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| Titel |
Birth and death of oceanic core complexes |
| VerfasserIn |
C. J. MacLeod, R. C. Searle, B. J. Murton, JC007 Scientific Party |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250026003
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| Zusammenfassung |
| Oceanic core complexes (OCCs) are the uplifted footwalls of very-large-offset low-angle
normal faults that exhume lower crust and mantle rocks onto the seafloor at slow-spreading
ridges. Although it is suggested on the basis of numerical modelling that they form during
periods of relatively reduced magma supply, little is known about how they initiate or how
they are terminated, nor why only certain normal fault systems develop into core complexes.
Here we present results from a near-bottom sidescan sonar/bathymetric profiler survey and
sampling study of the Mid-Atlantic Ridge near 13Ë N that demonstrate the critical controls
on OCC development and evolution. OCC detachment faults initiate as high-angle (65Ë ±10Ë
) normal faults no different from surrounding valley-wall faults and, like them,
rapidly flatten to dips of ~30Ë in response to flexural unloading; however, on
certain structures displacement continues rather than jumping inward onto a new
normal fault, resulting in locally enhanced uplift of the footwall and further flattening
of the fault to the horizontal or beyond. Detachment fault formation is triggered
primarily by local waning of magma supply, greatly aided by strain localisation
due to seawater penetration and talc formation along the fault zones. Volcanism is
suppressed or absent when the OCCs are active. The detachments are terminated
as neovolcanic ridges propagate laterally across them from magmatically robust
segments along strike. Our observations demonstrate how spatial (~100-101km) and
temporal (105-106yr) variations in magma flux to the ridge axis directly control the
formation, extent and duration of tectonic spreading at the Mid-Atlantic Ridge. |
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