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Volcanoes and Their Products
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
The rock shown in Figure 7.25, from the Sierra Madre Occidental volcanic field in Mexico, is an ignimbrite containing consolidated volcanic ash with coarser-grained rock fragments of variable composition. Some of the fragments are pumice that has been squashed into flattened shapes called fiamme. The fiamme weathered and eroded, in places leaving long skinny holes.
Paleomagnetism of the Carboniferous Gresford Block, Tamworth Belt, southern New England Orogen: minor counter-clockwise rotation of a primary arc segment
Published in Australian Journal of Earth Sciences, 2020
Samples have been drilled with a Stihl auger with its gearbox adapted for higher rotation, water cooling and a self-centring chuck, using barrels of non-magnetic steel for minimal magnetic contamination and bits with high diamond content and soft matrix for optimal penetration in quartz-rich ignimbrites. Cores have been oriented with integrated solar and magnetic compasses and a clinometer, with confirmation between both compass orientations generally within 1°. Bedding has been determined from tuff and/or sedimentary surfaces and from planar ‘fiamme’ structures if developed in ignimbritic flows. At least 10 and up to 16 individually oriented cores have been sampled at each volcanic or volcaniclastic site (N = 87), bar one (7 cores), with cores sandblasted to remove magnetic contamination, sliced into specimens of 2.2 cm height and 2.5 cm diameter and with top and bottom slightly ground down on a diamond lap to minimise contamination and shape irregularities.
Geochronology and geochemistry of the Devonian Gumbardo Formation (Adavale Basin): evidence for cratonisation of the Central Thomson Orogen by the Early Devonian
Published in Australian Journal of Earth Sciences, 2018
P. Asmussen, S. E. Bryan, C. M. Allen, D. J. Purdy
Juvenile clasts in the ignimbrites are usually welded forming fiamme with phenocrysts of K-feldspar, plagioclase and quartz (Figure 6c), but also occur as nonwelded, vesiculated clasts in one ignimbrite (ALL-1A). The ash matrix in all ignimbrites exhibits variably sericitised, moderately welded vitriclastic shard textures (Figure 6e, f). Lithic fragments are only present in three samples (ALL-1A, ALL-1B and COT-1) comprising a variety of igneous lithologies including plagioclase-bearing lava clasts showing trachytic texture (inferred to be of intermediate composition), devitrified aphyric silicic lava clasts, granitic clasts, hornblende- and pyroxene-phyric pilotaxitic lava clasts and ignimbrite clasts (Table 4). The ignimbrites of the Gumbardo Formation are flat-lying to gently dipping (eutaxitic fabrics at 65–90° to the core axis) but core material was not oriented; thus bedding measurements remain uncorrected for the deviation angles and should be viewed as semiquantitative (Table 2).
New age constraints for the Tommy Creek Domain of the Mount Isa Inlier, Australia
Published in Australian Journal of Earth Sciences, 2023
A. Brown, C. Spandler, T. G. Blenkinsop
The Milo beds can be separated into an upper and lower sequence, with the lower sequence comprising feldspathic psammites and volcano-sedimentary rocks with lenses of dolomitic marble. The volcano-sedimentary rocks include ribbon breccias, as well as probable relict fiamme, and correlate to the Tommy Creek Beds of Hill et al. (1992). The upper sequence comprises biotite metasiltstones, muscovite schist, graphitic phyllite (generally 5–15% total graphitic carbon), lenses of dolomitic marble and biotite–garnet schist. The graphitic phyllite locally contains andalusite, staurolite and sillimanite.