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Roof-rock contamination of magma along the top of the reservoir for the Bishop Tuff

January 1, 1995

The Bishop Tuff, a Quaternary high-silica rhyolite in east-central California, is widely considered the type example of a vertically and monotonically zoned pyroclastic deposit that represents zoning in the source magma reservoir, inverted during the process of pyroclastic emplacement. However, the deposit of plinian pumice, which forms the base of the Bishop Tuff and represents the initial 10% or so of all magma erupted during the event that produced the Bishop Tuff, contains features at odds with monotonic zoning for the reservoir. Relative to overlying ignimbrite, the plinian deposit contains a reversal in trace-element zoning. The data have been previously interpreted as due to processes of chemical fractionation and evolution operating within a magma system closed to chemical interactions with its roof rocks. However, it is suggested here that the reversed zoning and other above-noted features can be explained equally well as consequences of minor assimilation of roof rocks into a magma reservoir that was erupted from the top down. -from Authors

Citation Information

Publication Year 1995
Title Roof-rock contamination of magma along the top of the reservoir for the Bishop Tuff
DOI 10.1016/0377-0273(95)00026-7
Authors W. A. Duffield, J. Ruiz, J.D. Webster
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Volcanology and Geothermal Research
Series Number
Index ID 70018734
Record Source USGS Publications Warehouse
USGS Organization Volcano Hazards Program