四川盐边冷水箐岩体的形成时代和地球化学特征

Format on age and geochemical characteristics of the Lengshuiqing body, Yanbian, Sichuan province.

四川盐边冷水箐岩体主要由辉长岩组成,它侵位于中元古代盐边群上部岩系中,盐边群接触变质作用发育,岩体分带清楚,是一个典型的同心环状侵入体。因此,它不属于蛇绿岩套范畴,锆石U-Pb年龄为936±7Ma,表明它是新元古代早期岩浆活动产物,该岩体的主要元素显示拉斑玄武质分异趋势;富集大离子不相容元素(Ba,Sr),亏损高场强元素(Nb,Ta,Zr,Hf);LREE轻微富集((La/Yb)_N=1.19～4.28),分配型式略呈右倾型;ε_(Nd)(t),(^(87)Sr/^(86)Sr)_i和δ^(18)O值分别为3.0～4.3,0.70446～0.70452和5.9‰～7.5‰;在构造环境判别图上,它们都投影子岛弧拉斑玄武岩区域内。上述特征表明,冷水箐岩体可能是在一个相对原始的岛弧环境中形成,岩浆源区已受到俯冲组分影响而产生不同程度富集。

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 εNd (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.