南海海盆三维重力约束反演莫霍面深度及其特征

利用南海海盆及周边最新的重力，经过海底地形、沉积层的重力效应改正，并采用岩石圈减薄模型的温度场公式，校正了从张裂边缘到扩张海盆的热扰动重力效应.通过研究区的地震剖面和少量声呐数据得到的莫霍面深度点作为约束，采用基于"起伏界面初始模型"的深度修正量反演迭代公式，反演、计算了研究区的莫霍面深度及地壳厚度.结果表明，海盆区莫霍面深度在8~14 km之间，地壳厚度在3~9 km之间；东部海盆和西南海盆残留扩张中心沿NNE向展布向西南延伸至112°E，莫霍面深度超过12 km，地壳厚度在6 km以上，而西北海盆没有明显的增厚扩张中心；在西南海盆北缘的中沙地块南侧，存在一个近EW向地壳减薄带，地壳厚度在9~10 km；莫霍面深度14 km的等深线和地壳厚度9 km的等值线可指示洋陆边界位置.

Moho depth of the South China Sea basin from three-dimensional gravity inversion with constraint points

We calculate the gravity anomalies due to lateral changes in bathymetry from an independent topography compilation and those due to changes in sediment thickness and density. To estimate the Moho depth and the crustal thickness of the South China Sea basin,the 3D gravity inversion method is employed, which is based on the "initial model of fluctuated interface" from the constraint points from seismic data and sonobuoys. And then, the gravity data is corrected by the lithosphere thermal gravity anomalies within the continental margin of thinned lithosphere. Over most of the South China Sea basin, the Moho depth ranges 8~14 km, the crustal thickness is 3~9 km. The NNE trending fossil spreading center of the East and the Southwest subbasins extend to 112°E, the Moho depth is more than 12 km, and the crustal thickness is over 6 km in the spreading center. However, the crust of the spreading center at the northwest basin is not obviously thickened. In the northern margin of the southwest basin, south of Zhongsha block, there is a crustal thinning belt, nearly EW trending, where crustal thickness is about 9~10 km. The 14 km isoline of the Moho depth and the 9 km isoline of the crustal thickness are very close to the continent-ocean boundary (COB), respectively.