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Subject: 地球科学::地质学
Title: 藏东南镁铁-超镁铁质岩墙地球化学特征及其构造意义
Author: 徐晓霞
Issued Date: 2008
Supervisor: 丁林
Major: 构造地质学
Degree Grantor: 中国科学院研究生院
Place of Degree Grantor: 北京
Degree Level: 硕士
Keyword: (超)镁铁质岩墙 ;  地幔柱 ;  冈瓦纳大陆 ;  新特提斯洋 ;  青藏高原
Call Number: 68
Department: 图书馆
Abstract: 青藏高原东南部出露有大量近东西向展布的镁铁-超镁铁质岩墙和少量与之对应的喷出相火山岩,结晶年龄聚集在145-120Ma之间。哲古地区的超镁铁苦橄质岩石源于150-180km深处富集的石榴石二辉橄榄岩地幔高比率的部分熔融;岩浆在演化过程中受到了少量地壳物质的混染,不仅具有富集地幔的特征而且表现出弱的Nb、Ta亏损。碱性超镁铁质岩石源于稍浅位置的石榴石二辉橄榄岩和尖晶石二辉橄榄岩转换带,是地幔低比率部分熔融的产物;岩浆在演化过程中也受到了地壳物质的混染。镁铁质岩石是更浅的尖晶石二辉橄榄岩地幔部分熔融的产物;其成分包含了富集地幔、亏损地幔和地壳岩石混合的信息;岩浆在演化过程中遭受了低压下结晶分离作用的改造;具有中到强的Nb、Ta亏损,可能卷入了较多的地壳物质。藏东南地区镁铁-超镁铁质岩石是不同源区不同深度地幔物质不同比率部分熔融的产物,岩浆经历了地壳混染和结晶分离作用,这一过程反映了145-120Ma时段内印度板块北缘经历的大深度、高比率的有富集地幔参与的部分熔融事件,指示了早白垩世印度大陆北缘地幔柱的存在和影响。该地幔柱引起了冈瓦纳大陆的裂解和新特提斯洋的扩张,使印度大陆开始向北漂移并最终与欧亚大陆碰撞。
English Abstract: The ages of the East-west striking mafic-ultramafic dykes and associated eruptive rocks of southeast Tibet range between 145 Ma and 120 Ma. In Zhegu area, the ultramafic picritic dykes are characterized by high contents of incompatible trace elements, weak negative Ta and Nb anomalies, and interpreted to have been highly partial melted from a fertile garnet lherzolite mantle source in the depth of 150-180km. The magmas have been slightly contaminated by the crust later. Alkali ultramafic dykes tend to be the result of low partial melting in the spinel-garnet transitional zone, which suffers from some crust contamination subsequently. The mafic dykes carry mixed messages derived from enrich mantle, depleted mantle and crust, come into being in spinel stability field. The mafic magmas have experienced partial crystallization at a relatively low pressure and interfused lots of crust material on their way to an upper level, indicated by middle to high negative Ta and Nb anomalies. Magmas of the mafic-ultramafic dykes in southeast Tibet are diverse from the partial melting of deep to shallow mantle source, and the magmas have undergone fraciotnal crystallization as well as crust contamination. The extensivly highly melting of the deep fertile mantle indicates the existing of a mantle plume in the northern Indian continental margin during 145-120Ma, which may trigger the openning of the Neo-Tethyan ocean and push Great India northward on the following collision course with Eurasia.
Language: 中文
Content Type: 学位论文
URI: http://ir.itpcas.ac.cn/handle/131C11/1207
Appears in Collections:图书馆_学位论文

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Recommended Citation:
徐晓霞.藏东南镁铁-超镁铁质岩墙地球化学特征及其构造意义[硕士].北京.中国科学院研究生院.2008
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