Format on age and geochemical characteristics of the Lengshuiqing body, Yanbian, Sichuan province.
Format on age and geochemical characteristics of the Lengshuiqing body, Yanbian, Sichuan province.
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作者：
Shen Wei
四川延边冷水青体侵入中元古代延边群上层序，主要由辉长岩组成。延边群接触变质作用发育。该岩体岩相分带清楚，为典型的同心环状侵入体。因此，它不属于蛇绿岩套的范围。锆石U-Pb年龄为936±7 Ma，是新元古代早期岩浆活动的产物。冷水青体主要元素组成呈拉斑玄武岩分异趋势。它们相对富含大离子亲石元素(Ba和Sr)，亏损高场强元素(Nb、Ta、Zr和Hf)。REE数据表明，它们具有轻微的LREE富集度((La/Yb)N=1.19-4.28)，稀土配分模式为略右倾型。它们的END(T)，(87Sr/86Sr)Iδ_(18O)值分别为3.0-4.3，0。70446-0。70452和5.9‰-7.5‰。在构造背景识别图上，它们位于岛弧拉斑玄武岩范围内。上述地球化学特征表明，冷水青体形成于相对原始的岛弧环境，岩浆源区受到不同程度俯冲成分的富集。
The Lengshuiqing body, Yanbian, Sichuan Province, which is mainly composed of gabbro, is intruded into the upper sequence of Mid-Proterozoic Yanbian Group. Contact metamorphism of Yanbian Group is developed. Lithofacies zoning of this body is clear and it is a typical concentric ring intrusion. Therefore, it does not belong to the range of ophiolite suite. U-Pb age of zircon is 936±7Ma suggesting that it is a product of early Neoproterozoic magmatic activity. The Lengshuiqing body has tholeiitic differential trend in major element compositions. They are relatively enriched in large ion lithophile elements (Ba and Sr) and depleted in high field strength elements(Nb, Ta, Zr and Hf). REE data demonstrate that they have a slight enrichment of LREE (( La/Yb)N = 1. 19 - 4. 28) and the REE patterns are slightly right-inclined type. Their eNd (t), (87Sr/86Sr)i δ18O values are 3. 0 - 4. 3, 0. 70446 - 0. 70452 and 5. 9‰- 7. 5‰, respectively. On the identify diagram of tectonic setting, they are located at the range of island-arc tholeiite. The above-mentioned geochemical characteristics suggest that the Lengshuiqing body was formed at the relatively primitive island-arc setting and magma source was enriched by subducted components in different degres.