南海海盆区深部结构的不对称性及控制因素

南海海盆区具有复杂的构造演化史，但目前对其深部结构的不对称性的研究和控制因素的探讨还存在不足.利用南海最新的重力数据和从27条地震剖面上获取的海盆范围沉积物精确数据计算了全海盆的剩余地幔布格重力异常（residual mantle Bouguer anomaly，RMBA），并反演了海盆的地壳厚度，运用Crust1.0数据进行了相关性分析.研究结果表明，南海海盆的残留扩张脊两翼在地形、RMBA和洋壳厚度上存在明显的不对称性，北翼比南翼有更多的海山分布、更低的RMBA值以及更厚的洋壳.这种明显的南北不对称性表明北侧比南侧有更高的地幔温度和更活跃的岩浆活动，反映了南海深部结构的不对称性.南海深部结构的不对称性可能与洋中脊向南的跃迁有关.洋脊跃迁导致在新老洋脊之间产生部分熔融，使扩张中心北侧产生更高的地幔温度，以及更强烈的岩浆活动，从而显示出更低的RMBA值和更厚的洋壳，并形成更多的后扩张期海山. 

Asymmetric Deep Structure of the South China Sea Basin and Its Controlling Factors

The South China Sea basin has a complex tectonic evolutionary history, but the study of the asymmetry of deep structure and the control factors are still inadequate. The residual mantle Bouguer anomaly (RMBA) of the whole basin is calculated by using the latest gravity data collected from the South China Sea and the accurate sediment data based on the explanation of 27 seismic profiles. The crustal thickness of the basin is inverted, and the correlation analysis is carried out by using Crust1.0 data.The results show that there is obvious asymmetry in topography, RMBA and crustal thickness on each side of South China Sea basin, the north side has more sea mountains, lower RMBA value and thicker oceanic crust than the southern side. This apparent north-south asymmetry indicates a higher mantle temperature and more active magmatic activity on the north side, reflecting the asymmetry of the deep structure of the South China Sea. The asymmetry of this deep structure may be related to the southern jumping of the mid-ocean ridge. The mid-ocean ridge jumping resulted in partial melting between the old and new ridges, leading to higher mantle temperatures on the north side of the expansion center, as well as stronger magmatic activity, which showed more negative RMBA values, thicker oceanic crustal thickness and more after-expansion seamounts.