冲绳海槽沉积演化的时空特征

Spatio-temporal Characteristics of Depositional Evolution of the Okinawa Trough

冲绳海槽是晚中新世(9～6Ma)以来形成的与板块俯冲作用密切相关的弧后盆地。将冲绳海槽的沉积演化分成3个阶段:中新世晚期(9～6Ma)—上新世末期(2Ma)、上新世末期—晚更新世(130ka)、晚更新世—现在。研究分析表明,冲绳海槽北段发育最早(中新世晚期),但盆地演化程度最低;中段发育次之而演化程度高;南段发育晚(上新世末期)而演化程度高。现阶段的冲绳海槽,其北段处于衰退期,而中段和南段处于扩阔期。构造活动在盆地的演化中占主导作用,它首先为海槽相当长的地质时期内提供宏观的初始沉积格局,其次为盆地沉积提供部分沉积物质(火山物质和热液)。在构造活动强烈的时期,地壳拉伸对沉积层序的影响大于沉积作用,当构造活动趋于缓和时,相对海平面变化控制了盆地内部沉积结构的变化。

The Okinawa Trough (OT) is a back-arc basin related with the plate subduction since the late Miocene (9 to 6 Ma), and its depositional evolution can be divided into 3 stages, stage Ⅰ from the late Miocene (9 to 6 Ma) to the late Pliocene (2 Ma), stage Ⅱ from the late Pliocene (2 Ma) to the late Pleistocene (130 ka) and stage Ⅲ from the Pleistocene to the present. It is shown from the study results that the northern OT developed earlier in the late Miocence and has a low degree of depositional evolution, then the middle OT developed and has a high degree of depositional evolution, and the southern OT developed later in the late Pliocene and has a high degree of deposional evolution. At the present stage, the northern OT is in a decline phase, and the middle and southern OT is in a broadening phase. The tectonic activities play a leading role in the basin evolution because these activities built up the initial depositional framework of the basin in a geologic period of considerable length and provided some sediments (volcanic and hydrothermal materials) to the basin. During the intense tectonic activity period, the effect of crust extension on sedimentary sequence was greater than that of sedimentation, and during the weak tectonic activity period, the relative sea level changes controlled the variations in internal depositional structure of the basin.