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依据最新地震地质资料利用回剥法计算了南海北部深水区3条测线的构造沉降量.结果显示研究区不同于典型的被动陆缘盆地,虽然南海于32Ma开始扩张,但陆缘盆地的构造沉降速率此时没有减小反而增大,23Ma左右才显著减小,暗示裂陷作用一直持续到约23Ma才结束,地层厚度资料同样反映出这一现象,即裂陷期出现了延迟,热沉降开始时间滞后.认为形成该现象的机制可能有3个:(1)南海北部陆缘的岩石圈强度很弱,塑性相对较强,对南海扩张造成的应变衰减反应延迟;(2)岩石圈分层独立伸展的差异性可能也是导致裂后热沉降滞后的原因;(3)南海扩张脊在24~21Ma之间的向南跃迁及对应的海底扩张增速事件进一步诱发了研究区23Ma左右大规模裂后热沉降的开始.
Based on the latest seismic geological data, the tectonic subsidence of three lines in the northern South China Sea was calculated by the back-stripping method. The results show that the study area is different from the typical passive continental margin basin. Although the South China Sea began to expand at 32 Ma, The sedimentation rate did not decrease at this time but increased at about 23Ma, indicating a significant decrease until about 23Ma, indicating that the rifting continued until about 23Ma. The formation thickness data also reflects this phenomenon, namely, the delay in the rifting period and the heat sinking (1) The lithosphere strength of the northern margin of the South China Sea is weak and the plasticity is relatively strong, which delays the response of strain attenuation caused by the expansion of the South China Sea. (2) The lithospheric (3) Southward expansion of the ridge between 24 ~ 21Ma southward transition and the corresponding expansion and growth of the seabed further induced a large area of about 23Ma in the study area Post-crack heat sinking began.