Geochronology and Geochemistry of the Yagan Granite in the Northern Margin of the Alxa Block: Constraints on the Tectonic Evolution of the Southern Altaids
详细信息
- 责任者：Zheng Rongguo (Key Laboratory of Orogenic Belts and Crustal Evolution ; Ministry of Education ; School of Earth and Space Sciences ; Peking University ; Beijing 100871 ; China) ; Wu Tairan
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(8)
- 关键词：花岗岩 ; granite ; 铀—铅计时 ; U-Pb dating ; 阿拉善盆地 ; Alxa Basin
- 页码：p.2665-2675
- 图表：8 illus., 3 tables, 60 refs.
- 分类号：0801
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
The Yagan granites,which are located in the northern margin of the Alxa block,mainly consist of mzonogranites. The zircon SIMS U-Pb age of the granites is 283. 2 ± 2. 2Ma (n = 14,MSWD = 0. 016). The Yagan granites have relatively low SiO2 contents (66. 96% ～ 70. 71%) ,and high Al2O3 (15. 05% ～ 16. 05%) and Na2O + K2O (7. 24% ～ 9. 19%) contents. They also exhibit high K calc-alkaine and metaluminous-peraluminous characteristics. Total rare earth element (REE) contents of the Yagan granites range from 101. 9 × 10-6 to 133. 1 × 10-6. They show enrichments of LREEs,and exhibit relatively moderate-strong negative Eu anomalies (δEu = 0. 59 ～ 0. 77) in the chondrite-normalized REE patterns. They display depletions of high field strength elemens (Nb,Ta,P,Ti) and enrichments of large ion lithophile elements (Ba,Rb,Cs,Th,K) in the primitive mantle-normalized trace element spiderdiagram. The granites also have high (87Sr/86Sr)i values(0. 707654 ～ 0. 710235) and negative εNd(t) values. Based on the geochemical characteristics and related sedimentary formations,it is concluded that the Yagan granites should be formed in the postcollisional setting. The age of the Yagan granites (283. 2 ± 2. 2Ma) implies that the branch of the Paleo-Asian Ocean in the northern Alxa region had been closed before the Early Permian.