中橫公路德基至梨山地區在地質分區上屬於台灣中央山脈第三紀板岩層，依據前人研究的成果，本地區多為一組遍布發達的板劈理，屬於軸面劈理，劈理位態約呈東北─西南走向，為高角度傾斜。在實際觀察本地區公路沿線之地質現象後，發現公路上分布有低角度傾斜的劈理位態，此與前人研究結果有所差異，遂引發本研究進行深入探討的動機。 岩石劈理位態的統計分析乃利用JTS32統計程式，將野外375個調查址的代表性劈理位態予以分析。統計結果顯示研究地區劈理有三群，其平均位態與標準差角分別為：第一群劈理N48°E/37°S±17°、第二群劈理N39°E/89°S±17°及第三群劈理N53°E/41°N±18°。 各群劈理與坡向、坡度的關連性分析，乃使用MapInfo地理資訊系統製作相關圖層及進行套疊分析，結果顯示第一群劈理及第三群與坡向、坡度的關連性密切。第一群劈理大多落在西北領域的坡向，第三群劈理則在東南領域坡向者出露最多，第一群劈理及第三群劈理在坡度較陡的第四級以上分布較多。第二群劈理在每個坡向均有相當比例的出露，與坡度的關連性並不明顯。 第二群劈理主要分布在河谷底部、河流兩岸新鮮岩盤上及山脊內側等較不易受邊坡作用影響的地區，具有廣泛分布的特性，與坡向及坡度較無關連性。第二群劈理位態與岩層褶皺軸面位態近似，判斷應是此區板岩層的軸面劈理。第一群及第三群劈理與坡向、坡度的關連性密切，劈理位態多落於與走向平行的坡向，且多分布在較陡的坡度，推論此兩群劈理位態皆偏離過。 研究地區岩石劈理位態的變化，並非構造上的褶皺作用，推論為高山地區大規模的邊坡潛移作用所造成。經由野外查證後發現研究地區劈理位態偏離的地區確有邊坡潛移現象，其特徵為劈理被折彎、節理被截切、潛移後岩層破碎及植物因潛移而向邊坡外傾生長等。 The study area is from Techi to Lishan in central Taiwan. It is belonging to the Tertiary Slate formation of the orogenic belt. According to previous research, there is only one penetrative slaty cleavage set which belongs to axial plane cleavage and bears NE-SW strike with steep dip angle in study area. We can discover some low-angle cleavage attitude at slopes near the highway in the field. This result is different to the attitude of axial plane cleavage, therefore it brought us the reason to do this study. In this study, we have measured 375 typical attitudes of cleavage in the field, and has used statistical analysis to find out the characteristics of cleavage attitude distribution. The result shows that the cleavage attitudes may be divided into three groups. Mean attitude of the first group is N48°E/37°S±17°, the second is N39°E/89°S±17°, and the third is N53°E/41°N±18°. We use MapInfo geographic information system to analyze the relationships between the cleavage attitude and the slope direction, and also the slope gradient. The result shows that the first and the third group of cleavage attitude have close relationship with the slope direction and slope gradient. In general, the cleavage attitude is striking roughly parallel to the hill slope. The first group of cleavage attitude is closely related to NW facing slopes. The third group of cleavage attitude is closely related to SE facing slopes. Both the first and the third group cleavage attitude are almost located at the steeply slopes. The cleavage attitude of the second group generally located at riverside of the Tachia Creek and its major tributaries. It has no relationship with the slope direction and also slope gradient. The second group of cleavage attitude is similar to be the attitude of the fold axial plane, and is regarded as the axial plane cleavage of the Slate formation in the study area. The change of the cleavage attitude is thought to be affected by large-scale hill creep in the high mountain area. Field check results reveal that cleavage attitude affected by hill creep really appear in the study area. Facts include bended cleavage, joint cut by cleavage, and bowed trees on the surface.
