北呂宋島弧東側之構造特徵

Structural Characteristics Along the Eastern Flank of the Northern Luzon Arc

林聖心(Sheng-Hsin Lin)

指導教授 ： 劉家瑄

國立臺灣大學/理學院/海洋研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.02227

摘要

北呂宋火山島弧從呂宋島向北延伸，包括巴布煙島、巴丹、蘭嶼和綠島等火山島，其最北端的部分，因弧陸碰撞作用，現今已加積到台灣島之上形成海岸山脈，成為台灣島的一部份。以弧陸碰撞發展程度而言，北呂宋島弧在21°30’N以南為典型弧溝隱沒帶，在21°30’N到22°45’N之間為初始碰撞帶，而在22°45’N以北為碰撞成熟帶。本研究利用一系列切過北呂宋火山島弧的反射震測剖面，來探討北呂宋島弧由南到北、由典型的隱沒作用時期到弧陸碰撞成熟期的過程中，島弧東側的火成岩基盤和上覆沈積物之構造演化特徵。
在反射震測剖面的解釋方面，本研究利用在花東海盆辨識出的三個主要層序界面，觀察這些層序界面往北呂宋島弧區域延伸的變化情形，以對島弧及東側區域的沉積構造和演化做完整的描述。根據反射震測資料所顯示的結果，北呂宋島弧東側的地形、地貌和地質構造形貌依其受弧陸碰撞的時間先後不同可以大致分為三個區域，由南到北分別是典型隱沒帶、初始碰撞帶、碰撞成熟帶。
在典型隱沒帶，區域內的基盤和沈積物未見明顯受到構造活動的影響而呈現擾動的現象，沈積物整合的沈積在呂宋島弧和弧東海脊之間的斜坡盆地中，少部分的沈積物沈積在島弧的頂部平坦的區域。
在初始碰撞帶，北呂宋島弧和花東海盆之間的弧坡區有一明顯的南北走向朝東逆衝的斷層發育，斷層不僅切過花東海盆的沈積層，並向下延伸切過火成岩的基盤。此一斷層應是一個大尺度的逆衝斷層，推測是因島弧基盤和海盆基盤發生斷裂所形成。
在碰撞成熟帶，南北走向朝東逆衝的斷層繼續向北延伸，在22°45’N到23°N的區域，因北呂宋島弧開始加積到中央山脈東緣形成海岸山脈，使得在此區域有另一逆斷層的產生；而在23°30’N以北的弧坡區域，逆斷層轉為一系列分枝斷層的型式。
在沈積物的部分，沈積物多半在弧間斜坡盆地或弧坡處沈積，越往北邊、越靠近台灣造山帶，沈積物的厚度就越厚。在22°N以北的弧坡區域，許多的海底峽谷和深海塊體運動的特徵顯示出此區域為非常不穩定的沈積環境。

關鍵字

北呂宋島弧 ； 構造特徵 ； 反射震測 ； 台灣東部海域

並列摘要

Northern Luzon Arc extends northward from the Luzon Island to Taiwan, with Babuyan, Batan, Lanyu and Lutao volcanic islands in between. Its northernmost portion has accreted to the island of Taiwan and become the Coast Range of Taiwan by the arc-continent collision processes. In the framework of arc-continent collision, the area south of 21°30’ N is a typical subduction zone, the area between 21°30’ N and 22°45’ N is the incipient arc-continent collision zone, and the area north of 22°45’ N is a mature arc-continent collision zone. This study analyzes a series of seismic reflection profiles that cross the eastern flank of the northern Luzon Arc to image structural characteristics of the arc basement and overlying sediment from south to north, from the typical subduction zone to the mature arc-continent collision zone.
Three major sequence boundaries identified on the seismic profile, in the Huatung Basin are used to identify the degree of crustal deformation of the northern Luzon Arc eastern flank area. From seismic reflection profiles, the topography and geological structures along the eastern flank of the arc can be divided into three zones based on the degree of deformation. From south to north, they are the typical subduction zone, the incipient arc-continent collision zone, and the mature arc-continent collision zone.
In the typical subduction zone, the basement and sediments are little deformed. The sediments conformably deposited in the slope basin between the northern Luzon Arc and the East Ridge of Luzon Arc, and some sediments deposited on top of the arc.
In the incipient arc-continent collision zone, an N-S trending east vergent thrust fault has developed in arc-slope area between the northern Luzon Arc and the Huatung Basin. This thrust fault not only offsets the sequence boundaries in the Huatung Basin, but also extends downward to deform the volcanic basement. We speculate that this fault may separate the Luzon Arc basement from the Huatung basin basement.
In the mature arc-continent collision zone, the N-S trending east vergent thrust continues to extend northward. A thrust fault is observed in the area between 22°45’ N and 23°N where the northern Luzon Arc becomes the Coast Range of Taiwan Island. North of 23°30’ N, this thrust fault develops into a series of branch fault, which could be the result of Huatung basin basement gradually subducted beneath the Eurasian plate.
In the study area, sediments are mostly deposited in the intra-arc slope basins or in the arc-slope area. The sediment thickness increases northward and toward Taiwan orogenic belt. In the arc-slope area north of 23°30’ N, there are numerous submarine canyons and submarine mass movement features, indicating that this area is a very unstable depositional environment.

並列關鍵字

Northern Luzon Arc ； structural characteristics ； seismic reflection ； offshore eastern Taiwan

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