东天山图拉尔根大型铜镍矿区两个镁铁-超镁铁岩体的锆石U-Pb定年及其地质意义  

Precise zircon U-Pb age dating of two mafic-ultramafic complexes at Tulargen large Cu-Ni district and its geological implications

作　　者：三金柱[1,2] 秦克章[1] 汤中立[3] 唐冬梅[1] 苏本勋[1,2] 孙赫[1] 肖庆华[1,2] 刘平平[1,2] 

机构地区：[1]中国科学院地质与地球物理研究所中国科学院矿产资源研究重点实验室,北京100029 [2]中国科学院研究生院,北京100049 [3]长安大学地球科学与国土资源学院,西安710054

出　　处：《岩石学报》2010年第10期3027-3035,共9页Acta Petrologica Sinica

基　　金：中国科学院知识创新工程重要方向项目(KZCX2-YW-107);国家"十一五"科技支撑计划新疆305项目(2006BAB07B03-01);新疆有色集团公司项目资助

摘　　要：图拉尔根铜镍矿位于新疆黄山-镜儿泉铜镍矿带东段,其发现和探明是近年来该区带找矿的重大突破。矿区内分布有Ⅰ、Ⅱ、Ⅲ号3个小岩体,其中Ⅰ号岩体含矿性最佳,勘查程度也最高。Ⅰ号杂岩体为一同构造基性-超基性杂岩体,具有典型的环带状岩相分带结构。图拉尔根Ⅰ号岩体的辉长岩单颗粒锆石SHRIMP U-Pb精确定年结果为300.5±3.2Ma,而Ⅱ号岩体锆石SIMS U-Pb精确定年结果为357.5±2.5Ma,明显早于Ⅰ号岩体。Ⅰ号岩体成岩时代为晚石炭世-早二叠世,与东天山地区大多数镁铁-超镁铁岩体的形成时代相近,而Ⅱ号岩体时代为早石炭世,表明二者不是同期岩浆活动的产物,其形成背景与东天山早二叠世大规模成矿期的碰撞后伸展背景形成的基性-超基性侵入岩体不同。稀土元素及微量元素分析表明,两个岩体的轻重稀土分异明显,都为向右倾的轻稀土富集型配分模式,具负的Nb、Ta异常。但Ⅱ号岩体的斜率高于Ⅰ号岩体。Ⅰ号岩体富集大离子亲石元素Rb,Th轻微亏损,高场强元素Zr、Hf呈正异常,而Ⅱ号岩体明显亏损Rb,富集Ba,同时有Sr的正异常和Zr、Hf的明显负异常。Ⅰ号岩体微量元素具有Nb、Ta相对于Th、La亏损,Ba、Th、U含量高的特点,表现出地壳物质混染的特征。Ⅱ、Ⅲ号岩体目前所见均以辉长岩为主体岩石类型,含矿性较差。Ⅱ号岩体和Ⅰ号岩体微量元素富集特征不一致,也显示这两个岩体的母岩浆性质可能不尽相同,但两个岩体的微量元素特征都显示出遭受了一定程度的地壳混染,这对成矿是有利的。由于Ⅱ、Ⅲ号岩体发育有高磁、高重力和低阻异常,我们尚不能排除其深部产出矿化的可能性,有必要开展进一步的勘查评价。图拉尔根两个镁铁-超镁铁岩体的最新定年结果,将东天山地区与铜镍硫化物矿床相伴的镁铁-超镁铁质岩浆活动时限提前了10Ma,为在该区进一步找矿Tulargen Cu-Ni deposit,its discovery was the most important exploration breakthrough of recent years,located in the eastern section of Huangshan-Jingrquan ore belt,eastern Xinjiang. There are three small intrusions in the ore district which named Ⅰ,Ⅱand Ⅲ complex,respectively. The ore-bearing property and exploration degree are both best in Ⅰ intrusion. It shows typical ring-band structural lithofacies zones,soⅠcomplex is a syntectonic mafic-ultramafic intrusion. The result of gabbro zircon SHRIMP U-Pb age of Ⅰ intrusion is 300.5±3.2Ma,determined zircon SIMS age of Ⅱintrusion is 357.5±2.5Ma. So the emplacement of Ⅱcomplex is earlier than Ⅰcomplex. Ⅰ Intrusion formed in Late Carboniferous-Early Permian,which consists with formation ages of most east Tianshan mafic-ultramafic intrusions and associated Cu-Ni deposits. Furthermore the age makes the mafic-ultramafic magma activity related with magmatic Cu-Ni sulfide deposits ahead of about 10Ma in eastern Tianshan. While Ⅱ intrusion formed in Early Carboniferous. So the two intrusions of Tulargen ore district are not formed in the same period of magmatic activity. The tectonic setting of Ⅱ intrusion is different from the major metallogenic structure,extension setting of the late collision,of large-scale Early Permian magmatic Cu-Ni sulfide deposits in eastern Tianshan. REEs and trace elements analysis data of two intrusions both show LREE and HREE clear fractionation,enrichment of LREE and negative Nb and Ta anomalies. However,the slope of Ⅱintrusion is higher thanⅠintrusion. Ⅰintrusion have Rb,Zr and Hf positive anomalies,while significant loss of Rb,enrichment of Ba in Ⅱ intrusion. Furthermore,there are Sr positive anomalies and Zr,Hf negative anomalies. The trace elements characteristics of these two intrusions both display the feature of crustal contamination. Ⅱand Ⅲ intrusions are both mainly consist of gabbro and ore-poor. The significant difference of forming age and geochemical characteristics of these two complexes indica

关 键 词：图拉尔根铜镍矿区 Ⅰ、Ⅱ号镁铁-超镁铁岩体 岩石地球化学 锆石U-PB定年 东天山 

分 类 号：P588.125[天文地球—岩石学]