- 學位論文
臺灣中部眉溪砂岩及其兩側地層之伊萊石結晶度分析
Analysis on Illite Crystallinity of the Meichi Sandstone in the Middle Part of Hsuehshan Range, Taiwan
摘要
雪山山脈地層由低度變質的板岩和變質砂岩所組成，依水系分布以大漢溪與濁水溪為界，地層系統可分為北部、中部西側及中部東側。其中，中部西側白冷層與東側眉溪砂岩和達見砂岩，兩側在地層對比上一直爭議不斷。主要關鍵在於東側眉溪砂岩在地層系統中的層位問題，由於缺少可確認年代的指準化石，因此衍生出上覆脊樑山脈廬山層與下伏眉溪砂岩之間的接觸問題，即眉溪砂岩與廬山層之間有一斷層存在，或者是眉溪砂岩與廬山層之間為整合接觸。 本研究由北至南進行夫布爾溪、四季郎溪、大甲溪、人止關、武界和孫海林道之連續野外地質調查眉溪砂岩與西側佳陽層、東側廬山層的地質構造特性及其位態變化，以及岩石標本黏土礦物伊萊石結晶度與微組構之分析結果的變化趨勢。結合野外調查與室內分析結果藉以釐清三者之間的上下層序關係，以及所謂的梨山斷層存疑性。 研究成果顯示眉溪砂岩岩性於人止關及武界地區單層厚砂岩較多且厚度最厚。往南北兩側延伸單層厚砂岩比例變少，岩性改以砂岩與板岩互層為主，顯示眉溪砂岩側向延伸性佳。構造方面各剖面的眉溪砂岩岩層大致朝東傾斜，似乎並無構造存在。但於夫布爾溪、四季郎溪及大甲溪、人止關、武界區域可發現中視褶皺構造存在。伊萊石結晶度由北至南各剖面之伊萊石結晶度大致趨勢往南結晶度逐漸變佳，而西至東各剖面除了孫海林道結晶度逐漸變差外，其餘剖面眉溪砂岩之結晶度較差，往兩側結晶度逐漸變佳。此現象有可能是褶皺所造成的現象，而斷層造成的結晶度驟降僅在人止關眉溪砂岩東側出現。黏土礦物種類在各剖面的眉溪砂岩以伊萊石黏土礦物為主，其兩側地層的佳陽層及廬山層的高嶺土及綠泥石含量相對較多，且黏土礦物的伊萊石含量有逐漸向兩側板岩地層遞減的趨勢。 本研究指出眉溪砂岩由北至南延伸並無疑問，但部分位置受到褶皺及斷層的影響，導致厚度發生增厚的情形。而眉溪砂岩的上下地層關係應為下伏佳陽層，上覆為廬山層，三者之間為漸變的接觸關係，且眉溪砂岩與廬山層之間並無所謂的梨山斷層存在。
並列摘要
The stratigraphy of Hsuehshan Range is composed by low-grade slate and metasandstone. It is bordered by the Tahanchi at north and the Choshui River at south, and based on stratigraphic system it can be divided into northern, central western and central eastern parts, respectively. The stratigraphic relationship between Paileng Formation in the central western part and Meichi Sandstone, Tachien Sandstone in central eastern part of Hsueshan Range is still a controversial issue. Owing to lake of index fossils record in Meichi Sandstone, the contact of Meichi Sandstone (Hsueshan Range) and Lushan Formation (Backbone Range) becomes an open debate. In this study, the field characteristics and attitude variation of structural geology on Mechi Sandstone, western Chiayang Formation, eastern Lushan Formation in conjunction with clay minerals composition, illite crystallinity and microfabrics analysis from Fubuerchi, Shichilangchi, Tachiachi, Meichi, Wujie and Subhai logging road are conducted to clarify the sequence of three formations and the existence of Lishan fault. According to the lithological characters, the thickest Meichi Sandstone is located at Meichi and Wujie region and it composed by single-layered thick sandstone. Its lateral variation shows the number of single-layered thick sandstone proportionally decrease northward and southward and mainly composed by the interlayered sandstone and slate. Meichi Sandstone is roughly leaned eastward and without marked structure inside, but mesoscopic fold structures were found in Fubuerchi, Shichilangchi, Tachiachi, Meichi and Wujie regions. In the study area, from north to south, the illite crystallinity of Chiayang Formation, Meichi Sandstone and Lushan Formation all increases southward. Besides Sunhai logging road, all other west–east sections show best crystallinity in the Chiayang Formation (west side) and worst in the Meichi Sandstone. The Sunhai logging road section shows the crystallinity descending from west to east. All the facts imply the variation of crystallinity may caused by the folding process in study area and the abrupt descend of crystallinity which may cased by fault activity is only recognized at Meichi section between Meichi Sandstone and Lushan Formation. The clay minerals composition of Meichi Sandstone is dominate in illite and the kaolinite and chlorite are higher in Lushan and Chiayang Formations. According to all evidences, Meichi Sandstone is continuously extended from north to south, but probably can be affected by the fold and fault activities induced thickening at some locations in the study area. The contact relationship between Chiayang Formation, Meichi Sandstone and Lushan Formation should be conformable contact and there is no so-called “Lishan Fault” exists between Meichi Sandstone and Lushan Formation.