Multi-channel Seismic Reflection Imaging of a Magma Chamber Beneath the East Scotia Ridge
Abstract
The East Scotia Ridge (ESR) is an active back-arc spreading centre located in the Scotia Sea (western South Atlantic). It separates the Scotia plate from the eastward-migrating Sandwich plate, which includes the South Sandwich volcanic arc. Regional mapping has shown that the ESR is composed of nine ridge segments (E1-E9), separated by non-transform discontinuities, and that it has a full spreading rate of 65-70 mm/yr. We present analyses of the first multi-channel seismic reflection (MCS) profiles from the ESR, collected during RRS James Clark Ross cruise JR18 as part of the British Antarctic Survey Sandwich Lithospheric and Crustal Experiment (SLICE). These new data extend across segment E2 (centred on 56° 05'S) where an earlier geophysical survey revealed a prominent magma chamber reflection (MCR) beneath an axial volcanic high. The JR18 profiles were collected using an airgun source with a combined chamber capacity of 61.8 l, and a streamer with an active length of 2400 m. They show the acoustic architecture of the crustal magma chamber in detail. The MCR lies at 1.1 s two-way-time (TWT) below sea floor beneath the summit of the axial high, increasing to 1.8 s TWT below sea floor with increasing water depth along the ridge axis. Analyses of common-mid-point gathers suggest that this is equivalent to a sub-bottom depth of 2.6 +/- 1.4 km beneath the apex of the high. We can trace the MCR > 23 km along axis, although it is faint beneath much of the high, and has a highly variable seismic character. At the summit of the high, the MCR shows a bright, comparatively simple waveform, which is inverted in polarity relative to the overlying sea-floor reflection. Nearby however, the MCR is more complex, and shows vertical offsets and bifurcation of the waveform.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.T52A0922C
- Keywords:
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- 3025 Marine seismics (0935);
- 3035 Midocean ridge processes