HR: 1330h
AN: T12D-0502    [PDF]
TI: Upper Crustal Variations due to Mantle Temperature Variations Along the Southeast Indian Ridge
AU: * Baran, J M
EM: baran@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory, 61 Route 9w, Palisades, NY 10964 United States
AU: Cochran, J R
EM: jrc@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory, 61 Route 9w, Palisades, NY 10964 United States
AU: Carbotte, S
EM: carbotte@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory, 61 Route 9w, Palisades, NY 10964 United States
AU: Nedimovic, M
EM: mladen@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory, 61 Route 9w, Palisades, NY 10964 United States
AB: A systematic variation in axial morphology and axial depth is observed along the Southeast Indian Ridge (SEIR) with distance away from the Australian Antarctic Discordance, an area of cold mantle downwelling. Since spreading rate and mantle geochemistry appear constant nearly along this portion of the SEIR, variations are attributed to a gradient in mantle temperature. We carried out a multichannel seismic (MCS) survey on the SEIR to determine the effect of changes in mantle temperature on melt supply and crustal structure. The MCS reflection data was collected along six segments, showing a range of axial morphology. The MCS data demonstrate a systematic variation in upper crustal structure. Segment P1 (101$\deg$E) is characterized by a well developed axial high. It shows an axial magma chamber under $\sim$60% of the axis at an average depth of 680 ms twtt ($\sim$1800 m) and average layer 2a thickness of 270 ms twtt ($\sim$325 m). Segment P2 (102$\deg$E) is characterized by a poorly developed axial high. Axial magma chambers are found underneath $\sim$40% of the axis, at an average depth of 1000 ms twtt ($\sim$2200 m) and an average layer 2a thickness of 400 ms twtt ($\sim$ 475 m). Segment P3 (105$\deg$E) shows a transition along the segment from an axial high in the west to an axial valley in the east. The axial high portion of the segment has an axial magma chamber (AMC) under almost the entire section located at an average depth of 975 ms twtt ($\sim$2000 m), and an average layer 2a thickness of 350 ms twtt ($\sim$420 m). The transitional part of the segment again has an axial magma chamber found almost along the entire section, located at a deeper average depth of 1000 ms twtt ($\sim$2200 m), and an average layer 2a thickness of 400 ms twtt ($\sim$ 475 m). The axial valley part of the segment has no magma chambers, and an average layer 2a thickness of 750 ms twtt ($\sim$890 m). Segment S1 (110$\deg$E), characterized by an axial valley, shows only a few scattered deep AMC reflections located at an average depth of 1200 ms twtt ($\sim$2250 m), and highly variable average layer 2a thickness of 600 ms twtt ($\sim$900 m). This section of the SEIR is characterized by a clear relationship between axial morphology, depth to the AMC and thickness of layer 2a along this section of the SEIR. Although axial morphology changes progressively along the axis, AMC extent and layer 2a thickness show abrupt changes along the axis. Magma chambers are commonly observed under axial high segments. As the axial high becomes less developed, AMC reflections become deeper but are still imaged over significant parts of the segment. An axial magma chamber is rarely observed at segments with an axial valley. Layer 2a thickness roughly doubles with the transition from an axial high to an axial valley.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3025 Marine seismics (0935)
DE: 3035 Midocean ridge processes
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3045 Seafloor morphology and bottom photography
SC: Tectonophysics [T]
MN: 2003 Fall Meeting