HR: 1330h
AN: T12A-0442    [PDF]
TI: Structure of the Laxmi Ridge Ocean-Continent Transition Zone
AU: * Lane, C I
EM: cil1@soc.soton.ac.uk
AF: School of Ocean and Earth Sciences, Southampton University, Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AU: Collier, J S
EM: jenny.collier@imperial.ac.uk
AF: Dept. Earth Sciences and Engineering, Imperial College, RSM Building, Prince Consort Road, London, SW7 2BP United Kingdom
AU: Minshull, T A
EM: tmin@soc.soton.ac.uk
AF: School of Ocean and Earth Sciences, Southampton University, Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AU: Whitmarsh, R B
EM: rbw@soc.soton.ac.uk
AF: School of Ocean and Earth Sciences, Southampton University, Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH United Kingdom
AU: Sansom, V
EM: victoria.sansom@imperial.ac.uk
AF: Dept. Earth Sciences and Engineering, Imperial College, RSM Building, Prince Consort Road, London, SW7 2BP United Kingdom
AB: Seismic profiles were acquired in Jan-Feb 2003 across a pair of conjugate rifted margins in the NW Indian Ocean. These margins are thought to have formed under significantly higher strain rate (59mm/a half-rate) than the much studied Atlantic Margins, which typically separated at $\sim$10-20mm/a half-rate. Here we present results from the northern study area - the Laxmi Ridge continental margin. Our long-term aim is to investigate the influence of extensional strain rate on rift architecture and magmatism. Laxmi Ridge is a NW-SE trending basement high. It is 200km at its widest point, extends for 1200km, and rises up to 1400m above the background basement relief. Free-air gravity models suggest it consists of continental crust. South of Laxmi Ridge there are undisputed sea floor spreading anomalies; as old as Chron 27. The northern limit of Laxmi Ridge abuts Gop Rift. Within Gop Rift the magnetic field consists of a series of high-amplitude, linear, positive and negative SSE-NNW trending anomalies whose origin is currently unresolved. We collected data from Chron 27 to the continental rise north of Gop Rift. The main profile trends N-S for 480km. 32 ocean bottom instruments recorded shots from a 6920cu.in airgun source, fired every 60s. Coincident MCS profiles were recorded with a 2.4km 96-channel streamer, and part of the main line was re-shot with a 3890cu.in source, fired every 30s. A preliminary velocity structure of the Laxmi Ridge margin has been generated from tomographic inversion of first arrivals seen out to offsets of 70km; uncertainties are 20ms for close ranges, $<$200ms for offsets $>$50km. Generally, the crust thins to the south and Pn arrivals indicate a crustal thickness of 7km seaward of Laxmi Ridge. A bright package of reflections $\sim$200ms twt thick covers the Gop Rift and oceanic basement surfaces. It is laterally discontinuous, and thickens to $\sim$300ms in basins. Seaward-dipping intrabasement reflectors are seen for $\sim$100km south of the crest of Laxmi Ridge.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 7205 Continental crust (1242)
DE: 8010 Fractures and faults
DE: 8105 Continental margins and sedimentary basins
DE: 8109 Continental tectonics--extensional (0905)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting