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The interpretation of thermal neutron properties in ocean floor volcanics

By
T. S. Brewer
T. S. Brewer
Department of Geology, University of Leicester, Leicester, LE1 7RH, UKtsb5@leicester.ac.uk
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P. K. Harvey
P. K. Harvey
Department of Geology, University of Leicester, Leicester, LE1 7RH, UKtsb5@leicester.ac.uk
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S. R. Barr
S. R. Barr
Department of Geology, University of Leicester, Leicester, LE1 7RH, UKtsb5@leicester.ac.uk
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S. L. Haggas
S. L. Haggas
Department of Geology, University of Leicester, Leicester, LE1 7RH, UKtsb5@leicester.ac.ukIHS Energy, Enterprise House, Cirencester Road, Tetbury, Glos, GL8 8RX, UK
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H. Delius
H. Delius
Department of Geology, University of Leicester, Leicester, LE1 7RH, UKtsb5@leicester.ac.uk
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Published:
January 01, 2005

Abstract

Using near-complete chemical analyses, computed thermal absorption cross-section values (σ) are calculated for ocean-floor basalts from ODP Holes 896a and 1179D. Comparison with nuclear measurement of σ, demonstrates that this computational method is valid and clarifies the interpretation of σ in ocean-floor basalts. Boron, lithium and the rare-earth elements are important controls on the σ-values, and, of these, the distribution of the rare-earth elements is controlled by primary magmatic processes, whereas the distribution of boron and lithium is strongly influenced by secondary low-temperature alteration processes. Consequently, computed σ-values can be used to discriminate between various basalt types and to identify areas of secondary alteration.

Following calibration of the ‘fresh basalt’ signature, it is possible to interpret log derived neutron absorption measurements of a sample (Σ-values), which, when integrated with other log responses, allow the distribution of alteration within a drilled section to be mapped. Examples from ODP Hole 801C demonstrate the potential of this technique.

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Contents

Geological Society, London, Special Publications

Petrophysical Properties of Crystalline Rocks

P. K. Harvey
P. K. Harvey
University of Leicester, UK
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T. S. Brewer
T. S. Brewer
University of Leicester, UK
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P. A. Pezard
P. A. Pezard
Université de Montpellier II, France
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V. A. Petrov
V. A. Petrov
IGEM, Russian Academy of Sciences, Russia
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Geological Society of London
Volume
240
ISBN electronic:
9781862394889
Publication date:
January 01, 2005

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