南海被動大陸邊緣位於臺灣西南方海域，與台灣碰撞帶西半部的歐亞板塊相連，有類似的大地構造演化史和地殼性質。早古近紀時期大陸地殼開始形成裂谷，海洋地殼在漸新世時以南北向擴張形成西北次海盆與東次海盆。早中新世時期古中洋脊向西南延伸，在洋脊跳躍（Ridge Jump）後擴張方向轉為西北—東南向，形成西南次海盆。過去研究多著重微大陸的岩石圈分布如何影響中洋脊擴展方向。然而同時，臺灣島西北部與南海被動大陸邊緣皆發現與公館期年代相近的火成岩，廣泛分佈的岩漿作用如何影響海洋地殼演化則未詳細分析。本研究遂希望研究南沙群島周圍的大陸—海洋地殼過渡帶（COT）的岩漿分布，探討西南次海盆海底擴張初期的岩漿活動，如何影響南沙群島周圍海域的地殼構造。本研究使用多頻道反射震測（MCS）和重力資料，挑選五條經過疊前時間移位（PSTM）的長、短支距震測剖面，提供了淺部盆地主要的地層邊界。另外利用全球布蓋重力異常反演和長支距震測剖面得到的莫荷面深度結果，建立二維重力模型，比較模擬與重力異常觀測值的差異，進一步推測地殼密度構造。震測剖面顯示張裂後期，太平島東邊測線在大陸—海洋地殼過渡帶中高振幅且高傾角的反射訊號，對應重力模擬的高密度體結果，顯示為沉積盆地底部之岩漿作用。然而位於此測線西側約40公里的震測剖面則未見此特徵，顯示岩漿噴發的範圍有限。南沙群島全區域的重力模擬顯示部分的大陸地殼密度獲得比觀測值低的重力值，暗示大陸地殼並非均質，可能存在岩漿底侵作用形成的高密度體。本研究因此推測西南次海盆擴張時的岩漿系統，從下部地殼的底侵作用沿著中南—禮樂斷層，可連接到淺部地殼的火成岩體。並從殘餘深度異常中，此事件影響海洋地殼初期具有高熱流，隨後逐漸降低。此短暫岩漿活動可能導致微大陸塊的岩石圈強度減弱，使中洋脊能完整往西南方向擴展。

Rifting of the South China Sea Margin began in the Early Paleogene, and N-S oriented seafloor spreading took place during the Oligocene, generating the Northwest and East Sub-basins. In the Early Miocene, southwestward propagation of the paleo-spreading ridge reoriented the spreading direction to a NW–SE trend, forming the Southwest Sub-basin.
The mechanism of the ridge jump is mostly discussed in their thermo-mechanical modelling to focus on the microcontinent distribution; However, the involvement of magmatic activity is still not fully understood, nor is its influence during the breakup process of the Southwest Sub-basin. This study, therefore, characterizes syn-breakup magmatism by geophysical approaches within the Continent–Ocean transition (COT) surrounding the Spratly Islands to assess how early spreading of the Southwest Sub-basin influenced crustal architecture.
Five pre-stack time migration MCS profiles further enhanced imaging of lateral stratigraphic architectures. The Moho surface in the South China Sea was derived from global Bouguer anomaly data and a long-offset seismic profile, integrated into a 2D forward gravity model with other stratigraphic interfaces.
The seismic profile and gravity simulation results indicate a late-rifting extrusive rock in the COT along the Zhongnan-Liyue fault. On the other hand, the gravity simulations of the five survey lines show similar trends in certain areas. Overestimated anomalies on the oceanic crust near the COT are attributed to lithospheric heterogeneities produced by hydrothermal alteration. And the homogeneous continental-crust density is insufficient to fit the observed anomalies, implying a heterogeneous crust locally modified by high-density magmatic additions in the lower crust. We infer that these high-density bodies represent lower-crustal underplating linked to shallow-level intrusions, constituting the magmatic plumbing system active during Southwest Sub-basin opening. Their proximity to the Zhongnan–Liyue fault tentatively suggests the fault served as a conduit for magma ascent, weakened the lithosphere, and facilitated the development of the Southwest Sub-basin spreading ridge.

中文文獻
邱寧、姚永堅、張江陽、王利節、徐東海。南海東南部邊緣地殼結構特徵及其構造意義。地球物理學報，第62卷，第7期，第2607-2621頁。2019年。
郭建、邱學林、李子正、黃海波。南沙地塊 OBS2019-2 測線數據處理與震向識別。熱帶海洋學報，第41卷，第5期，第43-46頁。2022年。
程子華、丁巍偉、董崇志、方銀霞、唐勇。南海南部地殼的重力模擬及伸展模式探討。高校地質學報，第20卷，第2期，第239-248頁。2014年。

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