豫西焦沟正长岩锆石U-Pb定年、地球化学特征及其地质意义  

LA-ICP-MS zircon U-Pb dating and geochemical characteristics of the Jiaogou syenite in western Henan Province and its geological implications

作　　者：梁涛 卢仁 卢欣祥[3] 温静静 LIANG Tao;LU Ren;LU Xinxiang;WEN Jingjing(General Institute of Non-ferrous Metals Geologic Exploration of Henan Province,Zhengzhou 450052,Henan,China;Key Laboratory of Deep Ore-prospecting Technology Research for Non-ferrous Metals of Henan Province,Zhengzhou 450052,Henan,China;Institute of Land and Resources of Henan Province,Zhengzhou 450051,Henan,China)

机构地区：[1]河南省有色金属地质勘查总院,河南郑州450052 [2]河南省有色金属深部找矿勘查技术研究重点实验室,河南郑州450052 [3]河南省国土资源科学研究院,河南郑州450051

出　　处：《地质通报》2020年第5期681-691,共11页Geological Bulletin of China

基　　金：河南省国土资源厅科技攻关项目《河南省锂矿成矿规律及找矿方向研究》(编号:2018-01);《河南省东秦岭碱性侵入岩岩石成因及成矿预测研究》(编号:2014-06);国家自然科学基金项目《河南省嵩县南部正长岩的U-Pb定年、锆石Hf同位素及地球化学特征》(批准号:U1504405)。

摘　　要：豫西纸房—黄庄地区是东秦岭造山带印支期碱性侵入岩规模最大的出露区,对其中的焦沟岩体进行了LA-ICP-MS锆石U-Pb定年和元素地球化学分析,探讨其源区特征及深部动力学背景。焦沟岩体定年样品JG1701为霓辉正长岩,出现了约2.6 Ga、约2.5 Ga、约2.4 Ga、约2.3 Ga、约2.1 Ga、约1.9 Ga和约243 Ma 7个年龄组,形成了锆石年龄谱,最晚一组6颗锆石测点的206Pb/238U年龄为243.2±4.8 Ma,表明其形成于中三叠世。焦沟岩体的Na2 O+K2 O含量为11.50%~14.01%,碱度率(AR)和K2O/Na2O值分别为3.92~9.17和3.78~10.25,属于碱性-过碱性系列,且具有超钾质岩石的特征。焦沟岩体的稀土元素总量介于176×10^-6~315×10^-6之间,(La/Yb)N范围为9.51~20.43,稀土元素配分模式具有右倾、轻稀土元素富集、重稀土元素亏损和无明显负Eu异常的特征。焦沟岩体强烈富集大离子亲石元素、亏损高场强元素,在微量元素蛛网图中显示了一致的Th、Nb、Ta、P、Ti异常谷,以及Ba、K、Zr、Hf异常峰。它的部分熔融源区位于石榴子石-尖晶石过渡带,埋深介于60~80 km之间,残余矿物包括金云母、富钛矿物(如金红石和钛铁矿)、石榴子石和尖晶石。焦沟岩体是幔源富钾岩浆/流体与壳源岩浆/流体库混合活化之后形成的,深部控制过程为岩石圈拆沉作用。The Zhifang-Huangzhuang(ZH)area in western Henan Province has the largest outcrop of Indosinian alkaline intrusives in eastern Qinling orogenic belt.In this paper,the LA-ICP-MS zircon U-Pb ages as well as major elements and trace elements of the Jiaogou syenite were tested in order to obtain new constraint on formation time,rock source of partial melting and tectonic process of syenites in the ZH area.The U-Pb dating sample JG1701 is aegirine-augite syenite,and zircon age spectrum is composed of 7 age groups(~2.6 Ga,~2.5 Ga,~2.4 Ga,~2.3 Ga,~2.1 Ga,~1.9 Ga and^243 Ma).The weighted mean age of 6 zircon spots form the last group is 243.2±4.8 Ma,which suggests that it was formed in Middle Triassic.The Jiaogou syenite is ultrapotassic rocks and belongs to alkaline-peralkaline series with higher Na2O+K2O content(11.50%~14.01%),alkalinity ratios(3.92~9.17)and K2O/Na2O ratios(3.78~10.25).The total rare earth elements(REEs)and(La/Yb)N ratios of the Jiaogou syenite are 176×10^-6~315×10^-6 and 9.51~20.43,which shows the characteristics of LREE enrichment and HREE depletion without obvious Eu negative anomaly.They are enriched in large ion lithophile elements and depleted in high field strength elements,exhibiting negative anomalies of Th,Nb,Ta,P and Ti and positive anomalies of Ba,K,Zr and Hf in spider diagram.The source rock of the Jiaogou syenite was situated in the garnet-spinel transition zone at the depth of about 60~80 km,and its residual phases included phlogopite,Ti-enriched minerals such as rutile and ilmenite,garnet and spinel.The Jiaogou syenite is the mixed product of mantle-derived K-enriched magmas/fluids and crust-derived magmas/fluids,and it was controlled by regional lithosphere delamination in Middle Triassic.

关 键 词：焦沟岩体 霓辉正长岩 中三叠世 纸房—黄庄地区 岩石圈拆沉 东秦岭 

分 类 号：P534.51[天文地球—古生物学与地层学] P597[天文地球—地质学]