Evidence for a Widespread Tethyan Upper Mantle with Indian-Ocean-Type Isotopic Characteristics
Evidence for a Widespread Tethyan Upper Mantle with Indian-Ocean-Type Isotopic Characteristics
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DOI：
10.1093/petrology/egi002
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发表时间：
2005-04
影响因子：
3.9
通讯作者：
S.-Q. Zhang;J. Mahoney;X. Mo;A. Ghazi;L. Milani;A. Crawford;T. Guo;Zhidan Zhao
中科院分区：
文献类型：
--
作者：
S.-Q. Zhang;J. Mahoney;X. Mo;A. Ghazi;L. Milani;A. Crawford;T. Guo;Zhidan Zhao
来自伊朗、西藏、东喜马拉雅山脉、澳大利亚附近海底，可能还有阿尔巴尼亚的特提斯玄武岩和辉长岩的地幔来源，在同位素上与现今印度洋海脊和热点的地幔来源相似。许多样品的抗蚀不相容元素组合物类似于洋脊玄武岩，虽然洋岛状组合物也存在。印度洋型地幔在侏罗纪和早白垩世广泛存在于新特提斯之下，早在早石炭世至少部分存在于古特提斯之下。因此，今天印度洋下的地幔可能主要是“继承”的特提斯地幔。虽然一些特提斯岩石可能形成于洋内弧后或弧前，软流层的污染物质俯冲前不久mogmatism不能是一个普遍的解释，他们的印度洋洋脊状低-206 Pb/204 Pb签名。通过羽流向软流圈提供低206 Pb/204 Pb物质的说法，既不支持现今的印度洋热点，也不支持洋岛状的特提斯岩石。古老的大陆下地壳或岩石圈地幔，包括增生的，很少脱水的海洋沉积物质，提供了一个潜在的低206 Pb/204 Pb的储层，只有当足够数量的这种材料可以随着时间的推移引入到软流圈。古俯冲海洋沉积物是一个可能的低-206 Pb/204 Pb源，只有当大量增加的U/ Pb，发生在俯冲相关的脱水以某种方式避免。在古代脱水过程中，低U/Pb流体直接流入软流层，以及古辉石质下地壳残积岩或玄武质下弧地壳进入软流层，提供了另外两种形成特提斯-印度洋地幔的方式，但这些机制也存在潜在的重大问题。作者2005牛津大学出版社出版。All rights reserved.
The mantle sources of Tethyan basalts and gabbros from Iran, Tibet, the eastern Himalayas, the seafloor off Australia, and possibly Albania were isotopically similar to those of present-day Indian Ocean ridges and hotspots. Alteration-resistant incompatible element compositions of many samples resemble those of ocean-ridge basalts, although ocean-island-like compositions are also present. Indian-Ocean-type mantle was widespread beneath the Neotethys in the Jurassic and Early Cretaceous, and present beneath at least parts of the Paleotethys as long ago as the Early Carboniferous. The mantle beneath the Indian Ocean today thus may be largely 'inherited' Tethyan mantle. Although some of the Tethyan rocks may have formed in intra-oceanic back-arcs or fore-arcs, contamination of the asthenosphere by material subducted shortly before mogmatism cannot be a general explanation for their Indian-Ocean-ridge-like low- 206Pb/ 204Pb signatures. Supply of low- 206Pb/ 204Pb material to the asthenosphere via plumes is not supported by either present-day Indian Ocean hotspots or the ocean-island-like Tethyan rocks. Old continental lower crust or lithospheric mantle, including accreted, little-dehydrated marine sedimentary material, provides a potential low- 206Pb/ 204Pb reservoir only if sufficient amounts of such material can be introduced into the asthenosphere over time. Anciently subducted marine sediment is a possible low- 206Pb/ 204Pb source only if the large increase of U/ Pb that occurs during subduction-related dewatering is somehow avoided. Fluxing of low-U/Pb fluids directly into the asthenosphere during ancient dewatering and introduction of ancient pyroxenitic lowercrustal restite or basaltic lower-arc crust into the asthenosphere provide two other means of creating Tethyan-Indian Ocean mantle, but these mechanisms, too, have potentially significant problems. © The Author 2005. Published by Oxford University Press. All rights reserved.