Carbonated Inheritance in the Eastern Tibetan Lithospheric Mantle: Petrological Evidences and Geodynamic Implications
Carbonated Inheritance in the Eastern Tibetan Lithospheric Mantle: Petrological Evidences and Geodynamic Implications
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DOI：
10.1029/2019gc008495
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发表时间：
2020-02
期刊：
影响因子：
3.7
通讯作者：
F. Goussin;N. Riel;C. Cordier;S. Guillot;P. Boulvais;P. Roperch;A. Replumaz;K. Schulmann;G. Du
中科院分区：
文献类型：
--
作者：
F. Goussin;N. Riel;C. Cordier;S. Guillot;P. Boulvais;P. Roperch;A. Replumaz;K. Schulmann;G. Du
由于地球物理数据的相互矛盾的解释，青藏高原的形成时间和机制仍然难以捉摸，甚至青藏高原岩石圈目前的结构也很难得到解决。我们在这里表明，通过更好地评估青藏高原岩石圈最深处的组成和流变特性，可以在我们对造山运动的理解上取得重大进展，特别是导致对全球层析剖面的重新解释。我们报道了东羌塘地体始新世钾质岩中保存的地幔金云母异晶和含碳酸盐超镁铁质堆积物，这为印亚碰撞之前西藏中部岩石圈地幔富含H 2 O和CO 2 提供了证据。流变学计算和数值模拟表明：（1）这种交代地幔明显弱于正常地幔，但浮力足以防止其沉入地幔深处； (2) 西藏中部下方的慢震异常可能表现为正常厚度的弱化岩石圈，而不是由于其下部的对流去除而变薄和加热的岩石圈； （3）在陆内俯冲过程中，这种柔软且易熔的交代地幔可能会熔化，这支持了所研究的始新世钾质岩浆作用的俯冲起源。这些结果表明，柔软而有浮力的碰撞前青藏高原岩石圈的继承可能决定了青藏高原的生长和当今的结构。
The timing and mechanism of formation of the Tibet Plateau remain elusive, and even the present‐day structure of the Tibetan lithosphere is hardly resolved, due to conflicting interpretations of the geophysical data. We show here that significant advances in our understanding of this orogeny could be achieved through a better assessment of the composition and rheological properties of the deepest parts of the Tibetan lithosphere, leading in particular to a reinterpretation of the global tomographic cross sections. We report mantle phlogopite xenocrysts and carbonate‐bearing ultramafic cumulates preserved in Eocene potassic rocks from the Eastern Qiangtang terrane, which provide evidence that the lithospheric mantle in Central Tibet was enriched in H 2 O and CO 2 prior to the India‐Asia collision. Rheological calculations and numerical modeling suggest that (1) such metasomatized mantle would have been significantly weaker than a normal mantle but buoyant enough to prevent its sinking into the deep mantle; (2) the slow seismic anomalies beneath Central Tibet may image a weakened lithosphere of normal thickness rather than a lithosphere thinned and heated by the convective removal of its lower part; and (3) melting of such soft and fusible metasomatized mantle would have been possible during intracontinental subduction, supporting a subduction origin for the studied Eocene potassic magmatism. These results demonstrate that the inheritance a soft and buoyant precollisional Tibetan lithosphere may have conditioned the growth and the present‐day structure of the Tibet Plateau.