Geochemistry of Darwin glass and target rocks from Darwin crater, Tasmania, Australia

Howard, K. T.

doi:10.1111/j.1945-5100.2008.tb00667.x

Cited by 17 publications

(21 citation statements)

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“…The focus of this paper is on the physical properties and distribution trends in Darwin glass, relative to Darwin crater, that provide evidence for a genetic relationship between the glass and crater independent of the corroborating petrographic, geochemical and isotopic evidence published elsewhere (Howard and Haines 2007;Howard 2008). However, to provide a framework for later discussion that attempts use the glass distribution trends to gain insights into the impact process, it is necessary to briefly describe the geochemistry of Darwin glass and its relationship to the target rocks at Darwin crater.…”

Section: Geochemistry Of Darwin Glass and Target Rocksmentioning

confidence: 94%

“…Geochemical analyses in Howard (2008) show 2 groups of glass. Group 1 is composed of: SiO 2 (85%), Al 2 O 3 (7.3%), TiO 2 (0.05%), FeO (2.2%), MgO (0.9%), and K 2 O (1.8%).…”

Section: Geochemistry Of Darwin Glass and Target Rocksmentioning

confidence: 98%

“…Darwin glass was formed during a meteorite impact on the island of Tasmania, Australia, at about 800 ka (Loh et al 2002). After prolonged historic uncertainty, recent petrographic and chemical studies have concluded that the source of the glass is the proposed 1.2 km diameter Darwin crater, located at 42°18.39′S 145°39.41′E (Howard 2008;Howard and Haines 2007). During investigations into the origin of Darwin glass, thousands of samples of the glass were collected.…”

Section: Introductionmentioning

confidence: 99%

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Physical distribution trends in Darwin glass

Howard

2009

Meteorit & Planetary Scien

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Abstract— Darwin glass formed by impact melting, probably during excavation of the 1.2 km diameter Darwin crater, Tasmania, Australia. The glass was ejected up to 20 km from the source crater and forms a strewn field of >400 km2. There is at least 11,250 m3of glass in the strewn field and relative to the size of the crater this is the most abundant ejected impact glass on Earth. The glass population can be subdivided on the basis of shape (74% irregular, 20% ropy, 0.5% spheroid, 6% droplet, and 0.7% elongate) and color (53% dark green, 31% light green, 11% black, and 5% white). The white glasses contain up to 92 wt% SiO2 and are formed from melting of quartzite. Black glasses contain a minimum of 76 wt% SiO2 and formed from melting of shale. Systematic variations in the proportion of glasses falling into each of the color and shape classes relative to distance from the crater show: 1) a decrease in glass abundance away from the crater; 2) the largest fragments of glass are found closest to the crater; 3) small fragments (<2 g) dominate finds close to the crater; 4) the proportion of white glass is greatest closest to the crater; 5) the proportion of black glass increases with distance from the crater and 6) the proportion of splashform glasses increases with distance from the crater. These distribution trends can only be explained by the molten glass having been ballistically ejected from Darwin crater during impact and are related to 1) the depth of excavation from the target rock stratigraphy and/or 2) viscosity contrasts between the high and low SiO2 melt. The high abundance and wide distribution of ejected melt is attributed to a volatile charged target stratigraphy produced by surface swamps that are indicated by the paleoclimate record.

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Section: Geochemistry Of Darwin Glass and Target Rocksmentioning

confidence: 94%

“…Geochemical analyses in Howard (2008) show 2 groups of glass. Group 1 is composed of: SiO 2 (85%), Al 2 O 3 (7.3%), TiO 2 (0.05%), FeO (2.2%), MgO (0.9%), and K 2 O (1.8%).…”

Section: Geochemistry Of Darwin Glass and Target Rocksmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Physical distribution trends in Darwin glass

Howard

2009

Meteorit & Planetary Scien

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“…Other megascopic impact glasses include: (1) the ~0.8 million year old Belize glasses, which are found scattered over a large area in western Belize and which are probably tektites, (2) the ~0.8 million year old impact glasses, called Darwin glass, scattered over parts of Western Tasmania, (3) the Libyan Desert Glasses (LDG) which are masses of ~30 million year old silica‐rich glass (~98 wt% SiO 2 ) found scattered over ~6500 km 2 in the Libyan Desert of western Egypt …”

Section: Impact Glassesmentioning

confidence: 99%

Glass: The Geologic Connection

Glass

2016

Int J of Appl Glass Sci

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Silicate glasses can be formed by several geological processes all of which involve melting of rock and rapid cooling to prevent crystallization. The most common and widespread natural glasses are volcanic glasses produced when magma is extruded onto the Earth's surface. The type of volcanic glass is determined by the composition of the magma and type of eruption, which in turn are related to the geological setting. During high velocity impacts of large extraterrestrial bodies, melted rock can be ejected into the atmosphere — and sometimes into space — where it cools to form large glass bodies centimeters in size or larger, called tektites, and smaller glass bodies, called impact spherules. Tektites and spherules can be thrown over large areas of the Earth's surface. Impact spherules can also form by condensation from an impact plume of vaporized surface rocks and impactor. Lightning strikes generate high enough temperatures to melt and vaporize rock. When they hit sand, they can produce tube‐like structures called fulgurites. Burning of organic material, like oil or coal, underground can melt rock and produce combustion‐metamorphic glasses. Glasses called frictionites can be produced by frictional heating at the base of massive landslides. Friction glasses can also be generated during faulting.

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“…Another discovery of organic matter was made in studies of impact glasses from the Darwin crater in Tasmania (Howard ; Howard et al. ).…”

Section: Introductionmentioning

confidence: 99%

Remnants of paleoflora in impact melt rocks of the El'gygytgyn crater (Chukotka, Russia)

Gurov

Permiakov

Koeberl

2019

Meteorit & Planetary Scien

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Remnants of paleoflora were discovered in impact melt rocks from the El'gygytgyn crater, Chukotka, Russia. El'gygytgyn is a 3.58 Ma, 18 km diameter impact structure in Chukotka, northeastern Russia. A circular crater basin is surrounded by an uplifted rim. The crater floor is occupied by the El'gygytgyn Lake, 12 km in diameter, surrounded by lacustrine terraces up to 80 m in height. Impactites found at the El'gygytgyn crater include impact melt rocks, glass bombs, and shock metamorphosed volcanic rocks. Most impact melt rocks occur only in redeposited state in the terrace lake deposits. Floral remnants were discovered in impact melt rocks from various locations in the terrace deposits. The floral remnants include fragments of leaves, cell tissue, and undetermined organic matter that occur in vesicles within glassy melt rocks and impact melt breccias. After the discovery of floral remnants in impact melt breccias from upper Miocene strata in Argentina, and the description of floral imprints in the Dakhleh Glass of proposed impact origin in Egypt, the detection of paleoflora remnants in impact melt rocks of the El'gygytgyn structure is the first such occurrence in a confirmed impact crater on Earth.

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Geochemistry of Darwin glass and target rocks from Darwin crater, Tasmania, Australia

Cited by 17 publications

References 17 publications

Physical distribution trends in Darwin glass

Physical distribution trends in Darwin glass

Glass: The Geologic Connection

Remnants of paleoflora in impact melt rocks of the El'gygytgyn crater (Chukotka, Russia)

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