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Titel |
Reykjanes Ridge evolution and the elimination of transform faults in the North Atlantic |
VerfasserIn |
Fernando Martinez, Richard Hey, Ármann Höskuldsson |
Konferenz |
EGU General Assembly 2014
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 16 (2014) |
Datensatznummer |
250094526
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Publikation (Nr.) |
EGU/EGU2014-9939.pdf |
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Zusammenfassung |
The ridge-transform stair step geometry of the Mid-Atlantic Ridge is it’s most prominent
structural expression. An exception is along the Reykjanes Ridge where a single
oblique-spreading and un-segmented plate boundary has replaced a set of earlier
ridge-transform structures. This large-scale tectonic reconfiguration extends southward for
nearly 1000 km from Iceland to the Bight transform fault that marks the resumption of
orthogonal ridge-transform spreading farther to the south. The elimination of transform
faults flanking the Reykjanes Ridge has been interpreted in geodynamic models as a
southward migrating thermal effect of the Iceland hotspot but direct geophysical
observations of the tectonic mechanisms involved have not been previously made. In
August-September 2013 R/V Marcus G Langseth conducted a geophysical survey of the
southern Reykjanes Ridge and flanks to the Bight transform fault including the first
orthogonally spreading segment to the south. The objectives were to better understand
how the Reykjanes Ridge replaced the earlier transform fault-dominated structure.
The survey acquired full-coverage multibeam bathymetry and acoustic backscatter
imagery and coincident gravity and magnetic profiles. Preliminary analyses of the
Bight transform fault and surrounding segments indicate a geologic mechanism
for the elimination of transform faults. The Bight transform fault is a narrow and
well-defined tectonic boundary. The ridge segment to the south is undergoing small but
clearly discernible relocations of the neovolcanic zone such as to decrease the offset
with the ridge segment to the north. The short segment to the north of the Bight
transform fault appears to have recently eliminated its northern bounding transform
fault by propagating across it and replacing it with a highly oblique neovolcanic
zone linking it to the next northward segment. The preliminary analysis suggests
that small-scale ridge propagation events occur within transform-bounded ridge
segments such as to decrease the offset distance between neighboring ridge segments.
When the ridge offset distance shortens to about the width of the plate-boundary
zone (on the order of 10 km) a volcanic axis can propagate across the transform
fault, eliminating it and forming a non-transform offset. The non-transform offsets
can then further migrate to align with the linear trend of the oblique axis to the
north to form a continuous, non-transform, wide, plate boundary zone comprised of
en-echelon axial volcanic ridges, as characterizes the present-day Reykjanes Ridge. |
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