User:Kayau/Geology of Hong Kong

This is a userspace draft intended for Geology of Hong Kong.

The geology of Hong Kong is dominated by Mesozoic volcanic and granite rocks, which together make up about 85% of the total land area. The remaining area is underlain by Palaeozoic meta-sedimentary rocks, Mesozoic to Cenozoic sedimentary rocks and superficial deposits.

Located at the southern coast of China,

Geological structure
Hong Kong is located on the eastern portion of the Cathaysian Block of the South China Subplate, which is characterised by well-developed Mesozoic magmatism Although the structural development of Hong Kong's rocks began during the Precambrian period, the most significant period of folding, faulting and volcanism was the Yanshanian orogeny during the Jurassic and Cretaceous Periods. Structural evolution remained active in Hong Kong until recent times.

The majority of the rock outcrops in Hong Kong were formed during the Mesozoic period, and no early Paleozoic or Precambrian rocks are exposed to the surface. However, efforts have been made to model the basement structure of the city. Regional geology and geochemical evidence suggest that Paleozoic and late Precambrian rocks reside underneath the Mesozoic-formed rock surface.

Faulting
Hong Kong is located at the southwesternmost extreme of the Lianhuashan Fault Zone (LFZ), a northeast-to-southwest-trending fault system. Hong Kong's faults are in line with the orientation of the LFZ, its major faults orienting northeast to southwest and some secondary faults from northwest to southeast or north to south. Its main faults include Tai Lam Fault, Tolo Channel Fault and Sha Tau Kok Fault.

Faulting has an important impact on the geomorphology of Hong Kong. Faults are more prone to denudation processes; thus valleys are formed along faults. Tolo Channel is a water inlet that runs along the Tolo Channel Fault, while Tai Lam Fault created a valley at Tai Lam.[note to self: to cite] The formation of lowlands at Yuen Long and specifically Mai Po have also been partially attributed to the existence of faults.

Sedimentary and meta-sedimentary rocks
The oldest rocks in Hong Kong form the Bluff Head Formation (Db). These Devonian sedimentary rocks are mainly composed of siltstone, sandstone and conglomerate formed by the deposition and lithification of silt, sand, pebbles at rivers near the coast, and later underwent repeated folding and faulting to form upright bedding planes. The well-exposed section north of Tolo Channel is bounded by faults and dips to the northwest. The type secton of the formation is at Wong Chuk Kok Tsui, where the cliffs display complex, well-folded strata. The rocks around Ma On Shan, by contrast, dip to the southeast and are mostly concealed underground. West of Ma On Shan, the rocks gained higher resistance by metamorphosis and form the Hunch Backs.

During the Carboniferous period, South China was submerged under a shallow sea,, The Carboniferous sedimentary rocks of Hong Kong consist of three formations: the Yuen Long and Ma On Shan Formations (Csy), and the Lok Ma Chau Formation (Csl). All three structures gained their present structure through a combination of contact and dynamic metamorphism. The marble of both the Yuen Long and Ma On Shan Formations are metamorphosed from limestone with no discernable differences between the two formations, while the Lok Ma Chau Formation is mainly made up of siltstone and sandstone.

Permian

Economic geology
mining ores

Landscape modifications
reclamation slope cutting

fluvial environments coastal environments - filling beaches

Preservation
Hong Kong Geopark