云南武定左所辉绿岩铂族元素地球化学、Pb同位素及其地质意义

发布时间：2018-12-09 08:38

【摘要】：古元古代晚期至中元古代早期,西南康滇地区发生过一次强烈的构造、岩浆及成矿事件,即昆阳裂谷,以广泛出露1.8~1.5 Ga基性岩浆岩及铁铜矿床为重要标志。文章报道了滇中武定地区左所辉绿岩的岩石化学、微量元素、Pb同位素及铂族元素地球化学特征,通过铂族元素地球化学对昆阳裂谷期的岩石圈演化、壳幔相互作用进行了探讨。左所辉绿岩相对富碱(w(Na_2O+K_2O)平均为3.55%),低w(Si O_2),较高的w(Ti O_2)(均值为3.30%)、w(P_2O_5)(平均值0.35%),Ca O/Ti O_2比值(平均值为2.4)及Al_2O_3/Ti O_2比值(平均值为3.4)低,具有典型地幔热柱玄武岩的岩石化学特征。左所辉绿岩微量元素中相对富集大离子半径元素,高场强元素弱亏损,稀土元素中出现弱的Eu负异常,反映了斜长石的轻度结晶分异。辉绿岩具有较高的铂族元素含量,PPGE和IPGE明显分异,PGE原始地幔标准化配分曲线呈较明显的左陡倾型。辉绿岩的Cu/Pd比值均低于原始地幔值,表明原始岩浆S不饱和,亦未发生硫化物的熔离过程,较高的PGE含量可能与初始岩浆本身的S含量较高有关。高的Pd/Ir比值可能与IPGE在部分熔融过程中更倾向于残留相以及岩浆演化早期铬铁矿和橄榄石的结晶分异有关。低程度的地幔部分熔融、Pb同位素特征暗示左所地区辉绿岩的形成过程:陆内裂谷环境下,富硫的原始岩浆在上升过程中受到较少下地壳物质的混染,侵位至浅表并较快冷却,形成辉绿岩。
[Abstract]:From the late Paleoproterozoic to the early Middle Proterozoic, a strong tectonic, magmatic and metallogenic event, the Kunyang rift, occurred in the Kangdian area, southwest China, marked by the widespread exposure of 1.8O1.5 Ga basic magmatic rocks and iron-copper deposits. This paper reports the petrochemistry, trace elements, Pb isotopes and the geochemical characteristics of platinum group elements of Zaosuo diabase in Wuding area, central Yunnan. The lithospheric evolution of Kunyang rift period is studied by platinum group element geochemistry. The crust-mantle interaction is discussed. The average value of (w (Na_2O K _ 2O in the left diabase is 3.55%, the average value is 3.35%, the average value is 3.30%), w (P_2O_5, the average value is 0.35%, the average value is 3.30%), w (P_2O_5, the average value is 0.35%. The ratio of Ca O/Ti _ O _ 2 and Al_2O_3/Ti _ O _ 2 (average value is 2.4) and Al_2O_3/Ti _ O _ 2 (average value is 3.4) are low and have the petrochemical characteristics of typical mantle plume basalt. The trace elements in the left diabase are relatively rich in large ion radius elements, the high field strength elements are weakly depleted, and the Eu negative anomalies are weak in rare earth elements, which reflects the slight crystallization differentiation of plagioclase. Diabase has high platinum group element content, PPGE and IPGE are distinct, and PGE primitive mantle standardized partition curve is obviously left steep dip. The Cu/Pd ratios of diabase are all lower than those of the original mantle, indicating that S is not saturated in the original magma and no sulfide melting process has taken place. The higher PGE content may be related to the higher S content of the original magma itself. The high Pd/Ir ratio may be related to the tendency of IPGE to the residual phase during partial melting and the crystallization differentiation of chromite and olivine in the early magmatic evolution. In the low degree of partial melting of the mantle, Pb isotopic characteristics indicate the formation process of diabase in Zaohe area: in the intracontinental rift environment, the sulfur rich primitive magma is mixed with less lower crust material during the process of rising, emplacement to the surface and cooling rapidly. Forming diabase.
【作者单位】：中国地质调查局成都地质调查中心;中国地质大学地球科学与资源学院;
【基金】：国家重点基础研究发展计划项目(编号:2014CB440903) 中国地质调查局成都地质调查中心项目(编号:12120114022501) 国家自然科学基金项目(编号:41171302;41372093)联合资助
【分类号】：P597;P618.53

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