Mantle wedge control on back-arc crustal accretion.

Area of Science:

• Geology
• Geophysics
• Tectonics

Background:

• Mid-ocean ridges involve mantle advection and partial melting, with depleted mantle flowing away.
• Back-arc basins are influenced by subducting slabs affecting mantle advection, melt extraction, and gradients.
• Mantle wedge dynamics are predicted to significantly impact back-arc spreading processes.

Purpose of the Study:

• To investigate magma supply variations at back-arc basin spreading centers.
• To correlate magma supply with distance from the volcanic front and spreading rate.
• To propose a model explaining observed magma supply patterns in back-arc basins.

Main Methods:

• Analysis of spreading center magma supply in the Lau back-arc basin.
• Correlation of magma supply with distance from the arc volcanic front.
• Correlation of magma supply with spreading rate.
• Development of a model involving subduction-induced corner flow and mantle overturning.

Main Results:

• Magma supply at spreading centers varies, correlating with distance from the volcanic front but not spreading rate.
• Enhanced magma supply occurs near the volcanic front.
• Diminished melting is observed within overturned depleted mantle farther from the corner.
• Normal melting conditions exist in undepleted mantle farther away.

Conclusions:

• Subduction-induced corner flow overturns depleted upper mantle, reintroducing it beneath back-arc basins.
• This model explains enhanced, diminished, and normal melting conditions at different spreading centers.
• The proposed mechanism accounts for fundamental differences in crustal accretion between back-arc and mid-ocean settings.