The Dupal isotopic anomaly in the southern Paleo-Asian Ocean: Nd-Pb isotope evidence from ophiolites in Northwest China
The Dupal isotopic anomaly in the southern Paleo-Asian Ocean: Nd-Pb isotope evidence from ophiolites in Northwest China
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古亚洲洋南部的Dupal同位素异常：来自中国西北蛇绿岩的Nd-Pb同位素证据
DOI：
10.1016/j.lithos.2013.08.020
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发表时间：
2014-02
期刊：
影响因子：
3.5
通讯作者：
Guo, Lin
中科院分区：
文献类型：
--
作者：
Xiao, Wenjiao;Shi, Yu;Feng, Zuohai;Guo, Lin
有人认为，地幔中的Dupal同位素异常可以追溯到来自新-古特提斯洋（275-350 Ma）的古生代蛇绿岩。准噶尔盆地东西两角的卡拉麦里蛇绿岩（KO）和达拉布特蛇绿岩（DO）代表了较古老（> 350 Ma）的古亚洲洋壳（PAO）的残余。因此，这些蛇绿岩可以提供额外的约束的长期组成和演化的古生代洋下地幔。我们提出了新的主微量元素和Sr，Nd和高精度的铅同位素数据的玄武岩，辉长岩和斜长石分离的KO和DO。我们的研究结果表明，PAO地壳确实有一个Dupal样同位素签名。详细地，对于给定的206 Pb/204 Pb（t）比率（即，正Δ8/4值），类似于印度洋洋中脊玄武岩（MORB）的Dupal同位素特征。DO基性岩石的微量元素特征与正常和富集的MORB相似，而KO则介于MORB和弧玄武岩之间。因此，DO地幔域反映了PAO软流层，而KO地幔域还反映了俯冲过程的影响。地球化学建模使用Th/Nd以及Nd和Pb同位素比值表明，高达2%的俯冲成分已被添加到一个耗尽的印度MORB型地幔产生大部分的KO岩石。KO岩石中的俯冲成分由不同比例的≤ 1%的非放射性沉积物部分熔融组成，类似于现代伊豆-小笠原海沟沉积物和俯冲蚀变洋壳脱水的含水流体。泥盆纪软流圈地幔下的PAO南部的同位素是不均匀的，但借给支持的想法，Dupal同位素异常存在之前，印度洋的开放。最后，板块构造重建表明，在晚古生代期间，异常存在于南半球的新特提斯洋和古特提斯洋以及北方的PAO南部。
It has been suggested that the Dupal isotopic anomaly in the mantle can be traced in the Paleozoic ophiolites from the Neo- and Paleo-Tethyan Ocean (275–350 Ma). The Karamaili ophiolite (KO) and Dalabute ophiolite (DO) in the eastern and western corners, respectively, of the Junggar basin in NW China represent remnants of the relatively older (> 350 Ma) Paleo-Asian Ocean (PAO) crust. Thus, these ophiolites can provide additional constraints on the long-term composition and evolution of the Paleozoic suboceanic mantle. We present new major-trace element and Sr, Nd and high-precision Pb isotope data for the basalts, gabbros and a plagioclase separate from the KO and DO. Our results indicate that the PAO crust indeed has a Dupal-like isotopic signature. In detail, all samples have relatively low εNd(t)and high208Pb/204Pb(t)for given206Pb/204Pb(t)ratios (i.e., positive Δ8/4 values), similar to the Dupal isotopic characteristics of Indian Ocean mid-ocean ridge basalts (MORB). The trace element signature of DO mafic rocks is similar to that of normal- and enriched-MORB whereas that of the KO is transitional between MORB and arc basalt. Therefore, the DO mantle domain reflects the PAO asthenosphere and the KO domain additionally shows the influence of the subduction process. Geochemical modeling using Th/Nd as well as Nd and Pb isotopic ratios indicates that up to 2% subduction component had been added to a depleted Indian MORB-type mantle to produce the bulk of KO rocks. The subduction component in the KO rocks consisted of variable proportions of ≤ 1% partial melt of unradiogenic sediment similar to modern Izu–Bonin trench sediment and hydrous fluid dehydrated from the subducted altered oceanic crust. The Devonian asthenospheric mantle beneath the southern PAO is isotopically heterogeneous, but lends support to the idea that the Dupal isotopic anomaly existed prior to the opening of the Indian Ocean. Finally, plate tectonic reconstruction indicates that the anomaly was present in the Neo- and Paleo-Tethyan oceans in the southern hemisphere and in the southern part of PAO in the northern hemisphere during the late Paleozoic.
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影响因子：
3.9
作者：
J. Mahoney;D. Graham;D. Christie;K. Johnson;L. S. Hall;D. Vonderhaar
通讯作者：
J. Mahoney;D. Graham;D. Christie;K. Johnson;L. S. Hall;D. Vonderhaar
DOI：
--
发表时间：
--
期刊：
--
影响因子：
--
作者：
Un;L. -;In;Hung
通讯作者：
Un;L. -;In;Hung
影响因子：
6.1
作者：
Jian‐Lin Chen;Wenbin Zhao;Ji‐Feng Xu;Bao-di Wang;Z. Kang
通讯作者：
Jian‐Lin Chen;Wenbin Zhao;Ji‐Feng Xu;Bao-di Wang;Z. Kang
DOI：
--
发表时间：
2009-06
期刊：
--
影响因子：
--
作者：
X. J. Liu;P. Castillo;J. Xu;Q. Hou
通讯作者：
X. J. Liu;P. Castillo;J. Xu;Q. Hou
影响因子：
2.7
作者：
A. Hall
通讯作者：
A. Hall