The isotopic and chemical evolution of Mount St. Helens

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doi: 10.1016/0012-821X(83)90040-7
Authors:Halliday, A. N.; Fallick, A. E.; Dickin, A. P.; Mackenzie, A. B.; Stephens, W. E.; Hildreth, W.
Author Affiliations:Primary:
Scott. Univ. Res. and React. Cent., Glasgow, United Kingdom
Other:
Univ. St. Andrews, United Kingdom
U. S. Geol. Surv., United States
Volume Title:Earth and Planetary Science Letters
Source:Earth and Planetary Science Letters, 63(2), p.241-256. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X
Publication Date:1983
Note:In English. 33 refs.; illus. incl. 9 anal., 5 tables
Summary:Isotopic, major- and trace-element analyses of 9 samples of eruptive products spanning the history of this volcano suggest three different episodes: 1) 40 000-2500 yr ago, eruptions of dacite; 2) 2500-1000 yr ago, eruptions of basalt, andesite and dacite (thought to represent melting of differing mantle-crust reservoirs); and 3) 1000 yr ago to the present, eruptions of andesite and dacite. None of the products exhibits Eu anomalies and all are light-REE-enriched. There is a strong correlation between 87Sr/86Sr and differentiation indices. The data are interpreted in terms of a mantle heat source melting young crust bearing zircon and garnet, but not feldspar, followed by intrusion of this crustal reservoir by mantle-derived magma which caused further crustal melting and contaminated the crustal magma system with mafic components. Since 1000 yr ago all eruptions have come from the same reservoir, which has displayed a much more gradual re-equilibration of Pb-isotopic compositions than of other components, suggesting that Pb is being transported by a fluid phase. Nd- and Sr-isotopic compositions lie along the mantle array and suggest that the mantle beneath Mt. St. Helens is not as depleted as MORB sources. There is no indication of sea-water involvement in the region. [P.Br.]
Subjects:Alkaline earth metals; Basalts; Cenozoic; Crust; D/H; Deuterium; Eruptions; Geochemistry; Holocene; Hydrogen; Igneous rocks; Isotopes; Lava; Lead; Magmas; Major elements; Metals; Nd-144/Nd-143; Neodymium; O-18/O-16; Oxygen; Periodicity; Pleistocene; Pollution; Pyroclastics; Quaternary; Rare earths; Sr-87/Sr-86; Stable isotopes; Strontium; Trace elements; Upper Pleistocene; Volcanic rocks; Volcanism; Volcanoes; Volcanology; Cascade Range; Mount Saint Helens; Skamania County Washington; United States; Washington; Evolution; Ratios
Coordinates:N461200 N461200 W1221100 W1221100
Abstract Numbers:84M/0588
Record ID:1983048831
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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