A new class of “pseudofaults” and their bearing on plate tectonics: A propagating rift model

Abstract

The pattern of magnetic anomaly offsets striking obliquely to the Blanco fracture zone near the Juan de Fuca spreading center appears to be incompatible with the rigid-plate hypothesis. Previous workers have thus called upon complex, or anomalous, mechanisms to explain the tectonic evolution of this area. According to the “propagating rift” model developed here, the basic observations that previous hypotheses have attempted to explain, i.e., the oblique trends of the fracture zones, are in fact misinterpretations. The previously proposed faults are instead “pseudofaults” consisting of en echelon sets of fracture zones frozen into progressively younger crust; these en echelon fracture zones have resulted from sequences of spreading center jumps propagating down the Juan de Fuca spreading center. Although the overall trends of the en echelon fracture zones are oblique to the Blanco transform fault, the strike of each individual fracture zone is quite different, and is compatible with transform motion between the rigid Pacific and Juan de Fuca plates.