Hong Kong lies on the SE margin of the Cathaysia Block and straddles the NE-trending Lianhuashan Fault Zone, one of the dominant structural features of SE China. Isotope signatures of the Mesozoic granites have indicated that the zone overlies a major crustal discontinuity. The proposed gravity model of Hong Kong consists of a heterogeneous upper crust underlain by middle to lower crust composed of a felsic Archaean segment, approximately 25 km wide, flanked by more mafic Proterozoic crust. The southern boundary of the felsic segment dips steeply to the north, whereas the northern boundary is subvertical. Euler gravity anomalies define the fundamental faults in the upper crust, and many of these can be correlated with faults that have been mapped at surface. The middle to lower crustal discontinuities are considered to be associated with a major shear zone within the Cathaysia Block that has similar dimensions to transcratonic structures in other Precambrian shield areas. The geological development of Hong Kong and neighbouring SE China has largely been controlled by periodic reactivation of this deep crustal shear zone since the late Neoproterozoic.

Scientific editing by Alan Roberts.
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