Objective Eclogites are important indicators of ancient plate boundaries or paleosuture zones. Despite their great geological significance, very few investigations have been carried out in the Kunlun region. The Central East Kunlun fault zone was believed to be an Early Paleozoic suture zone, but there has been no reliable evidence for this, though studies on ophiolite, granite, and basic granulite indicate that the Early Paleozoic orogeny occurred in the East Kunlun. This work focused on the Dagele eclogites in Central East Kunlun to provide new constraints for the Central East Kunlun suture zone.
DU WeiJIANG ChangyiTang ZhongliXIA MingzheXIA ZhaodeLING JinlanZHOU WeiWANG Bangyao
选取塔里木东北部的笔架山二叠纪火山岩带为研究对象，通过年代学、岩石学和地球化学等研究，论证火山岩的亲缘关系以及火山岩与侵入岩的关系，探讨岩浆演化过程与源区性质。笔架山一带二叠纪火山岩分布于笔架山镁铁质超镁铁质岩带北侧。火山岩的岩石类型主要有玄武岩、玄武质安山岩、安山岩、英安岩和流纹岩。流纹岩的 LA ICP MS锆石 U Pb年龄为（285．0＆#177;2．9）Ma，属二叠纪乌拉尔世。该火山岩多属拉斑玄武岩系列。玄武岩、玄武质安山岩、安山岩的岩石学及地球化学特征表明，它们都是由拉斑玄武质岩浆通过分离结晶作用演化而成，玄武岩岩浆在上升过程中经历了一定程度的同化混染作用。玄武岩的w（TiO2）（2．35％～3．81％）、w（TFeO）（10．59％～13．87％）、w（P2 O5）（0．35％～0．50％）高，属于高钛玄武岩系列，富集轻稀土元素和大离子亲石元素，Nd Sr同位素组成具有 OIB亲和性，地球化学特征显示出玄武岩的岩浆源区属尖晶石稳定域。笔架山二叠纪侵入岩和火山岩的时空关系、岩石地球化学特征和岩浆演化程度的研究表明：二者是同源岩浆分异的产物，岩浆进入现存岩浆房后，大量的堆晶相形成了镁铁-超镁铁质侵入岩，而演化的岩浆沿岩浆房顶部或旁侧的断层带溢出而形成基性中性火山岩；酸性火山岩是由幔源岩浆的热量引起地壳重熔形成的。
The Xingdi mafic-ultramafic intrusions occur in the northeastern margin of the Tarim craton. The Xingdi No. 3 intrusion is the smallest of four intrusions, with an exposed area of 1.7 km2, and the zircon U-Pb age of the intrusion is 752±4 Ma. The intrusion consists of gabbros, pyroxenites and peridotites, and exhibits a crystallization sequence of the main rock-forming minerals as olivine, orthopyroxene, clinopyroxene and plagioclase. Mineralization occurred at or near the boundaries of the intrusion between pyroxenites and peridotites, and appears as a layered or lenticular shape about 500 m long and 4–15 m wide. The primary sulfides have a relatively simple mineralogy dominated by pyrrhotite-pentlandite-chalcopyrite assemblages, which occur as droplet, star-like and graphic texture and locally sideronitic structures. Geochronological and geochemistry investigations suggest that the Xingdi mafic-ultramafic intrusions and coeval volcanic rock in the Kuluktag area of the Tarim craton formed in an intracontinental breakup environment. Based on the composition of the dominant rockforming minerals and covariant relationships of other oxides versus Mg O, the parental magma of the Xingdi No.3 intrusion belongs to high-Mg tholeiitic basaltic magmas with Mg O of 10.78 wt%. The Xingdi No.3 intrusive rocks are characterized by light REE enrichment relative to heavy REE, negative Nb-Ta anomalies, low 143Nd/144Nd ratios（from 0.511183 to 0.511793） and high initial 87Sr/86Sr ratios（from 0.7051 to 0.7113）. The magma was derived from the enriched-lithospheric mantle and was contaminated during emplacement. According to rock assemblages, mineralization, olivine characteristics, geochemical characteristics and mass balance, there are better copper-nickel ore prospects in the Xingdi No.3 intrusion than in the other three intrusions in the area.
