Morphological characteristics in the area off eastern Taiwan Island and their tectonic implications

On the basis of bathymetric data and other geological and geophysical data obtained during the first survey conducted by Chinese Mainland in the area off eastern Taiwan Island from May to June in 2000, the morphological features of the region, the tectonic control to the seafloor topography and their tectonic implication are studied and discussed. The results have revealed that both the slope zone of the Ryukyu arc and the Ryukyu Trench present a typical morphotectonic characteristics controlled by the trench-arc system in the West Pacific Ocean. At the slope of eastern Taiwan Island the isobathic lines parallel to the coastline and distribute densely in nearly N-S direction and the slope gradient of topography is large. Such a unique feature is attributed to the collision of the Luzon arc and Eurasia continent. In the Huatung Basin, turbidity fans and submarine canyons are well developed, the formations of which are mainly related to the steep topography of the slope of the Luzon arc and the abundant supply of sediments. These submarine canyons are controlled by basement highs and strike-slip faults. On eastern side and western side of the Gagua Ridge, both the water depth and morphological features are different, but the basement of Gagua Ridge belongs to the Huatung Basin. The eastern side of the Gagua Ridge (123°12' E) corresponds to the boundary of two plates with different ages. In the West Philippine Basin, linear ridges and troughs in a NW trending are identified, which are dissected by a NE trending transform fault. According to the seafloor topography features, the direction of the transform fault and the magnetic anomaly lineations, the seafloor of this region was formed during 60-45 Ma B.P when the West Philippine Basin was spreading along NE-SW relative to the present orientation.

Characteristics of seismostratigraphy and analysis of structurallithofacies in the southern Yellow Sea Cenozoic basin

In this paper,the upper structural layer of the southern Yellow Sea Basin (SYSB) is further divided into three layers based on the latest obtained high-resolution single-channel seismic profiles.Combined with the borehole data,the characteristics and evolvement of structure and environment since middle-late Tertiary are discussed.The study shows that the acoustic-base indicated by shallow seismic profiles represents the basic shape of the SYSB in late Oligocene-early Miocene.Based on the comprehensive analysis of some typical profiles crossing the basin about seismostratigraphy,gravity and magnetics,the basin about seismostratigraphy,gravity and magnetics,the basin edge fault and some basin inner structure are identified.Furthermore,the acoustic-base is classified into four types of basal lithofacies:Eogene basin basement,Paleozoic basement,Mesozoic basement and magma intrusion basement.

Tectonic geomorphology of the Ryukyu Trench-Arc-Backarc System:geological-geophysical exploration and mapping

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.