【摘要】 青海玉树地区的东莫扎抓和莫海拉亨铅锌矿床位于青藏高原金沙江缝合带和班公湖-怒江缝合带夹持的羌塘地体东北缘,是"三江"北段铜铅锌多金属成矿带铅锌矿床的典型代表,处于玉树逆冲推覆构造带的前锋带位置,但矿床与逆冲推覆构造之间的关系并不明确。野外研究表明,方解石为乳白色,结晶粗,呈不规则状、囊状,被后期矿化所穿切,形成于挤压(逆冲推覆阶段)到拉伸(成矿阶段)的过渡阶段,是联系逆冲推覆构造与铅锌矿床之间的"纽带"。本文对该阶段方解石开展了Rb-Sr和Sm-Nd等时线方法定年,测定东莫扎抓铅锌矿床过渡阶段的年龄为35.2~35.5 Ma,平均为35.4 Ma,与其成矿时代35 Ma非常接近;测定莫海拉亨铅锌矿床过渡阶段的年龄为34.0~34.6 Ma,平均为34.3 Ma,与其成矿时代33 Ma也非常接近。结合区域成矿地质背景,建立了玉树地区铅锌矿床从逆冲推覆阶段到成矿阶段的构造控矿模式:伴随着印度-亚洲大陆持续碰撞,青藏高原北缘中生代构造岩片向盆地中央推覆叠置,形成逆冲推覆构造(37~40 Ma),之后处于由挤压到拉伸的松弛状态,早期造山带流体、盆地流体混合形成巨晶方解石脉(34~35 Ma),最后,流体从造山带沿拆离滑脱带长距离向前陆盆地方向运移,运移过程中淋滤围岩的金属物质,并与先期造山带流体混合,形成富铅、锌的成矿流体,通过主逆冲断裂垂向沟通,进入浅部的反冲断层形成铅锌矿床(33~35 Ma)。更多还原

【Abstract】 Located in the northeast margin of Qiangtang terrane between Jinshajiang suture zone and Bangonghu-Nujiang suture zone,the Dongmozhazhua and Mohailaheng Pb-Zn deposits in Yushu area of Qinghai Province are typical Pb-Zn deposits in the Cu-Pb-Zn polymetallic mineralization belt within the northern part of the Nujiang-Lancangjiang-Jinshajiang area.Although these Pb-Zn deposits are in the front belt of Yushu thrust nappe system,the connection between Pb-Zn ore deposits and thrust nappe system remain unclear.Field investigations show that calcite is milk white in color,macrocrystalline,irregular and sack-like in form and is intersected by late mineralization.It was formed during the transitional stage from the compression stage(thrust nappe stage) to the extension stage(mineralization stage) and can be regarded as the link between Pb-Zn ore deposits and the thrust nappe system.Formation ages of the transitional stage in the Dongmozhazhua and Mohailaheng ore districts,determined by both Rb-Sr and Sm-Nd isochron methods for calcite,are 35.2～35.5 Ma with an average of 35.4 Ma and 34.0～34.6 Ma with an average of 34.3 Ma,respectively.Formation ages of such a transitional stage are synchronous with Pb-Zn mineralization epoch(35 Ma and 33 Ma,respectively).In combination with regional mineralization geological setting,the authors established a tentative tectonic model for metallogeny of the Pb-Zn deposits from the thrust nappe stage to the mineralization stage in Yushu area,i.e.,India-Asian collision led to the lifting of the orogenic belt relative to the Tertiary foreland basins in the northern margins of the Qinghai-Tibetan plateau, and strong compression resulted in the thrusting of these basins(37～40 Ma).During the transitional stage from the compression stage to the extension stage(34～35 Ma),the mixing of early orogenic fluid and basin fluid resulted in the formation of macrocrystalline calcite.At last,fluids generated from the orogen migrated laterally along gently-dipping detachment faults of the thrust systems toward the basins and evolved into Pb-Zn ore-forming fluids through the interaction with country rocks and the mixture of early orogenic fluid.The ore-forming fluids migrated vertically along major thrust faults and finally accumulated in the back thrust induced by thrust-nappe structures at shallow levels to form PbZn ore deposits.更多还原