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RHYOLITE (Gr. p€ v, to flow, because of the frequency with which they exhibit fluxion structures), the group name of a type of volcanic rock, occurring mostly as lava flows, and characterized by a highly acid composition. They are the most siliceous of all lavas, and, with the exception of the dacites, are the only lavas which contain free primary quartz.
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Abstract Measurement of 18 O / 16 O ratios of pyroxene phenocrysts in the 179-Ma Lebombo rhyolites of the Karoo Volcanic Province provides a means of estimating δ 18 O values of the original magmas. Results show that the inferred magma δ 18 O values were generally lower than those of normal rhyolites. The average magmatic δ 18 O value for a Lebombo rhyolite is calculated to be about 5.6 ...
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Lebombo's Rhyolite (GC20F0J) was created by Bouts777 on 10/30/2009. It's a Not chosen size geocache, with difficulty of 2, terrain of 1.5. It's located in Mpumalanga, South Africa.This EarthCache is situated at N'wanetsi lookout point which is on the most eastern border of the Kruger Park.
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Border Cave is a rock shelter on the western scarp of the Lebombo Mountains in KwaZulu-Natal near the border between South Africa and Swaziland.Border Cave has a remarkably continuous stratigraphic record of occupation spanning about 200 ka.Anatomically modern Homo sapiens skeletons together with stone tools and chipping debris were recovered. Dating by Carbon-14, amino acid racemisation and ...
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South Africa was undertaken by the Geological Survey of ... During this period, basalts, rhyolites and dyke swarms were emplaced in South-East Africa and Antarctica. This marked the early phase of the rupture between East Africa and Antarctica at 188Ma, followed by the break-up .
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Dec 01, 2018 · Stratigraphy and Geochemistry of the Goedgenoeg and Makwassie Formations, Ventersdorp Supergroup, in the Bothaville area of South Africa P.G. Meintjes Department of Geology, University of the Free State, P.O. Box 339, Bloemfontein 9300, South Africa
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ARCHEAN FORELAND BASIN TECTONICS IN THE WITWATERSRAND, SOUTH AFRICA Kevin Burke Lunar and Planetary Institute 3303 NASA Road One Houston, Texas 77058 MAR1986 BEOIMEB W.S.F. Kidd and T.M. Kusky Department of Geological Sciences State University of New York at Albany 1400 Washington Avenue Albany, New York 12222 JNAS&-CR-176561) ARCHBAN FORELAND ...
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Palaeoarchaean felsic magmatism: A melt inclusion study of 3.45 Ga old rhyolites from the Barberton Greenstone Belt, South Africa
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Nov 13, 2017 · Abstract. The Saldanha eruption centre, on the West Coast of South Africa, consists of 542 Ma, intracaldera, S-type, rhyolite ignimbrites divided into the basal Saldanha Ignimbrite and the partly overlying Jacob's Bay Ignimbrite.
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U-Pb zircon (SHRIMP) ages for the Lebombo rhyolites, South Africa: Refining the duration of Karoo volcanism Article (PDF Available) in Journal of the Geological Society 161(4):547-550 · July 2004 ...
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The high silica content of rhyolites (usu 70-75%) compared to the common 60-65% in trachytes cf 55% in some phonolites makes a direct comparison difficult. Trachytes: Pantellerites are an unusual form of trachyte named after the island of Pantellaria between Sicily and Africa (near Carthage).
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Exceptionally high whole-rock δ18O values in intra-caldera rhyolites from Northeast Iceland - Volume 82 Issue 5 - Sylvia E. Berg, Valentin R. Troll, Chris Harris, Frances M. Deegan, Morten S. Riishuus, Steffi Burchardt, Michael Krumbholz
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This radical movement of the earth's crust caused rifting – cracking and splitting apart – along the margins of the present African continent. Rifting first started on the eastern margin of South Africa and caused the explosion of great volcanoes. Rhyolites – forms of volcanic rock that is high is silica – poured out as molten lava.
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Certain tholeiites, formerly regarded as normal Karroo basalts, occuring in South West Africa, have recently been shown also to be of Cretaceous age. A brief description of the intrusive rocks associated with the Jurassic and Cretaceous vulcanism is also given.
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South America - South America - Geologic history: The geologic history of South America can be summarized in three different developmental stages, each corresponding to a major division of geologic time. The first stage encompassed Precambrian time (about 4.6 billion to 541 million years ago) and was characterized by a complex series of amalgamations and dispersals of stable blocks of ...
