Reconciling geochemical and geophysical observations of magma supply and melt distribution at the 9N overlapping spreading center, East Pacific Rise
Abstract
Early studies of mid-ocean ridge discontinuities, such as transform faults and overlapping
spreading centers, suggested a lower magma supply compared to ridge segment centers.
This is reflected in bathymetrically deeper ridge axes, decreased hydrothermal activity,
and the eruption of more evolved lava compositions. While many signatures of lower
magma supply are observed at the 9N overlapping spreading center on the East Pacific
Rise, geophysical studies indicate extensive sub-surface melt in the region, suggesting
that the present magmatic system is not diminished. Here major and trace element concentrations
of erupted lavas are used to better understand magma supply at a large second-order
ridge discontinuity. We show that the wide range of lava compositions erupted at the
9N overlapping spreading center is generally consistent with early petrologic models
of ridge propagation and require variable degrees of fractional crystallization, extensive
magma mixing, and in some instances crustal assimilation. Moderately evolved ferrobasalts
and FeTi basalts erupted at the OSC indicate that crustal residence times are long
enough for significant crystallization of all magmas within the region, but the presence
of dacitic lavas reflects periods of even lower magma supply, where melt replenishment
is subordinate to cooling and crystallization. The geophysical observations of extensive
melt within the shallow crust are reconciled with the geochemistry of the lavas, if
melts are supplied intermittently to the propagating ridge over relatively short timescales.
© 2012. American Geophysical Union. All Rights Reserved.
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https://hdl.handle.net/10161/9356Published Version (Please cite this version)
10.1029/2012GC004168Publication Info
Wanless, VD; Perfit, MR; Klein, EM; White, S; & Ridley, WI (2012). Reconciling geochemical and geophysical observations of magma supply and melt distribution
at the 9N overlapping spreading center, East Pacific Rise. Geochemistry, Geophysics, Geosystems, 13(11). 10.1029/2012GC004168. Retrieved from https://hdl.handle.net/10161/9356.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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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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