Structural and volcanic expression of a fast slipping Ridge‐Transform‐Ridge‐Plate Boundary: Sea MARC I and photographic surveys at the Clipperton Transform Fault

Publisher Website
Google Scholar
Abstract
A high‐resolution near‐bottom survey has been conducted of the Clipperton transform fault and adjoining segments of the East Pacific Rise (EPR), using the Sea MARC I side‐looking sonar system and the Lamont‐Doherty Geological Observatory Olympus‐based camera system. The transform fault zone (TFZ) is a narrow, well‐defined belt of transform‐parallel lineaments, which varies along strike from a single, sharp‐edged notch to a complex band of subparallel lineaments up to 1 km wide. The TFZ is set within a 5‐km‐wide band of unusually fine‐grained side scan texture, which could indicate nonbasaltic seafloor and/or pervasively sheared and mass‐wasted basaltic crust The fine‐grained swath is surrounded by constructional volcanic terrain with no hint of strike‐slip motion; this observation puts an upper limit of 5 km on the extent of lateral migration of the TFZ in the last 1.5 m.y. Both ridge transform intersections (RTIs) are dominated by bathymetric highs located on the old plate opposite the spreading center. A mantling of fresh‐looking constructional volcanic terrain on side scan images suggests that the highs are built in part by recent extrusive and intrusive volcanism; thermal expansion may also play a part. The EPR south of Clipperton has recently experienced extrusion of high effusion rate basalts, burial of faults and fissures by lava flows, and development of vigorous hydrothermal circulation. On the EPR north of Clipperton, the axial zone of faults and fissures tapers toward the transform fault; this may reflect a change in the shape or size of the underlying shallow level magma feeders as a function of distance from the site of magma upwelling or distance toward the transform fault.