Role of the Ryukyu Arc towards the Taiwan orogeny

琉球西南部地区是了解弧形沟-弧-弧后体系对台湾造山作用的关键；以菲律宾海板块向欧亚板块俯冲的西北终止和吕宋弧向台湾的东北碰撞为观点。我们加入了TAIGER计划，并在TAIGER-2009 Leg2巡航期间，通过Marcus G.Langseth号R/V上的EM-122带状水深回声测深仪收集了该地区的新地形数据。我们还从JAMSTEC舰队巡航和NOAA/NGDC多波束数据库中收集了该地区所有可用的多波束测深数据。宫古岛和八山岛以南的琉球海沟地区被划分为地带性地形域。最北端的特征是沿南海岸分布着发育良好的海底峡谷。其次是圆形剧场、滑塌沉积物块体及其大规模沉降。南区地形十分复杂，有多处断崖、山脊、沟槽和一个东西向的半地堑。最南端为海沟轴区，深度约6500。6600米，其特点是平面平坦。八山群岛的轴向平原宽度约为40 km，呈现出向东向西最大和减小的趋势。然而，在加瓜岭碰撞的西侧（123°E），海沟的地形特征尚不清楚。利用多波束测深和ROV侦察技术对石垣岛东岸的一条跨弧正断层进行了研究。对数据的精确分析揭示了断层的幕式西北扩展，可能是由于冲绳海槽的裂谷引起的弧平行伸展。观测到的地形特征表明，在123°E的东侧，由于斜向俯冲，菲律宾海板块发生了俯冲回滚，海沟轴向南后退，与冲绳海槽西部的延伸相对应。然而，在东经123°西侧，华东盆地是否存在俯冲，目前尚不清楚。华东盆地可能与弧前、弧后地区形成耦合，并与台湾地块发生碰撞。在华东盆地北部弧前区下方可见明显的贝尼奥夫带。然而，这可能是由于西菲律宾盆地向西北斜俯冲欧亚板块所致。少

The southwestern Ryukyu area is the key to understanding the role of the arcuate-shaped trench-arc-backarc system towards the orogeny of Taiwan ; with the viewpoint of the northwestern termination of subduction of the Philippine Sea Plate against the Eurasian Plate and the consequent collision of the Luzon Arc against Taiwan from the northeastern side. We joined the TAIGER programme and collected the new topographic data in this area by EM-122 swath bathymetric echo sounder on board R/V Marcus G.Langseth during the TAIGER-2009 Leg2 cruise. We also compiled all the available multibeam bathymetric survey data in this area from JAMSTEC fleet cruises and NOAA/NGDC multibeam database.The Ryukyu Trench area south of Miyako and Yaeyama Islands is classified into zonal topographic domains. The northernmost zone is characterised by the distribution of well-developed submarine canyons along the southern coasts. The next is by amphitheatres, slump sediment blocks and their large-scale subsidence. … More The southern zone is by quite complicated topography, such as several escarpments, ridges and troughs and an E-W trending half graben. The southernmost zone is the trench axis area with depth of about 6500. 6600 m, which is characterised by a flat plane. The width of the axial plain is about 40 km of Yaeyama Islands which shows maximum and decreases towards both east and west. However, the topographic features of the trench is unclear on the western side of the Gagua Ridge collision(123°E).One of the across-arc normal faults located off the eastern coast of Ishigaki Island was already studied by multibeam sounding and ROV reconnaissance. Precise analyses of the data revealed an episodic northwestward propagation of the fault, probably due to the arc-parallel extension caused by the rifting of the Okinawa Trough.The observed topographic features suggest that the roll back of the subducting Phippine Sea Plate and the southward retreat of the trench axis is taking place on the eastern side of 123°E due to the oblique subduction, which corresponds to the extension of the western Okinawa Trough. However, on the western side of 123°E, it is unclear whether subduction of Huatung Basin is taking place. It may be possible that Huatung Basin couples with the fore-arc and back-arc areas and that these three areas altogether collides against the Taiwan block. Clear Benioff zone is observed below the fore-arc area on the north of Huatung Basin. However, this might be derived from the West Philippine Basin subducting northwestward obliquely against the Eurasia Plate. Less