TOPOGRAPHIC AND MORPHOLOGIC CHARACTERISTICS AND GENESIS ANALYSIS OF XISHA TROUGH SEA AREA IN THE SOUTH CHINA SEA
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摘要: 应用多波束测量资料绘制了详细的西沙海槽海域地形图、地貌图,并把研究区划分为3个地貌单元。其中陆坡斜坡位于北部,呈北东向延伸,地形较为简单,斜坡面单一平整,地貌类型单一,主要为堆积型斜坡;西沙海槽位于中部,呈北东东向延伸,地形起伏较大,主要由槽底平原和槽坡组成,且在槽坡上发育陡坎、冲刷沟谷、阶地等次一级地貌类型;西沙海台位于南部,呈近东西向展布,地形变化复杂,地貌类型众多,表现为海山、海丘、小台地、洼地等相间排列的波状起伏的地貌特征。地貌形成与演化主要受南海新生代两次海底扩张控制。第1次海底扩张期间,西沙海槽可能已开始发生张裂。第2次海底扩张期间,西沙海槽分3个阶段发生张裂断陷,而且其强弱在东西方向上差别巨大,致使形成了现今东深西浅、东窄西宽、槽壁陡峭的近东西向延伸的海槽地貌,奠定了研究区内地貌的基本轮廓。而地质构造、火山活动、海平面变化等内外营力的共同作用则控制次级地貌类型的形成与演化。Abstract: Detailed topography and geomorphology of Xisha Trough sea area were mapped with multibeam sounding survey data that were acquired by Guangzhou Marine Geological Survey since 1997. The study area can be divided into three geomorphic units. The northern unit is a slope of the continental slope, mainly formd by accumulation and extending to NE, and its topography is simple, the slope surface is smooth and its geomorphic type is single. The middle unit is Xisha Trough and extending to NNE, whose landform change is great. Xisha Trough consists of trough bottom plain and trough slopes that have some sub-order geomorphic units such as scarp, eroded canyon and terrace etc. The southern unit is Xisha plateau and extending near EW, whose landform changes greatly and geomorphic type is complex, with a lot of seamounts, seaknolls, mesa and depressions that are arranged alternatively. The two seafloor spreadings of the South China Sea controlled the origin and evolvement of geomorphic types of the study area. During the first seafloor spreading, Xisha Trough probably rifted. During the second seafloor spreading, Xisha Trough had three stages of rift-fault, and the intensity differed greatly between east and west parts, and consequently, the Xisha Trough has had the present geomorphology, deeper, narrower, steeper in the east part than in the west which reprensents the basic geomorphology of the study area. And collective effects of endogenetic and exogenic forces such as geologic structure, volcanic activity and sea level change controlled the origin and evolvement of the sub-order geomorphic types.
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Key words:
- topography /
- geomorphology /
- multibeam /
- Xisha Trough
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