Search results for "Andesite"
showing 10 items of 30 documents
Extensive, water-rich magma reservoir beneath southern Montserrat
2016
South Soufriere Hills and Soufriere Hills volcanoes are two km apart at the southern end of the island of Montserrat, West Indies. Their magmas are distinct geochemically, despite these volcanoes having been active contemporaneously at 131-129 ka. We use the water content of pyroxenes and melt inclusion data to reconstruct the bulk water contents of magmas and their depth of storage prior to eruption. Pyroxenes contain up to 281 ppm H2O, with significant variability between crystals and from core to rim in individual crystals. The Al content of the enstatites from Soufriere Hills Volcano (SHV) is used to constrain melt-pyroxene partitioning for H2O. The SHV enstatite cores record melt water…
Antisana volcano: A representative andesitic volcano of the eastern cordillera of Ecuador: Petrography, chemistry, tephra and glacial stratigraphy
2017
Antisana volcano is representative of many active andesitic strato-volcanoes of Pleistocene age in Ecuador's Eastern Cordillera. This study represents the first modern geological and volcanological investigation of Antisana since the late 1890's; it also summarizes the present geochemical understanding of its genesis. The volcano's development includes the formation and destruction of two older edifices (Antisana I and II) during some 400 + ka. Antisana II suffered a sector collapse about 15,000 years ago which was followed by the birth and growth of Antisana III. During its short life Antisana III has generated >= 50 eruptions of small to medium intensity, often associated with andesitic t…
Geochemical signature of Paleozoic accretionary complexes of the Central Asian Orogenic Belt in South Mongolia: Constraints on arc environments and c…
2006
Abstract We report a reconnaissance geochemical and Nd-isotopic study for 33 metaigneous and metavolcaniclastic rocks from the ca. 470 to 290 Ma old Gurvan Sayhan, Zoolen, Nemegt Uul, Bayanleg-Hatuu, and Tseel mountain ranges in southern Mongolia, in order to infer tectonic environments, test a recently proposed multiple terrane model, and explore the late-stage development of the southern Central Asian Orogenic Belt (CAOB). Samples from the Gurvan Sayhan and the Zoolen ranges have a predominantly intermediate, calc-alkaline composition; they display LREE enrichment, excess abundances of fluid-soluble elements, and low concentrations of high-field strength elements. These data, in combinati…
GEOCHEMICAL CONSTRAINTS ON THE ORIGIN OF CALCALKALINE AND ALKALINE MAGMAS OF THE EASTERN TRANS-MEXICAN VOLCANIC BELT
1988
Se presentan datos de elementos mayores, elementos trazas y tierras raras de rocas calco-alcalinas y alcalinas de la parte este del cinturón volcánico transmexicano (TMVB), así como conclusiones acerca de su origen y de su significado tectónico. Las andesitas y dacitas muestran características geoquímicas que descartan su derivación de los magmas basálticos por el proceso de cristalización fraccionada. Las distribuciones gráficas de los elementos LIL y HFS son interpretadas como indicadoras de la formación de magmas en el manto superior modificado por procesos de subducción. Las riolitas se interpretan como resultado de la fusión parcial de la corteza continental.
Syn- and post-eruptive mechanism of the Alaskan Ukinrek Maars in 1977
2008
The two alkali olivine basaltic Ukinrek Maars (East Maar and West Maar) and one scoria cone within East Maar erupted within eleven days (March 30–April 9, 1977) on the Alaskan Peninsula, 13 km north of Mt. Peulik, an andesite volcano of the Aleutian Range. The East Maar, with a diameter of 300 m, is located within a small graben system striking N 1100 E, oblique to the Aleutian trench in a distance of 350 km. On these tensional faults two eruption centres occur: The East Maar and a scoria cone on the southeastern margin of its crater bottom. The scoria cone was active more or less during the whole eruption activity of East Maar. The West Maar, with a diameter of 140 m, is located just west …
Steam and gas emission rate from La Soufriere volcano, Guadeloupe (Lesser Antilles): Implications for the magmatic supply during degassing unrest
2014
Abstract Since its last magmatic eruption in 1530 AD, La Soufriere andesitic volcano in Guadeloupe has displayed intense hydrothermal activity and six phreatic eruptive crises. Here we report on the first direct quantification of gas plume emissions from its summit vents, which gradually intensified during the past 20 years. Gas fluxes were determined in March 2006 and March 2012 by measuring the horizontal and vertical distributions of volcanic gas concentrations in the air-diluted plume and scaling to the speed of plume transport. Fluxes in 2006 combine real-time measurements of volcanic H2S concentrations and plume parameters with the composition of the hot (108.5 °C) fumarolic fluid at …
Late proterozoic island arc volcanics from Gebeit, Red Sea Hills, north-east Sudan
1994
The area of Gebeit Mine in the northern Red Sea Hills, Sudan, is built up of voluminous volcanic rocks and minor volcaniclastic and clastic sequences. According to their chemical and modal compositions the Gebeit volcanics can be devided into four groups: (a) cpx-physic basalts with clinopyroxene and plagioclase as the dominant phenocrysts and minor opaques; (b) hbl-physic basalts with hornblende, clinopyroxene, plagioclase and subordinate magnetite including one rare dacite; (c) pl-phyric andesites with plagioclase phenocrysts in a matrix that is rich in magnetite; and (d) aphyric basalts. The compositional variation within the distinct volcanic groups can only partly be explained by fract…
Halogens in Mafic and Intermediate-Silica Content Magmas
2018
As volatile and variably mobile components, halogens play key roles in magmatic, metasomatic, mineralizing, and volcanic processes by influencing the physical and chemical properties of melts, fluids, and minerals. Volcanic emission of halogens to the atmosphere leads to long- and short-term impacts on atmospheric chemistry that range from global perturbation of the stratospheric O3 budget to more localized life-threatening contamination of soils and fresh water. The concentrations of F, Cl, Br, and I in melts, fluids, and minerals provide crucial geochemical information and insights into magmatic processes ranging from partial melting to volcanic eruptions. Halogen research is useful for e…
Crystal size distribution in Jurassic Ferrar flows and sills (Victoria Land, Antarctica): evidence for processes of cooling, nucleation, and crystall…
1996
Jurassic Ferrar rocks in Victoria Land (Antarctica) occur predominantly as basaltic or andesitic flows and sills. Both show characteristic petrographical and chemical variations, which can be related to in-situ differentiation processes. Such characteristics have been investigated at one flow (“Colonnade flow”) and one sill (“Thumb Point sill”) in the Prince Albert Mountains (Central Victoria Land) based on a statistical grain size analysis and the application of the crystal size distribution theory. A third magma body (“HiTi-unit”), which in previous literature was described as a flow, does not show clear similarities to either the flow or sill. Sill and flow are in-situ differentiated wit…
The Nevados de Payachata volcanic region (18�S/69�W, N. Chile) II. Evidence for widespread crustal involvement in Andean magmatism
1990
Volcanism extending over 11 Ma is represented in the rocks of the Nevados de Payachata region, culminating in the formation of two large composite stratocones within the last 500 000 years. Chemically distinct mafic magmas are erupted at a number of parasitic centers. These cannot be related to each other by crystal fractionation and do not appear to be direct parents for the differentiated suites of the composite cones. Two distinct trends are defined by the intermediate and evolved rocks; a high LILE (large ion lithophile element), TiO2 and Ce/Yb lineage among the youngest rocks (including the two major stratocones), and a more typical calc-alkaline trend among the older (>1 Ma) rock type…