Isua greenstone belt
| Isua Greenstone Belt | |
|---|---|
 |
|
| Highest point | |
| Elevation | 5 m (16 ft) |
| Dimensions | |
| Length | 35 km (22 mi) |
| Area | 3,000 km2 |
| Countries | Greenland |
| Geology | |
| Orogeny | 357 million years to form |
| Age of rock | Archean |
| Type of rock | Tonalites, mafic rocks, metasedimentary rocks, banded iron formations, granite, granodiorites |
The Isua Greenstone Belt is an Archean greenstone belt in southwestern Greenland. The belt is aged between 3.7 and 3.8 billion years. The belt contains variably metamorphosed mafic volcanic and sedimentary rocks. The occurrence of boninitic geochemical signatures, characterized by extreme depletion in trace elements that are not fluid mobile, offers evidence that plate tectonic processes in which lithic crust is melted may have been responsible for the creation of the belt. Another theory posits that the belt formed via a process known as vertical plate tectonics.
In 2016 melting snow revealed 3.8-billion-year-old stromatolite fossils, the oldest by several hundred million years thus far discovered on Earth. The discovery of complex stromatolite structures at Isua, formed from accreted biofilm layers so early in the history of the Earth suggests that life first evolved on Earth over 4 billion years ago.
The Isua Greenstone Belt, also known as the Isua supracrustal belt since it is composed of supracrustal rock deposited upon basement rock strata, is located in the southwestern portion of Greenland, in the Isukasia terrane, near the Nuuk capital region. The greenstone belt is made up of metamorphosed mafic volcanic and sedimentary rocks that are usually juxtaposed by mylonites or fault boundaries. By using uranium-lead dating on zircon and titanite, the tectonic history was dated to be approximately 3,700–3,600 million years old. The Isua Greenstone has been studied by Earth scientists due to evidence the area holds for early Earth plate tectonics, since it houses one of the oldest, best-preserved ancient plate tectonic sequences. In addition, the area is large, exposed, and there are areas that have experienced relatively low deformation and alteration to the original rock sequences. The Isua Greenstone is divided into a northern and a southern section by the Ivinnguit Fault, shown on the map below right. The northern area of the Isua Greenstone Belt is mainly composed of amphibolite rocks, volcanic rocks, upper mantle peridotite, and layered gabbros; a suite which suggests crustal shortening.
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