Effects of Hotspot-Induced Long-Wavelength Mantle Melting Variations on Magmatic Segmentation at the Reykjanes Ridge: Insights From 3D Geodynamic Modeling

Abstract

Spatial variations in mantle melting induced by the Iceland hotspot have strong effects on meso-scale mantle upwelling and crustal production along the slow-spreading Reykjanes Ridge. The ridge-hotspot interaction has been recorded by diachronous V-shaped ridges and troughs extending away from Iceland, as well as by changes in ridge segmentation since 37 Ma. The origins of V-shaped structures are widely debated, while the causes of the gradual erasion of ridge segments bounded by transform faults are rarely investigated. Through 3D time-dependent geodynamic modeling, this study investigates how the hotspot-induced regional mantle melting variations affect ridge segmentation. Periodic temperature perturbations were initially imposed beneath the melting zone to trigger buoyant upwelling cells, which corresponded to the offset ridge segments at the Reykjanes Ridge. Iceland hotspot-induced long-wavelength mantle melting variations were generated by applying a regional linear temperature gradient at the bottom of the model domain. Modeling reveals a two-stage evolution of the buoyant upwelling cells that characterizes the segmentation transition at the Reykjanes Ridge. In Stage 1, the regional mantle melting variations trigger along-axis pressure-driven mantle flow, which alters the segment-scale mantle upwelling and promotes the propagation of segment boundaries away from the region with relatively higher mantle temperature. In Stage 2, buoyant upwelling cells are destroyed progressively as along-axis mantle flow dominants, leaving V-shaped diachronous boundaries between the segmented and unsegmented crust. These results advance our understanding of the effects of long-wavelength mantle melting variations induced by regional mantle heterogeneities on ridge segment evolution at slow-spreading ridges.

Key Points

• Evolution of ridge segmentation under ridge-hotspot interaction is simulated by 3D time-dependent geodynamic modeling

• Hotspot-induced long-wavelength mantle melting variations generate along-axis pressure-driven mantle flow

• Interactions between along-ridge mantle flow and buoyant upwelling cells cause segment propagation and destruction at the Reykjanes Ridge

Plain Language Summary

Mid-ocean ridges and hotspots are two important places of oceanic crustal accretion. Iceland is the most prominent example of an on-ridge hotspot and thus the Reykjanes Ridge is an ideal location to investigate ridge-hotspot interaction. The ridge segments offset by transform faults are gradually erased from north to south at the Reykjanes Ridge since approximately 37 Ma. This study uses 3D time-dependent geodynamic models to investigate whether this phenomenon is caused by the hotspot-induced regional mantle melting variations. In the model, offset ridge segments are approximated by a set of convective cells beneath a linear ridge axis. Regional mantle melting variations arise from the temperature gradients that prescribed at the base of the model. Modeling reveals that the regional mantle melting variations cause an along-axis mantle flow, which interacts with the segment-scale convective cells, generating a two-stage evolution that is comparable to the segment evolution at the Reykjanes Ridge. Stage 1 is characterized by systematic propagation of segment boundaries. Stage 2 is characterized by progressive destruction of ridge segmentation from high- to low-temperature part, leaving a distinct boundary between the segmented and unsegmented crust. This study provides new insights into ridge segmentation evolution of slow-spreading ridges as affected by ridge-hotspot interaction.