新生代南海區域盆地發展與地體構造之關係
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2015
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南海為一主要的大陸邊緣海，位於三大板塊(歐亞大陸、印澳板塊、太平洋板塊)交界處，自新生代以來，構造環境與演化進程複雜。塊體的相對運動帶動了此區多樣性的構造事件，包含了擠壓、張裂、錯動等，對南海周圍一系列的沉積盆地演化有相當程度的影響。為了探討塊體運動與沉積盆地之相關性，我們統整文獻中火成岩之時空分佈及盆地中震測剖面與構造形態等資料，將此區盆地演化以不整合面為界，分為同張裂作用(syn-rift)與後張裂作用(post-rift)。並利用Gplates軟體結合此區之地體構造：主要是印支地塊脫逸作用與南海海盆張裂等兩構造事件，以確立盆地演化之分期與大構造演化史，重建整個南海地區新生代(~60Ｍa)以來的發展。並根據重建結果，以內差法運算南海臨近地塊每隔2Ｍa之相對運動速度及角度之變化。結果顯示，中沙、禮樂灘原屬華南地塊，自古新世至始新世以來（60~30 Ma），華南陸緣伴隨西太平洋隱沒向東南後撤加上古南海往東南隱沒之拉力開始拉張剪薄，形成一系列雙峰火山岩。而中沙、禮樂灘亦由靜止狀態開始穩定向東南加速移動（0 mm/yr~50 mm/yr），初始以西北-東南拉張方向為主，並於南海西北及東南區形成一系列東北西南走向沉積盆地。此拉張事件一直持續到南海海盆打開（30 Ma），張裂速度開始持續減慢至16 Ma停止，而南海西北及東南區之盆地也相繼進入後張裂時期。南海西南區之盆地多有平移斷層通過，但盆地初始張裂皆較斷層滑移來的早，並以東-西及西北-東南向張裂為主，顯示印度與歐亞大陸的擠壓碰撞及古南海隱沒拉力為此區之主應力來源。由於塊體內部受應力後相對的滑移作用，造成此區各盆地演化差異大，不整合面的時空分佈較無區域性的統一，而盆地先後的反轉作用則與印支地塊向東南的脫逸作用較為相關。
South China Sea is a continental margin sea in Western Pacific that located in three plates boundaries including Eurasia, India and Pacific plates made this region evolving very complex. The relative motion of blocks drive divergent tectonic events happen here which includes collision, extension, strike slip and so on that affect the sedimentary basins evolving in South China Sea region. In order to realize the relation between motion of blocks and the development of basins, we collected the magmatism in space-time and the seismic profile and history of each basins form the previous studies, then use Gplates program to correlate the plates tectonics together and reconstruct the evolution of South China Sea region during Cenozoic time. The basins here can divide into two periods, which are syn-rift and post-rift by breakup unconformity in stable. According to the previous studies, the Indochina extrusion and the opening of SCS are two main tectonic events that result in strong deformation in Cenozoic so we use Gplates to calculate the relative velocity change of blocks motion per 2 Ma. We calculated India, Indochina via Eurasia, Malaya via Indochina and MB, Reed bank via Eurasia to associate the 2D tectonic motion and the basins evolution also the time. The result showed that South China margin formed series of bimodal volcanic rocks result in MB, RB, which are the members of South China originally drifted SE ward stably while continental stretching during Paleocene to Eocene. It also evolved some basins around NW and SE South China Sea today suffering NE-SW rifting stress that related to the West Pacific Ocean Plate subduction rollback and pulling from Proto-SCS subduction SE ward. The seafloor spreading began on 30 Ma, and then MB and RB drifting slowed down until 16 Ma when the spreading stopped. The basins here formed breakup unconformity during the seafloor spreading and went into the post-rift period. The basins in SW South China Sea have strike slip fault zones cut trough normally but actually all the basins formed earlier than the faults slide that suffered E-W to NW-SE rifting at beginning. The stress maybe came from the collision of India and Eurasia and the subduction of proto-SCS. Because the relative strike slip within blocks after collision, the basins here developed differently and also the time of unconformity has no similarity in the same region. The invertions of basins in late stages were more related to the Indochina extrusion. According to the velocity of blocks relative motion, we can correlate tectonic setting with the evolution of basins easier and faster.
South China Sea is a continental margin sea in Western Pacific that located in three plates boundaries including Eurasia, India and Pacific plates made this region evolving very complex. The relative motion of blocks drive divergent tectonic events happen here which includes collision, extension, strike slip and so on that affect the sedimentary basins evolving in South China Sea region. In order to realize the relation between motion of blocks and the development of basins, we collected the magmatism in space-time and the seismic profile and history of each basins form the previous studies, then use Gplates program to correlate the plates tectonics together and reconstruct the evolution of South China Sea region during Cenozoic time. The basins here can divide into two periods, which are syn-rift and post-rift by breakup unconformity in stable. According to the previous studies, the Indochina extrusion and the opening of SCS are two main tectonic events that result in strong deformation in Cenozoic so we use Gplates to calculate the relative velocity change of blocks motion per 2 Ma. We calculated India, Indochina via Eurasia, Malaya via Indochina and MB, Reed bank via Eurasia to associate the 2D tectonic motion and the basins evolution also the time. The result showed that South China margin formed series of bimodal volcanic rocks result in MB, RB, which are the members of South China originally drifted SE ward stably while continental stretching during Paleocene to Eocene. It also evolved some basins around NW and SE South China Sea today suffering NE-SW rifting stress that related to the West Pacific Ocean Plate subduction rollback and pulling from Proto-SCS subduction SE ward. The seafloor spreading began on 30 Ma, and then MB and RB drifting slowed down until 16 Ma when the spreading stopped. The basins here formed breakup unconformity during the seafloor spreading and went into the post-rift period. The basins in SW South China Sea have strike slip fault zones cut trough normally but actually all the basins formed earlier than the faults slide that suffered E-W to NW-SE rifting at beginning. The stress maybe came from the collision of India and Eurasia and the subduction of proto-SCS. Because the relative strike slip within blocks after collision, the basins here developed differently and also the time of unconformity has no similarity in the same region. The invertions of basins in late stages were more related to the Indochina extrusion. According to the velocity of blocks relative motion, we can correlate tectonic setting with the evolution of basins easier and faster.
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南海, 盆地, 不整合面, Gplates軟體, 相對速度, South China Sea (SCS), basins, unconformity, Gplates program, relative velocity