Seismic evidence for variations in axial magma chamber properties along the southern Juan de Fuco Ridge

Canales, J. P. and Singh, S. C. and Detrick, R. S. and Carbotte, S. M. and Harding, A. and Kent, G. M. and Diebold, J. B. and Babcock, J. and Nedimovic, M. R. (2006) Seismic evidence for variations in axial magma chamber properties along the southern Juan de Fuco Ridge. Earth and Planetary Science Letters, 246 (3-4). pp. 353-366. ISSN 0012-821X DOI 10.1016/j.epsl.2006.04.032

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Abstract

Multichannel seismic data collected along the Cleft segment on the southern Juan de Fuca Ridge show that this intermediate-spreading center is underlain by a mid-crustal reflector interpreted as the top of an axial magma chamber (AMC). The AMC reflection is present along most of the segment, and deepens gently from 2.0 km near the southern end of the segment beneath the RIDGE Cleft Observatory Site, to 2.3 km at the northern end beneath the site of the mid-1980s submarine eruption. We analyzed the one-dimensional seismic structure of the AMC at two locations with contrasting lava chemistry beneath two different hydrothermal vent fields. At the northern site, waveform modeling in the time intercept–slowness (τ–p) domain indicates that the AMC is ∼ 100 m thick and it is characterized by a decrease in P-wave velocity from 6 km/s to 3.7 km/s. In contrast, the P-wave velocity within the shallower, ∼ 100-m-thick AMC at the southern site is higher (5.0 km/s). The decrease in seismic velocity within the AMC indicates that it is partially molten and that it is not a cracking front as previously suggested for other intermediate-spreading segments. The data show a coherent seismic phase interpreted as the P- to S-wave conversion at the AMC (PAMCS). Stacking of this event shows that the PAMCS is only present along the northern part of the segment. Our results thus suggest along-axis variations in the crystallinity of the AMC. The AMC along Cleft varies from a high crystal content (< 30% melt) sill at the southern end of Cleft, to a largely melt (60–75%) sill at the source of the 1980s eruption at the northern end. The variations in magma chamber properties inferred from our seismic data correlate with changes in lava chemistry and with the location of hydrothermal plumes, and they all suggest that focused, high-temperature hydrothermal venting along intermediate-spreading ridges is closely linked to the physical state of the underlying magma chamber.

Item Type: Article
Uncontrolled Keywords: 2006 AREP IA52 2006 P
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title: Earth and Planetary Science Letters
Volume: 246
Page Range: pp. 353-366
Identification Number: 10.1016/j.epsl.2006.04.032
Depositing User: Sarah Humbert
Date Deposited: 16 Feb 2009 13:01
Last Modified: 23 Jul 2013 10:01
URI: http://eprints.esc.cam.ac.uk/id/eprint/181

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