TECTONIC RECONSTRUCTION OF THE CLIPPERTON AND SIQUEIROS FRACTURE-ZONES - EVIDENCE AND CONSEQUENCES OF PLATE MOTION CHANGE FOR THE LAST 3 MYR

Bathymetry, side-looking sonar and magnetics data from the northern Ea st Pacific Rise have been analyzed to determine the tectonic history o f the Clipperton Fracture Zone (CFZ) and the Siqueiros Fracture Zone ( SFZ) over the last 2-3 m.y. Results of tectonic reconstructions indica te a series of counterclockwise changes in spreading direction at simi lar to 2.5 Ma (1-2 degrees), similar to 1.5 Ma (1-2 degrees), and simi lar to 0.5 Ma (4-5 degrees). Along the right-stepping Clipperton Trans form, the most recent change in spreading direction has resulted in fr acture zone normal compression, which we propose has created a median ridge and transform-parallel troughs along the active transform fault. Volcanic intersection highs located near the ridge-transform intersec tions (RTI) of the CFZ are interpreted to be the result;of fracture-zo ne-normal extension that has created pathways for magma emplacement in to/onto the older lithosphere across from the RTI. Along the left-step ping SFZ, we propose the changes in spreading direction have generated extension across the transform and have resulted in the formation of intratransform spreading centers and flexural transverse ridges. Tecto nic reconstructions indicate a single Euler pole is unable to describe the motion of the Pacific-Cocos plate boundary between the CFZ and SF Z during periods of spreading direction change since similar to 3 Ma. Transtensional transforms will adjust to a new spreading direction alm ost immediately, while transpressional transforms will experience comp ression for a period of time comparable to half the age offset of the compressional transform.