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| 西昆仑阿卡阿孜山岩体的年代、源区和构造意义 | |
| 引用本文： | 袁超,孙敏,周辉,肖文交,侯泉林,李继亮.西昆仑阿卡阿孜山岩体的年代、源区和构造意义[J].新疆地质,2003,21(1):37-45. |
| 作者姓名： | 袁超 孙敏 周辉 肖文交 侯泉林 李继亮 |
| 作者单位： | 1. 中国科学院广州地球化学研究所,广东,广州,510640 2. 香港大学地球科学系,香港特别行政区 3. 北京大学科学研究部,北京,100864 4. 中国科学院地质与地球物理研究所,北京,100029 |
| 基金项目： | 国家自然科学基金项目(40003005)，香港大学研究生基金共同资助 |
| 摘 要： | 阿卡阿孜山岩体是西昆仑造山带中面积最大的花岗岩侵入体，主要由花岗闪长岩和二长花岗岩组成。对其中花岗闪长岩的黑云母^40Ar/^39Ar定年获得了精确的213Ma的表面年龄。这一结果与较早前根据单颗粒锆石U-Pb法获得的年龄结果在误差范围内一致，表明阿卡阿孜山岩体并非是一个多期次的复式岩基，而是同一次岩浆活动的产物。地球化学研究表明阿卡阿孜山岩体为次铝质－轻微过铝质的钙碱性－高钾钙碱性岩体，尽管花岗闪长岩和二长花岗岩之间存在化学组分上的差异，二均具有轻稀土富集的稀土分布模式和相似的微量元素特征。然而二的初始Sr同位素组成存在一定的差异，表明二长花岗岩并非是花册 长岩分异作用的产物。二的Sr-O的同位素共同构成了负相关，排除了在其形成过程中幔源岩浆介入的可能性，反映其源区为包含长英质组分和基性－超基性组分的增生楔物质。由于增生楔的部分熔融需要较高的能量输入，因而阿卡阿孜山岩体不大可能形成于与消减作用有关的大陆边缘环境。此次的黑云母^40Ar/^39Ar年龄十分接近早前的锆石U－Pb年龄，表明该岩体的冷却速率相当快，应反映一种碰撞后抬升的环境。这种环境的出现表明西昆仑古特提斯洋在晚三叠纪时已经闭合。 |
| 关 键 词： | 古特提斯 阿卡阿孜山岩体 氩－氩年龄 增生楔 构造环境 花岗岩侵入体 西昆仑造山带 |
| 文章编号： | 1000-8845(2003)01-037-09 |
| 修稿时间： | 2002年1月14日 |
ARKARZ SHAN INTRUSIVE COMPLEX, WESTERN KUNLUN: AGE, SOURCE AND TECTONIC IMPLICATIONS |
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| Chao Yuan,Min Sun,Hui Zhou,Wen-jiao Xiao,Quan-lin Hou,Ji-liang Li.ARKARZ SHAN INTRUSIVE COMPLEX, WESTERN KUNLUN: AGE, SOURCE AND TECTONIC IMPLICATIONS[J].Xinjiang Geology,2003,21(1):37-45. | |
| Authors: | Chao Yuan Min Sun Hui Zhou Wen-jiao Xiao Quan-lin Hou Ji-liang Li |
| Abstract: | Biotite 40Ar/39Ar dating and systematic geochemical analyses have been conducted for the Arkarz Shan Intrusive Complex (ASIC), the largest granitic intrusion of West Kunlun. The Arkarz Shan Intrusive Complex consists of granitoids and monzogranite, with a transitional relationship in between. Stepwise degassing technique was applied to biotite 40Ar/39Ar dating of the granodiorite and yielded a stable argon-releasing spectrum and 213 Ma plateau age. The new Ar-Ar age is consistent, within error, to a previously obtained single-grain zircon U-Pb age (214+1) Ma), suggesting that the ASIC is not a multiple-phase batholith, and that the granitoids and monzogranite were generated together during a magmatic event. Geochemical data show that the ASIC is metaluminous to slightly peraluminous ACNK= 0.94(1.09). Although different in contents of major oxides and trace elements, both the granodiorite and monzogranite exhibit LREE-enriched pattern and similar trace element characteristics. However, there are considerable differences in their initial Sr and oxygen isotope compositions, indicating that the monzogranite was not derived from the granodiorite. The ASIC possesses relative radiogenic Sr isotope composition (0.708 3-0.711 0) and its oxygen isotope ratios (18O=+5.1%+8.5%) generally correspond to I-type granitoids. Data plots of the granodiorite and monzogranite forms a negative trend in Sr-O isotope relationship diagram, which precludes the possibility of mantle-derived magma involvement. Moreover, the negative Sr-O relationship suggests that the source of the ASIC contains both terrestrial felsic debris and altered basaltic materials and strongly favors an accretionary wedge model for the West Kunlun. The consistency of the biotite Ar-Ar and zircon U-Pb ages indicates an extraordinary cooling rate for the ASIC, which may imply a fast uplifting environment related to collision. Emergence of such an environment in the West Kunlun indicates that the Paleo-Tethys had been closed by the late Triassic. |
| Keywords: | West Kunlun paleo-Tethys Arkarz Shan complex Ar-Ar age accretionary wedge tectonic setting |
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