台灣西南海域含天然氣水合物地層之構造架構與沈積特徵; Structure and Sedimentary Characteristics of Gas Hydrate-Bearing Sediments off Southwest Taiwan

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题名:	台灣西南海域含天然氣水合物地層之構造架構與沈積特徵;Structure and Sedimentary Characteristics of Gas Hydrate-Bearing Sediments off Southwest Taiwan
作者:	林哲銓;Che-Chuan Lin
贡献者:	地球物理研究所
关键词:	天然氣水合物;增積岩體;沈積作用;逆衝斷層帶;褶皺;gas hydrates;thrust-and-fold;accretionary prism;sedimentation
日期:	2005-07-07
上传时间:	2009-09-22 09:55:34 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	台灣西南海域地體構造處於初期弧陸碰撞的階段，在變形前緣以東主要構造運動以褶皺、逆衝斷層與泥貫入體構造為主；變形前緣以西的大陸斜坡則以張裂作用為主。本研究分析了MCS647與MCS681兩批震測剖面，根據構造與沈積特徵，將研究區域劃分為：南中國海大陸斜坡區、褶皺區與逆衝斷層區。南中國海大陸斜坡區位於變形前緣至大陸坡折之間的區域，在本區西北方發育一主要鍬型生長正斷層。斷層將上盤地層產生旋轉，向陸棚方向傾斜，使深埋於陸棚下之上新統至更新統、以泥岩為主的地層，向斜坡延伸並被海床所截切。上部斜坡發育許多水下切蝕溝，顯示以侵蝕作用為主；下部斜坡則發育斜坡前端堆積，沈積過程以堆積作用為主。褶皺區介於逆斷層前緣到變形前緣之間，許多向西逆衝的盲斷層將地層抬升形成背斜。本區屬於澎湖海底峽谷的流域，由震測相顯示東半部受到水道侵蝕、沈積作用盛行，西半部則以半遠洋沈積物為主。逆斷層區介於出露逆斷層前緣到高屏峽谷之間，出露斷層以向西逆衝為主，亦有因盲斷層而形成的背斜構造。斷層上盤常發育斜坡盆地，沈積物可能為半遠洋沈積物或濁流堆積物。本區東部的高屏峽谷西岸常有濁流溢堤堆積物或改道遺跡。東北方的高雄峽谷在本區亦留下峽谷充填構造，可見本區東部的沈積作用主要受到高屏海底峽谷與高雄海底峽谷的影響。根據各構造之不整合面分析，發現構造發育年代大體上向西越來越年輕，顯示造山帶向西逐漸擴展。逆衝斷層區構造活動次數頻繁，褶皺區的構造活動次數由東向西逐漸減少。海底仿擬反射(BSR)指示天然氣水合物穩定基底之位置，分布以逆衝斷層區最為富集，在褶皺區的分布最零散。分布範圍約僅限於水深為600?1800公尺左右。研究區域的BSR深度與海床大致平行，並有隨著水深增加而BSR深度增加的趨勢。海床到BSR之厚度也與海床深度成正比，可知天然氣水合物在高壓環境下，可存在於較高的地溫。 A seismic interpretation study was carried out on a dense grid of multichannel seismic data off SW Taiwan. The study area can be divided into three geological domains on the basis of structure and sedimentary characteristics: the South China Sea (SCS) continental slope domain, the folded domain, and the thrusted domain. The folded and thrusted domains occupy the frontal accretionary prism. The SCS continental slope domain situates between the Taiwan Strait shelf break and the deformation front of the accretionary prism. There are many erosional gullies in the upper slope of this domain, manifesting an erosion dominant region. Beneath the upper slope, the strata are eroded and truncated at the seabed, exposing Pliocene-Pleistocene sediments that are deeply buried in the adjacent shelf. By contrast, in the lower slope, there has developed slope-front fills revealing a deposition dominant region. The region between the deformation front and the fringe of emergent thrusts is the folded domain. Several west-vergent blind thrusts have uplifted the strata and formed a series of anticlines. Seismic facies suggests that the western half of this region is dominated by hemipelagic sedimentation and the eastern half is dominated by the chanelling and deposition of the Penghu submarine canyon system. The thrusted domain lies in between the westernmost emergent thrusts and the Kaoping Canyon. Westward emergent thrusts and anticlines prevail in this area. On top of each thrust sheets, it has developed a slope basin. Seismic facies show that the sedimentation is governed by hemipelagic sediments and/or turbidite deposits. Sedimentation in the eastern half of this region is influenced by the Kaoping and Kaohsiung submarine canyons as evidenced by turbidite levee deposits, channel and canyon infills. In each thrust or anticline, there is an array of unconformities associated with the episodic development of the growing structures. An analysis of the timing for the development of these unconformities suggests that thrusts in the rear of the frontal prism occurred earlier (about 2.3Ma) than that in the region near the deformation front. Thrust activities were frequent in the thrust domain when compared to the folded domain. Bottom simulating reflectors(BSRs), marking the base of hydrate stability zone, exist in the region deeper than c.600m and are commonly observed in thrusted domain, whereas it is less commonly found in the folded domain. The sub-bottom depth of the BSRs increases with icreasing water depths, a characteristic which is governed by the phase diagram of hydrate stability.
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