Regional structure characteristics of crustal root of mountain beneath the Sulu orogenic belt
苏鲁造山带区域地壳山根结构特征

The depth distribution of Moho discontinuity and P-wave velocity structure beneath the Orogenic Belt and the ultra-high-pressure metamorphic belts (UHPM) in the Sulu and Dabie regions were analyzed in the present analysis, respectively. The results suggest that the orogenic structure beneath the Sulu region evidently differ from those beneath the Dabie region, although there are some similar structure characteristics in the two regions. The mountains already are worn away in the Sulu region. The crustal thickness is about 32 - 33 km, greater than those in its surrounding areas. The Moho discontinuity beneath the Sulu orogenic region does not obviously cave in. The crustal root of mountain probably has exhumed. The upper crustal velocity in the Sulu region is about 5. 6 -6.2 km/s, being 1-1. 2km/s greater than those in its surroundings and also greater than that in the Dabie region. This velocity difference between the Sulu and Dabie regions shows that more UHPM rocks of high velocity and density in the mantle exhumed into the upper crust and the surface in the Sulu region. The Dabie mountains, however, towers aloft still. The Moho discontinuity shaping like a series of ellipsoids along the NWW direction beneath Dabie caves in obviously. The remnant crustal root of old mountain is as deep as 38 km. These results show that the orogenic motions and the evolutions in the Sulu region are different from those in the Dabie orogen region although they are in identical orogenic belt. The orogeny started late in Sulu, the orogeny, however, ends early. The orogeny in Sulu entered in the late period of the orogeny much earlier than that in Dabie. The early exhumation of the crustal root of old mountain in Sulu may probably relate to the left turning strike-slip motions of the Tanlu fold and the effects of the extensional tectonic stress field in NW-SE in East China. The crustal root of old mountain gradually exhumes in response to the decrease of buoyancy of the crustal root, as the continuing erosion progressively wore away surface relief in the Sulu region because of the tectonic motions in the wide region. The velocity structure characteristics in the present analysis probably reflect the exhuming procedure of the crustal root with the wearing away surface relief due to the erosions.