Quartz latite rheoignimbrite flows of the Etendeka Formation, north-western Namibia

Milner, Simon; Duncan, A. R.; Ewart, A.

doi:10.1007/bf00278389

Cited by 127 publications

(93 citation statements)

References 15 publications

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“…This is consistent with conclusions from studies of other ignimbrites in the Snake River Plain volcanic province (Ekren et al 1984;Honjo et al 1992;Cathey and Nash 2004) and some large igneous provinces, such as Etendeka-Parana (Bellieni et al 1984;Milner et al 1992;Kirstein et al 2001), the Whitsunday volcanic province, Australia (Bryan et al 2000), the Keweenawan rift, Minnesota (Green and Fitz 1993), and Trans-Pecos, Texas (Henry et al 1988). …”

Section: Pre-eruptive Temperaturesupporting

confidence: 88%

Rhyolitic ignimbrites in the Rogerson Graben, southern Snake River Plain volcanic province: volcanic stratigraphy, eruption history and basin evolution

Andrews

Branney

Bonnichsen³

et al. 2007

Bull Volcanol

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Section: Pre-eruptive Temperaturesupporting

confidence: 88%

Rhyolitic ignimbrites in the Rogerson Graben, southern Snake River Plain volcanic province: volcanic stratigraphy, eruption history and basin evolution

Andrews

Branney

Bonnichsen³

et al. 2007

Bull Volcanol

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“…Individual sheets in Namibia are 70-250 m thick, exceed 25,000 km 2 (Milner et al 1995;Jerram 2002), and have estimated magmatic temperatures exceeding 1,000°C. They have been interpreted as predominantly lava-like ignimbrites, although few unequivocal pyroclastic features are preserved and some have basal breccias (Milner et al 1992;Ewart et al 1998). Some units contain non-flattened globules, some larger than those in the Snake River ignimbrites.…”

Section: Cretaceous Etendeka-paraná Volcanic Province Namibia Angolmentioning

confidence: 97%

‘Snake River (SR)-type’ volcanism at the Yellowstone hotspot track: distinctive products from unusual, high-temperature silicic super-eruptions

et al. 2007

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A new category of large-scale volcanism, here termed Snake River (SR)-type volcanism, is defined with reference to a distinctive volcanic facies association displayed by Miocene rocks in the central Snake River Plain area of southern Idaho and northern Nevada, USA. The facies association contrasts with those typical of silicic volcanism elsewhere and records unusual, voluminous and particularly environmentally devastating styles of eruption that remain poorly understood. It includes: (1) largevolume, lithic-poor rhyolitic ignimbrites with scarce pumice lapilli; (2) extensive, parallel-laminated, medium to coarsegrained ashfall deposits with large cuspate shards, crystals and a paucity of pumice lapilli; many are fused to black vitrophyre; (3) unusually extensive, large-volume rhyolite lavas; (4) unusually intense welding, rheomorphism, and widespread development of lava-like facies in the ignimbrites; (5) extensive, fines-rich ash deposits with abundant ash aggregates (pellets and accretionary lapilli); (6) the ashfall layers and ignimbrites contain abundant clasts of dense obsidian and vitrophyre; (7) a bimodal association between the rhyolitic rocks and numerous, coalescing lowprofile basalt lava shields; and (8) widespread evidence of emplacement in lacustrine-alluvial environments, as revealed by intercalated lake sediments, ignimbrite peperites, rhyolitic and basaltic hyaloclastites, basalt pillow-lava deltas, rhyolitic and basaltic phreatomagmatic tuffs, alluvial sands and palaeosols. Many rhyolitic eruptions were high mass-flux, large volume and explosive (VEI 6-8), and involved H 2 O-poor, low-δ 18 O, metaluminous rhyolite magmas with unusually low viscosities, partly due to high magmatic temperatures (900-1,050°C). SR-type volcanism contrasts with silicic volcanism at many other volcanic fields, where the fall deposits are typically Plinian with pumice lapilli, the ignimbrites are low to medium grade (non-welded to eutaxitic) with abundant pumice lapilli or fiamme, and the rhyolite extrusions are small volume silicic domes and coulées. SR-type volcanism seems to have occurred at numerous times in Earth history, because elements of the facies association occur within some other volcanic fields, including Trans-Pecos Texas, EtendekaParaná, Lebombo, the English Lake District, the Proterozoic Keewanawan volcanics of Minnesota and the Yardea Dacite of Australia.

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“…They form a significant component of volcanism in diverse volcanic settings, including intracontinental volcanic provinces (e.g. Leat 1985;Henry et al 1989;Milner et al 1992); ocean island volcanoes (Wolff and Wright 1981;Schmincke et al 1993); and in continental arcs Kokelaar and Königer 2000).…”

Section: Introductionmentioning

confidence: 99%

Sheathfolds in rheomorphic ignimbrites

2004

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Structural reappraisal of several classic rheomorphic ignimbrites in Colorado, Idaho, the Canary Islands and Italy has, for the first time, revealed abundant oblique folds, curvilinear folds and sheathfolds which formed during emplacement. Like their equivalents in tectonic shear-zones, the sheathfold axes lie sub-parallel to a pervasive elongation lineation, and appear as eye structures on rock surfaces normal to the transport direction. With the recognition of sheathfolds, ignimbrites previously inferred to have undergone complex rheomorphic deformation histories are re-interpreted as recording a single, progressive deformation event. In some examples, the trends of sheathfolds and related lineations change with height through a single ignimbrite suggesting that rheomorphism did not affect the entire thickness of ignimbrite synchronously. Instead, we infer that in these ignimbrites a thin ductile shear-zone rose gradually through the aggrading agglutinating mass whilst the flow direction varied with time. This suggests that, in some cases, both welding and rheomorphism can be extremely rapid, with ductile strain rates significantly exceeding rates of ignimbrite aggradation.

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Quartz latite rheoignimbrite flows of the Etendeka Formation, north-western Namibia

Cited by 127 publications

References 15 publications

Rhyolitic ignimbrites in the Rogerson Graben, southern Snake River Plain volcanic province: volcanic stratigraphy, eruption history and basin evolution

Rhyolitic ignimbrites in the Rogerson Graben, southern Snake River Plain volcanic province: volcanic stratigraphy, eruption history and basin evolution

‘Snake River (SR)-type’ volcanism at the Yellowstone hotspot track: distinctive products from unusual, high-temperature silicic super-eruptions

Sheathfolds in rheomorphic ignimbrites

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