Evolution of magma storage conditions along the track of Yellowstone Hotspot: investigation of the volcanic rocks from Snake River Plain
Zusammenfassung der Projektergebnisse
The proposed project was a contribution to the determination of magma storage conditions and differentiation processes 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 magma storage conditions of rhyolitic and basaltic magmas were constrained using three complementary approaches: (1) chemical analysis of natural minerals and glasses, (2) high pressure experimental studies to determine phase equilibria and (3) thermodynamic modeling. The application of thermodynamic models on basaltic compositions and the experimental results obtained for rhyolitic melts show that magmas in the Snake River Plain are nearly dry. The experimental results obtained for older rhyolitic systems (Bruneau Jarbidge eruptive center, 12.8–8.1 Ma) indicate pre-eruptive temperatures in the range 900 to 1000°C, depending on the eruptive sequence. The composition of clinopyroxene and pigeonite pairs, occurring in most of the samples, can only be reproduced if the water content of silicate melts is below 1.5 wt% H2O at 900°C or even lower if the temperature is higher. Water contents in melts as low as 0.5 to 1 wt% H2O are realistic, indicating the extremely low water activities in the rhyolitic systems. The temperatures are lower (825-875 °C) and the melt water content are estimated to be slightly higher (1.5 – 2.5 wt% H2O) in the younger rocks from the Heise eruptive center (6.6-4.4 Ma). The results confirm the general decrease of temperature of rhyolitic melts with time, with temperatures close to 800 °C for the youngest units (~ 2 Ma.). Magma storage pressures seem to vary significantly between different eruption centers over time and a general decrease of pressure with time is observed. The magma storage pressure for the oldest rhyolites, 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 rhyolites from the Yellowstone Plateau complex that has been active for the last 2 Ma. This 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.
Projektbezogene Publikationen (Auswahl)
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(2011): Preliminary estimates on magma storage conditions of the Heise volcanic field, Snake River Plain, Goldschmidt- 2011, 14-19 August 2011, Prague, Czech Republic, Mineralogical Magazine, Vol. 75 (3), 548
Bolte, T., Erdmann, M., Nash, B.P., Cathey, H.E., Almeev, R., Holtz F.
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(2012) High temperature, low H2O silicic magmas of the Yellowstone hotspot: an experimental study of rhyolite from the Bruneau-Jarbidge eruptive center. Journal of Petrology, 53, 1837-1866
Almeev R., Bolte T., Nash B., Holtz F., Erdmann M., Cathey H.
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(2012): The ternary Qz-Ab-Or system as a geobarometer for natural rhyolite: new experiments and implications for the Snake River Plain silicic magmas, 2012 AGU Fall Meeting, 3-7 December 2012, San Francisco, California
Almeev, R., Bolte, T., Holtz F., Nash, B.P.
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(2013) Empirical equation on minimum water content of a ryolithic melt as a function of temperature and pressure. Annual Meeting of the DMG (German Mineralogical Society), 15-18 September 2013, Tübingen, Germany
Ciazela J., Holtz F.
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(2013): Petrology of the Rhyolites in the Kimberly Drill Core, Project Hotspot, Snake River Plain, Idaho, 2013 AGU Fall Meeting , 9-13 December 2013, San Francisco, California
Christiansen, E.H., McCurry, M., Bindeman, I., Champion, D., Knott, T., Branney M.J., Bolte, T., Holtz, F., and Shervais, J.
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(2013): T Magma storage conditions of the Heise volcanic field, Snake River Plain – an experimental study -, 91. Annual meeting of the German Mineralogical Society (DMG), 15-19 September 2013, Tübingen, Germany
Bolte, T., Holtz F., Almeev, R., Nash, B.P.
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(2015) The Blacktail Creek Tuff: An analytical and experimental study of rhyolites from the Heise volcanic field, Yellowstone hotspot system. Contrib Mineral Petrol, 169, 2, 1-24
Bolte T., Holtz F., Almeev R., Nash B.
