| 胡义,王明志,李景晨,周斌,杨志军,秦臻,唐力.西藏冈底斯西段松多复式岩体锆石U-Pb定年及地球化学特征[J].矿产勘查,2021,12(3):511-524 |
| 西藏冈底斯西段松多复式岩体锆石U-Pb定年及地球化学特征 |
| Zircon U-Pb age and geochemical characteristics of Songduo intrusive rock in the western Gangdese,Tibet |
| 投稿时间：2020-07-16 |
| DOI： |
| 中文关键词: 西藏 冈底斯西段 地球化学特征 锆石U-Pb定年 松多复式岩体 |
| 英文关键词: Tibet,Western Gangdise, geochemical characteristics, zircon U-Pb dating, Songduo intrusion |
| 基金项目:中国地质调查局《西藏1∶5万许如错西地区(H45E011008、H45E011009、H45E012008、H45E012009)4幅区域地质矿产调查》(编号:1212011221068)资助。 |
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| 中文摘要: |
| 冈底斯岩浆岩带的岩石成因和动力学过程对于揭示新特提斯洋俯冲、印度-亚洲大陆碰撞和之后的高原隆升具有重要意义。通过对松多区岩体地球化学和锆石LA-ICP-MS U-Pb定年研究,结果表明:二长花岗斑岩锆石206 Pb/238 U年龄为(44.5±1.6)Ma(95%置信度,n=18,MSWD=1.5),黑云二长花岗斑岩锆石206 Pb/238U年龄为(50.3±1.1)Ma(95%置信度,n=24,MSWD=0.92),为始新世早期岩浆活动的产物,代表了该区岩石成岩年龄。岩石地球化学特征表明,松多岩体花岗岩为高钾钙碱性的过铝质I型花岗岩,里特曼指数(σ)为2.2~2.64,稀土元素配分曲线呈右倾型,负Eu异常明显,富集Nd、Th、La、U等大离子亲石元素,亏损Ti、Nb、Ta等高场强元素。Rb/Sr值为0.37~0.53,显示出壳幔混染特征。结合前人成果表明,始新世早期新特提斯洋俯冲板片的阻力加大,在后期演化中板块回转、断离,导致上地幔岩部分熔融,在就位过程中,熔融下地壳物质形成混合岩浆,在快速侵位过程中又混染部分地壳物质,最后形成了松多地区微粒-细粒花岗斑岩体,丰富了冈底斯西段新生代岩浆-构造成岩模式与地球化学特征。 |
| 英文摘要: |
| The petrogenesis and dynamic process of the Gangdise magmatic belt are of great significance to reveal the subduction of the Neo Tethys ocean, the collision between the Indian and Asian continents and the subsequent uplift of the plateau. According to the result of zircon LA-ICP-MS U-Pb dating, the zircon206Pb /238U age of monzonitic granite porphyry is 44.5 ± 1.6 Ma (95% confidence level, n = 18, MSWD = 1.5), and that of biotite monzonitic granite porphyry is 50.3 ± 1.1 Ma (95% confidence level, n = 24, MSWD = 0.92), implying the products of early Eocene magmatism and representing the diagenetic age of the rocks in this area. The geochemical characteristics of the rocks indicate that the Songduo granite is a alkaline peraluminous I-type granite with high potassium and calcium. The Rittmann Index (σ) is 2.2 ~ 2.64. The distribution curve of rare-earth element is right inclined, with obvious negative Eu anomaly, enriched in large ion lithophile elements such as Nd, Th, La, U, and depleted in high field strength elements such as Ti, Nb, Ta. The ratio of Rb/Sr ranges from 0.37 to 0.53, which shows the characteristics of crust mantle contamination. Combined with previous studies, it is shown that the resistance of the subducted plate of the Neo-Tethys increased in the early Eocene. In the late evolution, the plate rotated and broke off, resulting in the partial melting of the upper mantle rocks, then the crust materials were melted to form mixed magma during the emplacement process, and in the rapid emplacement process, some crustal materials were mixed. Finally, the fine-grained granite porphyry in Songduo area was formed. These processes enriched the formation of Cenozoic magmatic tectonic diagenetic model and geochemical characteristics in the western Gangdese,Tibet. |
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