En echelon magmatic segments commonly develop along obliquely spreading oceanic ridges. To clarify some of the dynamic aspects of this plate boundary, we performed a series of thermo-mechanical numerical tests. When extension of oceanic lithosphere becomes oblique, deformation within the axial region localizes into distinct upwelling centers. Temperatures are elevated in the upwelling cells, which are shallow mantle features that form the new plate boundary. The predicted features are similar to the axial volcanic ridges documented at Mohns and Reykjanes Ridges, and we conclude that they become the new loci of extensional deforma tion, upwelling, and magmatic activity. These ridges, suborthogonal to the plate spreading direction, only develop when the axis rift zone is weak. The subsegment length and spacing depend primarily on obliquity and axial width. Predicted crustal thickness along the subsegmented axis varies discernibly; this might explain the morphology and satellite gravity of the flanks of oblique spreading ridges.

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