| 摘要: |
| 岩相学和岩石地球化学特征表明，西天山阿吾拉勒西段低压麻粒岩相片麻岩的原岩为杂砂岩，具有近源、快速沉积的特点。在稀土元素的球粒陨石标准化图解上，片麻岩具轻稀土元素陡倾、重稀土元素平坦的分布型式，并具明显的Eu负异常，Nb、Ta、Ti、Ba、P、Sr均相对亏损。片麻岩中Cameca离子探针锆石U-Pb年代学结果显示，上交点年龄为（1609±40）Ma，代表了原岩的岩浆结晶年龄；下交点年龄为（764±72）Ma，代表了引起Pb丢失的热事件的时代，可能代表麻粒岩相变质事件的年龄。该麻粒岩相片麻岩的产出表明伊犁地块可能具有中元古代的结晶基底，也表明伊犁地块经历了764Ma的热事件。该热事件可能是伊犁地块对全球Rodinia超大陆解体事件的响应。 |
| 关键词: 伊犁地块 西天山 锆石Cameca U-Pb年龄 麻粒岩相片麻岩 |
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| Zircon Cameca U-Pb dating and its significance for granulite-facies gneisses from the western Awulale Mountain, West Tianshan, China. |
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LI Ji-lei1,2, SU Wen1, ZHANG Xi1,2， LIU Xin1,21,2
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1.1. Key Laboratory of Mineral Resources, Institute of Geology and Geophysics,Chinese Academy of Sciences, Beijing 100029, China;2.2. Graduate University of Chinese Academy of Sciences, Beijing 100049, China
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| Abstract: |
| Petrographic and geochemical characteristics of low-pressure granulite-facies gneisses from the western Awulale Mountains (in the western Tianshan Mountains) indicate that the protolith was a graywacke, which is featured by proximity of its origin and rapid deposition. In the chondrite-normalized diagram, the distribution patterns of rocks show steep LREE-type (light rare earth elements) and flat HREE-type, which suggests negative Eu anomaly and Nb, Ta, Ti, Ba, P and Sr depletions. The Cameca ion probe zircon U-Pb dating gave an upper interception age of 1609Ma±40Ma and a lower interception age of 764Ma±72Ma, representing the ages of magma crystallization and Pb-loss thermal event, respectively. The latter thermal event may represent the low-pressure metamorphic age. The outcrop of granulite-facies gneisses suggests that the Yili block may be underlain by Middle Proterozoic crystalline basement. The ~764 Ma thermal event probably records the break-up of the Rodinia supercontinent. |
| Key words: Yili block west Tianshan Mountains Cameca zircon U-Pb age granulite-facies gneisses |