A kinematic model of ridge-transform geometry evolution

Abstract

Spreading ridge-transform geometries will remain stable so long as accretion is symmetric. Asymmetric accretion, however, will cause lengthening or shortening of transforms and, in extreme cases, may result in zero-offset transforms (ZOTs) and very-long-offset transforms (VLOTs) such as the Ninetyeast and Chagos transforms. We use a simple kinematic model to examine the effects of various parameters on the evolution of zero-offset transforms and very-long-offset transforms. Starting with the transform length spectrum found along the Mid-Atlantic Ridge distributed in a randomly determined ridge-transform configuration, we allow for asymmetric accretion along ridge segments, assuming that individual ridge segments act independently. We analyze the effects of initial configuration, degree of asymmetry, and degree of bias in asymmetry on the generation of very-long-offset and zero-offset transforms. Finally, we examine the effect of these parameters on the possible steady-state nature of the transform length spectra. This model predicts that zero-offset transforms can be generated with a minimum of asymmetry, and that bias in asymmetry and initial ridge-transform-ridge configuration have no effect on generation of ZOTs. Similarly, random variations in spreading asymmetry have difficulty generating significant increases in transform length, so VLOTs may be manifestations of dynamic processes. Of the parameters tested, only lack of ‘memory’ of zero-offset transforms has any effect on transform length distribution, and therefore, the transform length spectrum remains steady-state if ZOTs have some degree of memory.