1. Constraints on the preeruptive volatile concentrations in the Columbia River flood basalts
- Author
-
Lange, Rebecca A.
- Subjects
Columbia River -- Natural history ,Basalt -- Composition ,Basalt -- Environmental aspects ,Earth sciences - Abstract
Many of the Columbia River flood basalts that erupted in the states of Oregon, Washington, and Idaho during the Miocene are remarkably iron rich (12-17 wt% total FeO) and under volatile-free conditions would have been too dense to erupt through continental crust. Their eruption through >20 km of sialic crust sets limits oil their minimum, pre-eruptive total volatile ([H.sub.2]O + C[O.sub.2]) concentrations. These limits are obtained by quantitatively comparing the average density, of the overlying crustal column with the calculated effect of dissolved [H.sub.2]O or exsolved C[O.sub.2] on the density of various Columbia River tholeiitic basalts as a function of depth. Minimum total volatile ([H.sub.2]O + C[O.sub.2]) concentrations range to >4 wt% and are therefore considerably higher than those found in tholeiitic basalts at oceanic islands, like Hawaii. These conclusions are consistent with the strong enrichments in other incompatible elements (e.g., K, P, Ba) observed in the Columbia River flood basalts. Such high concentrations of [H.sub.2]O + C[O.sub.2] would have had a marked effect on the solidus temperature of the source region, which may explain the remarkably large individual flow volumes (~[10.sup.3] [km.sup.3]) that characterize this flood-basalt province. Keywords: Columbia River, flood basalts, volatiles, melt density.
- Published
- 2002