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標題: | 越南西北部奠邊府斷層之新期構造運動及其大地構造隱示 Kinematics of the Dien Bien Phu fault, northwest Vietnam: Implications for the neotectonics of northern Indochina |
作者: | Kuang-Yin Lai 賴光胤 |
指導教授: | 陳于高 |
關鍵字: | 奠邊府,新期構造,構造地形,中南半島,旋轉地塊, Dien Bien Phu,neotectonics,tectonic geomorphology,Indochina,block rotation, |
出版年 : | 2010 |
學位: | 博士 |
摘要: | 奠邊府(Dien Bien Phu)斷層帶在越南西北部以右移的方式截切了馬河(Song Ma)縫合帶,以及古生代與中生代的地層,為中南半島上最引人關注的斷層之一。雖然奠邊府斷層因其頻繁的地震活動,已長期被視為中南半島上重要的新期活動構造,但對其斷層運動機制的瞭解仍相當缺乏。本研究於越南西北部奠邊府斷層帶的範圍內,利用地形圖、航空照片、ASTER衛星影像與野外調查,嘗試繪製現今的活動構造分佈,期能更瞭解奠邊府斷層在區域構造上所扮演的新期構造運動的角色,並探究其在晚新生代中南半島北部的構造演化中的意義與隱示。
現今活動的奠邊府斷層,包括了數個主要的躍階(step over)與斷層分支,且以左移運動為主。沿著斷層可觀測到許多因斷層運動而錯移的河流,藉由回復河流形貌,奠邊府斷層大約已左移12.5公里。而區域大地應力的轉變顯示左移的奠邊府斷層約在5 Ma時開始運動,因此從上新世至今,奠邊府斷層的平均滑移速率約為每年2.5公釐。另有數個不同機制形成的盆地分佈在斷層沿線,其中位於斷層南段最大的奠邊府盆地是由成長斷層(growth fault)發育的半地塹所造成,顯示斷層南段有明顯的伸張分量。根據結合中國南部與越南西北部的全球定位系統(GPS)資料,跨越奠邊府斷層每年約有2至3公釐的左移位移量,顯示構造應力確從每年有著10公釐左移的鮮水河(Xianshuihe)小江(Xiaojiang)斷層往南傳至奠邊府斷層,但滑移速率卻突然降低。同時位於奠邊府斷層西側的中南半島北部區域卻呈現更重要的東西方向伸張,暗示中南半島北部可能有著廣佈的內部變形。本研究結果認為,奠邊府斷層是一個再度活動的斷層,但其運動方向與前期活動相反。基於斷層所處位置與幾何型態,奠邊府斷層扮演中南半島北部地殼變形的東側邊界,而中南半島北部廣佈的內部變形則是東喜馬拉雅山結(Eastern Himalaya Syntaxis)外圍,沿著鮮水河小江斷層順時針旋轉的地塊的構造應力穿過紅河(Red River)斷層所造成。 The north- to northeast-trending Dien Bien Phu fault (DBPF) zone is one of the most conspicuous fault systems in Indochina, extending over a distance of 150 km from Yunnan, China through northwest Vietnam into Laos, and dextrally displaces the northwest-trending Song Ma suture, and Mesozoic and Paleozoic strata, acting a great geological discontinuity. Detailed mapping, compiled from topographic maps, stereographic aerial photos, ASTER satellite imageries, and field reconnaissance, along the DBPF reveals information about the fault geometry, the slip magnitude and distribution along the fault, and the relationship between river offset and fault activity. The geometry of the modern DBPF is complex, consisting of step overs and strands, and is currently dominated by left-lateral strike-slip displacement. Numerous multiple offsets along the fault can be detected and reconstructed, and the largest sinistral displacement on the DBPF is ca. 12.5 km. Since sinistral motion is likely to have initiated around 5 Ma, the most probable Pliocene to present average slip rate on the DBPF is on the order of 2.5 mm/yr. There are several basins developed along the fault zone resulted from different kinematics. The largest basin, Dien Bien Phu basin, developed by a half graben with growth fault and growth strata indicates the extensional component of displacement in the southern part of the fault. Based on the combined Global Positioning System velocity fields observed from northwest Vietnam and south China, about 2 to 3 mm/yr left-lateral slip is measured across the DBPF, indicating the left-lateral slip rate of ~10 mm/yr of the Xianshuihe-Xiaojang fault (XSHF-XJF) has been transferred to DBPF but with an abrupt decrease in magnitude. Furthermore, the northern Indochina located at the western side of DBPF represents more significant east-west extension, implying the non-rigid behavior with internal deformation. Results of this study suggest that the modern DBPF zone performs as a reactivated fault, yet different slip sense from its previous phase, and plays a role as an eastern boundary of the crustal deformation in northern Indochina. However, the present-day kinematics in northern Indochina may be dominated by east-west extension and be accommodated by internal distributed deformation different from the crustal fragment defined by XSHF-XJF zone with a clockwise rotation around the Eastern Himalayan Syntaxis. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/45961 |
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