Extensional tectonics and two-stage crustal accretion at oceanic transform faults

Area of Science:

• Geophysics
• Tectonics
• Marine Geology

Background:

• Oceanic transform faults are active plate boundaries forming fracture zones.
• Plate tectonics theory models them as conservative strike-slip boundaries.
• Existing models do not fully explain observed seafloor depths.

Purpose of the Study:

• To investigate discrepancies between observed seafloor depths and plate-cooling models at oceanic transform faults.
• To analyze the accretion processes at transform fault-ridge intersections.
• To understand the role of plastic-shear failure in transform fault dynamics.

Main Methods:

• Compilation of high-resolution multibeam bathymetric data from 41 oceanic transform faults.
• Analysis of seafloor depth variations relative to fracture zones.
• Three-dimensional viscoplastic numerical modeling of shear failure and extension.

Main Results:

• Seafloor along transform faults is systematically deeper (up to 1.6 km) than associated fracture zones.
• Accretion at transform fault-ridge intersections is asymmetric, with deeper nodal basins at inside corners.
• Numerical models show oblique shear and extension at depth, thinning crust and lithosphere.

Conclusions:

• Transform faults are not purely conservative; they involve crustal thinning and lithospheric extension.
• Accretion at transform fault systems is a two-stage process, involving ridge intersection dynamics.
• Observed bathymetry challenges the simple plate-cooling model for transform fault evolution.