前人研究指出，南海北部應為大陸地殼拉張（Continental Rifting）的構造環境。然而，由於過去大多數的震測測線多集中於南海的最北部區域，尤其對於在大陸邊緣附近的筆架海山區域幾無資料，因而對於南海北部由大陸地殼拉張至海洋地殼生成的過程還不清楚。本研究分析2019年，使用國家實驗研究院台灣海洋科技研究中心勵進研究船蒐集一筆470公里長的長支距多頻道震測資料，搭配舊有的震測資料整合分析，以探討南海東北部大陸邊緣的震測地層與構造演化。 本研究整合震測地層，計算地殼的拉張係數，並挑選筆架海山區域盆地進行地層反剝法分析。其結果顯示，南海北部大陸邊緣大規模的火成事件發生在約23百萬年前的漸新世時期至早中新世時期，該火成事件亦使得筆架海山附近基盤抬升，推測應為海洋地殼拉張後的張裂後期火成事件，另一期的火成事件發生在上新世至更新世時期，區域較集中僅發生在東沙隆起周邊地區。另外，研究區域的地殼拉張係數大致上呈現北低（約1.1）南高（約3.75）趨勢，最靠近大陸海洋交界帶區域，地殼厚度還有約八公里厚，而區域地殼厚度呈現有如串腸構造（boudinage）的特徵，表示南海在大陸地殼拉張階段應屬於多中心盆地拉張特徵，但有由北往南遷移的特性，因此我們推測南海北部大陸地殼遭完全拉斷（break up）應是在短時間之內完成。 ;It is suggested that the northern South China Sea (SCS) passive continental margin is a 300 kilometers wide rifted margin. Previous seismic reflection/refraction studies focused on northernmost margin whereas tectonics and rifted history of the continental oceanic transition in particular to Bijia seamount area is still unclear. In this study, we collected a 470 kilometer long offset multi-channel seismic data across whole northern SCS margin by using Taiwan Ocean Research Institute (TORI) seismic system. Integrated seismic stratigraphy analyses on a new seismic profile and previous studies were performed to build up a tectonic evolution since early Miocene to present. Based on results from seismic stratigraphy analyses, stretching factor deamination and back stripping of Bijia Seamount area, a major volcanic event occurred at early Miocene which is covered whole continental margin. This event also developed Bijia seamount uplift. After major event, a later minor volcanic event developed adjacent to Dongsha island at Pliocene. Besides, the stretching factors (beta) increases from north (~1.1) to south (~3.75) seaward in general whereas a 8 kilometer thick crust still remains just close to continental and oceanic boundary (COB). The seismic structures also show plenty of crustal-scale boudinage rifted basins during continental rifting period of the northern SCS which is different from typical Atlantic type continental margin. Therefore, we suggested there are rifted jump events in the northern SCS from north to south connect to a very short period continental breakup in prior to early staged oceanic crust creation.
