HR: 09:30h
AN: V31F-07 [Abstracts]
TI: Melt Production and Morphology Variations Along the Southeast Indian Ridge
AU: Janet, B M
EM: Janet.Baran@noaa.gov
AF: Lamont-Doherty Earth Observatory, Columbia University
61 Route 9W, Palisades, NY 10964, United States
AU: Janet, B M
EM: Janet.Baran@noaa.gov
AF: NOAA, Rm 6121
14th St. and Constitution Ave, NW, Washington, DC 20230, United States
AU: * Cochran, J R
EM: jrc@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University
61 Route 9W, Palisades, NY 10964, United States
AU: Holmes, R C
EM: chomes@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University
61 Route 9W, Palisades, NY 10964, United States
AB:
The Southeast Indian Ridge (SEIR) is an intermediate spreading rate ridge with an along-axis transition in axial
ridge morphology from an axial high to an axial valley, which occurs independently of geochemistry and spreading
rate. We investigate possible mechanisms for this transition by considering two segments separated by 600
km, one characterized by an axial high and the other by a shallow axial valley. The crustal structure of these two
segments is well constrained through seismic reflection and refraction studies. We find that crustal structure
differences account for only 70 m difference in off-axis (isostatic) depth, compared with an observed 237 m depth
difference. We explore two models to account for the variation in morphology, crustal structure and depth by
varying mantle properties. First, we consider a model that assumes a decrease in mantle temperature
approaching the Australian-Antarctic Discordance. Mantle melt production models imply a 12°- 15°C
mantle temperature difference between the two ridge segments based on the difference in crustal thickness.
This result is compatible with the observed difference in mantle Bouguer anomalies between the two segments.
Since the transition from an axial high to an axial valley occurs within a single segment located between the two
segments for which we have seismic data, the actual temperature difference over which the change in the mode
of crustal accretion occurs must be significantly less than 15°C.
In the second model, we consider a constant temperature asthenosphere that thins toward the AAD. If the base
of the asthenosphere lies above or cuts across the base of the potential melting zone, melt production would
decrease as the AAD is approached. If a 100°C difference in temperature between the asthenosphere and
mesosphere is assumed, then an ~3° slope (33 km depth difference over 600 km) on the base of the
asthenosphere is required to match the gravity data.
Both models predict that axial morphology and shallow crustal structure are highly sensitive to small changes in
melt production. This is consistent with a threshold type relationship between melt production and the mode of
crustal generation that can result in an abrupt along-axis transition in crustal structure and axial morphology
driven by small-scale changes in mantle properties.
DE: 3010 Gravity and isostasy (1218, 1222)
DE: 3025 Marine seismics (0935, 7294)
DE: 3035 Midocean ridge processes
DE: 7245 Mid-ocean ridges
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting