台灣海岸山脈最南端利吉混同層構造演化;Structural Evolution of Lichi Melange in Southern tip of the Coastal Range, Taiwan

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題名:	台灣海岸山脈最南端利吉混同層構造演化;Structural Evolution of Lichi Melange in Southern tip of the Coastal Range, Taiwan
作者:	龐麒修;Pang, Chi-Hsiu
貢獻者:	地球科學學系
關鍵詞:	海岸山脈最南端;利吉混同層;古應力分析;岩象分析;構造演化;Southern tip of Coastal Range;Lichi Mélange;Paleostress Analysis;Petrographic Analysis;Structural Evolution
日期:	2019-01-10
上傳時間:	2019-04-02 15:27:49 (UTC+8)
出版者:	國立中央大學
摘要:	台灣東部為歐亞大陸板塊和菲律賓海板塊碰撞隱沒的交界。而在台灣東部海岸山脈西南緣出露特別的地質構造單元—利吉混同層(Lichi Mélange)，它為台灣弧陸碰撞下的產物，記錄了整個弧陸碰撞的歷史以及弧前盆地關閉的過程。根據前人在海岸山脈中南段利吉混同層內的野外調查以及古應力研究，利吉混同層應來自受到強烈剪切作用的下部弧前盆地地層，且最大主應力軸有兩個主要的方向，ㄧ是平行於板塊聚合的方向（方位角335°），另一為垂直於火山島弧的構造線型（方位角315°）。然而在海岸山脈最南端出露大範圍的利吉混同層的古應力研究資料卻相當稀少，此區域東側無火山島弧的推擠，而上陸的火山島弧出露在此區域北側，與海岸山脈中南段利吉混同層之於火山島弧的關係明顯不同。並且在此區域出露眾多外來岩塊如富岡砂岩，因火山島弧位置和外來砂岩塊等等因素使得此區域內的應力十分複雜。為瞭解海岸山脈最南端的古應力以及此處大範圍利吉混同層出露的原因，本研究以野外調查、應力分析及岩象分析進行研究。結果指出，海岸山脈最南端的西側的應力軸方向由北至南，從西北-東南向至轉向東北-西南向，而在其東之伽溪流域利吉混同層內的應力軸方向主要為南北向，此應力軸的轉變可能與火山島弧的相對位置變化有關。另外在伽溪流域內外來岩塊所造成古應力影響無特定方向，可能與外來岩塊和利吉混同層接觸位態不同有關。透過野外調查的結果，在伽溪流域內發育有許多背衝斷層的構造，可能為此區域大範圍利吉混同層出露的原因。;Taiwan is the junction of Eurasia Plate (EU) and Philippine Sea Plate (PSP). On the southwestern edge of the Coastal Range, eastern Taiwan, outcrops a special geological unit, Lichi Mélange. It’s the remaining product of the Taiwan arc-continental collision. It records the history of the entire arc-continental collision during the closure of the Luzon forearc basin. According to previous field investigations and paleostress studies of Lichi Mélange in the central part and southern part of the Coastal Range, the Lichi Mélange should originate from lower part of the forearc basin sequence with intensive shearing; the maximum principal stress axis has two main directions: one is parallel to the direction of plate motion of PSP (azimuth 335°), and the other is perpendicular to the structural lineation of the volcanic island arc (azimuth 315°). However, paleostress data is sparse in the southern tip of the Coastal Range, where Lichi Mélange outcrops extensively. There is no arc body buttressing on the eastern side of the mélange, and the onshore accreted arc is exposed north of the area, a different relationship between the Lichi Mélange and the volcanic arc than observed in the central to southern Coastal Range. Furthermore, there outcrop vast numbers of exotic blocks, including the Fukang Sandstone, in the southernmost tip of the Coastal Range. The stress regime in this area may be complicated due to the relative location of the arc body and the presence of exotic blocks. To understand the structural evolution of Lichi Mélange in this area, field observations, paleostress analysis and petrographic analysis are applied. The results show that the paleostress axis from north to south in the west side of the southern tip of the Coastal Range changed from northwest-southeast to northeast-southwest direction, and the paleostress axis in the Jia river drainage to the east is mainly north-south direction; such transformation of the paleostress direction may be related to the change in the relative position of the arc body. In addition, influences from presence of exotic blocks seem generally controlled by the contact geometry with the mélange matric. Numerous backthrust structures are documented through field investigations in the Jia river drainage, and may be the mechanism for extensive Lichi Mélange exposures in this area.
顯示於類別:	[地球物理研究所] 博碩士論文

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