Results 191 to 200 of about 20,254 (256)

Pyroclastic Rocks and Tectonic Environment

1984
The close proximity of continental borderlands, active and ancient tectonic regions, and modern and ancient volcanoes has long been known. Pre-plate tectonic ideas about this association culminated in Kay’s (1951) masterful synthesis showing the relationship between volcanic island arcs and ancient eugeosynclinal sedimentary basins containing abundant ...
Hans-Ulrich Schmincke, Richard V. Fisher
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Potassium—argon ages of sedimentary and pyroclastic rocks

Geological Society, London, Special Publications, 1964
Summary It is rarely possible to obtain reliable potassiumargon ages from sedimentary rocks. Glauconites generally give dates that are too low and very scattered, though the largest of a group of such measurements may be useful to define minimum ages of sediments that cannot be dated in any other way.
Halfdan Baadsgaard, Martin Henry Dodson
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Pyroclastic rocks in the Cnapan Breaca felsite, Rhum

Geological Magazine, 1985
AbstractThe Cnapan Breaca felsite sheet contains strongly devitrified pyroclastic rocks including welded tuffs. These indicate formation in a high level, surficial or sub-volcanic environment. The gross structure and lithological associations of the sheet are similar to those of some ignimbrites. These observations support a resurgent caldera model for
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Stratigraphy of Jurassic pyroclastic rocks in the Transantarctic Mountains

Journal of African Earth Sciences, 2000
Abstract Jurassic pyroclastic rocks cap the Antarctic Gondwana sequence and document an important event in the evolution of the continent. The Hanson Formation, which crops out in the central Transantarctic Mountains, consists of ca 240 m of silicic tuffs, tuffaceous sandstones, and subordinate quartzose sandstones of probable Early Jurassic age.
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Recognition and Significance of Pumice in Marine Pyroclastic Rocks

Geological Society of America Bulletin, 1969
Pumice is abundant in many ancient sequences of marine pyroclastic rocks and is regarded as important evidence that contemporaneous, or nearly contemporaneous, volcanic activity was the source of at least some of the fragmental debris. The pumice in many such sequences of rocks, however, is easily overlooked, chiefly because most marine pyroclastic ...
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The Mechanical Behaviour of a Pyroclastic Rock: Yield Strength and "Destructuration" Effects

Rock Mechanics and Rock Engineering, 1998
A research programme on the mechanical behaviour of a homogenous volcanic tuff found in the centre of the city of Naples (Italy) was carried out at the University of Naples a few years ago. Isotropic and drained triaxial tests were performed in a very wide range of confining pressures (up to 60 MPa). After presenting the stress-strain curve pattern and
S. Aversa, EVANGELISTA, ALDO
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Experimental Evidence of Non-Linear and Creep Behaviour of Pyroclastic Rocks

1994
An analysis of the mechanical behaviour of pyroclastic rocks is discussed in this paper, with particular evidence to non-linear and creep behaviour. This topic is treated presenting experimental results obtained on Neapolitan tuffs at the University of Naples.
AVERSA S., EVANGELISTA, ALDO
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Altered pyroclastic rocks in South African iron-formation [PDF]

Economic Geology, 1966
Hundreds of layers composed dominantly of stilpnomelane occur in thick extensive iron-formation in the Transvaal system in South Africa. Examination of thin sections reveals that many of these layers contain axiolitic shard-like structures, suggesting that they are altered pyroclastic material, presumably water-laid tuffs.
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Pyroclastic rocks and calderas associated with strongly peralkaline magmatism

Journal of Geophysical Research: Solid Earth, 1984
Strongly peralkaline volcanic complexes tend to be shieldlike due to coalescence of low‐viscosity lavas from numerous vent areas and blanketing by pyroclastic flows and falls. Dense welding and rheomorphism commonly mask the nature of pyroclastic units; welded pumice falls are common.
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Upper Jurassic pyroclastic rocks in Skye, west Scotland

Nature, 1977
DURING a systematic sampling of shale lithologies in the Jurassic beds of Skye, an examination was made of sections in the Staffin Shales1–3 in Staffin Bay. Two localities were visited, one immediately south of the landslip at point 6 (ref. 4) [NG470712] and the other at point 7 (ref.
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