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Magmatic and tectonic extension at the Chile Ridge: Evidence for mantle controls on ridge segmentation

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Title:Magmatic and tectonic extension at the Chile Ridge: Evidence for mantle controls on ridge segmentation
Authors:Howell, Samuel M.
Ito, Garrett
Behn, Mark D.
Martinez, Fernando
Olive, Jean-Arthur
show 1 moreEscartin, Javier
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Keywords:Chile Ridge
active upwelling
abyssal hill evolution
faulting and magmatism
ridge morphology
Date Issued:May 2016
Publisher:American Geophysical Union
Citation:Howell, S. M., G. Ito, M. D. Behn, F. Martinez, J.-A. Olive, and J. Escartín (2016), Magmatic and tectonic extension at the Chile Ridge: Evidence for mantle controls on ridge segmentation, Geochem. Geophys. Geosyst., 17, doi:10.1002/2016GC006380.
Abstract:We use data from an extensive multibeam bathymetry survey of the Chile Ridge to study tectonomagmatic processes at the ridge axis. Specifically, we investigate how abyssal hills evolve from axial faults, how variations in magmatic extension influence morphology and faulting along the spreading axis, and how these variations correlate with ridge segmentation. The bathymetry data are used to estimate the fraction of plate separation accommodated by normal faulting, and the remaining fraction of extension, M, is attributed primarily to magmatic accretion. Results show that M ranges from 0.85 to 0.96, systematically increasing from first-order and second-order ridge segment offsets toward segment centers as the depth of ridge axis shoals relative to the flanking highs of the axial valley. Fault spacing, however, does not correlate with ridge geometry, morphology, or M along the Chile Ridge, which suggests the observed increase in tectonic strain toward segment ends is achieved through increased slip on approximately equally spaced faults. Variations in M along the segments follow variations in petrologic indicators of mantle melt fraction, both showing a preferred length scale of 50620 km that persists even along much longer ridge segments. In comparison, mean M and axial relief fail to show significant correlations with distance offsetting the segments. These two findings suggest a form of magmatic segmentation that is partially decoupled from the geometry of the plate boundary. We hypothesize this magmatic segmentation arises from cells of buoyantly upwelling mantle that influence tectonic segmentation from the mantle, up.
Pages/Duration:20 pages
Rights:© 2016. American Geophysical Union. All Rights Reserved.
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