Results 201 to 210 of about 623,895 (284)

Factors governing the formation of pyroclastic rocks

Bulletin Volcanologique, 1970
The basic condition governing the formation of pyroclastic rocks is the relationship between the disruptive force of gas pressure in bubbles to the strength of the liquid for short term stresses and surface tension. The latter factor controls the coalescence of bubbles, because it is strongly dependent on the composition, temperature, and water content
A. R. McBirney, T. Murase
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Stratigraphic Problems of Pyroclastic Rocks

1984
Stratigraphic methods used to study volcanic rocks are similar to those used to study sedimentary rocks and have similar purposes: establishing correlations, vertical time sequences, determining facies changes and the like. Additional aid in pyroclastic stratigraphy comes from igneous petrology, studies of magma evolution, and studies of the growth ...
Richard V. Fisher, Hans-Ulrich Schmincke
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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 ...
Richard V. Fisher, Hans-Ulrich Schmincke
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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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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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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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Early-stage smectites from pyroclastic rocks of Almería (Spain)

Chemical Geology, 1991
Abstract In the volcanic region of Cabo de Gata (Almeria, Spain) bentonite deposits were formed from pyroclastic rocks. There is evidence that the smectite composition changed from Fe-rich to Al-rich members as the degree of hydrothermal alteration increased. Because true initial stages of alteration do not occur in this region, artificial hydrolysis
E. Caballero, E. Reyes, F. Huertas, J. Linares, A. Pozzuoli   +4 more
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Altered pyroclastic rocks in South African iron-formation

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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Monitoring a deep excavation in pyroclastic soil and soft rock

, 2021
M. Nicotera, G. Russo
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