Skip to Main Content
Book Chapter

Fragmentation, nucleation and migration of crystals and bubbles in the Bishop Tuff rhyolitic magma

By
Guilherme A. R. Gualda
Guilherme A. R. Gualda
Search for other works by this author on:
David L. Cook
David L. Cook
Search for other works by this author on:
Rahul Chopra
Rahul Chopra
Search for other works by this author on:
Liping Qin
Liping Qin
Search for other works by this author on:
Alfred T. Anderson, Jr
Alfred T. Anderson, Jr
Search for other works by this author on:
Mark Rivers
Mark Rivers
Search for other works by this author on:
Published:
January 01, 2004

The Bishop Tuff (USA) is a large-volume, high-silica pyroclastic rhyolite. Five pumice clasts from three early stratigraphic units were studied. Size distributions were obtained using three approaches: (1) crushing, sieving and winnowing (reliable for crystals > 100 µrn); (2) microscopy of ∼ 1 mm3 fragments (preferable for crystals <100 urn); and (3) computerised X-ray microtomography of ∼ 1cm3 pumice pieces.

Phenocryst fragments coated with glass are common, and the size distributions for all crystals are concave-upward, indicating that crystal fragmentation is an important magmatic process.

Three groups are recognised, characterised by: (1) high-density (0.759–0.902 g cm−3,) high-crystal content (14.4–15.3 wt.%) and abundant large crystals (>800 µm); concave-downward size distributions for whole crystals indicate late-stage growth with limited nucleation, compatible with the slow cooling of a large, gas-saturated, stably stratified magma body; (2) low-density (0.499 g cm−3), low-crystal content (6.63 wt.%) and few large crystals; the approximately linear size distribution reveals that nucleation was locally important, perhaps close to the walls; and (3) intermediate characteristics in all respects.

The volumetric fraction of bubbles inversely correlates with the number of large crystals. This is incompatible with isobaric closed-system crystallisation, but can be explained by sinking of large crystals and rise of bubbles in the magma.

You do not currently have access to this article.
Don't already have an account? Register

Figures & Tables

Contents

GSA Special Papers

The Fifth Hutton Symposium on the Origin of Granites and Related Rocks

S. Ishihara
S. Ishihara
Search for other works by this author on:
W.E. Stephens
W.E. Stephens
Search for other works by this author on:
S.L. Harley
S.L. Harley
Search for other works by this author on:
M. Arima
M. Arima
Search for other works by this author on:
T. Nakajima
T. Nakajima
Search for other works by this author on:
Geological Society of America
Volume
389
ISBN print:
9780813723891
Publication date:
January 01, 2004

GeoRef

References

Related

A comprehensive resource of eBooks for researchers in the Earth Sciences

This Feature Is Available To Subscribers Only

Sign In or Create an Account

This PDF is available to Subscribers Only

View Article Abstract & Purchase Options

For full access to this pdf, sign in to an existing account, or purchase an annual subscription.

Subscribe Now