Crystal sizes in evolving silicic magma chambers
- 1Department of Geology and Geophysics, University of Wisconsin, 1215 W. Dayton Street, Madison, Wisconsin 53706, USA
Abstract
Crystal size distributions (CSDs) of quartz and zircon phenocrysts in individual pumice clasts from several voluminous ash-flow tuffs provide a quenched snapshot view of conditions in preclimactic magma chambers. A common feature of these CSDs is a concave-down, lognormal shape, in contrast to the reported linear CSDs in more mafic systems. This feature is interpreted to be a general result of surface-controlled, size-dependent growth by a layer nucleation in silicic magmas at low supersaturation. Specific CSDs may be important for interpreting nucleation and crystal-growth conditions and mechanisms in magmas erupted as large ash-flow tuffs and smaller-volume volcanic units, and for fingerprinting different magma batches (layers) in products of the same eruption.
Footnotes
-
↵*inbindemgeology.wisc.edu
-
↵GSA Data Repository item 2003044, Table DR1, measured abundance, concentration, and sizes of phenocrysts, and Appendix, methods, is available from Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301-9140,editinggeosociety.org, or at www.geosociety.org/pubs/ft2003.htm.
-
- Accepted December 13, 2002.
- Received October 30, 2002.
- Revision received December 11, 2002.
- Geological Society of America
