宗务隆山角闪辉长岩LA-ICP-MS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,geochemistry and tectonic implication of the bojite in the Zongwulong Mountain

作　　者：王苏里[1] 周立发[1] WANG Suli ZHOU Lifa(State Key Laboratory of Continental Dynamics/Department of Geology, Northwest university, Xi＇an 710069, China)

机构地区：[1]西北大学大陆动力学国家重点实验室/地质学系,陕西西安710069

出　　处：《西北大学学报（自然科学版）》2016年第5期716-724,共9页Journal of Northwest University（Natural Science Edition）

基　　金：国家重点基础研究发展基金资助项目(2003CB214601)

摘　　要：对宗务隆山角闪辉长岩进行的岩石学、地球化学及锆石LA-ICP-MS U-Pb定年的研究表明,该岩体的成岩年龄为（254.3±1.5）Ma,形成时代为晚二叠世晚期,显示为海西—印支运动岩浆活动的产物。其Si O2质量含量为45.38%-52.65%,其低铝（Al2O3质量含量为13.76%-16.86%）、富钙（Ca O质量含量为9.92%-11.06%）、贫碱（K2O＋Na2O质量含量为2.86%-3.35%）的特点表明其属于钙碱性系列岩石。岩石明显富集大离子亲石元素（如Rb,Sr,Ba等）,而相对亏损高场强元如素（Nb,Ta,Zr等）。稀土总量较低（ΣREE含量为7.05×10-6-38.71×10-6）,显示为轻稀土元素相对富集的右倾型配分模式,δEu为0.9-0.97,呈弱的Eu负异常。主、微量及稀土元素特征反映出岩石具幔源岩浆的特点,但受到地壳物质的混染,构造判别图解显示宗务隆山角闪辉长岩形成的大地构造背景为洋壳俯冲造山阶段的岛弧环境。该研究结果结合同位采样的黑云花岗岩样本的定年结果及地球化学特征,为宗务隆洋盆俯冲提供了年代学及岩浆作用方面的依据。Detailed Petrographic, geochemical studies and zircon LA-ICP-MS U-Pb dating shows that the bojite in the Zongwulong Mountain was formed at （254.3 ± 1.5 ） Ma, in the late Late Permian, Hercynian-In- dosinian. The characteristic of the major elements of bojite, such as the SiO2 range at 45.38% -52. 65%, poor in Aluminum（A1203range at 13.76% - 16. 86% ）, rich in Calcium（ CaO range at 9. 92% -11.06% ）, poor in Alkali（K20 ＋Na20 range at 2. 86% -3.35% ）, shows that it belongs to the calc-alkaline series. This suite of bojite rocks are enriched in LILE （such as Rb, Sr, Ba）, relatively depleting in HFSE （such as Nb, Ta, Zr）. The total content of REE is low（ EREE range at 7.05 × 10 ^-6 - 38.71 ×10 ^-6 ）, rich in LREE and poor in HREE, with slightly negative Eu anomaly（ δEu = 0. 9 -0. 97）. The major, trace and rare earth elements reflect the characteristic of mantle-derived magma, and show that the magma may be contaminated by the crust material. Tectonic discrimination diagrams show that the Zongwulong bojite resulted from the island arc setting in the oceanic crust subduction orogenic stage. Combine with the dating result and the geochemical characteristic of the biotite granite sampled in the same place with bojite, it provides a basis of geochronology and mag- matism for subduction of the Zongwulong oceanic basin.

关 键 词：角闪辉长岩 锆石LA-ICP-MS U-PB定年 地球化学 宗务隆山 

分 类 号：P597.3[天文地球—地球化学]