chemia: Volcanism of Canada

Evidence: 45 • authority: 72

Komatiite is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava of at least 18 wt% magnesium oxide (MgO). It is classified as a 'picritic rock'. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Komatiite was named for its type locality along the Komati River in South Africa, and frequently displays spinifex texture composed of large dendritic plates of olivine and pyroxene. Komatiites are rare rocks; almost all komatiites were formed during the Archaean Eon (4.03–2.5 billion years ago), with few younger (Proterozoic or Phanerozoic) examples known. This restriction in age is thought to be due to cool…

Evidence: 36 • authority: 88

Plutonium-244 Fission Tracks: Evidence in a Lunar Rock 3.95 Billion Years Old. Tracks attributed to the spontaneous fission of plutonium-244 and of uranium-238 were detected in a large whitlockite crystal in the lunar breccia 14321 from the Fra Mauro formation. For a track-retention age of 3.95 ± 10 9 years the number of plutonium tracks relative to the number of uranium tracks is 0.51 ± 0.15, provided that the rock was not heavily neutron-irradiated 3.95 × 10 9 years ago.

Evidence: 36 • authority: 80

Sahara space rock 4.5 billion years old upends assumptions about the early Solar System

Evidence: 36 • authority: 72

Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash lithifies into solid rock. Rock that contains greater than 75% ash is considered tuff, while rock containing 25–75% ash is described as tuffaceous (for example, tuffaceous sandstone). A pyroclastic rock containing 25–75% volcanic bombs or volcanic blocks is called tuff breccia. Tuff composed of sandy volcanic material can be referred to as volcanic sandstone. Despite the name, tuff is a relatively soft rock, so it has been used for construction since ancient times. Because it is common in Italy, the Romans used it often for construction. The Rapa Nui people…

Evidence: 36 • authority: 72

Volcanic activity is a major part of the geology of Canada and is characterized by many types of volcanic landform, including lava flows, volcanic plateaus, lava domes, cinder cones, stratovolcanoes, shield volcanoes, submarine volcanoes, calderas, diatremes, and maars, along with less common volcanic forms such as tuyas and subglacial mounds. Though Canada's volcanic history dates back to the Precambrian eon, at least 3.11 billion years ago, when its part of the North American continent began to form, volcanism continues to occur in Western and Northern Canada in modern times, where it forms part of an encircling chain of volcanoes and frequent earthquakes around the Pacific Ocean called t…

Evidence: 27 • authority: 80

1.6 billion years old crater awes geologists

Evidence: 27 • authority: 80

A unique witness, 4 billion years old

Evidence: 27 • authority: 92

Erratic behavior of platinum-group elements along an olivine-Cr-spinel cotectic in sulfide-undersaturated basaltic magma: roles of Cr-spinel and alloys.. The behavior of platinum-group elements (PGE) in sulfide-undersaturated primitive magmas may be controlled by crystallization of either Cr-spinel, platinum-group minerals (PGM) or olivine. Evaluation of the PGM-hosted PGE portion is challenging because PGM in volcanic rocks are small and rare. We report on the sizes and compositions of PGM associated with Cr-spinel, the PGE content of Cr-spinel and olivine, and the bulk rock PGE content from sulfide undersaturated arc volcanics of the Tumrok range (Eastern Kamchatka). Platinum-iron and Ir-…