Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Ramos, F. C. Articles by Tollstrup, D. L. Search for Related Content GeoRef GeoRef Citation

Sr isotope disequilibrium in Columbia River flood basalts: Evidence for rapid shallow-level open-system processes

¹ Department of Geological Sciences, Central Washington University, Ellensburg, Washington 98926, USA
² Department of Geology, Washington State University, Pullman, Washington 99164, USA
³ Department of Earth Sciences, University of California, Santa Cruz, California 95064, USA

Geochemical variability among Columbia River Basalt Group flood lavas has been attributed to two different origins: derivation from heterogeneous mantle and modification of mantle-derived magmas by open-system processes involving continental crust. We present in situ analyses of Sr isotopes from core-to-rim transects of plagioclase phenocrysts and groundmass from each major Columbia River Basalt Group formation and show that plagioclase crystals are usually internally zoned in ⁸⁷Sr/⁸⁶Sr and are in ⁸⁷Sr/⁸⁶Sr disequilibrium with their host groundmass. These data unequivocally demonstrate that Columbia River basalt magmas, regardless of the nature of mantle sources, were modified by open-system processes operating at crustal depths. One-dimensional diffusion modeling indicates that observed isotopic heterogeneities cannot have existed at magmatic temperatures for more than a few years or decades. In general, results indicate that these flood basalt magmas were erupted while still in the process of assembly. A typical Columbia River flood basalt magma (melt plus phenocrysts) therefore only attains its final geochemical identity just before or during eruption, a fact that is generally obscured when evaluating conventional whole-rock isotope analyses.

Key Words: flood basalts • laser ablation • Sr isotopes • magma chambers • residence times

This article has been cited by other articles:

				L. Font, J. P. Davidson, D. G. Pearson, G. M. Nowell, D. A. Jerram, and C. J. Ottley Sr and Pb Isotope Micro-analysis of Plagioclase Crystals from Skye Lavas: an Insight into Open-system Processes in a Flood Basalt Province J. Petrology, August 1, 2008; 49(8): 1449 - 1471. [Abstract] [Full Text] [PDF]

				V. E. Camp and B. B. Hanan A plume-triggered delamination origin for the Columbia River Basalt Group Geosphere, June 1, 2008; 4(3): 480 - 495. [Abstract] [Full Text] [PDF]

				F. C. Ramos and F. J. Tepley III Inter- and Intracrystalline Isotopic Disequilibria: Techniques and Applications Reviews in Mineralogy and Geochemistry, January 1, 2008; 69(1): 403 - 443. [Full Text] [PDF]

				J. P. Chadwick, V. R. Troll, C. Ginibre, D. Morgan, R. Gertisser, T. E. Waight, and J. P. Davidson Carbonate Assimilation at Merapi Volcano, Java, Indonesia: Insights from Crystal Isotope Stratigraphy J. Petrology, September 1, 2007; 48(9): 1793 - 1812. [Abstract] [Full Text] [PDF]

				P. R. Hooper, V. E. Camp, S. P. Reidel, and M. E. Ross The origin of the Columbia River flood basalt province: Plume versus nonplume models Geological Society of America Special Papers, January 1, 2007; 430(0): 635 - 668. [Abstract] [Full Text] [PDF]