Carbonated Inheritance in the Eastern Tibetan Lithospheric Mantle: Petrological Evidences and Geodynamic Implications

Abstract

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 2O 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.

Two Phases of Crustal Shortening in Northeastern Tibet as a Result of a Stronger Qaidam Lithosphere During the Cenozoic India–Asia Collision

“…(2014), Goussin et al. (2020), and Ma et al. (2021), we assumed a metasomatic mantle–lithosphere lid beneath Tibet created in the late Mesozoic prior to the India–Asia collision.…”

Miocene Subsidence and Surface Uplift of Southernmost Tibet Induced by Indian Subduction Dynamics

“…In the absence of erosion or surface uplift, the magnitude should be divided by a factor of~6 (see Husson et al, 2014, for details). The age of magmatism contours by Goussin et al (2020) are also illustrated. 20 Ma onward, while subsidence started in the Himalayan foreland basin (Figures 6c and 7c).…”

“…Schematic structural framework of southern Tibet and the Himalaya. Age data of magmatism are from the Tibetan Magmatism Database ( https://www.jaychapman.org/tibet‐magmatism‐database.html) by Chapman and Kapp (2017), with contours from Goussin et al (2020). Thermochronological data are cited from (1) Kirstein et al (2006); (2) Carrapa et al (2014); (3) Tremblay et al (2015); (4) Li, Kohn, et al (2015); (5) Li, Tian, et al (2015); (6) Shen et al (2016).…”

“…The main belt is the Gangdese magmatic arc following the Indus‐Yarlung suture, related to the northward subduction of the Indian plate. Another belt is following the Jinsha suture, related to the southward subduction of the Asian lithosphere in an early phase of collision (e.g., Goussin et al, 2020; Horton et al, 2002; Spurlin et al, 2005). Finally, one belt follows the Kunlun suture, related to ongoing southward Asian lithosphere subduction since ~15 Ma (Figure 1).…”

“…In the absence of erosion or surface uplift, the magnitude should be divided by a factor of~6 (see Husson et al, 2014, for details). The age of magmatism contours by Goussin et al (2020) are also illustrated. (b-d) AFT, AHe, and ZHe ages of the Kailas Formation, Gangdese batholith, and Xigaze basin against the distance from Indus-Yarlung suture zone in different locations.…”