摘要
This paper discusses deep crustal architecture of the Baiyun Sag of the Pearl River Mouth Basin, northern South China Sea based on velocity analysis, time-depth con- version and seismic interpretation of the deep seismic reflec- tion profile DSRP-2002. The profile was acquired and proc- essed to 14 S TWT by the China National Offshore Oil Corp. (CNOOC) in 2002. It extends across the Baiyun Sag of the Pearl River Mouth Basin, from the northern continental shelf of the SCS to the deepwater province. As the first deep seismic reflection profile in the Pearl River Mouth Basin,this profile reveals seismic phases from basement down to upper most mantle. The Moho surface appears in the profile as an undulating layer of varying thickness of 1-3 km. It is not a single reflector interface, but a velocity gradient or intercon- version layer. The crust thins stepwisely from the shelf to the continental slope and the abyssal plain (from north to south), and also thins under depocenters. The crustal thickness is only 7 km in the depocenter of the main Baiyun Sag, which corresponds to a Moho upwelling mirroring the basement topography. In the lower slope and the ocean-continental transition zone of the southernmost portion of the profile, three sub-parallel, NW-dipping strong reflectors found at depths around 10-21 km are interpreted as indications of a subducted Mesozoic oceanic crust. Crustal faults exist in the northern and southern boundaries of the Baiyun Sag. The intense and persistent subsidence of the Baiyun Sag might be related to the long-term activity of the crustal faults.
This paper discusses deep crustal architecture of the Baiyun Sag of the PearlRiver Mouth Basin, northern South China Sea based on velocity analysis, time-depth conversion andseismic interpretation of the deep seismic reflection profile DSRP-2002. The profile was acquiredand processed to 14 S TWT by the China National Offshore Oil Corp. (CNOOC) in 2002. It extendsacross the Baiyun Sag of the Pearl River Mouth Basin, from the northern continental shelf of the SCSto the deepwater province. As the first deep seismic reflection profile in the Pearl River MouthBasin, this profile reveals seismic phases from basement down to upper most mantle. The Moho surfaceappears in the profile as an undulating layer of varying thickness of 1 — 3 km. It is not a singlereflector interface, but a velocity gradient or intercon-version layer. The crust thins stepwiselyfrom the shelf to the continental slope and the abyssal plain (from north to south), and also thinsunder depocenters. The crustal thickness is only 7 km in the depocenter of the main Baiyun Sag,which corresponds to a Moho upwelling mirroring the basement topography. In the lower slope and theocean-continental transition zone of the southernmost portion of the profile, three sub-parallel,NW-dipping strong reflectors found at depths around 10 — 21 km are interpreted as indications of asubducted Mesozoic oceanic crust. Crustal faults exist in the northern and southern boundaries ofthe Baiyun Sag. The intense and persistent subsidence of the Baiyun Sag might be related to thelong-term activity of the crustal faults.
基金
the NSFC Key Project(Grant No.40238060)
the National 97T3 Project(Grant No.G2000046702),SCSIO Project(Grant No.SJ200402)
the CAS Key Project(Grant No.KZCX2-117-5)
the Field Frontier Project of the SCSIO.and the Key Laboratory Project(Grant No.BYH03A05).
关键词
地壳结构
地表下陷
海洋
地震
deep seismic reflection profiles
crustal structure
Baiyun Sag
northernslope of the South China Sea
