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These sinking greenstones forced the granitic partial melts sideways and upwards, emplacing them into the margins of the belt and later folding them. The greenstone cover allows the granitic layer to remobilize and form the dome structure. This two stage event is dated between 3.26 and 3.22 Ga. [10]
Greenstones, aside from containing basalts, also give rise to several types of metamorphic rocks which are used synonymously with 'metabasalt' et cetera; greenschist, whiteschist and blueschist are all terms spawned from the study of greenstone belts. The West African early Proterozoic greenstone belts are similar to the Archean greenstone belts.
The Barberton Greenstone Belt is located on the Kaapvaal craton, which covers much of the southeastern part of Africa, and was formed by the emplacement of granitoid batholiths. [7] The Kaapvaal craton was once part of a supercontinent geologists term Vaalbara that also included the Pilbara craton of western Australia. [ 7 ]
The greenstone belts of the various Archean cratons are commonly altered to the greenschist facies. These ancient rocks are noted as host rocks for a variety of ore deposits in Australia, Namibia and Canada. Greenschist-like rocks can also be formed under blueschist facies conditions if the original rock contains enough magnesium.
A large number of geological and geochemical methods have been applied to the rocks of the Isua Greenstone Belt. These include subdivision of the various lithologies and units within the belt using a combination of geological mapping and U-Pb zircon dating, typically using sensitive high-resolution ion microprobe (SHRIMP), analyses; [3] major and trace element chemistry; [11] [12] structural ...
Archean stromatolites are the first direct fossil traces of life on Earth. A banded iron formation from the 3.15 Ga Moodies Group, Barberton Greenstone Belt, South Africa. Red layers represent the times when oxygen was available; gray layers were formed in anoxic circumstances.
The top layer is made by meta-sedimentary rocks, for example quartzite and marble. [16] According to the data of zircon dating, the bottom layer of the greenstone sequence formed in about 2.54 billion years ago, [24] while the middle and upper layers have the age later than 2.51 billion years. [23]
TTGs are an aggregation of certain rocks (tonalite-trondhjemite-granodiorite), that form when hydrous, mafic crust is melted at high pressure. These rocks are critical to the formation of Archean greenstone complexes due to the low density, intrusive nature of the rocks. TTGs are found in other Archean greenstone belts such as Isua and ...