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Structure and evolution of hydrothermal vent complexes in the Karoo Basin, South Africa

Henrik Svensen, Bjorn Jamtveit, Sverre Planke and Luc Chevallier
Structure and evolution of hydrothermal vent complexes in the Karoo Basin, South Africa
Journal of the Geological Society of London (July 2006) 163 (4): 671-682

Abstract

The Karoo large igneous province, formed at c. 183 Ma, is characterized by the presence of voluminous basaltic intrusive complexes within the Karoo Basin, extrusive lava sequences and hydrothermal vent complexes. These last are pipe-like structures, up to several hundred metres in diameter, piercing the horizontally stratified sediments of the basin. Detailed mapping of two sediment-dominated hydrothermal vent complexes shows that they are composed of sediment breccias and sandstone. The breccias cut and intrude tilted host rocks, and are composed of mudstone and sandstone fragments with rare dolerite boulders. Sandstone clasts in the breccias are locally cemented by zeolite, which represents the only hydrothermal mineral in the vent complexes. Our data document that the hydrothermal vent complexes were formed by one or a few phreatic events, leading to the collapse of the surrounding sedimentary strata. We propose a model in which hydrothermal vent complexes originate in contact metamorphic aureoles around sill intrusions. Heating and expansion of host rock pore fluids resulted in rapid pore pressure build-up and phreatic eruptions. The hydrothermal vent complexes represent conduits for gases and fluids produced in contact metamorphic aureoles, slightly predating the onset of the main phase of flood volcanism.


ISSN: 0016-7649
EISSN: 2041-479X
Coden: JGSLAS
Serial Title: Journal of the Geological Society of London
Serial Volume: 163
Serial Issue: 4
Title: Structure and evolution of hydrothermal vent complexes in the Karoo Basin, South Africa
Affiliation: University of Oslo, Department of Physics, Blindern, Norway
Pages: 671-682
Published: 200607
Text Language: English
Publisher: Geological Society of London, London, United Kingdom
References: 63
Accession Number: 2006-058840
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. geol. sketch maps, anals., strat. cols., 1 table, sect.
S31°16'00" - S31°10'60", E27°07'60" - E27°13'60"
Secondary Affiliation: Volcanic Basin Petroleum Research, NOR, NorwayCouncil for Geoscience, ZAF, South Africa
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data from The Geological Society, London, London, United Kingdom
Update Code: 200632
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