内蒙古岔沁基性-超基性杂岩体SHRIMP锆石U-Pb年龄、地球化学特征及其地质意义

SHRIMP ZIRCON U-Pb GEOCHRONOLOGY AND GEOCHEMISTRY OF CHAQIN MAFIC-ULTRAMAFIC INTRUSION,INNER MONGOLIA

内蒙古固阳县岔沁基性—超基性杂岩体位于华北克拉通北缘,主要岩石类型可分为透辉岩和辉长岩,岩体普遍发育热液蚀变作用和铜、铂钯矿化特征。热液蚀变现象在空间上与矿体关系密切,主要分布于近矿岩体附近。全岩主量元素分析结果表明,蚀变的透辉岩相对于新鲜的透辉岩均表现出富K,Na,H2O,贫Ca,P,认为岩体的铜、铂钯矿化很可能是富K,Na,H2O,高氧逸度的岩浆期后热液作用的产物。此外,岩体中部新鲜透辉岩样品SHRIMP锆石U-Pb同位素定年结果表明,岔沁岩体的侵位年龄约为415 Ma,相当于早泥盆世。结合最新的区域地质资料,华北克拉通北缘早在泥盆纪可能就已经接受了强烈改造,而岔沁岩体的形成年龄为这一构造-岩浆事件增添了新的证据。

The Chaqin mafic-ultramafic complex is located along the northern margin of the North China Craton, composed of pyroxenites, gabbros, and with extensive hydrothermal altera- tion and Cu-Pt-Pd mineralization. Hydrothermal alteration is spatially related to the mineraliza- tion,near to the Cu-Pt-Pd ore bodies. According to major elements analysis,the altered pyroxe- nites contain a higher level of K,Na,H2O,fO2 and a lower level of Ca,P than those of the fresh ones. Thus,it is concluded that Cu-Pt-Pd mineralization of the complex is likely to be the result of post-magmatic hydrothermal fluids action with rich K, Na, H2O and high fO2. In addition, SHRIMP zircon U-Pb dating indicated that the emplacement age of Chaqin complex is -415 Ma, equivalent to early Devonian. Based on the latest regional geological data, it is suggested that the northern margin of North China Craton has been strongly modified as early as the Devonian,and the Chaqin complex provides new evidence for this tectonic-magmatic event.