期刊
JOURNAL OF ASIAN EARTH SCIENCES
卷 127, 期 -, 页码 137-151出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jseaes.2016.05.026
关键词
High-K granitoid; Alamas; Tibet; Western Kunlun Orogen; Zircon Hf-O isotopes
资金
- Natural Science Foundation of China [41320104004, 41222023, 41102039]
- IGCP/SIDA project [600]
- Fundamental Research Funds for the Chinese Academy of Geological Sciences [YYWF201509]
- China Geological Survey [1212011020000150011-03, DD20160015]
The Alamas granitoid pluton in the eastern part of the Western Kunlun Orogen, the northwestern margin of the Tibetan Plateau, is composed of quartz diorite. Zircon separates from the pluton has SIMS U-Pb age of similar to 446 Ma. Rocks from the pluton have a narrow range of SiO2 (56.84-62.57 wt%), MgO (1.76-2.94 wt%), and total alkalis (Na2O + K2O = 5.14-9.59 wt%), and are metaluminous and high-K talc-alkaline to shoshonitic in composition. They are enriched in light rare earth elements (LREEs), with (La/Yb)(N) = 14-25, and show weakly negative Eu anomalies. These rocks are relatively enriched in Sr (472-676 ppm) and Ba (435-2388 ppm), and depleted in Nb, Ta, Th, and Ti. Their epsilon(Nd)(t) values range from -6.4 to -8.4, and (Sr-87/Sr-86)(i) = 0.7184-0.7200. Zircons from the pluton show epsilon(Hf)(t) values of -1.4 to -8.8, and delta O-18 = 6.4-9.0 parts per thousand. Geochemical data indicate that the granitoids were likely derived from the reworking of an ancient, deep crustal source, influenced by a minor mantle-derived component. Magmatic differentiation was dominated by the fractional crystallization of hornblende, biotite, and accessory minerals such as apatite, allanite, and Fe-Ti oxides. In summary, the Late Ordovician Alamas pluton is an I-type granitoid that was emplaced in a post-collisional environment, suggesting that this tectonic stage had already initiated prior to similar to 445 Ma. (C) 2016 Elsevier Ltd. All rights reserved.
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