GLORIA and other geophysical studies of the tectonic pattern and history of the Easter Microplate, southeast Pacific

Abstract

Abstract In October–November 1988 the RRS Charles Darwin surveyed the Easter Microplate using the GLORIA (long-range sidescan) sonar system and also obtained magnetic, bathymetric and gravity data. The aim of the cruise was to produce a sidescan mosaic covering most of the microplate, in order that a greater understanding of the region could be achieved. Previous geophysical studies of the area had enabled most of the microplate boundaries to be determined to a reasonable extent, but still little was known about the interior of the microplate, or its tectonic history. The major objectives of the GLORIA survey were to image the whole microplate including its boundary, discover the type of plate boundary element throughout (e.g. fast or slow spreading, transform or compressional zone), calculate the spreading directions and rotation poles, and determine the complex history of the microplate from the tectonic spreading fabric, fracture zone and propagating rift traces, and magnetic anomaly data. The GLORIA survey imaged virtually all of the Easter microplate in just 18 days, and revealed unprecedented detail and complexity in its tectonic fabric and history. There is clear evidence of rapid microplate rotation, of rapidly evolving plate boundaries and of complex deformation near the northern and southern microplate boundaries. Examination of GLORIA and magnetic data to the west of the East Rift of the Easter Microplate indicate that spreading may have been taking place for over 6 Ma and the calculation of poles of rotation for different stages of the Easter Microplate evolution have enabled a simplified history to be reconstructed.