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Title: | 東台灣火山碎屑岩內變形條帶之岩性控制模式 Lithological control on occurrences of deformation band in pyroclastic rocks of eastern Taiwan |
Authors: | Chih-Cheng Chung 鍾智承 |
Advisor: | 盧佳遇 |
Keyword: | 變形條帶,岩性控制,孔隙率,弧陸碰撞, Deformation Bands,Lithological control,Porosity,Arc-continental collision, |
Publication Year : | 2017 |
Degree: | 碩士 |
Abstract: | 變形條帶係形成於近地表多孔隙岩石的板狀脆韌性應變集中構造,能提供斷層在多孔隙岩石中初始發育之資訊並記錄近地表的構造變形歷史。由於變形條帶造成岩石的孔隙率及滲透率降低,因此對於地下水及石油天然氣的流動常有顯著的影響。然而前人研究之變形條帶大多形成於石英砂岩內,少有針對不同岩性中變形條帶的探討。石梯坪地區的變形條帶則提供瞭解火山碎屑岩中變形條帶發育的重要資訊。
石梯坪地區位於海岸山脈中段東側,即呂宋島弧之弧後。海岸山脈地層皆因菲律賓海板塊及歐亞板塊的擠壓而變形。石梯坪地區由成層的火山碎屑岩組成,出露大量變形條帶。依其運動學模式可分為四大類,其發育順序依序為純壓密型條帶(Type 1)、逆衝及背衝壓密剪切型條帶(Type 2)、走向滑移壓密剪切型(Type 3)及正向滑移型(Type 4)。條帶與地層位態的關係顯示褶皺發育前至褶皺後期皆有變形條帶發育。變形條帶及地層位態皆顯示最大主應力方向大致呈東西向,方位角090-100之間。本研究區域的變形條帶以走向滑移的壓密剪切碎裂型變形條帶(Type 3)發育最為廣泛。根據孔隙率變化計算之變形機制分析顯示即便是碎裂型變形條帶,顆粒流作用所導致的孔隙率降低量至少佔63.47%,碎裂化作用最多僅佔36.53%,顯示變形主要以顆粒流作用為主。此外,本研究結合野外量測所得的變形條帶滑移量側向變化及變形條帶在不同地層中的密度分布計算石梯坪地區不同塊體所累積的角應變。計算結果顯示石梯坪單面山區域僅累積0.20度順時針角應變,南單面山區域僅累積1.88度逆時針角應變,南段區域則累積13.05度逆時針角應變。 另一方面本研究整合變形條帶滑移量、厚度、寬度、密度與圍岩的孔隙率、平均粒徑、淘選係數、平均顆粒破裂應力提出岩性控制模式。研究結果顯示變形條帶的發育密度與地層的平均顆粒破裂應力及孔隙率呈正相關,與平均粒徑及淘選係數呈現負相關。此一結果顯示細粒高孔隙率、高平均顆粒破裂應力及低淘選係數之火山碎屑岩可能更容易受到變形條帶的影響而降低滲透率。 由於受到應變分配效應的影響,地層中變形條帶密度與地層中的條帶最大滑移量、最大厚度及最大寬度呈現負相關。另一方面,條帶的最大厚度也與地層的淘選係數及地層平均粒徑呈現正相關,顯示變形條帶的厚度除了受平均粒徑影響,其最大厚度或許也受到地層內最大粒徑所控制,進而使得高淘選係數地層內之條帶厚度增加。此外,變形條帶的最大厚度與平均顆粒破裂應力呈負相關,顯示在應變分配效應的影響下,高平均顆粒破裂應力地層的條帶密度高,進而使得最大寬度下降。 石梯坪地區的變形條帶具有蝕變現象,條帶內部由長石等礦物碎屑及蝕變產物所組成。蝕變之產物根據電子顯微鏡搭配EDS的觀察結果,發現其成分中矽、鈣、鈉的濃度降低,鋁和鐵則相對富集。此一現象也顯示變形條帶發育破裂時連接原先並不相連的孔隙,使變形條帶成為地下水流動的管道,而地下水在流動的過程中將鈉、鉀、鈣等成分溶解帶離變形條帶,留下相對難溶的元素。顯示在條帶形成過程中曾經是流體流動之管道,而條帶發育末期之斷層亦能扮演流體流動管道之角色。若要瞭解條帶對於地下流體流動之影響應結合條帶位態、發育階段、條帶厚度及密度的因素,並非單純仰賴條帶孔隙率及滲透率的降低即可完整解釋其對流場變化的影響。 Deformation bands are tabular strain localization structures occurring in highly porous rocks. They document progressive deformation, including formation of faults, in porous rocks at near-surface levels. Due to the reduction of porosity and permeability, deformation bands affect the flow of hydrocarbon and groundwater. While most studied deformation bands are in sandstones, their exceptional development is found in a pyroclastics locality in eastern Taiwan which help us understand their development in pyroclastic rocks. The outcrop area, Shitiping, is in the central part of the Coastal Range, the accreted Luzon Arc resulted from South China Sea subduction. Rocks of the Coastal Range including Shitiping were deformed by the active convergence between the Philippines Sea and Eurasian plates. Geology of the Shitiping area consists of layered pyroclastics of mostly tuffaceous sandstone and welded tuff lithologies, and folds and fractures are common. Base on the kinematics, we classified deformation bands in Shitiping into pure compaction band(type 1), thrust and back-thrust type compactional shear band(type 2), strike-slip compactional shear band(type 3) and normal sense shear band(type 4). Altitude relationships with bedding suggest these bands formed pre- or post-folding. All these bands shows that the maximum principle stress axes trend between 090-100. The deformation bands are mostly dextral or sinistral shear compaction bands, and are cataclastic; pure compaction bands, which are disaggregation band, are only found in layers with porosity higher than 30%. Analysis of porosity change between cataclasis band and disaggregation band shows that granular flow has the minimum reduction of porosity for 63.47% of the total reduction of cataclasis bands, indicating that granular flow is the main mechanism of porosity reduction. Combining band density and offset data, we calculate the angular shear of Shitiping area and find that cuesta and southern cuesta accumulate angular shear 0.20 degree clockwisely and 1.88 degree anti-clockwisely while southern part has angular shear 13.08 degree anti-clockwisely. We documented the altitude, deformation style, density, length, offset, and microstructure of the deformation bands as well as the porosity, grain size, sorting coefficient, and the derived mean grain crushing pressure of their host layers. The density of deformation bands seems to be positively related to the mean grain crushing pressure and porosity, and inversely proportional to average grain size and sorting coefficient of host pyroclastic layer. These results imply that permeability in fine-grained pyroclastic rocks with high porosity are more prone to be affected by deformation bands than in coarse-grained rocks. Due to the effect of strain allocation, the band density is negatively correlated to maximum displacement, thickness and width of deformation band. On the other side, maximum thickness of deformation band is positively correlated to sorting coefficient and average grain size of host rock, implying that the maximum band thickness might be controlled by maximum grain size of layers. Besides, maximum band thickness is negatively correlated to mean grain crushing pressure, indicating that strain allocation also plays a role in affecting the relationship between maximum band thickness and mean grain crushing pressure. Crystals in bands are usually highly altered, depleted in Si, Ca, Na and rich in Al and Fe, which may imply that these bands were conduit of underground flow along bands preventing across-band flows. This result shows that in order to understand the effect of deformation bands on underground flow, band altitude, band evolution stages, band thickness and density should be considered. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/67478 |
DOI: | 10.6342/NTU201702333 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 地質科學系 |
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