B isotopes reveal Eocene mélange melting in northern Tibet during continental subduction
B isotopes reveal Eocene mélange melting in northern Tibet during continental subduction
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B同位素揭示了大陆俯冲期间西藏北部始新世混杂岩的熔化。
DOI：
10.1016/j.lithos.2021.106146
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发表时间：
2021-04
期刊：
影响因子：
3.5
通讯作者：
Shen Xiao-Ming
中科院分区：
文献类型：
--
作者：
Ma Lin;Gou Guo-Ning;Kerr Andrew C;Wang Qiang;Wei Gang-Jian;Yang Jin-Hui;Shen Xiao-Ming
大陆俯冲是地壳向地幔迁移的一种重要但鲜为人知的方式。大陆俯冲作用也被认为是形成广泛分布于西藏的新生代陆内钾质岩和青藏高原隆升的原因。然而，这种古老的大陆俯冲只是偶尔被发现，是有争议的。在这篇文章中，我们探索使用硼及其同位素，提供新的约束新识别的始新世富钾火山岩在北方的起源和潜在的大陆地壳俯冲。我们的研究结果表明，最新的始新世（约。富钾火山岩具有中等SiO2、类埃达克岩微量元素、富集Sr-Nd-Pb和轻硼同位素（δ 11 B = −20.12‰ ~ −7.95‰）特征。硼的同位素特征表明，混合岩源由地幔楔橄榄岩和再循环的脱水大陆地壳组成。始新世富钾岩浆可能来源于俯冲通道内底辟混杂岩在高压中温条件下的低度部分熔融。我们的工作表明，西藏板块对亚洲板块的潜在仰冲，从而触发陆内俯冲在始新世结束之前。在新生代印度和亚洲之间的快速会聚期间，这种大陆仰冲可能容纳了大量的地壳物质。我们的结论是，在这个过程中，同位素轻组分很可能已被输送到地幔中，形成一个独特的源区。因此，B同位素具有追踪大型碰撞造山带中陆壳再循环的潜力。
Continental subduction is an important but poorly known means of transporting the Earth's crust into the mantle. Continental subduction has also been proposed to responsible for the formation of the Cenozoic intracontinental potassic rocks widespread in Tibet and uplift of the Tibetan Plateau. However, such ancient continental subduction only occasionally been identified and is controversial. In this contribution, we explore the use of boron and its isotopes, to provide new constraints on the origin of newly identified Eocene potassium-rich volcanic rocks in northern Tibet and potential subduction of continental crust. Our results indicate that the latest Eocene (ca. 34 Ma) potassium-rich volcanic rocks are characterised by moderate silica, adakite-like trace elements, enriched Sr-Nd-Pb and light boron isotope (δ11B = −20.12‰ to −7.95‰) signatures. This isotopically light signature of boron suggests a mélange source composed of mantle wedge peridotite and recycled dehydrated continental crust. The Eocene potassium-rich magmas were likely derived from low-degree partial melting of diapir mélange at high-pressure and medium temperature within subduction channel. Our work indicates potential obduction of the Tibetan plate over the Asian plate thus triggering intracontinental subduction before the end of Eocene. This continental obduction may have accommodated a huge amount of crustal material during Cenozoic rapid convergence between India and Asia. We conclude that during this process an isotopically light component is likely to have been transported into the mantle to form a distinct source region. B isotopes therefore have the potential to trace the continental crust recycling in large collisional orogens.
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影响因子：
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作者：
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影响因子：
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通讯作者：
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