Search results
Results from the WOW.Com Content Network
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.
No broad blocks as old as 3 Ga are found in Precambrian shields. Toward the end of the Archean, however, some of these blocks or terranes came together to form larger blocks welded together by greenstone belts. [2] Two such terranes that now form part of the Canadian shield collided about .
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]
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 ]
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 ...
Local preservation of 3.6–3.0 Ga gneisses and widespread isotopic evidence for crust of this age incorporated into younger plutons indicates that the Wyoming Craton originated as a 100,000 km 2 middle Archean craton that was modified by late Archean volcanic magmatism and plate movements and Proterozoic extension and rifting. [2]
For premium support please call: 800-290-4726 more ways to reach us
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.