Magma productivity and early seafloor spreading rate correlation on the northern Vøring Margin, Norway - constraints on mantle melting

Breivik, A. J., Faleide, J. I., Mjelde, R. and Flueh, Ernst R. (2009) Magma productivity and early seafloor spreading rate correlation on the northern Vøring Margin, Norway - constraints on mantle melting Tectonophysics, 468 . pp. 206-223. DOI 10.1016/j.tecto.2008.09.020.

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Abstract

Continental rifting at the Vøring Margin off mid-Norway was initiated during the earliest Eocene (~54 Ma),
and large volumes of magmatic rocks were emplaced during and after continental breakup. In 2003, a marine
survey collecting ocean bottom seismometer, single-channel re!ection, and magnetic data was conducted on
the Norwegian Margin to constrain continental breakup and early sea!oor spreading processes. The pro"le
described here crosses the northern part of the Vøring Plateau, and the crustal velocity model was
constructed through a combination of ray-tracing and forward gravity modeling, the latter corrected for the
thermal effects remaining from the sea!oor spreading. We found a maximum igneous crustal thickness of
18 km, decreasing to 6.5 km over the "rst ~6 M.y. after continental breakup. Both the volume and the
duration of excess magmatism are about twice as large as that of the Møre Margin south of the East Jan
Mayen Fracture Zone, which offsets the two margin segments by ~170 km. A similar reduction in magmatism
occurs to the north over an along-margin distance of ~150 km to the Lofoten Margin, but without a margin
offset. Both the geochemical data and the mean P-wave velocity indicate that there is active mantle
upwelling combined with a moderate temperature increase during the earliest mantle melting at the Vøring
Margin. The mean P-wave velocity versus crustal thickness also indicates that there is a transition from
convection dominated to temperature dominated magma production ~2 M.y. after breakup. The magnetic
data were used to derive plate half-spreading rates for the Northern Vøring Margin, which are very similar to
that obtained at the Møre Margin. There is a strong correlation between magma productivity and early plate
spreading rate, suggesting a common cause. A model for the breakup-related magmatism should be able to
explain this correlation, but also the magma production peak at breakup, the along-margin magmatic
segmentation, and the active mantle upwelling. Proposed end-member hypotheses comprise elevated uppermantle
temperatures caused by a hot mantle plume, or edge-driven small-scale convection !uxing mantle
rocks through the melt zone. Edge-driven convection does not easily explain these observations, but a mantle
plume model in which buoyant plume material !ows laterally to pond in the rift-topography at the base of
the lithosphere close to breakup time is promising: When the continents break apart, the hot and buoyant
plume-material can !ow up into the rift zone from surrounding areas as the rift transits to drift, and the
excess temperature of this material will then cause excess magmatism which dies off as the rift-restricted
material is spent. The buoyancy of the plume-material may in addition cause active upwelling which can
increase the melting furthermore, and also increase the force on the plate boundaries to enhance plate
spreading rate. This conceptual model explains how both excess magmatism and spreading rate will be
reduced similarly with time as the plume material is consumed by plate spreading, and thus correlate.

Document Type: Article
Keywords: Ocean bottom seismometers; Magnetic anomalies; Plate spreading; Large igneous provinces; Passive margins; Mid-Norway
Research affiliation: OceanRep > The Future Ocean - Cluster of Excellence
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Refereed: Yes
DOI etc.: 10.1016/j.tecto.2008.09.020
ISSN: 0040-1951
Projects: Future Ocean
Date Deposited: 20 Mar 2009 09:24
Last Modified: 15 Jun 2016 10:30
URI: http://eprints.uni-kiel.de/id/eprint/596

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