云南个旧三叠纪高钾质火山岩锆石U-Pb年代学、岩石成因及构造意义  

Zircon U-Pb Chronology, Origin and Tectonic Significance of the Triassic High Potassic Volcanic Rock from Gejiu, Yunnan, Southwestern China

作　　者：张贵山[1,2] 方维萱 彭仁[1] 郑厚义 ZHANG Guishan;FANG Weixuan;PENG Ren;ZHENG Houyi(School of Earth Science and Resources,Chang’an University,Xi’an 710065,Shaanxi,China;China Nonferrous Metals Geology Survey,Beijing 100012,China;General Institute of Geological Survey,China Chemical Geology and Mine Bureau,Beijing 100013,China)

机构地区：[1]长安大学地球科学与资源学院,陕西西安710065 [2]有色金属矿产地质调查中心,北京100012 [3]中化地质矿山总局化工地质调查总院,北京100013

出　　处：《大地构造与成矿学》2019年第6期1219-1235,共17页Geotectonica et Metallogenia

基　　金：国家自然科学基金(41073027);中央高校基本科研业务费专项资金(310827172003);矿床地球化学国家重点实验室开放基金项目(2009011);危机矿山元素综合查定和可行性评价技术(2008EG115074)联合资助

摘　　要：个旧卡房段三叠纪高钾质火山岩赋存于个旧组(T2g),锆石U-Pb测年结果显示火山岩年龄为214.5±2.2 Ma,代表了个旧地区三叠纪火山岩活动的重要期次。该火山岩为一套碱性高钾质苦橄岩,具有富Ti特征,其SiO2含量为39.28%~44.56%,MgO含量为11.87%~17.81%,Mg#值介于0.69~0.82之间,TiO2含量为1.79%~3.11%、Ti/Y=641~1124,K2O/Na2O值为1.25~25.95;不同程度富集轻稀土元素(LREE)、大离子亲石元素(Rb、Ba、K)和高场强元素(Nb、Ta、Zr、Hf),轻重稀土元素分馏明显,δEu和δCe异常不明显,研究表明岩浆演化过程中未发生地壳物质混染作用,具有原生岩浆的特征。个旧高钾质苦橄岩源自饱满型富含金云母地幔橄榄岩部分熔融,具有较高的熔融平衡温度(1554℃)和平衡压力(3.6GPa),岩浆熔融的深度大约在115km,可能来自地幔热点轴的部分熔融。个旧高钾质苦橄岩形成的大地构造背景为三叠纪弧后裂谷盆地,其形成与软流圈地幔物质上涌或地幔热点活动密切相关。The Triassic volcanic rocks of the Gejiu Group(T2 g)outcrop in the Kafang area of Gejiu.These rocks have zircon U-Pb ages of 214.5±2.2 Ma,and indeed,Triassic is an important period of volcanic activities in the Gejiu region.The Kafang volcanic rocks have SiO2 of 39.28%to 44.56%,MgO of 11.87%to 17.81%,Mg#from 0.69 to 0.82,TiO2 from 1.79%to 3.11%,Ti/Y ratios from 641 to 1124,and K2 O/Na2 O ratios from 1.25 to 25.95,indicating a high K alkaline picrite and titanium-rich signature.These volcanic rocks are relatively enriched in LREE,LILE(Rb,Ba,K)and HFSE(Nb,Ta,Zr,Hf).The rocks are characterized by steeply right dipping chondrite normalized REE patterns with insignificant Eu and Ce anomalies.It is inferred that the magma of the volcanic rocks was derived from the mantle without significant crustal contamination.The Gejiu high K picrite was likely derived from partial melting of phlogopite-rich mantle peridotite.Besides,the magma was formed at high temperature(1554℃)and pressure(3.6 GPa),i.e.,about 115 km deep,which may relate to mantle plume.We propose that the Gejiu high K picrite may have been formed in a Triassic back-arc rifted basin and possibly related to asthenospheric mantle upwelling or mantle plume.

关 键 词：锆石U-PB年龄 高钾质 苦橄岩 地球化学 个旧 

分 类 号：P597[天文地球—地球化学] P595[天文地球—地质学]