Extreme effusive eruptions: Palaeoflow data on an extensive felsic lava in the Mesoproterozoic Gawler Range Volcanics

McPhie, Jocelyn; Della-Pasqua, F. N.; Allen, Sharon; Lackie, Mark

doi:10.1016/j.jvolgeores.2006.11.011

Cited by 28 publications

(7 citation statements)

References 38 publications

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“…The Bracks Rhyolite of the Trans-Pecos in Texas covers 1,000 km 2 as a single tabular body that is 35 km long and ~100 m high (Henry et al 1990). The Keweenawan Plateau (USA) and Gawler Range (Australia) are also examples of volcanic fields that are composed of extensive silicic lava flows (Green & Fitz III 1993, McPhie et al 2008.…”

Section: Discussionmentioning

confidence: 99%

Morphology and stratigraphy of Serra Geral silicic lava flows in the northern segment of the Torres Trough, Paraná Igneous Province

2018

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The impetus for this research was the enigma regarding the origin of the extensive silicic volcanic units in the Paraná-Etendeka Igneous Province. Are they rheoignimbrites, lava flows, or a combination of both? The São Joaquim silicic eruptive sequence is comprised of Palmas-Type aphyric dacites and is located in the northern segment of Torres Trough, a dissected mountainous region in southern Brazil. These dacite outcrops form plateaus and remnant hills that are scattered above a basaltic andesitic landscape. The original morphology of the silicic volcanic flows was constrained based on the internal architecture, geometry, and cyclicity of the lithofacies, in conjunction with petrographic and geochemical information. The data suggests the presence of ancient large tabular and lobate silicic lava flows (~100 m thick and ~10-40 km extents). No pyroclastic features were found. Eight interdigitating units were mapped. These large aspect ratios are similar to ones for basaltic flows and those of Snake River-type rhyolites, and they suggest high effusion rates and high temperatures as well as the presence of well-insulated cooled crusts. Lavas would have overflowed from long fissure vents that had created an extensive volcanic silicic surface body composed of conjugated and interdigitated flows above the north segment of the Torres Trough region. KEYWORDS: Extensive silicic lavas; Paraná-Etendeka Large Igneous Province; Serra Geral volcanism; stratigraphy of Torres ARTICLE INTRODUCTIONExtensive silicic units are commonly associated with welded to rheomorfic high temperature (~1,100ºC) ignimbrites (White et al. 2009, Bryan et al. 2002, 2010, Ernest 2014, Wolff & Wright 1981. However, silicic lava flows can also form voluminous units, including those in some Large Igneous Provinces (LIPs) such as the North Atlantic, Madagascar, Snake RiverYellowstone, Chon Aike and Paraná-Etendeka LIPs (Mahoney & Coffin 1997, Ellis et al. 2013, Bonnichsen & Kauffman 1987, Pankhurst et al. 1998. The silicic volcanic units of the Cretaceous Paraná-Etendeka LIP were previously understood to be rheoignimbrites, in which pyroclastic textures would have been masked during emplacement. Therefore, extensive tabular silicic plateaus, high emplacement temperatures, and the presence of circular structures (e.g., Messum Crater in Namibia) led several pioneering authors to infer a pyroclastic origin for these rocks (Whittingham 1989, Garland et al. 1995, Roisenberg 1989, Milner et al. 1992. Since then, much important research on geochemistry and correlation has been conducted within the province, but there is still a lack of detailed cartographic and stratigraphic work, which could help in clarifying the origins of and relationships among the silicic rocks. Therefore, the emphasis of this study is on the physical aspects of the rocks, such as the internal architecture and geometry of bodies and their spatial distribution. The goal of this work is to begin to characterize the geologic framework of the wild and mountainous areas of the nor...

