Deep hydration and lithospheric thinning at oceanic transform plate boundaries.

Area of Science:

• Geophysics
• Tectonics
• Oceanography

Background:

• Transform faults accommodate plate motion and create fracture zones on the ocean floor.
• The deep structure of oceanic transform faults remains poorly understood.

Purpose of the Study:

• To investigate the deep structure of the Romanche transform fault using ultra-long offset seismic data.
• To understand the thermal and hydration processes within deep transform faults.

Main Methods:

• Acquisition and analysis of ultra-long offset seismic data.
• 3D thermal modeling of the fault zone.

Main Results:

• Identified a low-velocity anomaly extending to ~60 km depth.
• Interpreted extensive serpentinization (down to ~16 km) and a hydrated shear mylonite zone (down to ~32 km).
• Indicated a water-induced melting zone below 32 km, thinning the lithosphere.

Conclusions:

• Seawater-derived fluids likely drive deep hydration and serpentinization.
• Thinned lithosphere at transform faults can explain associated volcanism and crustal thickening.
• Water-induced melt may interact with melt beneath the ridge axis.