Seismic imaging of a basaltic Lesser Antilles slab from ancient tectonics

Area of Science:

• Geophysics
• Geochemistry
• Tectonics

Background:

• Lithospheric material sinks into the mantle transition zone (MTZ) at subduction zones.
• Factors influencing slab flow, such as chemical heterogeneity, are not well understood.
• Previous studies have faced challenges in constraining mantle flows and their influencing factors.

Purpose of the Study:

• To image the subducting slab and MTZ beneath the Lesser Antilles subduction zone.
• To investigate the factors controlling the fate of subducting lithosphere.
• To understand the role of chemical heterogeneity in mantle dynamics.

Main Methods:

• Utilized P-to-S receiver functions to image seismic discontinuities.
• Employed combined geodynamic and waveform modeling.
• Analyzed seismic data to identify deep mantle structures.

Main Results:

• Imaged a superdeep (>700 km) 660-km discontinuity within the subducting slab.
• Observed nearby normal and superdeep double 660 discontinuity phases.
• Geodynamic and waveform modeling indicated a large basalt-rich chemical anomaly, not solely temperature effects.

Conclusions:

• The observed seismic features suggest a significant basalt-rich chemical anomaly within the subducting slab.
• This anomaly is likely linked to a subducted extinct spreading ridge.
• Past tectonic events create chemical heterogeneities that influence slab sinking behavior and mantle flow.