Abstract

GLORIA long-range sidescan sonar images from a region of the Nazca plate immediately to the north of the Easter microplate have revealed a prominent series of anomalous ridges. These extend from lat 22°S, long 114°W, near the East Pacific Rise, to 23°S, 112°W, near Pito, deep at the northeast corner of the microplate. They are 20 to 50 km long and trend east-west, subparallel to the Pacific-Nazca spreading direction. Swath bathymetric data indicate that the ridges dip steeply to the south and gently to the north, and in places reliefs exceed 1 km. Earthquake focal mechanisms and predicted plate motions point to thrust faulting as the most likely mechanism for producing these ridges, and their morphology suggests that the crust to the north has over-ridden that to the south. The Nazca-Easter Euler pole predicts a maximum present-day convergence of about 50 km/m.y. at the western end of the Easter microplate's northern boundary, and we estimate that about one-third of this has been taken up by the intraplate thrusts during the past 2.5 m.y.

First Page Preview

First page PDF preview
You do not currently have access to this article.