Ye Guan

Deep seismic reflection profile across the juncture zone between the Tarim Basin and the West Kunlun Mountains

Fine structures of the crust and upper mantle of the basin-and-range juncture on the northwestern margin of the Qinghai-Tibetan Plateau are first delineated by the deep seismic reflection profile across the juncture zone between the Tarim Basin and the West Kunlun Mountains. Evidence is found for the northward subduction of the northwest marginal lithosphere of the Qinghai-Tibetan Plateau and its collision with Tarim lithosphere beneath the West Kunlun Mountains. The lithosphere image of the face-to-face subduction and collision determines the coupling relationship between the Tarim Basin and the West Kunlun Mountains at the lithosphere scale and reflects the process of continent-continent collision.

Fine crustal structure beneath the junction of the southwest Tian Shan and Tarim Basin, NW China

The geometry of the entire crust from the northern part of the Tarim Basin to the southwestern Tian Shan east of Kashi is imaged on a N-S–directed explosive-source deep seismic-reflection profile. The profile reflects the sedimentary formations in the northern part of the Tarim Basin and the fold-and-thrust belt of the southern Tian Shan. N-dipping reflectors of the lower crust, as well as fluctuations in Moho depth, below which several mantle reflectors were observed, reveal the fine crustal structure beneath the junction of the southwest Tian Shan and the Tarim Basin. Mesozoic–Cenozoic shortening of the southwestern Tian Shan occurred at a crustal scale involving detachment-related folding in the basin directed northward toward the mountains and reverse faulting in the mountains directed toward the basin. In addition, a crocodile fabric developed within the lower crust beneath the basin area. The lithospheric structure revealed by the seismic-reflection section between the Tarim Basin and the Tian Shan Mountains reflects a process of intracontinental collision.

Moho-mapping in the Dabie ultrahigh-pressure collisional orogen, central China

Eight wide angle reflection/refraction seismic profiles (with a total length of ∼1700 km) and near-vertical reflection seismic profiles (with a total length of ∼340 km) across the Dabie Orogen, eastern China have been completed in recent years, and allow the Moho depth and uppermost-mantle velocity to be mapped across ∼40,000 km2. These data reveal the detailed structure of the crust and upper mantle of this orogen that resulted from collision of the North China craton (NCC) with the Yangtze Craton (YC). The Dabie Orogen is an asymmetric orogen, with a thin crustal root (∼6 km) preserved in its northern part, highlighted by a north-dipping Moho. Compared to the nearly seismically-transparent lower crust, the Moho crust-mantle transition zone under the Dabie Orogen is a prominent north-dipping, strongly layered reflection, which is inferred to reflect the remnants of subduction of YC under the edge of the NCC or post-collisional exhumation of ultrahigh-pressure (UHP) rocks, and indicates the northward polarity of subduction of the YC. The Moho of the YC and NCC meet beneath the northern part of the Dabie Mountains, and the NCC Moho (north) is uplifted by ∼4 to 5 km (Offset 1) over the YC Moho (south), marking the NCC-YC collision zone. Along the southern margin of the Dabie Mountains, the Moho below the Yangtze foreland is underthrust beneath the Moho of the Dabie Mountains, forming another Moho overlap (Offset 2) with a depth difference of 5 to 6 km. The two Moho overlaps (offsets) at both flanks of the Dabie Mountains formed two crustal-scale boundaries at depth between the NCC and the Dabie Orogen, and the Dabie Orogen and the YC respectively. Offset 1 is considered to be the Triassic suture between the YC and NCC as supported by the metamorphic ages of UHP rocks. This displays a wedge-shaped offset zone opening towards the east that acted as a channel for exhumation of UHP rocks. Offset 2 under the southern margin of the Dabie Orogen is connected to the Xiangfan-Guangji fault that gave rise to a large-scale thrust detachment that propagated towards the foreland of the Dabie Orogen during the Jurassic. Thus our Moho mapping confirms that there are structural remnants of the Triassic deep continental subduction preserved, despite the superimposed Jurassic deformation.

Static corrections methods in the processing of deep reflection seismic data

Statics are big challenges for the processing of deep reflection seismic data. In this paper several different statics solutions have been implemented in the processing of deep reflection seismic data in South China and their corresponding results have been compared in order to find proper statics solutions. Either statics solutions based on tomographic principle or combining the low-frequency components of field statics with the high-frequency ones of refraction statics can provide reasonable statics solutions for deep reflection seismic data in South China with very rugged surface topography, and the two statics solutions can correct the statics anomalies of both long spatial wavelengths and short ones. The surface-consistent residual static corrections can serve as the good compensations to the several kinds of the first statics solutions. Proper statics solutions can improve both qualities and resolutions of seismic sections, especially for the reflections of Moho in the upmost mantle.