贵州罗甸晚二叠世辉绿岩及其区域构造意义

黔东南罗甸辉绿岩为拉斑系列岩石，其主量元素以高TiO2（2.36%～2.57%）、高CaO（9.40%~10.31%）、低MgO（5.65%~6.93%），低碱且Na2O>K2O为特征；稀土含量（ΣREE= 164.9×10-6~ 187.3×10-6）较高，反映轻稀土富集，重稀土亏损；Eu正异常（δEu=1.22~1.26），球粒陨石标准化配分曲线具有右倾分布特征。对辉绿岩中锆石进行的LA-ICP-MS U-Pb定年分析获得其谐和图下交点年龄为255.0±0.62Ma，代表岩体结晶时代。结合区域地质分析认为，罗甸辉绿岩可能起源于接近于原始的地幔橄榄岩的部分熔融作用，岩浆在快速上升过程中可能受到地壳物质的混染。罗甸辉绿岩具有与峨眉山玄武岩相似的地球化学特征，其形成年龄与峨眉山玄武岩的主喷发期基本同时。综合分析认为，黔东南晚二叠世辉绿岩是峨眉山玄武岩同质异相岩浆活动的产物，黔东南罗甸—望谟一带处于峨眉山玄武质岩浆活动的东部边缘地带。

Late Permian Diabase in Luodian, Southeastern Guizhou,and Its Tectonic Significances

The diabase exposed in Luodian area,southeastern Guizhou Province,belongs to tholeiite series.The major elements of the diabase are characterized by high TiO_2 (2.36%～2.57%),high CaO(9.40%～10.31%),low MgO(5.65%～6.93%),low alkali and Na_2O＞K_2O;the diabase have a higher content of ΣREE(164.9×10~(-6)～187.3×10~(-6)) with a remarkable fractionation between LREE and HREE reflecting the enrichment of LREE and the depletion of HREE.Meanwhile,the testing result pronounces a significant positive Eu anomaly and the chondrite-normalized distribution curve is right inclined.The U-Pb dating result from zircons in the diabase samples yields a concordant lower intersection age (tested by LA-ICP-MS),255.0±0.62Ma, which may represents the rock mass crystallization time.Combining with the regional geology analysis, we believe that the diabase of Luodian area possibly originates from the partial melting of the peridotite approaches in the primitive mantle,and the magmas probably suffer from the contamination of crust materials during the rapid rising process.The Luodian diabase has a similar geochemistry characteristic with the Emeishan basalt,and its formation age is nearly at the same time with the main eruption period of Emeishan basalt.The comprehensive analysis proves that the late Permian diabase from the southeastern Guizhou Province is the product of polymorphism magmatic activities of the Emeishan basalt,and the Luodian-Wangmo area of the southeastern Guizhou Province lies in the eastern boundary zone of the Emeishan basaltic magmatism.