Regional tectonic setting of Hong Kong: implications of new gravity models

Abstract

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.

Multilayer stress from gravity and its tectonic implications in urban active fault zone: A case study in Shenzhen, South China

“…The maximum amplitude minima are located in the Shenzhen Bay caused by a thick pile of sediments. Values close to the southern boundary are well consistent with those derived from Hong Kong gravity data (Fletcher et al, 1997). …”

“…It indicates that the fault zone has extended into the lower crust or even the upper mantle. The deep crustal discontinuity is confirmed by other geophysical studies (Xie et al, 1997;Fletcher et al, 1997;Sewell et al, 2000). The recent crustal structure from deep seismic sounding shows that a high-velocity (7.1-7.4 km/s) layer in lower crust is absent in the study area (Li et al, 2006).…”

Jurassic intraplate magmatism in southern Hunan-eastern Guangxi: 40 Ar/ 39 Ar dating, geochemistry, Sr-Nd isotopes and implications for the tectonic evolution of SE China

“…This implies that the lithosphere extension may have been active since the Middle Jurassic. Pulses of rapid extension during the Late Jurassic are also reported from the Hong Kong region (Fletcher et al 1997). The Upper Triassic-Cretaceous extensional basins, such as the Shiwandashan basin in SE Guangxi (Gilder et al 1996), mostly developed on the Palaeozoic to Middle Triassic basement that was ubiquitously folded by the Indosinian Orogeny (Li 1998).…”

Middle Jurassic collision of an exotic microcontinental fragment: Implications for magmatism across the Southeast China continental margin

“…High precision U-Pb zircon dating of Middle and early Late Jurassic volcanic rocks, plutons and dykes (Davis et al, 1997) constrain the timing of terrane amalgamation to between approximately 164 and 161 Ma followed shortly afterward by a pulse of plutonism. The Tolo Terrane coincides with isotopically distinct basement sources of Hong Kong granitoids which are reflected by regional gravity models (Fletcher et al, 1997).…”

“…Darbyshire and Sewell (1997) Busby and Langford (1995). Modeling of the regional gravity data by Fletcher et al (1997) revealed contrasting densities in the basement consistent with a felsic Archean crust in the northwest separating denser blocks of mafic Proterozoic crust in the southeast. The gravity map of the region around Hong Kong and neighbouring Guangdong Province compiled by Fletcher et al (2004) shows a prominent NE-trending gradient in Bouguer anomaly values extending along the coast consistent with the pattern observed in Hong Kong.…”