A clinopyroxene-basalt geothermobarometry perspective of Columbia Plateau (NW-USA) Miocene magmatism

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Journal Article
Terra Nova, 2005, 17 (3), pp. 265 - 277
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The origin of NW-USA Columbia River Basalt Group Miocene magmatism and its relation to tectonism has been widely debated and is still open to study. We investigated the pre-eruptive evolution of the magmas, to constrain pressures and temperatures of the ascending magmas, and plumbing conditions. We determined major element concentrations of 17-6 Ma tholeiites, and applied clinopyroxene - liquid geothermobarometry to calculate pre-eruptive pressures and temperatures. These ranged from 0 to 0.66 GPa and 1120 to 1222 °C, respectively, defining two age-related parallel trends in a P-T diagram. This indicates a consistent crustal evolution of the magmas, and records at least two distinct initial temperatures. Using clinopyroxene interdiffusion coefficients we estimated magma ascent speeds ≥ 0.6 km yr-1. Possible geological explanations for the calculated parameters are: lower-crust magma chamber processes; magmatism amd tectonism feedback consistent with an extensional environment. © 2005 Blackwell Publishing Ltd.
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