Journal Article

Persistent Heterogeneities in the Oceanic Lithosphere Due To Differential Freezing Beneath Ridges

Yu, Ting‐Ying, Sim, Shi Joyce, Havlin, Chris

2024

Overview

Oceanic lithosphere, which forms two‐thirds of Earth's surface, is generated at mid‐ocean ridge spreading centers. Yet the internal structure of the lithosphere is not well characterized and often considered to be homogeneous relative to the structure of continental lithosphere. While geophysical observations clearly delineate the crust‐mantle boundary and the lithosphere‐asthenopshere boundary, other seismic anomalies known as mid‐lithosphere discontinuities (MLDs) have been challenging to detect and poorly constrained. Here we present melt transport models applied to the mid‐ocean ridge system that indicate MLDs are a widespread fundamental feature of oceanic lithosphere. In our models, some melt generated from decompression melting is frozen back into the lithosphere, forming a layered refertilization pattern. These refertilized layers are due to the stacked horizontal layering pattern of melt pooling beneath the freezing front. If the recrystallized melt is incorporated into the lithosphere as mafic lenses, the predicted seismic velocity is compatible with observations. Plain Language Summary Using state of the art numerical models of magma transport within Earth's interior at mid‐ocean ridges, we found that the layers observed in the oceanic lithosphere are due to the process of melt freezing close to the ridge axis and are likely ubiquitous beneath the ocean floor. We find that the expected seismic signature would match current observations. This supports the idea of a heterogeneous oceanic lithosphere that will eventually be subducted at a convergence margin. Considering both seismic and electromagnetic observations, the models suggest that the mantle is less permeable and therefore likely stronger than previously thought. Key Points Melt transport at mid‐ocean ridge models reproduce observed frozen melt layers in the oceanic lithosphere Frozen melt layers are present regardless of model parameters Predicted seismic signatures require further mechanisms to be compatible with observations

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Current observations / Decompression / Earth axis / Earth mantle / Earth surface / Freezing / Lava / Lithosphere / Magma / Mathematical models / Numerical models / Ocean floor / Ocean models / Oceans / Recrystallization / Ridges / Seismic activity / Seismic velocities / Subduction (geology)