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Pressure increases, the formation of chromite seams, and the development of the ultramafic series in the Stillwater Complex, Montana

Journal of Petrology

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Abstract

This paper explores the hypothesis that chromate seams in the Stillwater Complex formed in response to periodic increases in total pressure in the chamber. Total pressure increased because of the positive ??V of nucleation of CO2 bubbles in the melt and their subsequent rise through the magma chamber, during which the bubbles increased in volume by a factor of 4-6. By analogy with the pressure changes in the summit chambers of Kilauea and Krafla volcanoes, the maximum variation was 0.2-0.25 kbar, or 5-10% of the total pressure in the Stillwater chamber. An evaluation of the likelihood of fountaining and mixing of a new, primitive liquid that entered the chamber with the somewhat more evolved liquid already in the chamber is based upon calculations using observed and inferred velocities and flow rates of basaltic magmas moving through volcanic fissures. The calculations indicate that hot, dense magma would have oozed, rather than fountained into the chamber, and early mixing of the new and residual magmas that could have resulted in chromite crystallizing alone did not take place. -from Author

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Pressure increases, the formation of chromite seams, and the development of the ultramafic series in the Stillwater Complex, Montana
Series title:
Journal of Petrology
Volume
34
Issue:
5
Year Published:
1993
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Petrology
First page:
955
Last page:
976
Number of Pages:
22