拉集山蛇绿岩带深海和俯冲上的橄榄岩:对原特提斯洋初始俯冲的启示

IF 16.4 1区 化学 Q1 CHEMISTRY, MULTIDISCIPLINARY
Changlei Fu, Zhen Yan, J. Aitchison, Xianqing Guo, Wenjing Xia
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引用次数: 11

摘要

南祁连带北缘出露了多个地幔橄榄岩地块,但其成因仍存在争议。西沟橄榄岩体是拉吉山蛇绿岩带中最大的一个,主要由二辉橄榄岩、方辉橄榄岩和蛇纹石化纯岩组成,并与斜长岩、角闪岩、粗玄岩脉和枕状玄武岩共生。二辉橄榄岩显示出相对肥沃的深海橄榄岩的典型特征,包括富铁橄榄石、铝尖晶石和铝辉石。辉橄榄岩和蛇纹石化纯橄榄岩的特征是U型稀土元素模式和低Pd族铂族元素,类似于俯冲上橄榄岩的地球化学特征。尖晶石Cr#(Cr/(Cr+Al))的范围从方辉橄榄岩的0.38到纯橄榄岩的0.75。尖晶石Cr#的逐渐增加与俯冲起始过程中熔体成分从类大洋脊玄武岩(MORB)变为玻安岩有关。西沟超俯冲橄榄岩、MORB类镁铁质岩石和玻碳岩可能构成了一个不完整的弧前壳幔剖面。弧前区域保存的深海二辉橄榄岩可能代表与转换断层相交的海沟-断裂带上较老的海洋岩石圈或较年轻的肥沃地幔残留物。因此,我们认为,原特提斯洋的洋内俯冲可能在535 Ma之前开始,也就是拉吉山洋内弧沟系统发育之前。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Abyssal and Suprasubduction Peridotites in the Lajishan Ophiolite Belt: Implication for Initial Subduction of the Proto-Tethyan Ocean
Several mantle peridotite massifs crop out along the northern margin of the South Qilian belt, but their origin remains controversial. The Xigou peridotite massif is the largest one within the Lajishan ophiolite belt and mainly consists of lherzolite, harzburgite, and serpentinized dunite, in association with anorthosite, amphibolite, dolerite dikes, and pillow basalt. Lherzolites show typical features of relatively fertile abyssal peridotites, with iron-rich olivine, Al-spinel, and aluminous pyroxene. Harzburgites and serpentinized dunites are characterized by U-shaped rare earth element patterns and low Pd-group platinum-group elements resembling the geochemical features of suprasubduction peridotites. Spinel Cr#’s ( Cr / ( Cr + Al ) ) range from 0.38 in harzburgite to 0.75 in dunite. The progressive increase in spinel Cr#’s is related to changing melt compositions from mid-ocean ridge basalt (MORB) like to boninitic during subduction initiation. The Xigou suprasubduction peridotites, MORB-like mafic rocks, and boninites probably constitute an incomplete forearc crust-mantle section. The abyssal lherzolite preserved in the forearc region might represent older oceanic lithosphere or younger fertile mantle residue along a trench–fracture zone intersection with a transform fault. Therefore, we suggest that the intraoceanic subduction of the Proto-Tethyan Ocean may have begun no later than 535 Ma, before the development of the Lajishan intraoceanic arc-trench system.
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来源期刊
Accounts of Chemical Research
Accounts of Chemical Research 化学-化学综合
CiteScore
31.40
自引率
1.10%
发文量
312
审稿时长
2 months
期刊介绍: Accounts of Chemical Research presents short, concise and critical articles offering easy-to-read overviews of basic research and applications in all areas of chemistry and biochemistry. These short reviews focus on research from the author’s own laboratory and are designed to teach the reader about a research project. In addition, Accounts of Chemical Research publishes commentaries that give an informed opinion on a current research problem. Special Issues online are devoted to a single topic of unusual activity and significance. Accounts of Chemical Research replaces the traditional article abstract with an article "Conspectus." These entries synopsize the research affording the reader a closer look at the content and significance of an article. Through this provision of a more detailed description of the article contents, the Conspectus enhances the article's discoverability by search engines and the exposure for the research.
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