南秦岭太平沟基性侵入岩的锆石U-Pb年代学、地球化学及其成矿意义

ZIRCON U-PB GEOCHRONOLOGY,GEOCHEMISTRY AND METALLOGENIC SIGNIFICANCE OF TAIPINGGOU BASIC INTRUSIVE ROCKS IN THE SOUTH QINLING MOUNTAINS

太平沟基性侵入岩出露于南秦岭镇安地区,产于近东西向凤镇—山阳深大断裂与北东向东川河断裂的交汇部位,东与小磨岭杂岩体毗邻,西与东江口岩体群相接。岩体地表呈NWW-SEE向的不规则椭圆状,出露面积约0.84 km^(2),局部被石英闪长岩、花岗岩侵入,是一个由基性、中性和酸性侵入岩构成的小型杂岩体。基性侵入岩主要由辉长苏长岩、辉长岩和角闪辉长岩组成,辉长岩中发育较强烈的铜(钴)矿化。锆石LA-ICP-MS U-Pb年代学研究表明,太平沟基性侵入岩中角闪辉长岩的成岩年龄为224.4±0.99 Ma,形成于晚三叠世。岩石地球化学研究表明,基性侵入岩SiO_(2)含量为47.39%~53.48%,稀土总量ΣREE=60.30×10^(-6)~94.12×10^(-6),富集轻稀土且轻重稀土分异明显((La/Yb)_(N)=3.11~10.68),具有较弱的铕负异常或正异常(δEu=0.67~1.22),具明显富集Ba、K、Sr等大离子亲石元素,亏损Ta、Nb等高场强元素特征;岩石具有较高的(^(87)Sr/^(86)Sr)_(i)值(0.7058~0.7091)和负的ε_(Nd)(t)值(-9.00~-1.50),暗示岩浆源区为富集地幔。综合分析认为,南秦岭太平沟地区基性侵入岩形成于秦岭造山带印支晚期的后碰撞环境,与之有关的铜(钴)矿化成矿时代为印支晚期,暗示该地区是形成和寻找与基性侵入岩有关的铜镍硫化物矿床的有利地区。

Adjacent to Xiaomoling complex in the east and Dongjiangkou rock group in the west,Taipinggou basic intrusive rock is exposed in Zhen′an area of South Qinling Mountains and occurs at the intersection of near East-West Fengzhen-Shanyang deep fault and northeast Dongchuanhe fault.The surface of the rock mass is an irregular ellipse at NWW-SEE direction,with an exposed area about 0.84 km^(2)and locally invaded by quartz diorite and granite,which is a small complex composed of basic,neutral and acid intrusive rocks.The basic intrusive rocks are mainly composed by gabbronorite,gabbro and hornblende gabbro,in which strong copper(cobalt)mineralization is developed.The LA-ICP-MS U-Pb chronology of zircon shows that the diagenetic age of Taipinggou amphibolite gabbro in basic intrusive rocks is 224.4±0.99 Ma,indicating that it was emplaced in the Late Triassic.Lithochemistry analysis shows that the content of SiO_(2) in basic intrusive rock is 47.39%~53.48%,and the total amount of rare earth is REE=60.30×10^(-6)~94.12×10^(-6),relatively enriched in LREE with(La/Yb)_(N)=3.11~10.68 and weakly-significant Eu negative or positive anomaly(δEu=0.67~1.22),obvious enrichment of Ba,K,Sr and other large ion lithophile elements,and loss of Ta,Nb and other high field strength elements.The rocks also have negativeε_(Nd)(t)(-9.00~-1.50)and higher(^(87)Sr/^(86)Sr)_(i)(0.7058~0.7091),suggesting that the magma source area is an enriched mantle.The comprehensive analysis shows that Taipinggou basic intrusive rock was formed in the post collision environment of late Indosinian in Qinling orogenic belt,and the metallogenic age of copper(cobalt)mineralization related to basic rocks in Taipinggou area is the late Indosinian period,suggesting that this area is a favorable area for the formation and search of copper-nickel sulfide deposits related to the basic intrusive rocks.