大西洋中脊26°S热液区玄武岩地球化学特征及其地幔源区性质  

GEOCHEMICAL CHARACTERISTICS OF BASALTS AND THEIR MANTLE SOURCE FEATURES AT 26°S HYDROTHERMAL FIELD ON THE MID-ATLANTIC RIDGE

作　　者：范蕾[1,2] 王国芝 石学法[3] 杨耀民[4] Holzheid Astrid Zoheir Basem A Fan Lei;Wang Guozhi;Shi Xuefa;Yang Yaomin;Holzheid Astrid;Zoheir Basem A(College of Earth Sciences,Chengdu University of Technology Chengdu,Sichuan 610059,China;Institut fiir Geowissenschaften,Christian-Albrechts-Universitat zu Kiel,Kiel 24118,Germany;Key Lab.of Marine Sedimentary and Environment Geology,the First Institute of Oceanography,State Oceanic Administration,Qingdao,Shandong 266061,China;National Deep See Center,Qingdao,Shandong 266237,China)

机构地区：[1]成都理工大学地球科学学院,四川成都610059 [2]基尔大学地球科学学院,德国基尔24118 [3]国家海洋局第一海洋研究所海洋沉积与环境地质国家海洋局重点实验室,山东青岛266061 [4]国家深海基地管理中心,山东青岛266237

出　　处：《矿物岩石》2020年第1期9-20,共12页Mineralogy and Petrology

基　　金：中国大洋矿产资源研究开发协会项目(DY135-S2-2-05,DY125-12-R-01)。

摘　　要：南大西洋中脊(SMAR)属于慢速扩张脊,26°S(SMAR 26°S)热液区是中国新近发现的以玄武岩为基岩的热液区。本次研究对热液区的玄武岩开展了岩相学和地球化学研究,揭示玄武岩的地球化学特征和岩浆源区性质,探讨其成矿潜力。结果表明,该热液区玄武岩地球化学特征和正常洋中脊玄武岩(N-MORB)相似,为钠质拉斑玄武岩;它们是由下伏亏损的尖晶石二辉橄榄岩地幔部分熔融而成。玄武岩所具有的低w(K2O)(0.05%~0.25%)、低(Ce/Yb)N比值(0.62~0.86),以及异常指数(Nb^*<1,P^*<1,Sr^*≤1,Zr^*>1)特征,表明源区地幔性质不均一,且受到了不同程度的陆壳物质混染;w(MgO)为7.52%~8.81%,指示热液区岩浆结晶分异程度低,岩浆演化不彻底。轻微的Eu正异常(δEu值为1.03~1.15),指示玄武岩形成过程中受到一定程度高温热液流体的影响,并处于强还原环境。与其他热液区玄武岩相比,研究区玄武岩Ba,Rb等高度不相容元素含量较低,均显示正Eu异常,岩石-海水相互作用弱。研究区玄武岩的Zn和Cu的含量分别为72.0~148.0×10^-6和79.9~138.5×10^-6,与MARK区和大西洋46°~32°S热液区玄武岩相比,研究区玄武岩可能具有更大的成矿潜力。The Southern Mid-Atlantic Ridge(SMAR)belongs to the slow-spreading ridge,and the SMAR 26°S is a newly discovered hydrothermal field with basalts as its main lithology.Study of petrography and geochemistry of the basalts is carried out in order to unravel the geochemical characteristics and magma source region properties of the basalt,and to discuss the metallogenic potential of the hydrothermal field.It shows that the basalts in the area is sodic tholeiite resulted from partial melting of the spinel lherzolite in the lithospheric mantle,and have similar geochemical characteristics to normal mid-ocean basalt(N-MORB).Geochemical characteristics of low w(K2O)(0.05%-0.25%)concentration and low(Ce/Yb)N(0.62-0.86)ratio,as well as the characteristics of anomaly index(Nb*<1,P*<1,Sr*≤1,Zr*>1),indicate that the source mantle is heterogeneous,and probably contaminated by continental crust.The crystallization differentiation of magma in hydrothermal region is low and the magma evolution is not complete,evidenced by the MgO concentration varied from 7.52%to 8.81%.The weak positive Eu anomalies(δEu=1.03-1.15)indicate that the basalt is influenced by the high temperature hydrothermal fluid during its precipitation,and formed in a strongly reducing environment.In comparison with other hydrothermal fields,basalt in this research area has a low concentration of highly incompatible elements,such as Ba and Rb,and positive Eu anomalies,which reflect lower contribution of seawater-rock interaction.The fact that Zn and Cu concentrations in the study area are 72.0-148.0×10^-6 and 79.9-138.5×10^-6 indicates that the SMAR 26°S hydrothermal field may have greater metallogenic potential than MARK area and 46°-32°S hydrothermal fields.

关 键 词：南大西洋中脊 26°S热液区 玄武岩 地球化学特征 成矿潜力 

分 类 号：P744[天文地球—海洋科学] P588.124