Isostatic gravity anomaly, lithospheric scale density structure of the northern Tibetan plateau and geodynamic causes for potassic lava eruption in Neogene

• The volcanic rocks areas in Northern Tibet exhibit ultra-low Bouguer gravity anomalies and low isostatic regional anomalies.
• Low density in the middle- lower crust and mantle beneath the high-to-ultra potassic areas, North Tibet.
• A new model along Profile 88.5°E presents breaking-off of the Asian mantle.

This paper will help to further constrain geodynamic models for the evolution of northern Tibet through two techniques that employ Bouguer gravity anomaly data: the first is isostatic correction of Bouguer gravity anomalies and the second is 2-D density modeling along a profile at 88.5°E from 30°N to 37°N within the Tibetan Plateau. Areas dominated by volcanic rocks exhibit ultra-low Bouguer gravity anomalies and low isostatic residual anomalies. The 2-D density structure beneath Profile 88.5°E shows a giant “upward dome” distributed body of low density in the middle-lower crust and mantle beneath the high-to-ultra-potassic areas, suggesting that the original middle and lower crusts were reformed and replaced extensively in the area. Based on existing regional geology and tectonics, geochemical data from magmatic rocks, and geophysical information, this paper proposes that the sustained northward subduction of the Indian plate has resulted in breaking off of the frontal margin of the Asian lithospheric mantle. Subsequently, the original lithosphere was reactivated by thermal-tectonic changes, high-to-ultra potassic volcanoes erupted extensively in the northern Tibetan Plateau during Neogene, and the plateau experienced rapid NE-trending uplift.