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標題: | 台灣西南褶衝帶增積岩體泥貫入體變形構造分析 Structural Deformation of Mud Diapirs in the Accretionary Wedge-Fold and Thrust Belt Offshore and Onshore of Southwestern Taiwan |
作者: | Kuo-Ying Peng 彭國瑛 |
指導教授: | 李建成(Jian-Cheng Lee) |
關鍵字: | 泥貫入體,台灣西南部, Mud Diapir,Diapir,Southwestern Taiwan, |
出版年 : | 2021 |
學位: | 碩士 |
摘要: | 本研究探討台灣西南部增積岩體中泥貫入體的變形構造特徵,包括幾何形貌、形成機制、變形速率等,及泥貫入體上拱與板塊聚合擠壓褶皺變形的交互關係。台灣西南部位於歐亞板塊及菲律賓海板塊從隱沒到弧陸碰撞的構造過渡帶,遠洋及近海沉積物因隱沒及造山運動形成寬廣的增積岩體。富含流體的沉積物受到板塊聚合作用的擠壓,於增積岩體上形成一系列垂直於聚合方向且平行排列的泥貫入體。我們收集並分析了陸海不同的資料,包括野外調查、反射震測資料等,並綜合文獻研究的井測、重力、地殼變形測量等資料,建構新的陸上及海域的地質剖面。基於台灣西南部泥貫入體多伴隨著背斜褶皺構造及逆衝斷層,本研究嘗試分析探討這些背斜褶皺的形成機制,有多少比例是由泥貫入體上拱及上部地殼的擠壓所組成。 結合陸域及海域的背斜分布位置,可以顯示陸上的台南背斜與外海泥貫入體MD14是相連接的。利用海域三條震測剖面的地層分析,包括層面的進覆關係,本研究嘗試判斷沉積與褶皺的相對活躍程度。我們在深度兩公里範圍內,區分出這個背斜褶皺的五個生長演化時期,並利用近海海床沈積物10Be同位素定年分析獲得的沈積速率(0.625 mm/yr),計算出各個褶皺發展期活動的年代,由老而新分別為T1:182-123萬年(沉積<褶皺)、T2:123-87萬年(沉積≧褶皺)、T3:87-41萬年(沉積<褶皺)、T4:41-35萬年(沉積≧褶皺)、T5:35-11萬年(沉積<褶皺)。 本研究並由震測剖面判釋出的地層長度,估算構造水平擠壓所導致的褶皺變形程度(水平縮短量、垂直抬升量),進而計算泥貫入體作用造成的抬升量,並探討在五個褶皺演化發育時期中,泥貫入體抬升及構造水平擠壓何者為主要的變形作用。從我們的結果可以得知,T1-T5整體演化趨勢最早從水平擠壓開始,隨後泥貫入體抬升作用的比重逐漸增加,各個時期各有幾次在兩機制之間的小反轉,顯示擠壓與抬升兩種作用在數十萬年來褶皺長期持續發育過程中較勁,並互有領先,造成頻繁的傾向反轉現象。 由陸域水準資料可以得知現階段台南台地持續快速抬升中,其抬升速率約為10 mm/yr,比海域震測剖面180萬年來的長期平均抬升速率0.4 mm/yr多一個級距,顯示現今台南台地區域似乎是個褶皺快速變形的構造地區。另外由台南台地GPS測量近20年來平均的速度場資料,台南台地東翼為縮短的情況,我們認為台南台地東側後甲里斷層目前可能是活躍的。 野外地質調查,配合參考既有文獻資料,我們建構出台南至三地門地質剖面,了解深部泥貫入體形貌,輔以外海對於泥貫入體觀測的結果,我們認為此處泥貫入體的發育深度深於5公里。 綜合以上所述,我們可以知道台灣西南海陸域地區的台南台地及MD14,其背斜褶皺的抬升機制是由「泥貫入作用」和「構造擠壓」兩個主要機制共同參與的。伴隨著增積岩體整體的逆衝褶皺,從第四紀開始發育的生長褶皺,在發展過程中,兩種機制之間以不同比例組成,而且泥貫入作用有逐漸佔有更重要的比例和角色。 In this study, we investigate the deformation characters and mechanisms of a mud diapir in the accretionary wedge onland and offshore southwest Taiwan. The morphological and structural characters and deformation of this diapiric ridge are investigated to discuss the interaction between crustal shortening mechanism and diapiric uplifting mechanism and the roles they play during each of the development stage of this diapiric structure. Southwest Taiwan is situated in the transition zone from subduction to arc-continent collision between the Eurasian plate and Philippine Sea plate. Fold and fault structures are the main structural features in SW Taiwan formed by tectonic convergence. Thick sediments derived from the Taiwan mountain belt formed a wide accretionary wedge, and these sediments are rich in fluid which allow diapirs to form easily. Many diapirs developed into parallel ridges aligned perpendicular to the tectonic compression direction onland and offshore SW Taiwan. We use field data onland and seismic reflection profile data offshore, together with published well data, leveling data, GPS data and gravity data, to discuss the deformation mechanisms and development of this diapiric ridge. Previous studies reveal that the Tainan anticline onshore and diapir MD14 offshore are connected. Based on the stratigraphic relationship (e.g. onlap) of seismic sequences on 3 seismic profiles, we have identified five sedimentary sequences from seafloor down to 2 km below seafloor. Based on published sediment deposition rate of 0.625 mm/yr, the ages of these sequences from old to young are T1: 1820-1230 kyr (Dia.<Fold); T2: 1230-870 kyr (Dia.≧Fold); T3: 870-410 kyr (Dia.<Fold); T4: 410-350 kyr (Dia.≧Fold): T5: 350-110 kyr (Dia.<Fold). Dia. in parenthesis means dirpiric mechanism while Fold means fold mechanism. Which mechanism played more significant role in each of the diaper development stages are estimated by assuming that the Tainan anticline is a box fold so that we can separate the diapiric uplifting component and tectonic compression component by the amount of uplifting and shortening values. From T1 to T5, the contribution of diapirism seems getting larger. There are 1-2 times reversal on the contributions of these two mechanisms in each of the stages, indicating that changing deformation mechanisms between these two are common. The leveling data (2000-2010) show that the Tainan anticline has been uplifting by a rate of 10 mm/yr which is one order of magnitude larger than the 0.4 mm/yr uplifting rate calculated offshore. There could be another mechanism contributes to the high uplifting rate of the Tainan anticline, as GPS data (2002-2016) shows that there is a 5 mm/yr shortening at SE limb of the Tainan anticline, we consider that there is a trust fault developed in SE limb there. Our study shows that for the development of Tainan anticline-MD14, the deformation started by tectonic compression, then diapirism gradually increased its contribution to the deformation, but due to the active tectonism, compressional mechanism still plays an important role in crustal deformation. Moreover, other mechanisms such as thrust fault may cause deformation at shallow depth. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/69549 |
DOI: | 10.6342/NTU202100706 |
全文授權: | 有償授權 |
顯示於系所單位: | 海洋研究所 |
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