Rift topography linked to magmatism at the intermediate spreading Juan de Fuca Ridge

Publication Type  Journal Article
Year of Publication  2006
Authors  Carbotte, S. M.; Detrick, R. S.; Harding, A.; Canales, J. P.; Babcock, J.; Kent, G.; Van Ark, E.; Nedimovic, M.; Diebold, J.
Journal Title  Geology
Volume  34
Issue  3
Pages  209-212
Journal Date  Mar
ISBN Number  0091-7613
Accession Number  ISI:000235959300022
Key Words  juan de fuca ridge; magma chambers; dikes; faulting; spreading centers; midocean ridge; ocean ridge; crust; centers; zones

New seismic observations of crustal structure along the Juan de Fuca Ridge indicate that the axial rift topography reflects magma-induced deformation rather than alternating phases of magmatism and tectonic extension, as previously proposed. Contrary to predictions of the episodic models, crustal magma bodies are imaged beneath portions of all ridge segments surveyed at average depths of 2.1-2.6 km. The shallow rift valley or axial graben associated with each Juan de Fuca segment is similar to 50-200 m deep and 1-8 km wide and is well correlated with a magma body in the subsurface. Analysis of graben dimensions (height and width) shows that the axial graben narrows and graben height diminishes where the magma body disappears, rather than deepening and broadening, as expected for rift topography due to tectonic extension. We propose an evolutionary model of axial topography that emphasizes the contribution of dike intrusion to subsidence and fault slip at the seafloor. In this model an evolving axial topography results from feedbacks between the rheollogy of the crust above a magma sill and dike intrusion, rather than episodic magma delivery from the mantle.


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