The fold illusion: The origins and implications of ogives on silicic lavas

Folds on the surfaces of mafic lavas are among most readily recognized geological structures and used as first-order criteria for identifying ancient Earth other planetary bodies. However, presence surface-folds surface silicic is contested in this study we challenge widely accepted interpretation that lava contain folds using examples from western United States Sardinia, Italy. We interpret ridges troughs their upper surfaces, typically referred to ‘ogives’ or ‘pressure ridges’, fracture-bound rather than folds. report absence large-scale, buckle-style note instead ubiquitous multiple generations scales tensile fractures comparable crevasses glaciers formed ways similar already crease structures. viscosity data results stress analyses preclude folding (ductile deformation compression) at timescales emplacement (weeks months). Therefore, analysis fold geometry (wavelength, amplitude, etc.) erroneous, signal produced reflects strength thickness brittle stretching over a ductile interior. The ogives bodies may help elucidate rheological properties crustal thicknesses, but relating strength, not viscosity.