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Carbonated Inheritance in the Eastern Tibetan Lithospheric Mantle: Petrological Evidences and Geodynamic Implications
Author(s) -
Goussin Fanny,
Riel Nicolas,
Cordier Carole,
Guillot Stéphane,
Boulvais Philippe,
Roperch Pierrick,
Replumaz Anne,
Schulmann Karel,
DupontNivet Guillaume,
Rosas Filipe,
Guo Zhaojie
Publication year - 2020
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2019gc008495
Subject(s) - geology , lithosphere , mantle (geology) , subduction , magmatism , mantle convection , mantle plume , crustal recycling , geochemistry , mantle wedge , orogeny , craton , kimberlite , geophysics , earth science , petrology , paleontology , continental crust , tectonics
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 H2 O and CO2prior 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.

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