Geological and geophysical studies of the Canton Trough Region

Abstract

The Canton Trough is an extremely deep linear feature flanked by large en echelon ridges. This system, located in the equatorial Central Pacific Basin, can be traced ENE from the Phoenix Islands for a distance of more than 500 km. The surrounding topography is lineated parallel to the ridge‐trough‐ridge system and probably originated by block faulting. A similar mode of formation is inferred for the main trough itself, the implication being that the vertical displacement may exceed 3000 m in some localities. This interpretation is reinforced by the occurrence near the base of the trough of an unusually diverse assemblage of igneous rocks, including normal oceanic tholeiitic basalts, coarse‐grained diabases, anorthositic gabbros, pegmatitic gabbros, and cumulate gabbros. Simple vertical displacements of crustal blocks also could produce the major components of the observed gravity anomaly signatures as well as explain the necessity in the gravity models for a crustal root beneath the Canton Trough. Sediments within the Canton Trough region are predominately radiolarian oozes and calcareous turbidites, which correlate with transparent layers and highly stratified units observed on reflection profiler records. Magnetic studies of the region reveal 650‐γ residual anomalies, which are at least partly produced by the great topographic relief of the ridge‐trough‐ridge zone. However, the anomalies appear to obliquely cross the structural fabric and extend beyond the bathymetrie terminus of the trough and ridges. This configuration indicates that some components of the magnetic signatures are generated by another mechanism. Although there is some evidence that the Canton Trough and its surrounding structures represent an extension of the Clipperton Fracture Zone into the Central Pacific Basin, the absence of structural continuity, the lack of regional depth changes, and the limitations imposed by the regional tectonic patterns argue against this hypothesis. It is possible that the Canton Trough zone was created by an abrupt change from the Phoenix spreading direction to that inferred across the Manihiki Plateaus.

Magnetic anomaly lineations from Late Jurassic to Early Cretaceous in the west-central Pacific Ocean

“…Larson, Smith & Chase (1972) claimed that the Nova-Canton Trough is an extension of the Clipperton Fracture Zone situated east of this trough. On the other hand, Rosendahl et al (1975) and Winterer (1976) postulated that this trough is an abandoned Pacific-Phoenix Ridge. Joseph et af.…”

Bathymetry and Regional Tectonic Setting of the Line Islands Chain

“…The Phoenix magnetic anomaly set, which can be traced eastward toward the Line Islands to about 170°W is paralleled along its south edge by a band of lineated sea floor. The most prominent feature in this bathymetric pattern is Nova-Canton Trough (Rosendahl, 1972), but smaller scale features with the same trend can be identified and contoured from echo sounder and seismic profiler records. From new soundings obtained during SIO Expedition Eurydice, Leg 2, Nova-Canton Trough can now be traced eastward as a series of slightly en echelon features all the way to the Line Islands.…”