Seismic reflection images of a near-axis melt sill within the lower crust at the Juan de Fuca ridge
Seismic reflection images of a near-axis melt sill within the lower crust at the Juan de Fuca ridge
Date
2009-04-28
Authors
Canales, J. Pablo
Nedimovic, Mladen R.
Kent, Graham M.
Carbotte, Suzanne M.
Detrick, Robert S.
Nedimovic, Mladen R.
Kent, Graham M.
Carbotte, Suzanne M.
Detrick, Robert S.
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Abstract
The oceanic crust extends over two thirds of the Earth’s solid surface and is
generated along mid-ocean ridges from melts derived from the upwelling mantle.
The upper and mid crust are constructed by dyking and seafloor eruptions
originating from magma accumulated in mid-crustal lenses at the spreading axis,
but the style of accretion of the lower oceanic crust is actively debated. Models
based on geological and petrological data from ophiolites propose that the lower
oceanic crust is accreted from melt sills intruded at multiple levels between the
Moho transition zone (MTZ) and the mid-crustal lens, consistent with
geophysical studies that suggest the presence of melt within the lower crust.
However, seismic images of molten sills within the lower crust have been elusive.
To date only seismic reflections from mid-crustal melt lenses and sills within
the MTZ have been described, suggesting that melt is efficiently transported
through the lower crust. Here we report deep crustal seismic reflections off the
southern Juan de Fuca Ridge that we interpret as originating from a molten sill
presently accreting the lower oceanic crust. The sill sits 5-6 km beneath the
seafloor and 850-900 m above the MTZ, and it is located 1.4-3.2 km off thespreading axis. Our results provide evidence for the existence of low permeability
barriers to melt migration within the lower section of modern oceanic crust
forming at intermediate-to-fast spreading rates, as inferred from ophiolite
studies.
Description
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 460 (2009): 89-93, doi:10.1038/nature08095.