Abstract The northeastern of the South China Sea (SCS) has undergone tectonic inversion from a Mesozoic convergent continental margin to a Cenozoic divergent continental margin. The remnant subduction-related structures, such as volcanic arc and forearc basin, likely preserve key clues to reveal the dynamic mechanism of this tectonic inversion. We applied ocean bottom seismometers (OBS) data, combining with multi-channel seismic data, gravity data, drilling data, and petrologic observations, to reveal geophysical and structural features of the Dongsha Basin, a Mesozoic basin in the northeastern SCS. The Mesozoic strata are characterized by large thickness (~1–8 km), relatively high P-wave velocities (3.5–5.5 km/s), high densities (2.55–2.65 g/cm3), alternating folds, and thrust faults, which are significantly different from the features of Cenozoic strata. The Dongsha Basin is flanked by a Mesozoic granitic arc to the northwest and an inferred Palaeo-Pacific subduction zone to the southeast, indicating that it is geographically located in the Mesozoic forearc region. Considering the similar Mesozoic strata detected in the southern margin of the SCS and the contemporaneous accretionary complex outcrops observed in the Palawan Continental Terrane, we propose that the Mesozoic strata in these two regions originated from a common Mesozoic forearc basin, which was broken by the forearc rifting and subsequently separated by the spreading of Cenozoic SCS. Accordingly, a continuous Palaeo-Pacific subduction system is reconstructed, including the “arc-forearc-accretionary wedge” tectonic sequences. Reviewing the mechanisms of forearc rifting globally and the retreat of volcanic arcs onshore South China, we speculate that rollback of the Palaeo-Pacific subduction slab might be one of the causes for the forearc rifting and the initial extension of the SCS.

中文翻译：

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南海东北部中生界残余前弧盆地的地震约束

摘要 南海东北部经历了中生代辐合陆缘向新生代辐散陆缘的构造反转。与俯冲相关的残余构造，如火山弧和弧前盆地，可能保留了揭示这种构造反转动力机制的关键线索。我们应用海底地震仪（OBS）数据，结合多道地震数据、重力数据、钻井数据和岩石学观测，揭示了南海东北部中生代盆地东沙盆地的地球物理和构造特征。中生界地层的特点是厚度大（~1-8 km）、相对较高的纵波速度（3.5-5.5 km/s）、高密度（2.55-2.65 g/cm3）、交替褶皱和逆冲断层，与新生代地层特征明显不同。东沙盆地西北侧为中生代花岗岩弧，东南侧为推测的古太平洋俯冲带，地理上位于中生代弧前区。考虑到在南海南部边缘发现的相似中生界地层和巴拉望大陆地块中观察到的同期增生杂岩露头，我们认为这两个地区的中生界地层起源于一个共同的中生界前弧盆地，该盆地被前弧断裂。裂谷，随后被新生代 SCS 的扩张分开。因此，重建了一个连续的古太平洋俯冲系统，包括“弧-前-弧-增生楔”构造序列。