複層岩層褶皺行為初探

Abstract

褶皺（fold）是指岩石的面狀構造（如層面、葉理）受到力的作用而呈現彎曲型態的地質構造。褶皺的型態千姿百態，且規模差別也極大，小至手標本或顯微鏡下的微型褶皺，大至衛星影像的區域性褶皺。由於岩層在形成褶皺過程中，常隨著褶皺作用的進行而伴隨產生一些其他種類的小型地質構造，這些小型的地質構造紀錄當時岩石力學性質與其所處的環境狀態。因此，褶皺的研究對於揭示一個地區的岩層分佈的影響及地質構造形成歷史的了解，具有重要意義。基本上，在台灣，西部麓山帶都為波長較長的褶皺。在雪山山脈與中央山脈地區的板岩帶的露頭，則可見到波長長短不一，各型各樣的褶皺。更東邊的中央山脈變質岩帶中，褶皺的波長更短。故台灣為一個非常適合研究褶皺構造的場所。研究以單層岩層褶皺力學基礎為出發，根據前人所提出的單層岩層褶皺理論解，以ABQUS建立複層岩層褶皺的模型。影響單層褶皺生成的主控因子為岩層厚度及阻抗比，而影響複層褶皺生成的主控因子則多了介質厚度。故以有限元素法分析結果，對複層褶皺的力學機制做初探，藉以了解介質與岩層之間互制的關係，並由數值分析的結果推導複層褶皺之理論解。複層褶皺為一套強弱岩層（弱岩層在本研究稱介質）相間組成的褶皺系統；由複層褶皺的幾何型態，可將其分為協調褶皺（harmonic folds）：各褶皺面彎曲的型態一致，其間沒有明顯不協調的突變現象；不協調褶皺（disharmonic folds）：各褶皺面的彎曲型態彼此有明顯的不同，上下不一致；複協調褶皺（polyharmonic folds）：各褶皺面的彎曲型態彼此有明顯的不同，但其間較小規模褶皺的包絡面的型態卻與較大規模褶皺的型態一致。研究的成果為：. 介質反力公式的推導以及數值解驗證. 以力平衡法推導存在夾層介質之複層褶皺理論解。. 以力平衡法推導夾層介質厚度極小的情況下，複層褶皺理論解推導與數值解驗證。. 複層褶皺的主控因子（材料性質、斷面性質及夾層介質厚度）對褶皺波長的影響。. 應用複層褶皺的主控因子對褶皺的影響，對三種野外常見的複層褶皺（協調褶皺、不協調褶皺、複協調褶皺）進行數值模擬。上成果對於複層褶皺之力學機制提供一個完整的說明。

Folds occur on all scales from the microscopic to the regional. Buckling is defined as the flexing or folding of a surface or series of parallel surface by a compressive stress directed along that surface or layer. Surfaces, either primary, such as bedding, or tectonically induced, such as cleavage, are common features in many rocks and are often buckled during formation. During the formation of folds, it usually accompanies with other small scale geological structure. These features record the property of rock mechanics and geological conditions. Therefore, It is significant to understand the influence of layers in a region and the history of geological structure by folds research.he primary factors forming multilayer folds are thickness of layer, competence ratio and thickness of matrix between layers. A general discussion of the reasons for the great variation in folded multilayered rocks is initialed by considering the way that folds in single layers can interact with each other to produce disharmonic, harmonic or polyharmonic association. So, the classifications of multilayer folds are 1) disharmonic fold: each layer would have its own characteristic wavelength depending upon its thickness and layer-matrix competence contrast. 2) harmonic fold: despite differences in thickness and mechanical properties of individual layers, all the layers have buckled with the same wavelength and amplitude. 3) two competent layers are of markedly differing thickness or show markedly different competent-incompetent layer ductility contrasts each competent layer is likely to induce its own characteristic wavelength in to the overall fold pattern. his research is based on theoretical solution of single layer. And, it uses the finite element method, ABAQUS, to simulate the formation of multilayer folds. Besides, we compare the numerical solution with the theoretical solution deriving by this study.he primary results of the study are:. the formula derivation of matrix reaction and verification of numerical simulation.. derivation the theoretical solution of multilayer fold with matrix between layers by force equilibrium method.. derivation the theoretical solution of multilayer fold with extreme thin matrix between layers by force equilibrium method.. the influence of facts (material property, section property, and matrix thickness) to multilayer fold wavelength.. numerical simulation of disharmonic fold, harmonic fold, and poly-harmonic fold.