The structure of the feeding channels of the ignimbrite and tufflava complexes of the northern Caucasus

Koronovsky, N. V.

doi:10.1007/bf02596775

Cited by 7 publications

(5 citation statements)

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“…One such dyke found by A. C. Waters in a late Oligocene-early Miocene formation near Prineville, Oregon, is briefly mentioned by Smith (1960, p. 818) who described how the 'dike several miles long appears to change from fluidal rhyolite in the deepest exposed part to fluidal-fragmental welded tuff near the surface and merge with a densely welded tuff" sheet on the surface'. In a personal communication Koronovski (1969) made it clear that a foliated groundmass of flattened glass shards makes its appearance in this transition zone, which lies some 200 m to 250 m below the base of the overlying sheet. .'…”

Section: Origin Of Eutaxitic Foliation In Dyke-shaped Ventsmentioning

confidence: 99%

Ignimbrite vents in the Sabaloka cauldron, Sudan

Almond

1971

Geol. Mag.

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Large ignimbrite dykes continuous with an overlying sheet of rhyolitic ignimbrite have been found at two localities in the centrally-subsided block of the Sabaloka cauldron. There is good evidence that these dykes fed ash-flow eruptions. Other possible feeder vents occur along the marginal fracture zone of the cauldron but evidence for the origin of some of these structures is ambiguous. Ignimbrites within the dyke-shaped feeders contain a very strong eutaxitic foliation oriented parallel to the contacts and this feature is thought to result from inwardly-directed pressures exerted by the dyke walls during a collapse which followed eruption of the ash-flows. Vents of this type are believed to originate by permissive intrusion through the roof of a shallowseated magma chamber, in contrast to forcefully injected diatreme vents. A broad genetic classification of these bodies is suggested, based on their mode of emplacement.

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Section: Origin Of Eutaxitic Foliation In Dyke-shaped Ventsmentioning

confidence: 99%

Ignimbrite vents in the Sabaloka cauldron, Sudan

Almond

1971

Geol. Mag.

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“…In young and active volcanoes, the deeper levels are typically buried by lavas and tephras, which likewise have been extensively studied. In contrast, exposures of volcanic conduit-vent structures are relatively rare and only some field investigations have been published (Almond 1971;Koronovsky 1971;Ekren and Byers 1976;Reedman et al 1987;Wolff et al 1989;Stasiuk et al 1996;Kano et al 1997). Due to limitations of exposure, fewer still of these studies have been able to link vent structures and their filling processes with proximal deposits produced during the same eruptions (Almond 1971;Koronovsky 1971;Ekren and Byers 1976).…”

Section: Introductionmentioning

confidence: 82%

“…Welding of pyroclasts has been interpreted to be produced by agglutination on steep conduit-vent walls (Reedman et al 1987;Kano et al 1997), thus the steep lower contact of Los Almendros Member is more likely to be interpreted as a conduit-vent wall rather than a fallout depositional surface. In addition, the structure of Los Almendros Member shows most of the features described in the literature for other conduit-vent structures: (1) the overall geometry is that of an inverted cone (though highly elongated) representing a flared vent (Reedman et al 1987); (2) it shows a steep welding foliation dipping inward and parallel to the wall-rock contact (Almond 1971;Koronovsky 1971;Ekren and Byers 1976;Wolff 1986;Reedman et al 1987;Kano et al 1997) and (3) the dip of welding foliation decreases towards the centre of the vent (Ekren and Byers 1976;Kano et al 1997).…”

Section: Los Almendros Member Welded Fallout and Elongated Ventmentioning

confidence: 92%

Conduit-vent structures and related proximal deposits in the Las Cañadas caldera, Tenerife, Canary Islands

et al. 2006

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The Las Cañadas caldera wall and the outer slopes of the caldera provide three-dimensional exposures of numerous proximal-welded fallout deposits and have been mapped in detail. As a result, some parts of the Ucanca and Guajara Formations of the stratigraphy of Martí et al. (1994) have been divided into members that correspond to individual eruptions. Mapping has also revealed the occurrence of conduit-vent structures associated with proximal-welded fallout deposits. Conduit-vent structures consist of an upper flaring area and a lower narrow conduit. Conduit-vent geometry and dimensions include cylindrical plugs and eruptive fissures steeply dipping towards the caldera depression and elongated vents. The flaring area can be rather asymmetric and is usually filled by down-vent rheomorphic flow of the proximal fallout deposit. The lower conduits are filled by lava plug, agglutination of juveniles onto conduit walls and dyke intrusion with eventual dome extrusion. The eruption dynamics of welded fallout deposits and magma fragmentation within the conduit are consistent with an evolution from explosive to effusive. In this context conduit flow regimes evolve from turbulent to annular flow in which the conduit is progressively choked, and laminar flow leading to the final conduit closure.

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“…For example, dikes feeding lava flows and spatter cones are common in many basaltic settings and, unless they show some particular features, do not normally deserve detailed studies (Atkinson and Lambert 1990;Gudmundsson et al 2008). In contrast, explosive felsic deposits physically connected to their conduits are rather unusual and in a few cases are well described (Almond 1971;Koronovsky 1971;Ekren and The processes of bubble nucleation, vesiculation and deformation have been widely studied in magmas containing small bubbles, and vesicles are also commonly used as magma-flow indicators (Coward 1980;Manga et al 1998;Philpotts and Philpotts 2007;Rust et al 2003). Vesicles and gas bubbles up to decimetre scale are common in volcanic rocks of any composition in the geological record.…”

Section: Introductionmentioning

confidence: 93%

Giant gas bubbles in a rheomorphic vent fill at the Las Cañadas caldera, Tenerife (Canary Islands)

et al. 2009

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During rheomorphism subsequent to fallout deposition, a portion of the densely welded fallout of the La Grieta Member flowed back into the vent from where it was erupted, while the rest of it flowed down the outer slopes of the Las Cañadas caldera in Tenerife. The welded fallout and conduit-vent structure are physically connected and constitute a rare example of this type of deposits rooted to its feeder conduit and exposed in the caldera wall. The lower part of the vent-filling rheomorphic rocks shows gas bubbles and cavities that increase in size (up to 4 m) down vent. Bubbles are deformed against other bubbles, against the steep vent walls, flattened parallel to the flow foliation planes, and elongated parallel to the flow lineation and flow fold axes. The preservation of such giant bubbles, rather than their formation, seems to be a pretty unique feature of the phonolitic products investigated here and it is likely the result of the combination of factors that acted to preserve, in the surrounding of the glass transition interval, the sealing and the late stage cooling of a pressurized system. In addition, strain drop at the base of the vent-filling rheomorphic flow caused by flow stopping against vertical vent walls may have promoted rapid gas exsolution and the formation of large bubbles.

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The structure of the feeding channels of the ignimbrite and tufflava complexes of the northern Caucasus

Cited by 7 publications

References 1 publication

Ignimbrite vents in the Sabaloka cauldron, Sudan

Ignimbrite vents in the Sabaloka cauldron, Sudan

Conduit-vent structures and related proximal deposits in the Las Cañadas caldera, Tenerife, Canary Islands

Giant gas bubbles in a rheomorphic vent fill at the Las Cañadas caldera, Tenerife (Canary Islands)

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