Qian Liu, T. Tsunogae, Guochun Zhao, Jianhua Li, Jinlong Yao, Yigui Han, Peng Wang
{"title":"塔里木东南部阿尔金北塔格造山带多期蛇绿岩形成","authors":"Qian Liu, T. Tsunogae, Guochun Zhao, Jianhua Li, Jinlong Yao, Yigui Han, Peng Wang","doi":"10.2475/06.2021.05","DOIUrl":null,"url":null,"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.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"321 1","pages":"788 - 821"},"PeriodicalIF":1.9000,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"2","resultStr":"{\"title\":\"Multiphase ophiolite formation in the Northern Altyn Tagh Orogen, southeastern Tarim\",\"authors\":\"Qian Liu, T. Tsunogae, Guochun Zhao, Jianhua Li, Jinlong Yao, Yigui Han, Peng Wang\",\"doi\":\"10.2475/06.2021.05\",\"DOIUrl\":null,\"url\":null,\"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.\",\"PeriodicalId\":7660,\"journal\":{\"name\":\"American Journal of Science\",\"volume\":\"321 1\",\"pages\":\"788 - 821\"},\"PeriodicalIF\":1.9000,\"publicationDate\":\"2021-06-01\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"2\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"American Journal of Science\",\"FirstCategoryId\":\"89\",\"ListUrlMain\":\"https://doi.org/10.2475/06.2021.05\",\"RegionNum\":3,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q3\",\"JCRName\":\"GEOSCIENCES, MULTIDISCIPLINARY\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"American Journal of Science","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.2475/06.2021.05","RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"GEOSCIENCES, MULTIDISCIPLINARY","Score":null,"Total":0}
Multiphase ophiolite formation in the Northern Altyn Tagh Orogen, southeastern Tarim
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.
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.