Potential sill intrusion recorded at ultraslow spreading Southwest Indian Ridge

Vera.Schlindwein [ at ] awi.de


Ultraslow spreading mid-ocean ridges with full spreading rates up to 15 mm/yr are described as the melt poor endmember of the entire ocean ridge system. The melt supply along ultraslow spreading ridges is uneven resulting in the formation of volcanic centres and amagmatic segments. Amagmatic segments show thicker brittle lithosphere of up to 30 km, whereas magmatic segments have much thinner lithosphere of up to less than 15 km. It is supposed that melt travels along the lithosphere asthenosphere boundary from amagmatic segments to magmatic events, where it can reach the seafloor and erupt. These spreading events are rare at ultraslow spreading ridges compared to faster spreading ridges. During an ocean bottom seismometer (OBS) experiment at the eastern Southwest Indian Ridge two earthquake swarms were recorded. The swarms occurred in January and April 2013 and both lasted for a few days. The events of the earthquake swarms were relative located with HypoDD for better spatial resolution. This unique dataset allowed for studying active spreading processes at an ultraslow spreading ridge. The earthquakes occurred in depths, where the magma chamber of the nearby Segment-8 volcano is located. This magma chamber potentially fed a sill intrusion, which was recorded as earthquake swarms. During the first hours of the first earthquake swarm a migration pattern was identified. The hypocentres migrated away from the Segment-8 volcanic centre and slightly downwards. Later events occurred more randomly in the active area. Simultaneously seismic tremor was recorded at the station closest to the swarm locations. The tremor lasted longer for the shorter earthquake swarm in April. During both tremor phases the signal was modulated with a 12 hour period, suggesting a hydrothermal system affected by the intrusion and modulated by the tides.

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Conference (Poster)
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AGU Fall Meeting, 11 Dec 2017 - 15 Dec 2017, New Orleans.
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Meier, M. and Schlindwein, V. (2017): Potential sill intrusion recorded at ultraslow spreading Southwest Indian Ridge , AGU Fall Meeting, New Orleans, 11 December 2017 - 15 December 2017 .

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