南秦岭中生代张家河煌斑岩的地球化学特征及其岩石成因探讨  

Geochemical Characteristics and Petrogenesis of Mesozoic Lamprophyres from Zhangjiahe,South Qinling,China

作　　者：杨朝贵 刘燊[1] 冯彩霞[1] 冯光英[1,2] 杨毓红[1,2] 齐有强[1] 唐亮[1,2] 

机构地区：[1]中国科学院地球化学研究所矿床地球化学国家重点实验室,贵州贵阳550002 [2]中国科学院研究生院,北京100039

出　　处：《矿物学报》2013年第1期119-128,共10页Acta Mineralogica Sinica

基　　金：中国科学院知识创新工程重要方向项目(KZCX2-YW-QN10);国家自然科学基金项目(批准号:40972071;40773020)

摘　　要：锆石LA-ICP-MS U-Pb年龄(225±1.5 Ma)表明,研究区煌斑岩为印支晚期岩浆活动的产物。化学组成上,煌斑岩的SiO2含量为49.31%～52.87%,w(K2O)=0.86%～1.34%,Na2O>K2O,属钙碱性系列。MgO含量高,变化范围较大(13.11%～15.88%),Mg#=77.74～80.44),富集大离子亲石元素(LILE)(Rb、Ba、Th、U和Sr)、LREE和Pb,亏损高场强元素(HFSE)(Nb、Ta、Zr和Hf)为特征。同位素组成上,岩石具有高的(87Sr/86Sr)i(0.714697～0.716534)和负的εNd(t)(-8.55～‐9.09),表明研究区煌斑岩源区可能为EM2型地幔。此外,煌斑岩具有较高的相容元素,Cr(1161×10-6～1597×10-6),Co(60.3×10-6～77.2×10-6)和Ni(220×10-6～366×10-6)含量。综合证据表明,张家河煌斑岩来自富集的岩石圈地幔,且源区受到了来自俯冲大洋(古勉略洋)沉积物析出流体的交代作用影响。原始岩浆在上升侵位过程中存在橄榄石和单斜辉石等矿物的分离结晶作用,但没有明显的地壳混染影响。构造和地球动力学背景分析表明,研究区煌斑岩为扬子板块和南秦岭微板块碰撞后伸展拉张阶段的产物。Zircon LA-ICP-MS U-Pb analysis yields an age of 225±1.5 Ma for lamprophyres from Zhangjiahe, South Qinling, China, indicating that these rocks were formed during late Indoehina stage. The contents of SiO2 range from 49.31% to 52.87%, with K20 （0.86 % - 1.34%） and NazO （1.87% - 2.84%） contents, and NaEOK20, indicating calc-alkaline series. High MgO contents range from 13.11% to 15.88% and with Mg# value （77.74 - 80.44）, enrichment in large ion lithosphile elements （LILEs, Rb, Ba, Th, U and Sr）, LREE and Pb, depletion in the high field strength elements （HFSEs）, such as Nb, Ta, Zr and Hf. The isotopic compositions of the rocks are characterized by high initial 87Sr/86Sr ratios （0.714697 - 0.716534） and negative erd（t） value （-8.55 - -9.09）, showing that the mantle source of the search area could be the EM2 type mantle. In addition, the lamprophyres have high contents of Cr （1161 X 10^-6- 1597 X 10-6）, Co （60.3X 10^-6- 77.2 X 10^-6） and Ni （220 X 10^-6- 366 X 10^-6）. Based on above discussions, we proposed that the studied lamprophyres are from an enrichment lithospheric mantle source which is metasomatized by the fluid from the dehydration of the subducted oceanic （Paleo-Mianlue Ocean） sediments. There is fractionation of olivine and clinopyroxene with the primary magma ascent, but without much influence. Tectonic and geodynamic investigation indicates that the studied lamprophyres are formed in a post-orogenic extensional setting after the collision between the Yangtze and South Qinling micro-plate.

关 键 词：勉略带 煌斑岩 富集地幔 后碰撞 

分 类 号：P581[天文地球—岩石学] P595[天文地球—地质学]