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Section: Discussionmentioning

confidence: 99%

Morphology and stratigraphy of Serra Geral silicic lava flows in the northern segment of the Torres Trough, Paraná Igneous Province

2018

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“…We conclude that although lineation trends and kinematic indicators combine to give an accurate local transport direction (cf. McPhie et al, 2008), they do not always provide a straightforward indication of source location, particularly without independent constraints on the substrate paleotopography.…”

Section: Can Rheomorphic Structures Reveal Ignimbrite Sources?mentioning

confidence: 99%

Emplacement and rheomorphic deformation of a large, lava-like rhyolitic ignimbrite: Grey's Landing, southern Idaho

Andrews

Branney

2010

Geological Society of America Bulletin

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The Miocene Grey's Landing ignimbrite reaches 70 m thick and covers at least 400 km 2 in the central region of the Snake River Plain. It shows particularly intense welding and rheomorphic deformation, and although parts are eutaxitic, most is lava-like with fl ow-banding and no fi amme. A nearubiquitous penetrative fl ow lamination, associated with a well-developed elongation lineation, is folded into small intrafolial tight to isoclinal oblique and sheath folds, which are refolded by larger folds in the upper parts. Structural and kinematic analysis reveals that welding and early deformation occurred rapidly during deposition from a very hot (≤1000 °C), high-mass-fl ux pyroclastic density current that fl owed westward across a graben-faulted landscape. As hot particles were deposited, they rapidly agglutinated and coalesced, and underwent noncoaxial shear in a subhorizontal ductile shear zone close to the current-deposit interface. The shear zone is interpreted to have been less than 2 m thick. It produced and deformed the rheomorphic fabric, and it migrated upward with the rising current-deposit interface during aggradation, so that it transiently affected all levels of the resultant thick ignimbrite. Deformation was progressive, and after the density current had dissipated, viscous spreading and downslope fl ow continued and involved an increasingly thick portion of the sheet. This folded the fl ow banding and F 1 intrafolial isoclines into larger sheath folds, and into more upright periclines near the top of the ignimbrite. We demonstrate that structural and kinematic analysis can elucidate the emplacement history of rheomorphic ignimbrites.

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“…Recent anisotropy of magnetic susceptibility (AMS) data obtained in independent studies from the interpreted lobe fronts in the southern Gawler Ranges preserve steeply dipping and bimodal orientations. We consider these orientations to be consistent with flow patterns at the termination of individual lobes, and a magma source to the northeast, contrasting with McPhie et al (2008) interpretation of a southwest source. In exposed southern areas, these lobes correspond with mappable single lobes within the upper Gawler Range Volcanics (e.g.…”

Section: Age and Morphology Of The Upper Gawler Range Volcanicsmentioning

confidence: 74%

A Mesoproterozoic continental flood rhyolite province, the Gawler Ranges, Australia: the end member example of the Large Igneous Province clan

et al. 2011

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Abstract. Rhyolite and dacite lavas of the Mesoproterozoic upper Gawler Range Volcanics (GRV) (>30 000 km 3 preserved), South Australia, represent the remnants of one of the most voluminous felsic magmatic events preserved on Earth. Geophysical interpretation suggests eruption from a central cluster of feeder vents which supplied large-scale lobate flows >100 km in length. Pigeonite inversion thermometers indicate eruption temperatures of 950-1100 • C. The lavas are A-type in composition (e.g. high Ga/Al ratios) and characterised by elevated primary halogen concentrations (∼1600 ppm fluorine, ∼400 ppm chlorine). These depolymerised the magma such that temperature-compositionvolatile non-Arrhenian melt viscosity modelling suggests they had viscosities of <3.5 log η (Pa s). These physicochemical properties have led to the emplacement of a Large Rhyolite Province, which has affinities in emplacement style to Large Basaltic Provinces. The low viscosity of these felsic magmas has produced a unique igneous system on a scale which is either not present or poorly preserved elsewhere on the planet. The Gawler Range Volcanic Province represents the erupted portion of the felsic end member of the family of voluminous, rapidly emplaced terrestrial magmatic provinces.

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Extreme effusive eruptions: Palaeoflow data on an extensive felsic lava in the Mesoproterozoic Gawler Range Volcanics

Cited by 28 publications

References 38 publications

Morphology and stratigraphy of Serra Geral silicic lava flows in the northern segment of the Torres Trough, Paraná Igneous Province

Morphology and stratigraphy of Serra Geral silicic lava flows in the northern segment of the Torres Trough, Paraná Igneous Province

Emplacement and rheomorphic deformation of a large, lava-like rhyolitic ignimbrite: Grey's Landing, southern Idaho

A Mesoproterozoic continental flood rhyolite province, the Gawler Ranges, Australia: the end member example of the Large Igneous Province clan

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