Volatile abundances and oxygen isotopes in basaltic to dacitic lavas on mid-ocean ridges: The role of assimilation at spreading centers
Abstract
Most geochemical variability in MOR basalts is consistent with low- to moderate-pressure
fractional crystallization of various mantle-derived parental melts. However, our
geochemical data from MOR high-silica glasses, including new volatile and oxygen isotope
data, suggest that assimilation of altered crustal material plays a significant role
in the petrogenesis of dacites and may be important in the formation of basaltic lavas
at MOR in general. MOR high-silica andesites and dacites from diverse areas show remarkably
similar major element trends, incompatible trace element enrichments, and isotopic
signatures suggesting similar processes control their chemistry. In particular, very
high Cl and elevated H2O concentrations and relatively light oxygen isotope ratios
(~5.8‰ vs. expected values of ~6.8‰) in fresh dacite glasses can be explained by contamination
of magmas from a component of ocean crust altered by hydrothermal fluids. Crystallization
of silicate phases and Fe-oxides causes an increase in δ18O in residual magma, but
assimilation of material initially altered at high temperatures results in lower δ18O
values. The observed geochemical signatures can be explained by extreme fractional
crystallization of a MOR basalt parent combined with partial melting and assimilation
(AFC) of amphibole-bearing altered oceanic crust. The MOR dacitic lavas do not appear
to be simply the extrusive equivalent of oceanic plagiogranites. The combination of
partial melting and assimilation produces a distinct geochemical signature that includes
higher incompatible trace element abundances and distinct trace element ratios relative
to those observed in plagiogranites. © 2011 Elsevier B.V.
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https://hdl.handle.net/10161/9357Published Version (Please cite this version)
10.1016/j.chemgeo.2011.05.017Publication Info
Wanless, VD; Perfit, MR; Ridley, WI; Wallace, PJ; Grimes, CB; & Klein, EM (2011). Volatile abundances and oxygen isotopes in basaltic to dacitic lavas on mid-ocean
ridges: The role of assimilation at spreading centers. Chemical Geology, 287(1-2). pp. 54-65. 10.1016/j.chemgeo.2011.05.017. Retrieved from https://hdl.handle.net/10161/9357.This is constructed from limited available data and may be imprecise. To cite this
article, please review & use the official citation provided by the journal.
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Show full item recordScholars@Duke
Emily M. Klein
University Distinguished Service Professor
Dr. Klein's research focuses on the geochemistry of oceanic basalts, using diverse
tools of major, trace and isotopic analyses. Her research involves sea-going expeditions
to sample and map the ocean floor.

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