Age and Geochemistry of the Caiyuanzi Granite in Sichuan, SW China: Mechanism of the Grenvillian Orogenic Movement in the Western Margin of Yangtze Block
详细信息
- 责任者：Wang Shengwei (Chengdu Institute of Geology and Mineral Resources ; Chengdu 610081 ; China) ; Liao Zhenwen
- 刊名：Acta Geologica Sinica
- 出版年：2012
- 卷期：87(1)
- 关键词：花岗岩 ; granite ; 铀—铅计时 ; U-Pb dating ; 云南 ; Yunnan Province
- 页码：p.55-70
- 图表：illus., 3 tables, 93 refs.
- 分类号：0801
- issnNo：ISSN0001-5717
- isbnNo：CN11-1951/P
摘要
This study conducted SHRIMP U-Pb age analyses for zircons from Caiyuanzi granites of two granitic bodies in the central Kangdian area,Sichuan,SW China,yielding the two ages of 1040.4±6.1 Ma(MSWD=0.53,n=18) and 1063.2±6.9 Ma(MSWD=1.15,n=11),which are highly in accordance with the time of the global Grenvillian orogenic movement.The Caiyuanzi granites are characterized by high SiO2(ave.74.96%),peraluminous(most A/CNK values higher than 1.1),medium alkali contents(ave.Na2O+K2O content of 6.5%),and low MgO(ave.0.17%),low TiO2(ave.0.28%),low CaO(ave.0.09%).They are also low in ∑REE contents with an average ∑REE of 36.99×10-6(14 samples),an average LREE/HREE value of 3.34,a(La/Yb)N value of 8.57 and a δEu value of 0.41.The chondrite-normalized REE pattern displays flat right dipping curves.The large ion lithophile elements,such as Rb,Th,U,and La are relatively enriched,whereas Ba,Eu and high HFSE,such as Nb,Zr and Ti,are relatively depleted.These characteristics show that the Caiyuanzi granites are typical S-type remelt granite.The geochemical features of the Caiyuanzi granites imply that material source is the paragneiss consisting mainly of pelite with minor sandstone.Calculation also shows that the melt of Caiyuanzi granites formed in an intraplate extension environment with a depth of 25 km and a temperature of 850℃ after the collision of blocks in the upper-middle crust and experienced strong differentiation of biotite and plagioclase.At the end of the mid-Proterozoic,the Dongchuan and Tangdan groups subducted northward along with Caiziyuan-Caimashui-Matang fault belt and collided with the Huili Group,resulting in the emplacement of Caiziyuan ophiolite and Caiyuanzi granite,and the eruption of the Tianbaoshan Formation intermediate-acidic volcanic rocks.The collision and collage mountain-building process maybe take place contemporaneously in Dongchuan and Kunyang groups in central Yunan province.The basement of the western margin of the Yangtze craton may be the result of accretion and expansion of the continental crust due to collision and collage of small blocks in different epochs and experienced a process of multiple extensions and collisions.
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