Multiphase ophiolite formation in the Northern Altyn Tagh Orogen, southeastern Tarim

IF 1.9 3区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY American Journal of Science Pub Date : 2021-06-01 DOI:10.2475/06.2021.05
Qian Liu, T. Tsunogae, Guochun Zhao, Jianhua Li, Jinlong Yao, Yigui Han, Peng Wang
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引用次数: 2

Abstract

Early Paleozoic ophiolitic mélanges in the Altyn Tagh Orogen, southeastern Tarim, yield a large range of formation ages and geochemical affinities. This study focused on the Hongliugou ophiolitic mélange in the North Altyn Tagh subduction-accretion belt and involved mineral chemical, zircon geochronological, and whole-rock elemental and isotopic investigations of the ultramafic and mafic rocks. In the studied lherzolite samples, Cr-spinel, olivine, and pyroxene show mineral chemistry akin to that of abyssal peridotite. Subhedral-anhedral Cr-spinel grains with high Cr# values (100*Cr/[Cr+Al] of 30–40) and negative oxygen fugacity (fO2) values represent original spinel formed during mid-ocean ridge basalt (MORB) melt extraction. Other subhedral-anhedral and euhedral Cr-spinel with low Cr# values of < 30 to 20 display a wide range of negative to positive fO2 values, indicating interaction of peridotite with MORB magma. New zircon U-Pb dating results record ages of ca. 490 Ma for gabbro and ca. 486 Ma for diabase in the Hongliugou ophiolitic mélange. Whole-rock geochemical compositions suggest that the gabbro and diabase samples are tholeiitic and show MORB affinities or transitional affinities between MORB and island arc tholeiite. These mafic rocks might have been derived from a depleted MORB-source mantle that was variably metasomatized by subduction-induced fluids based on their variable Th/Yb, high La/Nb, low Th/Nb, and depleted isotopes (initial 87Sr/86Sr ratios of 0.703073 to 0.703385 and εNd(t) values of +6.2 to +6.3). New results, when integrated with previous work, clarify that ca. 520 to 510 Ma ophiolites formed in the initial subduction setting and ca. 490 to 480 Ma ophiolites in a back-arc setting. Minor ca. 450 Ma ophiolite probably represents a late phase of ophiolite formation due to the presence of a very minor remnant ocean.
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塔里木东南部阿尔金北塔格造山带多期蛇绿岩形成
塔东南阿尔金-塔格造山带早古生代蛇绿混杂岩具有较大的形成时代和地球化学亲和性。本研究以北阿尔金-塔吉克俯冲吸积带红柳沟蛇绿混杂岩为研究对象,对超镁铁质和镁铁质岩石进行了矿物化学、锆石地质年代学、全岩元素和同位素研究。在所研究的二辉橄榄岩样品中,铬尖晶石、橄榄石和辉石显示出类似于深海橄榄岩的矿物化学性质。具有高Cr#值(100*Cr/[Cr+Al]为30–40)和负氧逸度(fO2)值的亚面体二面体Cr尖晶石颗粒代表大洋中脊玄武岩(MORB)熔体提取过程中形成的原始尖晶石。其他具有低Cr#值的半自形和自形Cr尖晶石 < 30至20显示出大范围的负至正fO2值,表明橄榄岩与MORB岩浆的相互作用。新的锆石U-Pb测年结果记录了红柳沟蛇绿混杂岩中辉长岩的年龄约为490 Ma,辉绿岩的年龄约486 Ma。全岩地球化学成分表明,辉长岩和辉绿岩样品为拉斑玄武岩,并显示出MORB亲和力或MORB与岛弧拉斑玄武岩之间的过渡亲和力。这些镁铁质岩石可能来源于一个贫化的MORB源地幔,该地幔根据其可变的Th/Yb、高La/Nb、低Th/Nb和贫化同位素(初始87Sr/86Sr比值为0.703073至0.703385,εNd(t)值为+6.2至+6.3)被俯冲诱导流体可变交代,阐明约520至510 Ma蛇绿岩形成于初始俯冲环境,约490至480 Ma蛇绿岩在弧后环境。小约450 Ma蛇绿岩可能代表了蛇绿岩形成的晚期,因为存在非常小的残留海洋。
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来源期刊
American Journal of Science
American Journal of Science 地学-地球科学综合
CiteScore
5.80
自引率
3.40%
发文量
17
审稿时长
>12 weeks
期刊介绍: The American Journal of Science (AJS), founded in 1818 by Benjamin Silliman, is the oldest scientific journal in the United States that has been published continuously. The Journal is devoted to geology and related sciences and publishes articles from around the world presenting results of major research from all earth sciences. Readers are primarily earth scientists in academia and government institutions.
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