宾川—程海二叠纪高镁火山岩的岩石地球化学及含矿性

【作者】 张蓬勃；

【导师】 姜常义；

【作者基本信息】 长安大学 ， 岩石学、矿物学、矿床学， 2003， 硕士

【摘要】 峨眉山玄武岩广布于扬子地块西缘，是目前地学界最为关注的地区之一。依据岩石组合、岩相学特征，将峨眉山玄武岩划分为西、中、东三大岩区。通过对构造背景及古地理环境分析，峨眉山玄武岩主要形成于地幔上涌和广泛的大陆伸展作用过程中。此外，扬子地块西缘二叠纪的大陆伸展作用类似于美国西部的盆岭区，总体表现为大陆板块陆内构造体制。 在前人研究成果的基础上，对峨眉山玄武岩的岩石地球化学及玄武岩浆活动特征进行了系统地阐述。宾川—程海地区被认为是峨眉地幔热柱活动的最强烈地区，也是热柱轴部物质大量出露的地区。该区二叠纪的火山岩依据MgO＞12％可分为两个岩石化学类型：低镁火山岩即峨眉山玄武岩；高镁火山岩。利用岩石地球化学的可示踪性，研究了高镁火山岩浆的源区特征、岩浆演化。高镁火山岩接近于原始岩浆的组成，岩浆源区与地球平均成分BSE的成分特征相近，起源深度为下地幔，为该地幔岩较高程度的部分熔融(＞25％)而形成的。高镁火山岩处于地幔柱的轴部，经历了橄榄石及一定程度的辉石分异结晶，并且橄榄石显示出一定的堆晶作用。岩浆演化过程中遭受到了含水流体的影响及轻微的陆壳混染。根据以上特征对高镁火山岩的形成机制作了分析。 从地幔柱成矿理论出发，以与大陆溢流玄武岩有关的典型硫化铜镍矿床为例，概括出该类矿床形成的基本地质条件。通过对研究区内与峨眉山玄武岩活动有关的高镁火山岩进行研究对比，发现区内与峨眉山玄武岩同期形成某些侵入岩体具有成镍矿(化)的地质条件。研究区内的昔腊坪岩体除了具有这些基本地质条件外，还显示不同程度的矿化，说明该地区作为寻找镍矿的靶区是有很大的潜力。更多还原

【Abstract】 Emeishan basalts widely spread out in the west margin of the Yangzi block. Because of this, Geo-science circles are interested in this region. According to characteristics of petro-assemblage and petrography, Emeishan basalts can be divided into three-big rock regions- west, middle and east. These basalts are mainly formed in the course of mantle upwelling and widely continental extensionism through analyzing tectonic setting and pale-geographical setting. This extensional activity is similar to the basin-and-range province of western America, and can be thought as an intra-continental tectonic system.On the basis of formers’ research results, the paper systemistically discuss some characteristics of Emeishan basalts’ petro-geochemistry and magma activation. Emei-mantle plume’s activity is very violent in Binchuan-Chenghai region,and a lot of its axis material is exposed in this region. According to the content of MgO, Emeishan basalt can de divided into high-Mg (MgO>12%) volcanic rock and lower- Mg (MgO<12%) basalt. Using the tracer ability of petro-geochemistry,the paper discusses on source characteristics and magma evolution of the high-Mg volcanic rocks. High-Mg volcanic rocks approach the primitive mantle compositions, and their magmatic source is close to the composition of BSE , derives from the lower mantle and formed by this type- mantle rocks’ fractional melting highly (>25% ) .High-Mg volcanic magma , formed in the axis of the Emei mantle plume, underwent the crystallization differentiation of olivines and some pyroxenes; some olivines reflect fair cumulus crystallization. During the magma evolution, this primary magma suffered effects of the containing water fluid and a small extent contaminate of continental crust.According to all of features above,the paper analyzes the formatting mechanism of high-Mg volcanic rocks.Beginning with the minerogenetic theory of mantle plume, the basic geological conditions of this type deposit can be summarized through studying typical copper-nickel sulfide deposits which have close bearing on continental flood basalt .In contrast with high-Mg volcanic magmatic activity,it can be found that some intrusive rock bodies have Ni-minerogenetic geology condiction.Xilaping rocks in Binchuan-Chenghai region has some basic geological condiction and reflects some extent minerogenetic.All these testify this region has very larger potentiality of finding copper-nickel sulfide deposits.更多还原