Rifting of the Indian passive continental margin: Insights from the Langjiexue basalts in the central Tethyan Himalaya, southern Tibet

The Triassic tectonic setting of the Tethyan Himalaya in southern Tibet remains controversial and is key to revealing the mechanism of Neo-Tethys Ocean opening and the breakup history of Gondwana. This paper reports 227-225 Ma mafic volcanic rocks interbedded within the Tethyan Himalaya sequence in southern Tibet, which were formed in a typical passive continental margin setting. The basalts are tholeiitic with high TiO2 (3.20-3.38 wt%) and moderate MgO (4.05-5.40 wt%) contents and exhibit enrichment in light rare earth elements and weak negative Nb, Ta, Eu, and Ti anomalies. These geochemical compositions, combined with uniform whole-rock epsilon(Nd)(t) (+1.50 to +2.70) values, indicate that the magmas were derived by low-degree melting of a deep-seated garnet source that was heterogeneously modified by an oceanic island -basalt-type of component. Given the other geological evidence, we propose that the magmatic evolution of the Tethyan Himalaya -during the late Paleozoic-Mesozoic was generally a lithospheric thinning process, that is, it evolved from a fully developed continental rift system during the Late Permian to wane during the Triassic. This interpretation further supports the hypothesis that the Neo-Tethys Ocean opened in a passive pattern and that the breakup of Gondwana in the late Paleozoic was initiated by lithospheric thinning. Therefore, the subsequent magmatism was related to the passive upwelling of normal asthenospheric materials.

Automated summary

This study reports the tectonic setting of the Tethyan Himalaya in southern Tibet during the Triassic period and its relationship with the opening of the Neo-Tethys Ocean and the breakup of Gondwana. The researchers analyzed volcanic rocks in the region and found that they were formed in a passive continental margin setting. The findings support the hypothesis that the Neo-Tethys Ocean opened in a passive pattern and that the breakup of Gondwana was initiated by lithospheric thinning.