Pre-eruptive conditions of the volcanic rocks from Snake River Plain, Yellowstone Hotspot-Constraints from experiments and phase equilibria modelling
Final Report Abstract
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 experimental results obtained for rhyolitic systems (Bruneau Jarbidge eruptive center) 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 contents 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 combination of results from phase equilibria and from the composition of glasses indicates that the depth of magma storage prior to eruption is in the range 200-400 MPa (~ 6 to 13km). The applicability of thermodynamic model COMAGMAT to basaltic samples from the Snake River Plain has been tested on the basis of own experiments and literature data. The model can reproduce previous experimental results and can be used to model the role of very small amounts of water on the differentiation paths at different pressures. The application of COMAGMAT to interpret whole rock compositions from the ICDP drilling localities should be helpful to discuss the amount of volatiles that may be released from crystallizing basalts at depth (these volatiles may react with crustal material to form rhyolitic melts).
Publications
- (2008) Phase relations and liquid lines of descent in hydrous ferrobasalt - Implications for the Skaergaard intrusion and Columbia River Flood basalts. Journal of Petrology, 49, 1687-1727
Botcharnikov R.E., Almeev R.R., Koepke J., Holtz F.
- (2008) Pre-eruptive conditions of the Bruno-Jarbidge Rhyolite, Snake River Plain-Yellowstone hotspot track. 86th Annual Meeting of the DMG (German Mineralogical Society), 14-17 September 2008, Berlin, Germany
Kuschel, L., Almeev, R.R., Holtz, F., Cathey, H.E., and Nash, B.P.
- (2008) Pre-eruptive conditions of the Bruno-Jarbidge Rhyolite, Snake River Plain-Yellowstone hotspot track: first experimental results. IAVCEI General Assembly, 18-22 August 2008, Reykjavík, Iceland
Almeev, R.R., Kuschel, L., Holtz, F., Cathey, H.E., and Nash, B.P.
- (2009) Experimental constraints on rhyolite magma genesis, Yellowstone hotspot. Goldschmidt Conference, 21-26 June, Davos, Switzerland
Almeev, R.R., Holtz, F., Kuschel, L., Nash, B.P., and Cathey, H.E.
- (2010) Crystallisation relations in Indian Batt and Cougar Point Tuff Rhyolites, Yellowstone Hotspot Track – an experimental study at 200MPa. EMPG-XIII, 12-14 April, 2010 Toulouse, France
Almeev, R.R., Nash, B.P., and Holtz, F.
