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《Geotectonica Et Metallogenia》 2005-04
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THE ADAKITE-LIKE INTRUSIVE ROCKS CHARACTERISTICS OF WESTERN TIBET AND THEIR PROSPECTING SIGNIFICANCE

CAI Zhiyong 1,2,3, QIU Ruizhao4, XIONG Xiaolin1, HUANG Guicheng4, ZHOU Su4 and MENG Xiangjin4 (1.Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, GD 510640, China; 2. Graduate School, Chinese Academy of Sciences, Beijing 100039, China; 3. Northwestern Hubei Survey of Geology and Mineral Resources, Xiangfan, HB 441003, China; 4. Yichang Institute of Geology and Mineral Resources Research, Yichang, HB 443003, China)  
The ages of intrusive rocks of western Tibet that occurred in the southern and middle Gangdese plutons with NW trends (between 88° longitudes and the western borders of China) are less than 25 Ma generally. Samples that were collected from the plutons, belonging to the series of continental alkaline magmatism, show the characteristics as follows: relatively high SiO2 (56.00%~70.6%), A12O3 ( 14.23%~ 16.85 %), K2O ( 1.74%~ 4.33%) and Na2O (Na2O/K2O1, generally), high Sr (420~938 μg/g), low Y (7.16~16.0 μg/g). They show a REE pattern rich in light REE and abnormality in Eu (weak) and Sr (positive) compared to the standardized pattern. These geochemical characteristics are typical of adakite. In considering the geological setting and isotopic ages of the samples as less than 25 Ma and the crustal thickness of the Tibetan plateau as about 60 km at that time based on petrologic evidence, and by comparing with the characteristics of adakite-like rocks reported in the eastern Tibet and eastern China, it is suggested that the subducted oceanic crust slab was not involved in generating adakite magmas which formed these rocks. So they probably belong to C-type adakites, which were derived from continued magmatic underplating and thickening at the base of the crust. It is well-known that copper and gold deposits are closely related to adakite in China and abroad. Also it is reported that the occurrences of many copper deposits in and around the cotemporaneous adakite or adakite-like rocks in the eastern part of the Qinghai-Tibetan Plateau. Therefore, the discovery of the Cenozoic adakites in this paper have geological significance in dynamics showing continental plumb growth in Cenozoic, especially, in ore-prospecting of porphyry copper and gold deposits showing brilliant prospect potential in the western part of the Qinghai-Tibetan Plateau.
【Fund】: 中国地质调查局地质大调查项目(200110200064);; 中国科学院创新工程项目(KZCX3-SW122)资助.
【CateGory Index】: P618.41;
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