Geochemistry and Geological Significance of Intermediate-Acid Intrusive Rocks in Chaganganuo Area, East Kunlun
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摘要: 查干尕诺地区位于东昆仑西段祁漫塔格中东部,该区中酸性侵入岩主要岩性为花岗闪长岩和二长花岗岩,侵入于白沙河组中,且从花岗闪长岩到二长花岗岩,岩石中SiO2(65.22%~72.42%)含量逐渐增高,Al2O3(14.90%~16.79%)、CaO(1.97%~4.20%)和MgO(0.61%~2.00%)逐渐降低;里特曼指数介于1.41~2.02,K2O+Na2O全碱含量为5.04%~8.8%,属高钾钙碱性系列;稀土总量中等(∑REE=69.78×10-6~148.9×10-6),稀土元素标准化曲线右倾,为轻稀土富集型,基本无Eu异常;岩石中Rb、Th等强烈富集,Nb、Zr、Ce、Ta、Hf等富集一般,Y弱亏损。LA-ICP-MS锆石U-Pb测年表明,其形成年龄为(246.8±1.7)Ma,时代为中三叠世。以上特征表明,本区的中酸性侵入岩属I型花岗岩,结合区域地质特征,该期花岗岩类含大量暗色微粒包体,具有明显的岩浆混合的证据。说明中三叠世该区构造处于洋壳俯冲结束-碰撞开始的转变期。该套侵入岩的发现对东昆仑西段祁漫塔格地区的构造岩浆带研究及发展演化史研究具有重要意义。Abstract: The Chaganganuo area is located in themiddle-east part of Qimantage Mountains, westernsectionof East Kunlun.The intermediate-acid intrusive rocks in this area are mainly granodiorite and adamellite intrusion, which are intruded into the Baishahe Group, varying from granodiorite to adamellite, with the increasing contents of SiO2 (65.22%~72.42%) and the decreasing values of Al2O3 (14.90%~16.79%), CaO (1.97%~4.20%) and MgO (0.61%~2.00%). Their Rittman indexesrange from 1.41 to 2.02, and the total alkali contents of K2O+Na2O are 5.04%~8.8%, belonging to high-K calcium-alkali series.The total REE contents are moderate, with ΣREE values of 69.78×10-6~148.9×10-6, and their REE patterns show enriched LREE and no Eu anomaly. Rb and Th elements in rocks are quiterich, while Nb, Zr, Ce, Ta and Hf elements are rich, but Y element is weakly loss.LA-ICP-MS zircon U-Pb dating shows that the formation ages of these rocks are (246.8±1.7)Ma, which belong to Middle Triassic.The geological characteristics mentioned above indicate that these intermediate-acidic intrusive rocks are I-type granites.Combining with regional geological information, it's shown that a large number of dark microgranular enclave contained in these granitic rocks, with the evidence of obvious magma-mixing characteristics.In Middle Triassic, this area was experienced the conversion stage from the end of oceanic suduction to the beginning of collision orogeny.Thus, the discovery of these intrusive rocks has a great significance for the further study on tectonic magmatic beltand the evolution history in Qimantage area, East Kunlun.
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Keywords:
- granodiorite /
- geochemistry /
- zircon U-Pb age /
- Chaganganuo /
- East Kunlun
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