Radiometric dating sediments just4udating
By about 600 million years ago, a large part of southeastern China was submerged beneath a shallow continental sea.
By 400 million years ago, sediments from rivers and their deltas were being deposited in the Hong Kong region.
The unexposed (buried) continental basement of Hong Kong is thought to be older than 550 million years.
However, in neighbouring Guangdong Province, crystalline rocks as old as 2.5 billion years have been discovered.
These Devonian, Carboniferous and Permian rocks crop out mainly in the northeast and northwest of Hong Kong.
The Mesozoic pre-volcanic sedimentary rocks comprise Early and Middle Jurassic sandstones, siltstones, and mudstones that were deposited in an alluvial, shallow marine, and sub-tidal environments.
Detailed studies of the rocks enable the geological history and the evolution of the tectonic setting to be deciphered.
Quartzite is composed mainly of recrystallised quartz with some tiny flakes of sericite, mica.
The crustal blocks have been joined together (sutured) by continent - continent collision events over the past 1,000 million years.
The present-day tectonic setting of southeastern China is what is termed a passive continental margin (i.e.
They comprise non-marine red bed and evaporitic sediments that were deposited in fault-controlled basins.
Weathering and erosion have shaped the present landscape of Hong Kong and led to the accumulation of locally thick Quaternary superficial deposits.