Crustal Deformation and Detachment in the Sulu Orogenic Belt: New Constraints From Onshore‐Offshore Wide‐Angle Seismic Data

We deployed the first dense onshore‐offshore seismic survey profile across the ultrahigh/high‐pressure metamorphic Sulu Orogenic Belt (SLOB). By applying multiple seismic and gravity modeling, we obtained the crustal P wave velocity and density model across the SLOB and extending into tectonic units on both sides, including the eastern Sino‐Korean Block (SKB), and the lower Yangtze Block (YZB). A ∼120‐km‐wide high‐velocity and high‐density upper crust in the southern SLOB reveals the distribution of ultrahigh/high‐pressure metamorphism, which should be linking with the deep subduction, detachment, and exhumation of YZB midcrust. In the northern SLOB, the U‐shaped velocity contours throughout the crust and the low‐density midcrust reveals the downward bending of the crustal deformation due to the collision between SKB and YZB. The crustal deformation and detachment in the SLOB revealed by our results indicate that the orogenic spatial distribution should be wider than what we know before. Plain Language Summary The Sulu Orogenic Belt has the world's largest ultrahigh‐pressure metamorphism and high‐pressure metamorphism tectonic unit, becomes a natural laboratory for studying the dynamics of formation and evolution of the solid earth. The tectonic boundaries of the Sulu belt, especially the offshore boundaries, are still in controversy due to the lack of high‐resolution deep structure studies in the offshore domains. Here we present the forward and inversion models from newly acquired dense onshore‐offshore wide‐angle seismic data, and discuss the different crustal structure features among the Sino‐Korean Block, the Yangtze Block, and the Sulu belt. The crustal deformation and detachment addressed the distribution of the Sulu belt, which should be much wider than what we know before, and the underestimation of the extent of collision belts might be widespread in other orogenic or suture belts. Key Points We deployed the first dense onshore‐offshore wide‐angle seismic line across the Sulu orogen to constrain a high‐resolution crustal model The Sino‐Korean crust bended downward in the northern Sulu belt, the Yangtze crust was detached and exhumed in the southern Sulu belt High‐speed orogen upper crust indicates linkage among ultrahigh‐pressure metamorphism, deep subduction, and exhumation of Yangtze midcrust