Based on an analysis of full-cover multi-beam bathymetric data,seismic and sub-bottom profiling data,and other geological-geophysical data sets,the geomorphologic features of the Ryukyu trench-arc-backarc(T-A-BA)syste...Based on an analysis of full-cover multi-beam bathymetric data,seismic and sub-bottom profiling data,and other geological-geophysical data sets,the geomorphologic features of the Ryukyu trench-arc-backarc(T-A-BA)system are delineated,and a geomorphologic map of the system is compiled.The re-sults show that the evolution and spatial distribution patterns of the geomorphologic types of the Ryukyu T-A-BA system are controlled mainly by tectonic move-ments.The tectonic geomorphologic characteristics of the Ryukyu Arc(RA) differ distinctly from those of the East China Sea(ECS) continental shelf and slope.In term of geological structures,RA consists of the Tokara volcanic ridge,the Ryukyu folded ridge,the fore-arc accre-tion-wedge ridge and the Amami Depression and the fore-arc depressions between the ridges,which is com-posed of a complex of alternating island-slope ridges and fault basins.The slope of the ECS is a passive continental margin with stepwise faults.The Okinawa Trough (OT)is a backarc rift in which tectonic movements are inten-sive,with active volcanic and hydrothermjal eruptions and sea floor spreading.The development of geomorphic features of the OT is controlled by the central en echelon spreading axes,the faults along the ECS slope and the marginal faults to the west of the Tokara vol-canic ridge.The geomorphic complex of the OT is ar-ranged in the following pattern:the en echelon grabens and volcanic chains formed by rifting and spreading lie in the central part of the trough,the turbidite plains inclining eastwards-southeastwards from the slope foot of the ECS lie in the western-northwestern parts of the OT,and the volcaniclastic deposit plains inclining westward-northwestwards from the western slope foot of the RA lie in the eastern-southeastern parts of the OT. In term of tectonic geomorphology,the OT forms a natural division between the shelf of the ECS and the RA.展开更多
Multiple magnetic parameters were measured for nine different grain-sized fractions separated from the sediment samples that are representatives of four different sedimentary environments of the Okinawa Trough. Based ...Multiple magnetic parameters were measured for nine different grain-sized fractions separated from the sediment samples that are representatives of four different sedimentary environments of the Okinawa Trough. Based on the measured results, the contributions of different grain-sized particles to total magnetic susceptibility of bulk sediments, the magnetic mineral assemblage and magnetic domain state as well as their relationships to sedimentary environment were discussed. Our research shows that the magnetic mineral is dominated by magnetite with a small amount of hematite and is primarily in pseudo-single-domain state. That indicates that the different sedimentary environ- ments in the Okinawa Trough have certain correlation in material provenance. The magnetic minerals enrich in dif- ferent grain-sized particles in response to different sedimen- tary environments. The contribution of the grain sizes from coarse to fine to coarse and fine to the magnetic susceptibility from the west to the east is in accordance with terrigenous material transportation from continental shelf of the East China Sea to the Okinawa Trough. It also shows difference in magnetic properties as a result of some environmental fac- tors.展开更多
文摘Based on an analysis of full-cover multi-beam bathymetric data,seismic and sub-bottom profiling data,and other geological-geophysical data sets,the geomorphologic features of the Ryukyu trench-arc-backarc(T-A-BA)system are delineated,and a geomorphologic map of the system is compiled.The re-sults show that the evolution and spatial distribution patterns of the geomorphologic types of the Ryukyu T-A-BA system are controlled mainly by tectonic move-ments.The tectonic geomorphologic characteristics of the Ryukyu Arc(RA) differ distinctly from those of the East China Sea(ECS) continental shelf and slope.In term of geological structures,RA consists of the Tokara volcanic ridge,the Ryukyu folded ridge,the fore-arc accre-tion-wedge ridge and the Amami Depression and the fore-arc depressions between the ridges,which is com-posed of a complex of alternating island-slope ridges and fault basins.The slope of the ECS is a passive continental margin with stepwise faults.The Okinawa Trough (OT)is a backarc rift in which tectonic movements are inten-sive,with active volcanic and hydrothermjal eruptions and sea floor spreading.The development of geomorphic features of the OT is controlled by the central en echelon spreading axes,the faults along the ECS slope and the marginal faults to the west of the Tokara vol-canic ridge.The geomorphic complex of the OT is ar-ranged in the following pattern:the en echelon grabens and volcanic chains formed by rifting and spreading lie in the central part of the trough,the turbidite plains inclining eastwards-southeastwards from the slope foot of the ECS lie in the western-northwestern parts of the OT,and the volcaniclastic deposit plains inclining westward-northwestwards from the western slope foot of the RA lie in the eastern-southeastern parts of the OT. In term of tectonic geomorphology,the OT forms a natural division between the shelf of the ECS and the RA.
基金supported by the National Natural Science Foundation of China(Grant No.40076019).
文摘Multiple magnetic parameters were measured for nine different grain-sized fractions separated from the sediment samples that are representatives of four different sedimentary environments of the Okinawa Trough. Based on the measured results, the contributions of different grain-sized particles to total magnetic susceptibility of bulk sediments, the magnetic mineral assemblage and magnetic domain state as well as their relationships to sedimentary environment were discussed. Our research shows that the magnetic mineral is dominated by magnetite with a small amount of hematite and is primarily in pseudo-single-domain state. That indicates that the different sedimentary environ- ments in the Okinawa Trough have certain correlation in material provenance. The magnetic minerals enrich in dif- ferent grain-sized particles in response to different sedimen- tary environments. The contribution of the grain sizes from coarse to fine to coarse and fine to the magnetic susceptibility from the west to the east is in accordance with terrigenous material transportation from continental shelf of the East China Sea to the Okinawa Trough. It also shows difference in magnetic properties as a result of some environmental fac- tors.
