Experimental Origin of Transform Faults and Straight Spreading-Center Segments

Experimental work based on a combination of Oldenburg and Brune9s wax model and Cox9s tennis ball experiment suggests a possible origin of the orthogonal mid-ocean system of ridges and transform faults. Various cuts were made in a crust formed by cooling on the surface of a pan of melted wax, and portions of the crust were rotated about a pole of rotation while other portions remained stationary. New thin crust formed in the gap between the rotated portions of the initial crust. The new crust is characterized by a medial spreading center offset by arcuate fractures concentric about the pole of rotation. At slow spreading rates (nearer the pole of rotation), the shape of the spreading center is distinctly zigzag, and concentric fractures are lacking. The straight sections of the zigzag possibly originate as shears. At faster spreading rates (farther from the pole of rotation), the zigzag becomes typically orthogonal with straight segments offset by concentric fractures. We propose that the oceanic ridge systems originate as zigzag spreading centers in the asthenosphere or at the base of the lithosphere and then evolve into orthogonal systems that are propagated upward.