Publication Date:
2022-05-25
Description:
Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 241 (2006): 932-951, doi:10.1016/j.epsl.2005.10.028.
Description:
We report volatile (H2O, CO2, F, S, Cl) and trace element data for submarine alkalic basalt
glasses from the three youngest Samoan volcanoes, Ta’u, Malumalu and Vailulu’u. Most
samples are visibly sulfide saturated, so have likely lost some S during fractionation. Cl/K ratios
(0.04 – 0.15) extend to higher values than pristine MORBs, but are suspected to be partly due to
source differences since Cl/K roughly varies as a function of 87Sr/86Sr. There are no resolvable
differences in the relative enrichment of F among sources, and compatibility of F during mantle
melting is established to be nearly identical to Nd. Shallow degassing has affected CO2 in all
samples, and H2O only in the most shallowly erupted samples from Vailulu’u. Absolute water
contents are high for Samoa (0.63 – 1.50 wt%), but relative enrichment of water compared to
equally incompatible trace elements (Ce, La) is low and falls entirely below normal MORB
values. H2O/Ce (58 – 157) and H2O/La (120 – 350) correlate inversely with 87Sr/86Sr
compositions (0.7045 – 0.7089). This leads us to believe that, because of very fast diffusion of
hydrogen in mantle minerals, recycled lithospheric material with high initial water and trace
element content will lose water to the drier ambient mantle during storage within the inner Earth.
The net result is the counter-intuitive appearance of greater dehydration with greater mantle
enrichment. We expect that subducted slabs will experience a two-stage dehydration history, first
within subduction zones and then in the ambient mantle during long-term convective mixing.
Keywords:
Water
;
Mantle
;
Hotspot
;
Basalt
;
Samoa
;
Volatile elements
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
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95232 bytes
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Format:
application/pdf
Format:
application/vnd.ms-excel
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application/pdf
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