On- and off-axis magma transport in dikes at axial discontinuities: 9N OSC EPR
Abstract
Growing evidence suggests that at segment centers along fast-spreading MORs, magma transport from melt lens to surface is dominated by vertical diking, while in the vicinity of axial discontinuities magma may travel significant distances horizontally (e.g., Macdonald et al., 1988). The east limb at 9N OSC EPR offers an excellent opportunity to explore lateral crustal magma transport because the seismically imaged melt sill is not centered beneath the ridge crest (e.g., Kent et al., 2000). Terrain modeling, photographic and geochemical results suggest that at the tip of the propagating east limb, recent eruptions are localized to a neovolcanic ridge that hugs the overlap basin and lies several km west of the plunging melt sill. Petrologic and geochemical data support the idea that the neovolcanic ridge formed by southward dike propagation (White et al., 2009) from the more robust melt sill >6 km to the north. Evidence for previous southward diking events at the east limb tip can be seen in progressively older volcanic ridges that fan out east of the current neovolcanic ridge, suggesting that each new intrusion is emplaced west of the prior intrusion. Along the northern portion of the east limb, recent eruptions are localized over the margins of the 4-km wide asymmetric melt sill: erupting off-axis to form a prominent off-axis pillow ridge, as well as on the bathymetric axis. The surprising absence of eruptions over the center of the wide melt sill is consistent with fracture mechanics modeling (Germanovitch et al., 2011), which suggests that dikes are more likely to initiate near the edges, rather than at the center, of an axial magma sill. Overall, our results suggest that long-term southward migration of the 9N OSC east limb occurs through a series of on- and off-axis diking events with a net southward propagation direction.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMOS42A..03K
- Keywords:
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- 3035 MARINE GEOLOGY AND GEOPHYSICS Midocean ridge processes;
- 1032 GEOCHEMISTRY Mid-oceanic ridge processes;
- 1036 GEOCHEMISTRY Magma chamber processes;
- 3045 MARINE GEOLOGY AND GEOPHYSICS Seafloor morphology;
- geology;
- and geophysics