The Effects of Changes in Plate Motions on the Shape of the Marquesas Fracture Zone

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The Marquesas fracture zone (MFZ), one of the great fracture zones that formed on the Pacific-Farallon ridge system, shows dramatic variations in morphology along its strike that cannot be explained by models for lithospheric flexure in response to thermal stresses and differential subsidence. Marine geophysical data collected by the R/V Maurice Ewing in fall 1991 show that major structures in the MFZ can be correlated with changes in plate motions as the fracture zone formed. The western MFZ shows two significant changes in trend: at 209°E and at 224°E. The change in strike at 209°E records a reorientation that put the transform fault under compression and created a 100 km-long sinuous ridge within the fracture zone. The change in plate motions at 224°E induced extension in the transform fault, creating three subparallel fracture zones. These results are in accord with observations of morphological changes observed at active transform faults and other fracture zones, and suggest that even relatively small changes (∼6°) in spreading direction can produce significant structures that are preserved in the fracture zone.

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Geophysical Research Letters, v. 21, issue 25, p. 2845-2848