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Petrogenesis and ^(230)Th-^(238)U disequilibrium at Mt. Shasta, California, and in the Cascades

Newman, Sally and Macdougall, J. Douglas and Finkel, Robert C. (1986) Petrogenesis and ^(230)Th-^(238)U disequilibrium at Mt. Shasta, California, and in the Cascades. Contributions to Mineralogy and Petrology, 93 (2). pp. 195-206. ISSN 0010-7999. doi:10.1007/bf00371321.

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Petrogenesis at Mt. Shasta is dominated by mixing of magmas and/or assimilation of wall rock, as is shown by petrographic, major and trace element chemistry, and ^(238)U-^(230)Th disequilibrium data. At least three end- members are involved in these mixing processes. Lavas of very young Cascades lavas, from Mt. Garibaldi in the north to Lassen Peak in the south, are characterized by a large range of thorium isotopic ratios, although series of samples from single volcanoes are characterized by approximately constant (^(230)Th/^(232)Th). There is a monotonic decrease in this ratio from Crater Lake south through Lassen Peak, perhaps reflecting increasing thickness of the underlying crust. Th/U fractionation in Cascades lavas, as evidenced by (^(230)Th/^(238)U) ≥ 1, is in the opposite sense to that in most island arc lavas. This trend suggests that fluid transport, which is thought to produce uranium enrichment in island arc, is lacking or somehow modified in the petrogenesis of the Cascades lavas.

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Newman, Sally0000-0003-0710-995X
Alternate Title:Petrogenesis and 230Th-238U disequilibrium at Mt. Shasta, California, and in the Cascades
Additional Information:© Springer-Verlag 1986. Received 16 April 1985. Accepted 16 December 1985.
Subject Keywords:Uranium; Fractionation; Assimilation; Mineral Resource; Isotopic Ratio
Issue or Number:2
Record Number:CaltechAUTHORS:20181016-153902608
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Official Citation:Newman, S., Macdougall, J.D. & Finkel, R.C. Contr. Mineral. and Petrol. (1986) 93: 195.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:90292
Deposited By: George Porter
Deposited On:22 Oct 2018 16:21
Last Modified:16 Nov 2021 03:31

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