藏北纳屋错地区蛇绿岩特征及构造意义

发布时间：2018-06-03 00:01

本文选题：班公湖-怒江缝合带西段 + 蛇绿岩　；参考：《成都理工大学》2017年硕士论文

【摘要】：在野外地质调查基础上,对班公湖-怒江缝合带西段纳屋错地区的蛇绿岩进行了详细的野外出露特征、岩石学特征、地球化学特征、稀土元素特征及微量元素特征等进行分析测试,查明了主要岩石类型、岩石组合;分析并探讨了该区的蛇绿岩成因及构造环境,讨论了班公湖-怒江缝合带西段的形成环境。研究区内纳屋错蛇绿岩主要零星分布于纳屋错东、生革拉北的局部地段和赛布仲久以西地段,局限于班公错-怒江结合带内,出露面积近10Km2,呈构造岩(残)块形式产出于木嘎岗日岩群砂砾岩或砂板岩中,为纳屋错构造混杂岩带的组成成员之一。对缝合带内蛇绿岩岩石学及岩相学研究表明,岩石主要为蛇纹岩(全蚀变辉石橄榄岩)、绿泥石化单辉辉石岩、纤闪角闪石岩、绢云绿泥石化角闪石岩、绿帘角闪斜长岩、强蚀变玄武岩、岩墙群、硅质岩组成。缝合带内超基性岩以高Cr、Ni、Co、稀土总量,低Mg值为特征,主量元素及稀土元素特征表明其与蚀变玄武岩具有同源岩浆的特点。蚀变玄武岩的主量元素显示其具有拉斑玄武岩向碱性玄武岩过渡的特征;微量元素结果分析表明它与典型大洋中脊玄武岩明显不同,分配形式近似平坦型,相对富集大离子亲石元素Rb、Ra、Sr和高强度元素Th、Ta、Hf,但Nb亏损;在稀土元素配分模式中为轻稀土富集的向右缓倾型式,无明显的Eu异常,但负Ce异常,与洋岛碱性玄武岩的特征相似。根据蛇绿岩的地球化学特征并应用构造环境判别图解,确定该地区蛇绿岩形成于洋脊扩张环境,但不是典型的大洋型蛇绿岩,类似于边缘海型蛇绿岩。
[Abstract]:On the basis of field geological survey, the characteristics of outcrop, petrology and geochemistry of ophiolite in Nawuco area of the western section of Bangong Lake-Nujiang suture zone are studied in detail. The characteristics of rare earth elements and trace elements are analyzed and tested, the main rock types and rock assemblages are identified, the genesis and tectonic environment of ophiolite in this area are analyzed and discussed, and the formation environment of the western section of Bangong Lake-Nujiang suture belt is discussed. In the study area, the Nawuco ophiolite is mainly scattered in the east of Nahuo, the part of Shengguela north and the west of Saibuzhongjiu, which is confined to the Bangongcao-Nujiang junction zone. The outcrop area is nearly 10km ~ 2, which is formed in the form of tectonic rock (remnant) in the grit or slate of Mugagangri rock group, and is one of the members of the Nawuso tectonic melange belt. The petrology and petrographic study of ophiolite in the suture zone indicate that the main rocks are ophiolite (total altered pyroxene peridotite, monopodiorite, diorite, sericite, hornblende, hornblende). Strong altered basalt, rock dike group, siliceous rock composition. The ultrabasic rocks in the suture zone are characterized by high Cr-NiCo, total rare earth elements and low mg values. The characteristics of principal elements and rare earth elements indicate that the ultrabasic rocks have the characteristics of homologous magma with altered basalt. The main elements of altered basalt show that it is characterized by the transition from tholeiite to alkaline basalt, and the trace element analysis shows that it is obviously different from typical basalt in mid-oceanic ridge, and its distribution is approximately flat. It is relatively rich in the large ion lithophile element RbPe Rau Sr and the high strength element Th TaTaHf, but NB is depleted. In the REE distribution model, there is no obvious EU anomaly, but negative ce anomaly, which is similar to the characteristics of the oceanic basalts. Based on the geochemical characteristics of ophiolite and the application of tectonic environment discriminant diagram, it is determined that ophiolite was formed in the spreading environment of the oceanic ridge, but not typical oceanic ophiolite, similar to the marginal sea ophiolite.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P588.1

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