Joint systems in granites on Hong Kong Island and neighbouring areas of Hong Kong
Abstract of thesis entitled ?Joint system In Granites Of Hong Kong Island And Neighboring Areas Of Hong Kong?submitted by Nau Pak-Sun for the degree of Master of Philosophy at the University of Hong Kong in January, 1984
This study falls into two parts. The first (Chapters III-IX) is the main part, dealing with the joint systems of the granites in the areas studied. The second (Chapters X-XIII) is a subordinate part concerned with some weathering and erosional features (slopes, soil profile and corestones) and the influence of jointing on their development.
Joint surveys were carried out in the following localities: - East Kowloon, the north of Hong Kong Island, the Stanley and D?guilar Peninsulas on the south side of Hong Kong Island, on Cheung Chau Island, Lamma Island and Po Toi Island. The granite masses include representative outcrops of several of the intrusive phases distinguished on the geological map of Hong Kong of Allen and Stephens (1971). A total of 3540 joint orientations have been recorded. A graphic computer program was used to construct stereoplots. The program plots data pairs on an equal area stereonet by means of a Calcomp plotter. A ?asking effect?in data processing has been demonstrated.
A total of 17 joint sets (31 joint subsets) are recognized in the granite bodies as a whole. The joint systems of the main granite masses (Hong Kong Granite, Cheung Chau Granite and Sung Kong Granite) are found to consist of 7 or 8 joint sets. The joint sets in these granites usually trend in seven directions. Sets trending approximately N-S, N20oE, N75oE, E-Wand N35oW are common and are found in the above granite studies.
Photogeological lineaments (presumed to be caused by joints, faults and also dykes and veins) were studied on aerial photographs. Ground data and aerial photograph measurements are compared. It is found that there are some discrepancies between measured joint systems and the observed patterns of photogeological lineaments, probably due to errors arising from the measurement of lineaments on aerial photographs.
There is a brief discussion of the relationship between jointing and topography, soil profile and corestone development. A case study of the control of sheet-jointing on local weathering and topography (slope) is given. It is suggested that in the context of local weathering of granite, the term ?eathering front?be restricted to meaning the interface between fresh granite and slightly decomposed granite (Zone IV), representing an incipient stage of weathering; while the term ?asal surface?is used for the interface between Zone II or Zone III and Zone IV, representing an intermediate to advanced stage of weathering.
The results of studies on chemical weathering in the vicinity of a joint and of diffusion rings at local sites are given. Locally, for weathering on both sides of a joint, removal of Na and K is mainly along the joint; and for the diffusion rings, the removal of Na and K from the whitish zones is relatively greater than that from the brown zones.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:joints geology china hong kong granite
Date of Publication:01/01/1984