弧陆碰撞背景下沉积物轴向与横向搬运转换*

板块俯冲碰撞拼合带是盆山相互作用最为强烈的地区,发育有弧前、弧间及弧后多种类型的盆地,沉积物的剥蚀搬运作用极为活跃。证据显示,沉积物搬运充填过程在构造—古地理控制型盆地中具有一定的演变规律,伴随盆地演化,沉积物轴向搬运与横向搬运呈此消彼长的互动关系。南海南北两侧均发育了大型板块俯冲拼合带及相关的沉积盆地,在盆地发育早期沉积物沿盆地长轴方向分别形成昆莺琼古河和巽他古河,以轴向搬运的方式分别把越南中部及马来半岛沉积物由西向东输送到南海,形成大型三角洲及前三角洲深水扇沉积,河流发育位置均在板块拼合转折地段。在盆地发育的成熟阶段,沉积物以横向搬运的方式进入盆地,与轴向搬运沉积物形成混合堆积。轴向搬运是洋陆碰撞拼合盆地中一种重要的沉积物搬运途径,主要受盆地形成时的构造古地理控制。

Mutual transformation between longitudinal and transverse transportation of sediments in arc-continental collision zone

Tectonic plates have been continually experiencing series of subduction, collision and merging processes along with the most drastic basin-mountain interaction within the converging zones. Various types of basins (e.g., fore-arc, intra-arc and back-arc basins) are formed in this area, where the erosion and transportation of sediments are very active. It is indicated that the transportation and infilling processes of sediments show certain evolution laws in the tectonic-palaeogeographic controlled basin. The transportation of sediments in the longitudinal and transverse directions show mutual restriction relations. The northern and southern South China Sea are characterized by extensive development of large-scale subduction-collision belts and the related sedimentary basins. Both Kontum-Ying-Qiong River and the paleo-Sunda River were initiated along the long axes of basins in the early stage of basin development. Large abundance of clastic materials delivered from the Central Vietnam and Malay Peninsula, respectively, were transported eastward to the South China Sea by the longitudinal transport current, causing the large river delta and deep-water fan delta structures. These types of river systems are exclusively found in the plate fragmentation zones. During the later stage, sediments were primarily transported by the transverse fluvial system in relatively mature basins and it formed the mixed stacking combined with the sediments from the longitudinal transportation. In the oceanic-continental plate collision basins, the longitudinal transportation is an important type of sediment transportation, which is mainly controlled by the tectonic-palaeogeographic settings during the formation of basins.