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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >The most ancient ophiolite of the Central Asian fold belt: U-Pb and Pb-Pb zircon ages for the Dunzhugur Complex, Eastern Sayan, Siberia, and geodynamic implications
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The most ancient ophiolite of the Central Asian fold belt: U-Pb and Pb-Pb zircon ages for the Dunzhugur Complex, Eastern Sayan, Siberia, and geodynamic implications

机译：中亚褶皱带最古老的蛇绿岩：Dunzhugur复合体，东萨彦岭，西伯利亚的U-Pb和Pb-Pb锆石年龄及其对地球动力学的影响

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摘要

Ophiolitic rocks with a zircon age of ～1020 Ma occur in the Dunzhugur complex of East Sayan, Siberia, and are part of a Neoproterozoic to early Palaeozoic segment of the Central Asian fold belt. The most spectacular suite is exposed along the Oka and Bokson rivers, where a complete ophiolite sequence with mantle tectonites, a layered sequence composed of dunite, wehrlite, and pyroxenite, a gabbro section, a sheeted diabase dyke complex and basaltic pillow laves are exposed. Petrologic and geochemical data suggest that all members of the ophiolite originally belonged to the same cogenetic mafic-ultramafic crustal section and support a supra-subduction zone setting in a fore-arc rifting environment for its origin. Two multigrain zircon size fractions from a plagiogranite are both slightly discordant but yielded a combined mean ~(207)Pb/~(206)Pb age of 1020 ± 10 Ma. Evaporation of three additional fractions of three to four grains each from the same sample produced a mean ~(207)Pb/~(207)Pb age of 1019.9 ± 0.7 Ma that we consider to most closely reflect the time of igneous crystallization of the plagiogranite. This is the oldest ophiolite so far dated from the Central Asian fold belt. The southern margin of the Siberian craton and the palaeo-Asian ocean were established at the end of the Mesoproterozoic, at least 1000 Ma ago. During the time interval 1000-570 Ma, one or several large ocean basins existed between Baltica, Siberia, Kazakhstan, Tarim and northern China, and these blocks are therefore unlikely to have been part of the supercontinent Roadinia. Rifting, initiation of subduction, and marginal basin formation began prior to 1000 Ma and continued through 570 Ma. The durzhugur ophiolite of Eastern Sayan provides evidence for the early opening of the palaeo-Asian ocean not later than 1000 Mg ago.
机译：锆石年龄为〜1020 Ma的蛇绿岩存在于西伯利亚东萨彦的敦珠古尔情结中，并且是中亚褶皱带的新元古代至早古生代的一部分。最壮观的套房暴露在奥卡河和博克森河沿线，那里有完整的蛇绿岩层序与地幔构造，由榴辉岩，辉绿岩和辉石组成的层状序列，辉长岩剖面，辉绿岩脉状岩性复合体和玄武质枕形熔岩。岩石学和地球化学数据表明，蛇绿岩的所有成员最初都属于同一个共生的镁铁质-超镁铁质地壳断面，并支持其前缘裂陷环境中的超俯冲带。斜长花岗岩中的两个多颗粒锆石大小分数均略有不一致，但组合的平均〜（207）Pb /〜（206）Pb年龄为1020±10 Ma。从同一样品中蒸发出三到四个颗粒的三个附加馏分，平均〜（207）Pb /〜（207）Pb年龄为1019.9±0.7 Ma，我们认为这最接近地反映了斜长花岗岩火成岩结晶的时间。 。这是迄今为止距中亚褶皱带最古老的蛇绿岩。西伯利亚克拉通的南缘和古亚洲海洋建立在中古生代末，至少1000 Ma以前。在1000-570 Ma的时间间隔内，波罗的海，西伯利亚，哈萨克斯坦，塔里木和中国北部之间存在一个或几个大型海盆，因此这些区块不太可能成为超大陆性Roadinia的一部分。裂谷，俯冲开始和边缘盆地形成始于1000 Ma之前，一直持续到570 Ma。东萨彦岭的durzhugur蛇绿岩为不晚于1000 Mg早古亚洲海洋的开放提供了证据。

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