Geochronology, Geochemistry and Petrogenesis of the Jietebutiao A-Type Granites in West Junggar, Xinjiang
详细信息
- 责任者：Yang Gaoxue (Earth Science & Resources College ; Chang’an University ; Xi’an 710054 ; China) ; Li Yongjun
- 刊名：Acta Geoscientica Sinica
- 出版年：2013
- 卷期：14(3)
- 关键词：A型花岗岩 ; A-type granite ; 铀—铅计时 ; U-Pb dating ; 准噶尔盆地 ; Junggar Basin
- 页码：p.295-306
- 图表：illus., 58 refs.
- 分类号：0801
- issnNo：ISSN1006-3021
- isbnNo：CN11-3474/P
摘要
Late Paleozoic post-collisional granitoids are widespread in West Junggar and even in the whole northern Xinjiang. As a representative of these intrusions, the Jietebutiao granite occurs in the southwestern margin of West Junggar, mainly comprises middle-coarse-grained monzogranite and syenogranite, and provides important clues for petrogenesis of granites and evolution of tectonic-magmatism in West Junggar. This paper reports the results of high-precision zircon LA-ICP-MS U-Pb dating of the Jietebutiao granite, which yields weighted mean 206 Pb/ 238 U ages of (287±9) Ma (n=10, MSWD=0.92)and (278±3) Ma (n=14, MSWD=0.43)for monzogranite and syenogranite, respectively, corresponding to the Early Permian and implying that the granite is the product of post-collisional magmatic activity around the Junggar area approximately at 300 Ma. Petrogeochemical analyses suggest that the Jietebutiao pluton which has long been thought to be of I-type granite actually belongs to A-type. The syenogranite is characterized by high silica (SiO 2 : 76.11%～76.82%), alkali (Na 2 O+K 2 O: 8.47%～8.49%), and low titanium and calcium (TiO 2 : 0.04%～0.05%, CaO: 0.36%～0.42%). Moreover, the monzogranite is similar to the syenogranite in such aspects as high silica (SiO 2 : 68.35%～71.80%) and alkali (Na 2 O+K 2 O: 6.80%～7.86%) as well as low titanium and calcium (TiO 2 : 0.29%～0.82%, CaO: 1.76%～2.87%); nevertheless, they both belong to metaluminous or peraluminous (ACNK: 0.98～1.09) high-K calc-alkaline series. Compared with the monzogranite, the syenogranite has relatively low REE content (ΣREE: 23.8×10 -6 ～49.3×10 -6 , 95.23×10 -6 ～222.2×10 -6 ) with significant negative Eu anomalies (Eu/Eu*: 0.01～0.02, 0.57～0.72). They are also enriched with large ion lithophile elements such as Rb, Th and K and high strength field elements such as Zr, Hf and Nb and strongly depleted in Ba, Sr, Eu and Ti, with high 10000Ga/Al ratios (>2.44). These characteristics are more clearly in syenogranite than in monzogranite. Based on trace element ratios and related discrimination diagrams, the Jietebutiao pluton can be further subdivided into A 1 and A 2 type granites, which are usually believed to have been formed in an post-collisional tectonic setting and derived from the lower crust composed of juvenile mantle-origin substance. In the early post-collisional magmatism, A 2 -type monzogranite magma characterized by island arc features was derived from partial melting of the lower crust and, with the further extension of the lithosphere, probably formed a rift-like environment in local area, producing the A 1 -type syenogranite magma.
© 2004-2018 中国地质图书馆版权所有 京ICP备05064691号 京公网安备11010802017129号 地址：北京市海淀区学院路29号 邮编：100083 电话：办公室：(+86 10)66554848；文献借阅、咨询服务、科技查新：66554700 |