THE ORIGIN OF BATHYMETRIC HIGHS AT RIDGE-TRANSFORM INTERSECTIONS - A MULTIDISCIPLINARY CASE-STUDY AT THE CLIPPERTON FRACTURE-ZONE

Bathmetric highs on the old crust proximal to ridge-transform intersec tions (RTIs), termed ''intersection highs'', are common but poorly und erstood features at offsets of fast to intermediate rate spreading cen ters. We have combined new reflection seismic, photographic, and geoch emical data with previously published Seabeam, SeaMARC I, and SeaMARC II data to address the nature of the intersection highs at the Clipper ton Fracture Zone. The Clipperton Intersection Highs are both topped b y a carapace of young lavas at least 100 m thick. These lavas, which w ere erupted on the intersection highs, are chemically similar to their adjacent ridge segments and different from the surrounding older crus t. At least some of the erupted magma traveled directly from the adjac ent ridge at a shallow crustal level. Ridge-related magma covers and i ntrudes at least the upper 500 m of the transform tectonized crust at the RTI. We suspect that additional magma enters the intersection high s from directly below, without passing through the ridge. The young oc eanic crust near the western Clipperton RTI is not thin by regional co mparison. The 1.4 m.y. old crust near the eastern Clipperton RTI thick ens approaching the transform offset. If the thermal effects of the pr oximal ridge were negligible, the eastern intersection high crust woul d appear to be in isostatic equilibrium. We believe that thermal effec ts are significant, and that the intersection high region stands anoma lously shallow for its crustal thickness. This is attributable to incr eased temperature in the mantle below the ridge-proximal crust. Althou gh ridge magma is injected into the proximal old crust, plate boundary reorganization is not taking place. Intersection high formation has b een an ongoing process at both of the Clipperton RTIs for at least the past 1 m.y., during which time the plate boundary configuration has n ot changed appreciably. We envision a constant interplay between the i ntruding ridge magma and the disrupting transform fault motion. In add ition, we envision a nearly constant input of magma from below the hig h, as an extension of the magma supply to the ridge from the mantle. B ecause the proximal ridge profoundly affects the juxtaposed crust at t he RTI, sea floor fabric along the aseismic extensions of this fast-sl ipping transform fault is primarily a record of processes at work at t he RTI rather than a record of transform tectonism.