The Relationship between Formation of Cleavage and Folding in Multilayer : A case study on an Anticline with Well-developed Cleavage in the Shihpachunghsi Formation , in Hsuehshan Range

• Main Authors: Ku, Yueh-ping, 古月萍
• Other Authors: Yang, Chao-Nan
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/02144745022385419592

碩士 === 國立臺灣大學 === 地質學研究所 === 88 === There appears a coexistent structure of well developed cleavage and fold in the outcrop which is located in the middle of Taiwan''s Hsuehshan, on the north of Nantou''s Choshuiche-- Shunglung. The outcrop consists of multi-layer of thin-layered sandstone and slate in Shihpachunghsi Formation. In the structure of middle scale anticline, there exist symmetrical micro-fold structure in the hinge and asymmetrical in the limb; in the limb of the micro-fold the development of cleavage can be found. In two limbs of the middle-scaled anticline cleavage orientation often tilts obviously when the cleavage passes into different layer while in the hinge area it doesn''t. In my view the genetic relationship between cleavage and fold can be analyzed through the microstructure appearing in this outcrop, where the geometric relationship between cleavage and bedding on a middle scale, microstructure analysis and Fry method-strain analysis are applied to it. The primary conclusions are as following: 1. The continuous cleavage and small-scaled symmetrical micro-fold in the mud-stone layer and sandstone layer are generated through parallel layer shortening. While the micro-fold is developing, the limb of the micro-fold causes pressure solution of solution materials（quartz, calcite, plagioclase ） because of high stress and begin to migrate. Relatively, the remaining non-solution materials（mica, clay）are rich and form spaced cleavage whose angle of the inclination crossing micro-fold envelopment is approximately 90o. 2.Flexural-flow causes the middle-scaled anticline gradually and the geometry of the microfold, as well as cleavage orientation, begins to have physical changes. There emerges asymmetrical microfold in the layer of the limb of the middle-scaled microfold. And in the both layers of the fold axial plane there appears fanning cleavage pattern. In addition, different layer possesses its own physical property, therefore resistance from force and deformation vary with it. Hence the cleavage plane tilts when it goes from sandstone layer into mudstone layer, then cleavage refraction occurs.