大巴山地区寒武系纽芬兰统黑色页岩风化剖面矿物、元素及Sr同位素特征:对风化地球化学过程的启示  

Mineralogical, Elemental and Sr Isotopic Characteristics of Samples from A Cambrian Terreneuvian Black Shale Weathering Profile in the Dabashan Area:Implications for the Weathering Geochemical Processes

作　　者：魏巍 巫锡勇 凌斯祥 李晓宁[2] WEI Weil;WU Xi-yong;LING Si-xiang;LI Xiao-ning(Faculty of Geosciences and Environmental Engineering,Southwest Jiaotong University,Chengdu 611756,China;School of Civil Engineering and Architecture,Southwest University of Science and Technology,Mianyang,Sichuan 621010,China)

机构地区：[1]西南交通大学地球科学与环境工程学院,成都611756 [2]西南科技大学土木工程与建筑学院,四川绵阳621010

出　　处：《矿物岩石地球化学通报》2022年第6期1241-1260,共20页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：国家自然科学基金资助项目(41877215,42077271,41472256);四川省科技厅项目(2020YFS0297)。

摘　　要：对大巴山地区寒武系纽芬兰统水井沱组黑色页岩风化剖面进行系统性采样,利用X射线衍射(XRD)、扫描电子显微镜-X射线能谱(SEM-EDS)、X射线荧光光谱(XRF)、电感耦合等离子质谱(ICP-MS)等手段,分析风化剖面的矿物组成,主、微量元素含量及Sr同位素组成特征,旨在揭示黑色页岩关键带的地球化学风化过程。黑色页岩风化剖面处于初始—中等风化阶段(CIA值为54.45~75.50)为典型的大陆风化趋势。随着风化程度的加深,风化剖面的岩石孔隙增多、增大,87Sr/86Sr值逐渐增大。研究结果表明,在黑色页岩风化过程中,黄铁矿经过氧化作用形成铁(氢)氧化物,且强烈亏损S、Mn、Cd、Co、Ni、Zn、As等元素;斜长石和白云母经蚀变分解生成伊利石,并伴随着Na、Ca、K、Mg、Li、Sr和Ba等元素的淋失。Si、Al、Fe、P、Zr、Hf、Ta、Th和Rb等元素倾向于保留在风化剖面中,微裂隙带中Si、Mg、Na和K的亏损主要受到差异性风化的影响,而断裂带中Si、Mg、Na、K、P和Fe的异常受到差异性风化和元素再沉积的共同控制。S、Ba和Cu元素在土-岩界面、微裂隙带、强-弱风化层过渡带和断裂带中发生了明显的富集,这与重晶石和铜矾类矿物的沉淀有关;断裂带中其它微量元素的富集则受到铁锰(氢)氧化物和高岭石吸附作用的控制。Black shale samples of a weathering profile of the Cambrian Terreneuvian Shuijingtuo Formation in the Dabashan area have been systematically collected to analyze their characteristics of mineralogical, major and trace elemental, and Sr isotopic compositions by using the XRD, SEM-EDS, XRF, and ICP-MS, aiming at revealing the geochemical weathering processes of the black shale critical zone. The results show that the black shale weathering profile is of the initial to medium weathering stages with CIA values of 54.45~75.50 with characteristics of the typical continental weathering trend. With the increase of weathering degrees(intensities), numbers and sizes of pores in rocks and87Sr/86Sr ratios of rocks in the weathering profile are gradually increased. The results suggest that pyrite was oxidized to Fe-(hydr)oxide which are strongly depleted in S, Mn, Cd, Co, Ni, Zn, and As in the weathering process of black shale. Plagioclase and muscovite were weathered to illite, and their Na, Ca, K, Mg, Li, Sr, and Ba were simultaneously leached out. Elements of Si, Al, Fe, P, Zr, Hf, Ta, Th, and Rb were tended to retain in the weathering profile. The depletion of Si, Mg, Na, and K in the micro-fracture zone was mainly caused by the differential weathering, while the geochemical anomalies of Si, Mg, Na, K, P, and Fe in the fault zone was jointly controlled by the differential weathering and elemental re-sedimentation. Elements of S, Ba, and Cu are obviously enriched in the soil-rock interface, the micro-fracture zone, the transition zone of strong and weak weathering layers, and the fault zone. This was related to the precipitation of barite and copper sulfate minerals. The enrichment of other trace elements in the fault zone was controlled by the adsorption of Fe-Mn oxides and kaolinite.

关 键 词：黑色页岩 矿物分解 元素迁移 SR同位素组成 风化地球化学过程 

分 类 号：P595[天文地球—地球化学]