南祁连裕龙沟岩体ID-TIMS锆石U-Pb年龄及其地质意义

ID-TIMS zircon U-Pb age of Yulonggou intrusive rocks in southern Qilian Mountain and its geological significance

日月山—化隆地区的基性—超基性岩带发育有多个与铜镍矿化有关的岩体,岩石类型主要有角闪辉长岩、辉长岩、苏长岩、辉石岩、辉橄岩、橄榄岩等。通过对裕龙沟岩体的实地调查和研究,利用ID-TIMS(同位素稀释热电离质谱法)对岩体进行锆石U-Pb同位素定年,获得成岩年龄442.7Ma±1.6Ma,为加里东期。岩石地球化学特征分析和区域对比研究表明,裕龙沟岩体为一铁质系列的基性—超基性岩类型的杂岩体,岩体分异好,有用元素Ni、Cu、Co丰度高,为有利成矿的岩体;440Ma左右整个祁连地区正处于由俯冲造山向碰撞造山过渡的转换时期,随着拉脊山小洋盆的闭合,进入陆内造山阶段,在后碰撞伸展环境中形成裕龙沟等基性—超基性侵入岩体。结合其它岩体信息认为,该岩带中的岩体可能形成于同一时期,有其特殊的动力学机制和演化过程。这期伸展裂解事件与成矿关系非常密切,因此对其研究具有非常重要的现实意义。

The Riyueshan-Hualong basic-ultrabasic rock belt has a number of well-developed intrusive bodies composed mainly of amphibole gabbro,gabbro,norite,pyroxenite,augite peridotite and peridotite,which are related to copper-nickel mineralization.This paper reports some achievements made in evaluation of magmatic type copper-nickel ore resources potential in Hualong County,Qinghai Province,on the basis of field survey and investigation of Yulonggou intrusive body.ID-TIMS U-Pb dating of zircon from the Yulonggou intrusive body yielded an age of 442.7Ma±1.6 Ma.Petrologic and geochemical characteristics and regional comparative investigation show that Yulonggou intrusive body is a ferruginous series ultrabasic-basic complex characterized by good magmatic differentiation and high abundance of useful elements such as Ni,Cu and Co,therefore favorable for mineralization.440 Ma was in the period when subduction orogeny was converted into collision orogeny in the whole Qilian Mountain and then into the orogenic stage with the closure of Laji Mountain small ocean basin,thus forming Yulonggou basic-ultrabasic intrusive body in a post-collision extensional environment.A comparison of information with other intrusive rocks in Riyueshan-Hualong basic-ultrabasic rock belt reveals that all the intrusive rocks might have been formed in the same period,characterized by specific dynamic mechanism and evolution process.This extensional rifting event had a very close relationship with mineralization,so the research has very important practical significance.