臺灣西南部車瓜林斷層之斷層岩石及變形機制;Fault rocks and deformation mechanism of the Chegualin active fault in SW Taiwan

NCUIR > College of Earth Sciences > Graduate Institute of Applied Geology > Electronic Thesis & Dissertation > Item 987654321/93653

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/93653

Title:	臺灣西南部車瓜林斷層之斷層岩石及變形機制;Fault rocks and deformation mechanism of the Chegualin active fault in SW Taiwan
Authors:	莊承家;Jhuang, Cheng-Jia
Contributors:	應用地質研究所
Keywords:	車瓜林斷層;微組構;礦物組成;非晶質材料;變形機制;Chegualin fault;Microstructures;Mineral assemblage;Amorphous materials;Deformation mechanism
Date:	2023-02-01
Issue Date:	2024-09-19 17:24:36 (UTC+8)
Publisher:	國立中央大學
Abstract:	車瓜林斷層於2021年被地調所歸類為第一類活動斷層，斷層跡主要分布在厚層泥岩所組成的古亭坑層中;多種大地測量皆顯示車瓜林斷層有持續性的潛移活動，對斷層跡通過處的建築產生結構變形及破壞。泥岩區容易受沖刷侵蝕影響使地形快速改變，斷層跡的分布無法利用地形明顯觀察，而過往的野外調查發現斷層作用可使泥岩產狀發生改變並出露於露頭。本研究基於陳新翰(2021)對車瓜林斷層所進行中視尺度觀察的發現，¬斷層岩內具有數公厘到一、兩公分寬的應變集中產物的黑色條帶，在其研究的斷層露頭及斷層岩心中採取圍岩及斷層岩樣本並利用微組構觀察、礦物組成分析及同步X光繞射，探討車瓜林斷層的變形機制。微組構觀察顯示斷層岩內具有S-C構造;黑色條帶內部礦物顆粒產生破碎、變形，片狀礦物及礦物顆粒長軸沿黑色條帶方向產生順向排列，黏土礦物沿S、C、C’面產生順向性排列，石英粒徑在黑色條帶中產生粒徑削減，顯示黑色條帶為岩體中的變形帶，主要透過摩擦滑動(fricitional sliding)並伴隨碎裂作用(cataclasis)產生，因此黑色條帶的寬度及密度可作為斷層岩變形程度的指標。全岩礦物組成分析顯示，在變形程度較高的斷層岩中黏土礦物的含量也相對較高，而伊萊石結晶度反倒較差。黏土礦物組成分析顯示斷層帶內有岩水反應發生;圍岩及斷層岩的EI值變化不明顯，顯示斷層帶內並沒有透過礦物相變所產生的伊萊石;而伊萊石在全岩中的結晶度降低表示伊萊石受到顆粒細化影響使結構產生缺陷。同步X光分析指出黑色條帶內有非晶質材料的存在，根據微組構及前人對非晶質材料形成機制的研究，本研究認為黑色條帶中的非晶質材料在斷層作用下透過碎屑細化產生，而黏土礦物在細化轉變為非晶質材料時脫水，使斷層帶內產生流體並引發岩水反應，而岩水反應可以將石英溶解消耗使黏土礦物相對含量增加，也能與非晶質材料反應生成膨潤石。斷層岩中的S-C構造發育及黏土礦物含量相對增加都會造成岩體摩擦係數降低，因此斷層作用的變形主要集中在黑色破碎泥岩出現的位置。而非晶質材料在斷層帶的存在顯示斷層作用引發的非晶質化正持續發生，可能與大地測量所揭示車瓜林斷層的潛移活動有關。 ;The Chegualin fault (CGLF) has been acknowledged as an active fault by the Central Geological Survey since 2021. The fault trace of CGLF mainly appeared in the Gutingkeng formation, which is mainly composed of thickly bedded mudstone. Onsite geodetic measurements suggested that the CGFL has continuous creeping movement. The movement caused damage to the infrastructures straddling the fault trace. But evidence of the fault trace like fault scarps are rarely preserved due to the rapid change of the topography caused by surface erosion in the mudstone region. Through field investigation in the areas which show high surface displacement velocity gradients revealed by geodetic monitoring. Previous research found out that the occurrence of the mudstone in the area was different from others and concluded that the occurrence difference was caused by the faulting of CGLF. Therefore, this research is based on the finding derived from the mesoscale observations by Chen (2021) that black bands with a thickness ranging from several mm to 1 or 2 cm , which is a product of strain localization, appear in argillaceous Chegualin fault rocks. Wall rock and fault rock samples were collected from the same fault outcrop and rock core as Chen (2021). Microscopic observations, mineral assemblage analysis and synchrotron XRD on these samples were performed to obtain understanding of the deformation mechanism of the CGLF. The microscopic observations show that S-C fabric occur in fault rocks and mineral grains are fractured, deformed and forming preferred orientation in the black bands. Within the black bands, clay minerals alignment along S, C and C’ shear surface and the grain size reduction of quartz are observed. These evidence suggests that the black bands are mainly formed by frictional sliding accompanied by cataclasis and serve as deformation bands within the rocks. The density of black bands within the fault rocks can indicate how severe they were deformed. The whole rock mineral assemblage analysis indicates that the content of clay minerals increase and the crystallinity of illite decreases with the increase of deformation intensity of the rock. The clay mineral assemblage analysis indicates that the fluid-rock interaction occurred within the fault zone. Comparing the EI (Esquevin-indices) of illite in between wall rocks and black fault rocks, we inferred that the smectite-illite transition did not occur within the fault zone. Therefore the decrease of illite crystallinity may result from the generation of defects in the lattices of illite during grain size reduction. The synchrotron XRD analysis indicates that black bands contain amorphous materials. Based on the result of the aforementioned observations and the previous research about the formation of amorphous materials, we interpreted that the amorphous materials in the black bands were formed through comminution of clasts during the faulting. The fluid-rock interaction occurs since the dehydration of clay minerals during comminution. The grinded minerals rich in mobile elements are dissolved and consumed which let the clay minerals preserved and increase relatively, also the fluid can react with amorphous materials forming smectite. The forming of the S-C fabric and the increasing content of the clay minerals will weaken the rock strength by reducing the frictional coefficient are documented by experiment test. Therefore we inferred that the deformation caused by the faulting is accommodated by the fault zone of CGLF but mainly localized in the position where black fractured mudstone distributed, forming distributed deformation. The presence of amorphous materials in the fault zone suggests the ongoing amorphization caused by the recent faulting of the CGLF, implicated that the forming of amorphous materials may be related to the creeping movement of the CGLF.
Appears in Collections:	[Graduate Institute of Applied Geology] Electronic Thesis & Dissertation

Files in This Item:

File	Description	Size	Format
index.html		0Kb	HTML	16	View/Open

社群 sharing

Loading...