Abstract To understand the crustal deformation of the Nansha Block (NB), this study presents an interpretation of a recently acquired multichannel seismic profile that traverses the Southwest Subbasin (SWSB), the NB, and the Nansha Trough (NT). A total of six Cenozoic unconformities and three stratigraphic sequences are identified. On the basis of tectonic, structural and stratigraphic features, the NB is divided from northwest to southeast into two structural domains, namely, the Hyper-stretched and Forebulge Domains. Based on the interpretation of the seismic profile, the fault-derived and whole crustal extension factors (βf and βc, respectively) for the NB are calculated. The calculation results show that βc is greater than βf in a limited space of appr. 200 km, where the crust underwent depth-dependent extension. We suggest that the crustal extensional pattern of the NB may be a combination of distal limited depth-dependent extension and proximal uniform extension. The interpretation of the unconformities is also used to calculated the fault-derived crustal extension at various stages. The two main extension stages, the syn-rift and syn-drift, account for appr. 70% and 25% of the total extension, respectively. A comparison with the seismic profiles of the eastern NB shows that the crustal extension along the continental margin of the NB is heterogeneous, with more significant crustal deformation on the west side of the NB. The heterogeneity of the crustal extension along the depth and margin may be related to the thermal condition and rheological structure of the crust or lithosphere.

中文翻译：

---

南海南沙地块地壳变形和运动演化的地震证据

摘要 为了了解南沙地块 (NB) 的地壳变形，本研究对最近获得的穿越西南子盆地 (SWSB)、NB 和南沙海槽 (NT) 的多道地震剖面进行了解释。总共确定了六个新生代不整合面和三个地层层序。根据构造、构造和地层特征，将NB由西北向东南划分为超张带和前隆带两个构造域。基于对地震剖面的解释，计算了 NB 的断层导出和整个地壳扩展因子（分别为 βf 和 βc）。计算结果表明，在有限空间内，βc 大于βf。200 公里，在那里地壳经历了依赖于深度的伸展。我们认为 NB 的地壳伸展模式可能是远端有限深度依赖伸展和近端均匀伸展的组合。对不整合面的解释也用于计算不同阶段断层衍生的地壳伸展。两个主要的扩展阶段，同步裂谷和同步漂移，占大约。分别占总扩展的 70% 和 25%。与NB东部地震剖面对比表明，沿NB大陆边缘的地壳伸展具有非均质性，NB西侧地壳变形更为显着。地壳沿深度和边缘伸展的非均质性可能与地壳或岩石圈的热条件和流变结构有关。