Renewed melting at the abandoned Skagi rift, northern Iceland: control by plume pulsing?
Abstract
The production of oceanic crust at Iceland has been subject to a series of rift relocations occurring on a 5-7 Ma cycle. These events have a significant impact on the rate of melt and crust production at each rift since associated changes in spreading rate directly affect mantle upwelling rate. Another cause of melt production variation at Iceland is plume pulsing. An excellent record of this phenomenon is provided by V-shaped topographic ridges formed at the Mid-Atlantic Ridge 300-1400 km south of Iceland. Rift relocation cycles and V-shaped Ridge melt productivity oscillations occur at a similar frequency, which might indicate a causal connection. In order to probe this link between rift relocation and plume pulsing, we carried out a detailed study of Quaternary activity (<2 Ma) on the abandoned Skagi rift in northern Iceland. Field observations and existing estimates of extinction age suggest that these Quaternary lavas were produced by a reactivation of the rift following several Myr of inactivity in the rift zone. New geochemical data show that these young lava flows have enriched incompatible element ratios (Nb/Y, Zr/Y and Sm/Yb) compared to Icelandic rift zone lavas. There is no field evidence for significant extension associated with the Skagi Quaternary lavas so a mechanism other than transient rifting and passive upwelling is required to rejuvinate melt production. One such mechanism may involve the passage of a pulse of hot mantle under a recently abandoned rift axis. We use a time-dependent numerical model of melting beneath a mid-ocean ridge to test the plausability of this mechanism. We assess the impact of a thermal pulse on melting under a recently abandoned rift zone. The model results show that it is possible to induce a short period of renewed melt production using a pulse, with a mantle potential temperature difference of less than 30°C. Renewed magmatism at fossil spreading centres has also been observed at several other locations; for example the Davidson Seamount in the eastern Pacific. The mantle processes which cause this anomalous magmatism are still not clear. Studying these anomalous oceanic features may provide further insights into other dynamic processes which may operate in the mantle and impact the production of oceanic crust.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.V11A2250W
- Keywords:
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- 1021 GEOCHEMISTRY / Composition of the oceanic crust;
- 8120 TECTONOPHYSICS / Dynamics of lithosphere and mantle: general;
- 8410 VOLCANOLOGY / Geochemical modeling;
- 8416 VOLCANOLOGY / Mid-oceanic ridge processes