南中國海位於歐亞大陸的東南邊緣，過去研究指出南海是印澳板塊向北碰撞歐亞大陸板塊所形成的拉張盆地。南海海洋地殼以呂宋─琉球轉形板塊邊界(LRTPB)為其最北界，南海北部地殼厚度，大致從西北到東南逐漸變薄，海洋地殼厚度為8到12公里，張裂後引起的火山活動是造成較厚的海洋地殼之原因。在大陸地殼與海洋地殼間，有個減薄大陸地殼帶(TCC)，此區不但基盤較低，且有較厚的沈積層，因而呈現低的磁力異常。本研究藉由處理分析磁力資料，進行二維及三維空間的磁性基盤及構造分析，來瞭解南海北部大陸邊緣的構造特性。 我們將新蒐集的磁力資料進行IGRF修正，得到磁力異常值，並與舊有的資料整編成北緯17度至24.5度，東經113度至122度之南海北部新的磁力異常圖。為了瞭解磁體的分布，我們用磁力異常逆推出等效磁化強度。另外 利用解析訊號及尤拉解迴旋法，對二維及三維空間進行磁力異常分析，藉此找到構造邊界處，並計算磁源深度及構造指標。 大陸邊緣有個東北─西南向的高解析訊號帶，它顯示構造邊界位置。構造邊界東邊為磁化低區，向東北延伸到台灣西南海域。尤拉解沿著磁化低區的邊緣分佈，為東北─西南向，在大陸邊緣的重力異常也呈現此走向，並且構造邊界及尤拉解大致落在重力異常較高處。構造邊界帶SB，從台灣西南海域沿著台南盆地、潮汕凹陷邊緣，向西南延伸到珠江口盆地內。台南盆地及潮汕凹陷可能因為有厚的沈積層存在，呈現低的磁化強度。尤拉解大致分佈在兩盆地的邊緣，顯示此區構造上的分界。另外在LRTPB以東的區域，可能因為沈積物太厚，沒有明顯的尤拉解分佈。 The South China Sea (SCS) is one of the marginal basins in western Pacific area. It may be a pull-apart basin which is relative to the collision between Indian Plate and Eurasian Plate. The northern extension of the SCS oceanic crust is terminated by Luzon-Ryukyu Transform Plate Boundary (LRTPB). The thicker SCS oceanic crust may be caused by post-spreading volcanism. There is thinning continental crust (TCC) zone between the continental crust and oceanic crust. In order to understand the crustal structures of the northern continental margin of SCS, we have analyzed the magnetic data in the area from 113°E to 122°E and 17°N to 24.5°N. We have performed a magnetization inversion to obtain the basement characters of the study area. We also used the analytic-signal method to determine the boundary of the structures. In addition, we have determined magnetic source locations, depths and structural types by Euler deconvolution method. As a result, there is a NE-SW trending high analytic-signal zone along the northern continental margin of SCS. The low magnetization zone is bordered in the east and the Euler solutions distribute along both sides of the low magnetization zone. The structural boundary zone SB is along the margin of Tainan Basin and finally extends into Pearl River Mouth Basin. The structural boundary zone SB and the Euler solutions distribute the area which slows the higher free-air gravity anomaly. The Tainan basin and the Chaoshan Depression generally reflect a low magnetization zone because the basement is overlain by thick sediment. The Euler solutions distribute along edges of the basins except for the northeast side of Luzon-Ryukyu Transform Plate Boundary (LRTPB).
