台灣西南外海之構造與地形特徵及澎湖海底峽谷演化

Structures, physiography and development of the Penghu submarine canyon off southwest Taiwan

陳冠宇(Gang-Yu Chen)

指導教授 ： 林殿順

國立中央大學/地球科學學院/地球物理研究所/碩士(2006年)

摘要

本研究分析台灣西南外海的多頻道反射震測資料與海底地形特徵，利用地形構造特徵將研究區域分成三區，分別為：南中國海大陸斜坡區、前段增積岩體區及中段增積岩體區。變形前緣由東北-西南走向，往南轉為南北向並沿構造前緣發展。褶皺與逆衝斷層之構造線由原本的北北東走向往南轉為北北西走向，且轉折後出露海床面之逆斷層數量驟減。推測因弧陸的斜向碰撞以及向東南傾之南中國海大陸斜坡，造成增積岩體北段所承受應力較南段大，因此北段以出露逆斷層為主，並使得構造線之走向逐漸平行南海大陸斜坡。南段則以盲斷層所產生之背斜構造為主。結合構造型態以及震測相，研究區域可分成五大類的震測相，分別為：大陸斜坡相、水道侵蝕相、褶皺相、出露逆斷層相及盆地相。
本研究分析位於南中國海大陸斜坡以及增積岩體上各主要水道的縱向梯度剖面。研究結果指出南海斜坡區的水道剖面呈下凹曲線且往增積岩體方向坡度越陡。另外，震測資料顯示南海大陸斜坡區上部(淺於2000公尺)為侵蝕環境；斜坡下部(深於2000公尺)則為堆積環境。在增積岩體內主要的沉積區位於斜坡盆地，大部分的地區受構造抬升造成小規模的侵蝕。增積岩體區主要的侵蝕區位於澎湖與高屏海底峽谷的流域。
澎湖海底峽谷的縱剖面梯度則較平緩且梯度受活動構造抬升影響呈區段性變化。最後，利用增積岩體內構構造活動的發育時期，可將澎湖海底峽谷的流域演化分成四個時期，各期的水道流域為活動構造抬升與濁流下切侵蝕所造成的結果。

關鍵字

震測 ； 澎湖海底峽谷

並列摘要

Structures, physiography and development of the Penghu submarine Canyon off southwest Taiwan
Abstract
A seismic study was carried out on a dense grid of multi-channel seismic data off SW Taiwan. The study area can be divided into three geological domains on the basis of its structural and topographic characteristics: the South China Sea (SCS) continent -al slope domain, the frontal and Middle segments of the accretionary prism.
The deformation front and strikes of folds and thrusts trend in an NE-SW direction in the north and turn into an N-S direction toward the south whilst the numbers of emergent thrusts decrease. This feature may result from the oblique arc-continent collision. We divided five topographic and tectono-seismic facies on the basis of seafloor topography, structure types and seismic facies in the study area. They are continental-slope facies、submarine canyon erosion facies, fold facies, emergent thrust facies and basin facies, respectively. Seismic data shows upper slope of SCS (shallower 2000 m) is an erosive environment and the lower slope (deeper 2000 m) is an area of deposition. In acctetionary prism, the main depozone is in the slope basin whereas the tectonic ridges exhibit minor erosion. Zones of major erosion lie in the drainage areas of Penghu and Kaoping Canyons In accretionary prism, the main depozone is in slope basin (or piggyback basin).The structure uplift resulted in small-scale erosion in most region. The main erosion zone is in drainage of Peng-Hu and Kao-Ping canyon.
A series of longitudinal channel profiles in the SCS slope and accretionary prism was analyzed to reveal the interaction among tectonic development, sedimentation and erosion. We analyzed the main submarine canyon longitude section of SCS continental. In SCS continental slope, the channel profile resembles that of an exponential curve. The gradient of individual channel profile becomes greater as the channel approaches deformation front.
The gradient of Peng-Hu submarine canyon is gentle. The gradient has various Channel gradient of the Penghu submarine canyon, which lies in the acctetionary prism, is gentler then that in the SCS slope. The Penghu channel profile shows several step-like nickpoints corresponding to structural uplift. Finally, development of the Penghu can be divided into four stages by analyzing the timing of movement for individual structures and seismic facies.

並列關鍵字

Taiwan ； Penghu submarine canyon

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