Zircon U-Pb Age, Geochemical Characteristics and Tectonic Significance of Metavolcanic Rocks from Naij Tal Group, East Section of East Kunlun
详细信息
- 责任者：Chen Youxin (Faculty of Earth Science and Land Resources ; Chang’an University ; Xi’an 710054 ; China) ; Pei Xianzhi
- 刊名：Earth Science Frontiers
- 出版年：2013
- 卷期：20(6)
- 关键词：变火山岩 ; metavolcanic rocks ; 铀—铅计时 ; U-Pb dating ; 岩石地球化学 ; lithogeochemistry ; 昆仑山 ; Kunlun Mountains
- 页码：p.240-254
- 图表：8 illus., 6 tables, 69 refs.
- 分类号：0802
- issnNo：ISSN1005-2321
- isbnNo：CN11-3370/P
摘要
Naij Tal Group is a metamorphic volcanic-sedimentary series in East Kunlun.It is also the important material record of the Early Paleozoic tectonic evolution.The zircon U-Pb age spectrum of meta-volcanic rock from Naij Tal Group is evidently divided into five groups:2559 Ma,1341-1472 Ma,918-1142 Ma,557-595Ma and 459-497Ma.The former four groups recorded the Precambrian tectono-magmatic events in this area.The zircon grains of the fifth group are of clear oscillatory zonation indicating their magmatic origin.The206Pb/238 U weighted average age of these zircon grains is 474±7.9 Ma(MSWD=0.59,n=11),which indicates that the forming age of the meta-volcanic rocks is the Ordovician.The major element data show that the protolith of meta-volcanic rocks are basalts which can be divided into two series:tholeiite(including plagioclase hornblende schist and hornblende schist)of lower Mg#(43.09-46.44)and alkali basalt(including epidotechlorite albite schist)of higher Mg#(57.20-76.00).These suggest that the tholeiite magma has undergone crystallization differentiation of femic minerals,whereas the alkali basalt magma is similar to primitive magma.Trace element data show that the tholeiite is of characteristic of island arc volcanic rocks,while the alkali basalt is similar to E-MORB and OIB.Zircon U-Pb dating and geochemical study indicate that these meta-volcanic rocks were formed in the early Paleozoic back-arc basin environment,it is the material record of the pull-apart of East Kunlun to form the backarc small basin caused by the northward subduction of Proto-Tethys oceanic crust.
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