Structural analysis of Mirs Bay, Hong Kong region
Abstract of thesis entitled
STRUCTURAL ANALYSIS OF MIRS BAY, HONG KONG REGION
LEUNG KAR FAI
for the degree of Master of Philosophy
at The University of Hong Kong
in May 2004
The Mirs Bay Basin, to the NE of Hong Kong, is a Cretaceous-Cenozoic red bed basin at the southeastern margin of South China and is structurally bounded by the NE-trending Linhuashan Fault Zone. The structural relations between the basin and the fault zone remain imperfectly understood, since the post-Early Cretaceous kinematic history of the fault zone and the structural aspects of the basin are still unclear. This study attempted to elucidate the tectonic structures of the Mirs Bay Basin and account for its formation, using a variety of field- and laboratory-based techniques.
Detailed mesoscopic structural analysis supplemented by Landsat 7 imagery analysis revealed a dominant dip-slip component of the NW-trending high-angle extensional fault system along the southwestern margin and the NNW-trending Feng Muk Long Fault along the eastern margin, suggesting a NE extension later than the Early Cretaceous. Widespread presence of fault breccia indicated a brittle deformation characteristic of the extension. The basin rhomboidal geometry was comparable to the mature stage of the pull-apart basin model. Post-rift deformations were characterized by a post-Eocene NW compression based on observed cross-cutting relationships and an Oligocene to Miocene NE extension which can be regionally correlated with asymmetrical monoclinal structures developed in other red bed successions.
Whole-rock 40Ar/39Ar dating was undertaken of the NW-trending aplite dykes along the southwestern margin and yielded ages of 162.3 ?0.8 Ma and 164.7 ?0.6 Ma, suggesting that the intrusion and associated NE extension occurred near the end of the Middle Jurassic.
Geochemical analysis was conducted for the aplite dykes and their country rocks of the Ngo Mei Chau Formation. Trace element analysis indicated a co-genetic relationship between the dykes and country rocks, inherited with a subduction signature consistent with the Jurassic tectonic setting of South China.
The Danshui and Duozhu Basins, located immediately to the NE of the Mirs Bay Basin and bounded by the Linhuashan Fault Zone, displayed a lazy-z shaped geometry and a rhomboidal geometry respectively on Landsat 7 images, equivalent to the transitional stage and mature stage of the pull-aparts model respectively.
The NE extensional tectonics observed in the Mirs Bay area, the structural geometries of the Mirs Bay Basin, Danshui Basin and Duozhou Basin, and the meshlike arrangement of extensional, thrust and strike-slip faults within the fault zone postulate a dextral-slip of the Linhuashan Fault Zone. These three basins probably developed as Riedel shears in an en echelon arrangement within the principal deformation zone. The fault zone presumably reversed its slip-sense from sinistral to dextral during the Early to Late Cretaceous. The reversal hypothesis is also supported by the paleomagnetic evidence obtained from coastal South China. Mechanisms of the dextral-slip were probably related to the reduced rate and the change in direction of the Pacific-Eurasia convergence during the Cretaceous. Subsequent Cenozoic right-lateral shearing can be accounted for by the indentation of India into Eurasia.
The study sheds important light on the post-Early Cretaceous structural history of the Linhuashan Fault Zone and its structural relations with the coastal basins in southeastern South China.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:plate tectonics china hong kong mirs bay
Date of Publication:01/01/2005