Life Cycle of Oceanic Core Complexes
Abstract
Oceanic core complexes 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. Numerical modelling has suggested that they form during periods of critically reduced magma supply, but this is yet to be confirmed by observation. Little is known about the mechanisms of their initiation and inactivation, nor why only certain normal fault systems develop into core complexes. We present results from a near-bottom sidescan sonar/bathymetric profiler survey and sampling study of the Mid-Atlantic Ridge near 13°N that allow us to infer the life cycle of oceanic core complexes and demonstrate the critical controls on their development and evolution. We show that core complex detachment faults initiate as high-angle (65°±10°) normal faults no different from surrounding valley-wall faults and, like them, rapidly flatten to dips of ~30° in response to flexural unloading. However, on some faults, displacement continues rather than jumping inward to a new normal fault, resulting in locally enhanced uplift of the footwall and further flattening of the fault to the horizontal or beyond. Active detachment faulting and core complex formation occurs - and only occurs - where active volcanism is locally absent from the axial valley, while detachment faults are terminated by renewed magmatism as neovolcanic ridges propagate laterally across them. Our observations strongly suggest that core complex development is primarily controlled by local waxing and waning of the magma supply near a critical threshold, supporting recent numerical models.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.T41D..02S
- Keywords:
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- 3035 Midocean ridge processes;
- 3045 Seafloor morphology;
- geology;
- and geophysics;
- 3075 Submarine tectonics and volcanism