Determination of the depth of rhyolitic magma chambers in the Snake River Plain province, USA,: an experimental calibration
Mineralogy, Petrology and Geochemistry
Final Report Abstract
The proposed project was a contribution to the determination of the depth of magma storage of rhyolitic magmas in the Snake River Plain volcanic province (western United States). The project is part of a larger initiative aimed to trace the Snake River Plain – Yellowstone (SRPY) hotspot and its interaction with the lithosphere. The depth of the rhyolitic magma reservoirs were constrained using a new geobarometer calibrated for CaO- and FeO-bearing rhyolitic systems relevant for the Snake River Plain province. The barometer is based on the composition of natural melts (glasses) coexisting with quartz and at least one feldspar. Such melts have cotectic compositions and their normative proportions of quartz/albite/orthoclase components can be used to constrain pressure because the position of the quartz–feldspar cotectic curves are known to be pressure dependent. Crystallization experiments were performed to constrain liquidus phase relations at 200 MPa and 500 MPa, at various water activities and at various melt CaO concentrations. The cotectic compositions were modeled empirically and a barometer DERP (DEtermining Rhyolite Pressures) was calibrated to calculate pressures of magma storage from cotectic glass compositions with up to 7wt % normative melt An. The application of DERP is restricted to high-silica rhyolitic systems saturated with respect to quartz and feldspar(s). The new barometer was tested against various independent methods for estimating rhyolite pressures available in the literature (with an overall error of less than 100 MPa). Comparing pressures estimated with DERP and rhyolite-MELTS, which are based on the same approach, suggests that rhyolite-MELTS underestimates the effect of An. The application of the barometer to volcanic rocks of the Snake River Plain indicates that Magma storage pressures may vary significantly between different eruption centers over time. A general decrease of magma storage pressure with time is observed. This pressure decrease seems to correlated with a decrease of the pre-eruptive temperature (from ~ 950 to 800 °C). The magma storage pressure of the hot rhyolites older than ~ 10 Ma, represented by the Bruneau-Jarbidge volcanic field, is estimated to be 340 ± 45 MPa. A storage at pressures of 260 ± 30 Ma is determined for younger rhyolites (10.5 to 4.4 Ma) of the Twin Falls and Heise eruptive centers. A very low pressure range of 80 ± 55 MPa is estimated for the youngest low-temperature rhyolites from the Yellowstone Plateau complex that has been active for the last 2 Ma. The general decrease of the depth of magma storage needs to be confirmed with more carefully selected eruptive units. Our preliminary results also indicate that there may be a strong variation of pressure (and may be temperature) within one eruptive unit. This would indicate that single rhyolitic eruptions may tap different reservoirs located at different depths. This feature is also observed for the basaltic systems.
Publications
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(2013): Experimental calibration of cotectic melt compositions coexisting with quartz and feldspar in rhyolitic systems - Application to Snake River Plain rhyolites, Yellowstone hotspot, AGU Fall Meeting, 9-13 December 2013, San Francisco, California
Holtz, F., Klahn, C., Bolte, T., Almeev, R. R., Christiansen, E.H., Nash, B.P.
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(2015): Cotectic Compositions: A New Geobarometer for “Dry” Rhyolites. Goldschmidt Conference, Prague
Wilke S. , Bolte T., Almeev R.R., Christiansen E.H., Holtz F.
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(2015): Experimental investigation of the effect of Ca, Fe and Ti on cotectic compositions of the rhyolitic system. European Journal of Mineralogy, 27(2), 147-159
Wilke, S., Klahn, C., Bolte, T., Almeev, R., & Holtz, F.
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(2015): The haplogranite system as a geobarometer for highly evolved melts – experimental investigations on the effect of Anorthite. Annual meeting of the German Mineralogical Society (DMG), Berlin
Wilke S. , Bolte T., Almeev R.R., Christiansen E.H., Holtz F.
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(2017) Crystallization experiments in rhyolitic systems: the effect of temperature cycling and starting material on crystal size distribution. American Mineralogist
Muniz da Silva M., Holtz F., Namur O.
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(2017) The effect of anorthite content and water on quartz feldspar-cotectic compositions in the rhyolitic system and implications for geobarometry. J Petrology
Wilke S., Holtz F., Almeev R., Neave D.
