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The Statistics and Distribution of Helium in the Mantle

Anderson, Don L. (2000) The Statistics and Distribution of Helium in the Mantle. International Geology Review, 42 (4). pp. 289-311. ISSN 0020-6814. http://resolver.caltech.edu/CaltechAUTHORS:20121010-104541909

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Abstract

An unbiased estimate of the ^3He/^4He ratio (R) along the Earth's spreading ridge system is 9.14 ± 3.59 Ra (n = 503) where Ra is the atmospheric ratio (1.38 × 10^6). By arbitrarily excluding all values with R > 11 Ra and from ocean depths less than 2500 meters, I obtain 7.91 ± 1.50 Ra (n = 212), which is close to previous “filtered” estimates based on the hypothesis that the excluded values have been influenced by plumes. These are biased estimates. Based on unbiased statistics, many of the so-called high^(-3)He hotspot regions have isotopic ratios well within the MORB range, and all have absolute ^3He concentrations much less than MORB. The high variance of some oceanic-island data compared to MORB reflects, in part, the difference between a small sample and a large sample, and magma-chamber processes. Values of 11 to 15 Ra are commonly attributed to deep mantle plumes and “indicative of lower mantle involvement,” but these values are within 2σ of the mean and are not exceptional. Much higher values combined with low absolute helium concentrations are commonly associated with the onset of rifting, or volcanism, and may reflect a shallow, or lithospheric, low^(-238)U/^3He (LONU) source. The temporal progression to average MORB-like values suggests that the bulk of the magmas at spreading ridges and large oceanic constructs comes from below the LONU level. The termination of spreading is associated with low ratios, 6 to 7 Ra, similar to values associated with the high^(-238)U/^(204)Pb (HIMU) mantle component and some oceanic islands.


Item Type:Article
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http://dx.doi.org/10.1080/00206810009465084DOIUNSPECIFIED
http://www.tandfonline.com/doi/abs/10.1080/00206810009465084PublisherUNSPECIFIED
Additional Information:© 2000 by V. H. Winston & Son. Inc. Version of record first published: 06 Jul 2010.
Record Number:CaltechAUTHORS:20121010-104541909
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20121010-104541909
Official Citation: The Statistics and Distribution of Helium in the Mantle Don L. Anderson International Geology Review Vol. 42, Iss. 4, 2000
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:34820
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:10 Oct 2012 18:10
Last Modified:23 Aug 2016 10:19

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