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Blueschist on Île de Groix, France Photomicrograph of a thin section of blueschist facies metamorphosed basalt, from Sivrihisar, Turkey. Blueschist (/ ˈ b l uː ʃ ɪ s t /), also called glaucophane schist, is a metavolcanic rock [1] that forms by the metamorphism of basalt and rocks with similar composition at high pressures and low temperatures (200–500 °C (392–932 °F ...
The world's thickest basalt flow may be the Greenstone flow of the Keweenaw Peninsula of Michigan, US, which is 600 meters (2,000 ft) thick. This flow may have been part of a lava lake the size of Lake Superior. [13] Deep erosion of flood basalts exposes vast numbers of parallel dikes that fed the eruptions. [17]
A now-ruined thirteenth-century religious complex called Nan Madol was built using columnar basalt quarried from various locations on the island of Pohnpei in Micronesia. Detail of columnar basalt pieces at Nan Madol. Hexagonal basalt was used to build retaining walls by early settlers in some places around Dunedin in New Zealand.
Flood basalts on Vancouver Island form a geologic formation called the Karmutsen Formation, which is perhaps the thickest accreted section of an oceanic plateau worldwide, exposing up to 6,000 m (20,000 ft) of basal sediment-sill complexes, basaltic to picritic pillow lavas, pillow breccia, and thick, massive basalt flows.
The Columbia River Basalt Group (including the Steen and Picture Gorge basalts) extends over portions of four states. The Columbia River Basalt Group (CRBG) is the youngest, smallest and one of the best-preserved continental flood basalt provinces on Earth, covering over 210,000 km 2 (81,000 sq mi) mainly eastern Oregon and Washington, western Idaho, and part of northern Nevada. [1]
During late Miocene and early Pliocene times, a flood basalt engulfed about 63,000 square miles (160,000 km 2) of the Pacific Northwest, forming a large igneous province. [2] Over a period of perhaps 10 to 15 million years, lava flow after lava flow poured out, ultimately accumulating to a thickness of more than 6,000 feet (1.8 km). [ 2 ]
The island Lítla Dímun in the Faroes. The Faroe Islands lie on the Eurasian Plate between Scotland, Norway and Iceland. The islands are of volcanic origin and are made up of three layers of basalt, with the top and bottom layers resembling each other. The age of this rock is between 54 and 58 million years, with the oldest material at the ...
Between the two zones is the Missouri Gravity Low, or MGL, a mass of low density granite including the Missouri batholith up to 370 miles long and 60 miles wide, identified in gravity surveys. Igneous activity ended around 1.3 billion years ago, with the intrusion of numerous dikes and sills into newly crystallized rhyolite and granite.