The Mabja Dome Structure in Southern Tibet Revealed by Deep Seismic Reflection Data and Its Tectonic Implications

The ongoing India-Asia collision has led to the formation of the northern Himalayan gneiss domes belt in southern Tibet. The domes are the result of the ongoing convergence and were formed by geological processes that may include crustal thickening, metamorphism, partial melting, and exhumation of middle crustal rocks to the surface. A combination of compressional, extensional, and diapiric processes has been invoked to explain the formation and evolution of these domes. Differentiating among these competing hypotheses requires well-defined geophysical images of the internal structure of the domes. The Mabja dome is the largest dome within the northern Himalayan gneiss domes belt. A 70-km long deep seismic reflection profile across Mabja dome was acquired in 2016. The seismic data could provide new information about the structural elements beneath the domes to the depth of 25 Km. We address the structure of the Mabja dome by conducting an integrated analysis of shallow crustal velocity structure and a normal-incidence seismic reflection image of deeper crust. Our work suggests that the Mabja dome is underlain by shear zones at depths of 10–15 km and two high-velocity bodies at depths of 3 km possibly representing the eclogitic-facies rocks or mafic intrusions. We propose that the dome formation may have been controlled by collision-induced north-south shortening expressed by thrust stacking of middle crustal rocks, which led to the doming of the upper-crustal rocks. The proposed mechanism inferred for Mabja dome can be applied to interpret the widespread domes throughout the southern Tibet and other related structures in orogenic mountain belts. © 2021. American Geophysical Union. All Rights Reserved.