No abstract

No abstract

No abstract

Seismic, sonic logging and geothermal data are analyzed to show the distribution of gas hydrates in the Dongsha region north of the South China Sea. Bottom simulating reflectors (BSRs) and amplitude blanking zones are revealed in seismic profiles. A high velocity interval and a velocity reverse are distinguished by sonic logging.The BSR depth is compared with thickness of gas hydrate stability zone from geothermal gradient data. The BSR at ODP sites 1144 and 1148 occur at 654 and 475 meters below sea floor respectively. The top of the amplitude blanking zone may be related to gas hydrate bearing strate in a region adjacent to ODP site 1144, at about 450 meters below the sea floor.

No abstract

Many researchers have estimated the thickness of the gas hydrate stability zone (GHSZ) and amount of gas hydrate at different areas in the South China Sea (SCS) using varying methods, but few have reported calculations for the whole of the SCS. In this paper, Milkov and Sassen's model is used to calculate the thickness of the GHSZ in the SCS. In addition, an estimation of the amount of gas hydrate and discussed in terms of gas composition and the effects of water depth. Average thicknesses for the GHSZ in the SCS are estimated to be ~440 m, ~477 m and ~553 m based on the relationship between GHSZ thickness and water depth established in this study for 3 kinds of gas hydrates with gas composition containing 100% methane, 96% methane, and 90% methane, respectively. Then, by assuming that gas hydrates are distributed in half of the continental slope area of the SCS, and that the gas hydrate saturation is 1.2% of sediment volume, the amounts of gas hydrate are estimated to be ~3. (Key words: Gas hydrate, Thickness of gas hydrate stability zone, South China Sea)

In light with Bouguer gravity data, various information on faults were obtained by means of analytical continuation, target field extraction, arbitrary horizontal direction derivative processing and discrete wavelet transform processing. According to synthetic analyses with geologic data, the 123°E longitude was chosen as a typical profile, then initial models were established based on seismic data to perform gravitational inverse iterative fitting, and finally density parameters of various modules and their distribution were given. Based upon which the geologic and geophysical properties of the principal faults of the study area were analyzed, resulting in fault zone and block binding distribution maps. The paper focuses on the discussion of west marginal fault zone of the Korean Peninsula and Wulian– Qingdao–Rongcheng fault zone in the study area and points out that Wulian–Qingdao– Rongcheng fault zone did not intrude Korean Peninsula to connect with Imjinhang fault zone. It also holds that northward translational movement of the portion belonging to the Yangtze Plate at the west side of west marginal fault zone of the Korean Peninsula once occurred under the action of northward stress. Only the fault zones consisting of Wulian– Qingdao–Rongcheng fault zone along with northern fault zone of South Yellow Sea, west marginal fault zone of the Korean Peninsula, and south marginal fault zone of Cheju Island should be the binding site of Sino‐Korean and Yangtze Plates.

The rifting and seafloor spreading of Southwest subbasin of South China Sea is the most important tectonic event in the forming process of South China Sea from the late Cretaceous period to Middle Eocene. We simulate the thermal evolution process of this region with 3‐D finite element method and research the rifting deformation of Southwest subbasin, the duration of seafloor spreading, the rising of mantle materials, the crush and spreading energy of the lithosphere dyke along the spreading center, and the magmatism by computing the deformation and temperature structure. The result indicates that the extension duration of the sea basin is 10 to 15Ma. Because of insufficient deep dynamics condition, the rising of mantle materials stopped gradually and the lithosphere lost the extension drive, and then the spreading center became a dead rift valley with a leftover spreading center but not ridge or central uplift belt. Though the rising potential of the mantle materials in this area is insufficient, there are quite violent magma spewing activities leading to the growing up of seamount after the molding of the sea basin in the region with the partial rifting, especially the extension and detachment of the boundary between basin and margin.