西昆仑北缘库斯拉甫一带寒武纪中酸性岩浆活动及地质意义

Cambrian intermediate-acid magmatic activity and its geological significance in the Kusilafu region at the north margin of the Western Kunlun

西昆仑北缘库斯拉甫一带寒武纪中酸性侵入岩广泛分布，据野外接触关系可分为前后两个序次。早序次岩石为浅灰一麻灰色似斑状石英（二长）闪长岩，具贫硅、中碱、高钙和过铝质等特征，岩石稀土总量较低，轻稀土元素富集（（La／Yb）N平均15.56），中等Eu负异常（δEu为0.56～0.88，平均0.73）。晚序次岩石为灰白色似斑状粗粒（二长）花岗岩，具富硅、低钙、富钾和过铝质等特征，稀土元素总量较高，轻稀土元素富集（（La／Yb）。平均13.39），Eu负异常明显（6Eu为0.25～0.57，平均0.40）。早序次岩体侵位规模大，出露广泛，为I型花岗岩；晚序次岩体规模小，以岩株、岩脉状穿插其中，属于S型花岗岩范畴。两序次岩石产出的大地构造环境均为岛弧，可能由昆仑洋的俯冲消减引起，不同之处在于早序次岩石产于活动大陆（西昆仑地块）边缘位置，而晚序次形成在俯冲消减带上，两序次岩石为消减洋壳上部不同源区地壳部分熔融的产物。

Cambrian intermediate-acid intrusive rocks （U-Pb age （511＋29） Ma） distribute widely around the Kusilafu region at the north margin of the Westem Kunlun. The intrusive rocks can be subdivided into early and later periods according to contact relationships. The early intrusion is greyish porphyritic quartz （monzonite） diorite, characterized by poor-SiO2 moderate-alkaline, high-Ca and strongly peraluminous, and is relatively low in ZREE with LREE enrichment （（La/Yb）N, 11.65 on average） and moderate negative Eu anomaly （δEu varied from 0.40 to 0.71, 0.73 on average）. While the later is offwhite porphyritic coarse-grained （monzonite） granite characterized by rich-Si, low-Ca, rich-K and peraluminous, and is relatively enriched in ZREE with an enrichment of LREE （（La/Yb）y average at 10.19） and moderate negative Eu anomaly （6Eu varied from 0.40 to 0.71, averaged at 0.73）. The early intrusion is larger with widespread outcrops, and belongs to I-type granite, whereas the later is smaller, and belongs to S-type granite, which intruded into the early one. Both intrusions formed in an island arc tectonic setting likely associated with the Kunlun Ocean subduction. The difference is that the early one formed at the active continental （the Western Kunlun） margin while the later were formed in the subduction zone; they were both results of partial melting crust from different source regions of the upper subducting oceanic crust.