GET PRICE >>Exceptionally high whole-rock δ18O values in intra-caldera rhyolites from Northeast Iceland - Volume 82 Issue 5 - Sylvia E. Berg, Valentin R. Troll, Chris Harris, Frances M. Deegan, Morten S. Riishuus, Steffi Burchardt, Michael Krumbholz
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Axel Hofmann holds a doctorate from the University of Mainz in Germany and has worked as a researcher and lecturer at the University of Zimbabwe, Wits University and the University of KwaZulu-Natal. His main interest and expertise is centred on the Archaean geological record of southern Africa.
GET PRICE >>South Africa was undertaken by the Geological Survey of ... During this period, basalts, rhyolites and dyke swarms were emplaced in South-East Africa and Antarctica. This marked the early phase of the rupture between East Africa and Antarctica at 188Ma, followed by the break-up .
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New geochronological constraints on the tectonic evolution of the Pan-African Zambezi belt, south-central Africa: Journal of African Earth Sciences, v. 27, no. 1A, p. 104-105 (special abstract issue for 10th International Gondwana Conference, Capetown, South Africa, June 28-July 4).
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Hormuz Island, a salt-gypsum dome in the Persian Gulf in southern Iran, is a complex halotectonic melange comprising evaporites, carbonates, volcanic and volcaniclastic rocks, as well as low-grade metamorphic and sedimentary rocks. Based on trace element (including rare earth elements REE) compositions of whole rocks and zircon, Hormuz rhyolites are inferred to have formed from .
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The Etendeka rhyolites (quartz latite, sensu stricto; MILNER, 1988) are important for the purposes of comparison as they formed in a similar tectonic setting to the Lebombo rhyolites just before the breakup of South America and Africa.
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Hormuz Island, a salt-gypsum dome in the Persian Gulf in southern Iran, is a complex halotectonic melange comprising evaporites, carbonates, volcanic and volcaniclastic rocks, as well as low-grade metamorphic and sedimentary rocks. Based on trace element (including rare earth elements REE) compositions of whole rocks and zircon, Hormuz rhyolites are inferred to have formed from .
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Nov 16, 2006 · The rhyolites have low water contents, ... Lesotho. (b) Geological map of the central and southern parts of the Lebombo Monocline in Swaziland and South Africa showing the location of the three rhyolite traverses sampled and their relationship to the distribution of the Sabie River Basalt Formation and extent of the Rooi Rand dyke swarm; ...
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Keywords: Lemombo rhyolites, U–Pb, flood basalts, rhyolites, Karoo. The Karoo volcanic province of southern Africa and East Antarc-tica is one of the largest flood basalt provinces of the Phanerozoic, and may be contiguous with the Ferrar magmatic province of the Transantarctic Mountains. Radiometric dating of the Karoo volca-
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Abstract The Jozini and Mbuluzi rhyolites and Oribi Beds of the southern Lebombo Monocline, southeastern Africa, have geochemical characteristics that indicate they were derived by partial melting of a mixture of high-Ti/Zr and low-Ti/Zr Sabie River
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Jul 01, 2004 · U–Pb SHRIMP ages are reported for three rhyolite flows from the Lebombo rift region of the Karoo volcanic province. Two flows are interbedded with the Sabie River Basalt Formation and a third sample is from the overlying rhyolitic Jozini Formation. The interbedded rhyolites yield ages of 182.0 ± 2.1 and 179.9 ± 1.8 Ma, whilst the overlying Jozini Formation rhyolite yields an age of 182.1 ...
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Low δ 18 O rhyolites and crustal melting: Growth and redistribution of the continental crust. Twin Falls, Idaho, and Yellowstone National Park, Wyoming, USA ... began with a discussion of the oxygen and radiogenic isotopic characteristics of Archean to Mesozoic magmatic rocks in South Africa.
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rhyolites and dacites of the Rooiberg Felsite, South Africa (Twist & French 1983); Late Devonian Comerong Volcanics, NSW (Dadd 1992); ca 36 Ma quartz trachytes and low-silica rhyolites of the Trans-Pecos volcanic field, Texas (Henry et al. 1988,
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The Etendeka rhyolites (quartz latite, sensu stricto; MILNER, 1988) are important for the purposes of comparison as they formed in a similar tectonic setting to the Lebombo rhyolites just before the breakup of South America and Africa.
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South America - South America - The Northern Andes: North of the Gulf of Guayaquil in Ecuador and Colombia, a series of accreted oceanic terranes (discrete allochthonous fragments) have developed that constitute the Baudo, or Coastal, Mountains and the Cordillera Occidental. They were accreted during Cretaceous and early Cenozoic times.
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