2517Ma in Alxa-1 and 2552Ma and 2670Ma in Alxa-2. Moreover, there are a few zircons older than 3000Ma. The youngest 206Pb/238U ages of the two samples are similar with 451±8Ma in Alxa-1 and 483±4Ma in Alxa-2. These zircon U-Pb ages combined with several lines of sedimentary evidence imply that the so-called Helan Aulacogen did not exist in the Ordovician; a peripheral foreland basin related to the North Qilian Orogenic Belt developed instead, the Early Paleozoic detritals mainly came from the North Qilian Arc, the Neoproterozoic detritals mainly came from the Alxa Block, the detrital zircon ages along the whole western Ordos showing that the North Qilian Orogenic Belt (Arc) came closer to the Alxa Block, and the ocean between them closed gradually, and the basement of the Alxa Block is different from that of North China Plate, the Alxa Block underwent important tectono-magmatic events during the Paleozoic and Neoproterozoic, which have not found in the North China Plate. The Alxa Block may connect with the North China Plate during the Middle Ordovician or after it.
%K Middle Ordovician
%K Alxa Block
%K detrital zircon
%K Miboshan Formation
%K Helan Aulacogen<br>中奥陶世
%K 阿拉善地块
%K 碎屑锆石
%K 米钵山组
%K 贺兰拗拉槽
%U http://www.alljournals.cn/get_abstract_url.aspx?pcid=E62459D214FD64A3C8082E4ED1ABABED5711027BBBDDD35B&cid=621CF755B1A341E5&jid=2013B5467E3054B1614CEC199353FCED&aid=B5A25D3BD3FB5FB82B52957712D21022&yid=99E9153A83D4CB11&vid=D3E34374A0D77D7F&iid=9CF7A0430CBB2DFD&sid=E0B0176609BEBAFD&eid=0C87310A2B6D3577&journal_id=1000-0569&journal_name=岩石学报&referenced_num=0&reference_num=117