Crustal magnetic structure and implications for the Eastern Himalayan Syntaxis revealed by EMAG2-v3

Abstract

The Eastern Himalayan Syntaxis (EHS) is located at the forefront of the collision between the Indian and Asian plates, representing the region with the most rugged terrain and intricate structural deformations along the southeastern margin of the Tibetan Plateau. A long-standing debate has revolved around two modes of tectonic evolution: “flat slab indentation” and “tectonic aneurysm”. This study, employing analysis and inversion of the EMAG2-v3 crustal magnetic anomalies, has obtained a 3D crustal magnetic structure. By integrating magnetic structures with rock susceptibilities, the rough crustal lithological structure is determined, and a simplified two-stage evolution model is established. The results reveal the presence of a strong magnetic body in the core of the EHS, particularly in the region of Namche Barwa Peak and Gyala Peri Peak. The 3D spatial characteristics of this strong magnetic body indicate that deep-seated materials beneath the EHS are uplifting from the plateau interior to the southeast. Both crustal magnetic and lithological structures support the “tectonic aneurysm” evolution model. The seismic hazard zone is identified as the region surrounding the boundary of strong magnetic body, particularly on the side adjacent to the strong magnetic body, with Namche Barwa Peak and Gyala Peri Peak as its center.