Quick
Search: 		  
advanced search
 GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help 
American Mineralogist Don't get GSW? Talk to your librarian.
JOURNAL HOME HELP CONTACT PUBLISHER SUBSCRIBE ARCHIVE SEARCH TABLE OF CONTENTS
American Mineralogist; February 2005; v. 90; no. 2-3; p. 417-427; DOI: 10.2138/am.2005.1456
© 2005 Mineralogical Society of America
This Article
Right arrow Figures Only
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (9)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Larsen, J. F.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation

Experimental study of plagioclase rim growth around anorthite seed crystals in rhyodacitic melt

Jessica F. Larsen*

Geophysical Institute, University of Alaska, Fairbanks, Alaska 99775, U.S.A.

Correspondence: * E-mail: faust{at}gi.alaska.edu

The purpose of this study was to replicate experimentally the growth of new rims around highly anorthitic plagioclase "core" phenocrysts, analogous to the incorporation of xenocrysts into a silicic magma body through magma mixing. Aniakchak rhyodacite forms the bulk starting composition, and phase-equilibria experiments constrained the pre-eruption magma conditions to be ~110 MPa and 870–880 °C. The experimental runs were seeded with Great Sitkin anorthite (An91–95) crystals. New rim growth of An28–38 plagioclase occurred at rates between 3.5 (±0.3) x10–10 to 60.6 (±20.0) x10–10 cm/s at pressures and temperatures from 50 to 150 MPa and 825 to 880 °C. The values in parentheses are ±1{sigma} standard deviation. Microlite crystallization (An27–41) occurred in all experiments within the plagioclase stability field, and their growth rates varied from 4.4 (±1.3) x10–10 to 65.7 (±10.1) x10–10 cm/s. The rim and microlite growth rates are similar to one another within each experiment, and microlite number density (NV) is correlated approximately inversely with rim growth rates. Microlite crystallinities increased from 4.2 to 49.7 vol% as a function of increasing {Delta}Teff up to 95 °C. The results indicate growth-dominated crystallization at low {Delta}Teff, and nucleation dominated crystallization at high {Delta} Teff, in agreement with previous studies. Assuming the experiments apply to nature, the rim growth rates can provide a minimum estimate on how fast magma mixing can occur. Rims that are 10 to 100 µm wide can grow in ~10 days to 4 months, recording fast mixing timescales as long as eruption occurs shortly after mixing. The growth rate estimates presented here generally agree with those derived from sodic rims growing around anorthite cores after mixing between basalt and andesite prior to the 1996 eruption of Karymsky volcano, Kamchatka.




This article has been cited by other articles:


Home page
 Eur J MineralHome page
A. Orlando, M. D'Orazio, P. Armienti, and D. Borrini
Experimental determination of plagioclase and clinopyroxene crystal growth rates in an anhydrous trachybasalt from Mt Etna (Italy)
European Journal of Mineralogy, August 1, 2008; 20(4): 653 - 664.
[Abstract] [Full Text] [PDF]

Home page
 GeologyHome page
S. de Silva, G. Salas, and S. Schubring
Triggering explosive eruptions--The case for silicic magma recharge at Huaynaputina, southern Peru
Geology, May 1, 2008; 36(5): 387 - 390.
[Abstract] [Full Text] [PDF]


JOURNAL HOME HELP CONTACT PUBLISHER SUBSCRIBE ARCHIVE SEARCH TABLE OF CONTENTS
Copyright © 2008 by Mineralogical Society of America