ISSN 1009-6248CN 61-1149/P 双月刊

主管单位:中国地质调查局

主办单位:中国地质调查局西安地质调查中心
中国地质学会

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    甘肃北山铭杨镁铁–超镁铁岩体锆石U–Pb年龄、地球化学特征及其地质意义

    Geochemistry and Zircon U–Pb Dating of the Mingyang Mafic–Ultramafic Rock Complex in Beishan Area of Gansu and Its Prospecting Significance

    • 摘要: 铭杨岩体位于甘肃北山南带古堡泉–红柳园断裂北侧,侵位于敦煌岩群,为甘肃北山地区新近发现的一处铜镍矿化镁铁–超镁铁岩体,主要由辉橄岩、二辉橄榄岩、橄榄辉长岩、辉长岩等组成。全岩成分以低碱、低钛为特征,轻稀土略富集,具有明显的正Eu异常;富集大离子亲石元素(LILE)Rb、Ba、Sr和K,相对亏损高场强元素(HFSE)Th、U、Nb、Ta、Zr和Hf。岩浆演化过程中发生了橄榄石、斜长石和辉石的分离结晶作用,经历了一定程度的地壳混染,地、物、化、遥综合信息显示具有较好的铜镍成矿潜力。通过LA–ICP–MS锆石U–Pb测年,首次获得铭杨岩体中橄榄辉长岩和辉长岩结晶年龄分别为(452.9±2.4) Ma和(457.7±2.1) Ma,岩体可能为早古生代陆缘裂谷环境下的产物。北山地区早古生代含铜镍岩体的发现对区域构造演化认识具有重要意义。

       

      Abstract: The Mingyang rock body is a newly discovered copper-nickel mineralized Mafic-Ultramafic rock body, which is located on the north side of the gubaoquan-hongliuyuan Fault in the southern belt of Beishan, Gansu. The rock intruding in the Dunhuang rock group,which mainly composed of gabbro, diabase peridotite, olivine gabbro, gabbro, etc. The rock composition is characterized by low alkali and low titanium, slightly enriched in light rare earths, with obvious positive Eu anomalies; enriched in large ion-lithophile elements (LILE) Rb, Ba, Sr and K, and relatively deficient in high field strength elements (HFSE) Th, U, Nb, Ta, Zr and Hf. During the magmatic evolution, the separation and crystallization of olivine, plagioclase and pyroxene occurred, it has experienced a certain degree of assimilation and contamination. The geological, geophysical and geochemical information show that it has the better potential of copper and nickel ore. The first crystallization ages of (452.9±2.4) Ma and (457.7±2.1) Ma for olivine gabbro and gabbro in the Mingyang rock mass were obtained by LA-ICP-MS zircon U-Pb dating. The rocks may be the products of the Early Paleozoic continental margin rifting environment. The discovery of early Paleozoic Cu-Ni-bearing rocks in the Beishan area is of great significance to the understanding of regional tectonic evolution.

       

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