HR: 1340h
AN: T33A-0514    [Abstracts]
TI: Variations in Shallow off-axis Crustal Structure and Ridge Segment Morphology Along the Southeast Indian Ridge
AU: * Baran, J M
EM: baran@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Carbotte, S M
EM: carbotte@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Cochran, J R
EM: jrc@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Nedimovic, M R
EM: mladen@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AB: Along the Southeast Indian ridge (SEIR) there is a systematic variation in axial morphology and axial depth with distance away from the Australian Antarctic Discordance. Since spreading rate (72-76 mm/yr) and mantle geochemistry appear constant along this portion of the SEIR, variations are attributed to a gradient in mantle temperature. In this study we report on a multichannel seismic survey investigation of ridge flank structure along the SEIR. There are three distinct forms of ridge crest morphology found within our study area: axial highs (shallow magma lens, thin layer 2A on-axis), rifted axial highs (deeper magma lens, and thick layer 2A on-axis), and shallow axial valleys (no magma lens and very thick layer 2A on-axis). We have produced 1-D models through ray tracing of CDP gathers to determine the velocity structure in the shallow crust. We have found that each of the 3 kinds of morphology (axial high, rifted axial high, and axial valley) corresponds to a characteristic velocity structure on-axis. Axial highs have an average interval velocity for layer 2A of 3.0 km/s, rifted axial highs have an interval velocity of 2.9km/s, and axial valleys have an interval velocity of 2.7 km/s. In addition, along segments with a transition in morphology and in layer 2A structure, we see the same changes reflected in the interval velocities (axial high- 3.0 km/s, rifted axial high- 2.9km/s, axial valley- 2.4 km/s). There is evidence of significant thickening of layer 2a off-axis (within 1-3 km) at axial high segments, with moderate thickening seen at rifted axial high, and no thickening seen at shallow valley segments. We will report on off-axis crustal velocity structure using 1-D ray tracing models for 3 segments representing the range of morphology seen at this ridge.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3025 Marine seismics (0935, 7294)
DE: 3035 Midocean ridge processes
DE: 3045 Seafloor morphology, geology, and geophysics
SC: Tectonophysics [T]
MN: Fall Meeting 2005