THE FOUNDATION SEAMOUNTS - TECTONIC SETTING OF A NEWLY DISCOVERED SEAMOUNT CHAIN IN THE SOUTH-PACIFIC

Large areas of the South Pacific remain unsurveyed because they are so remote. A major volcanic chain, the Foundation Seamounts lies between 33-degrees-S and 39-degrees-S and between 111-degrees-W and 125-degrees-W. Poorly defined on conventional bathymetric charts. it becomes very apparent when combining an analysis of conventional geophysical data with the satellite altimeter data. The length of the seamount chain is 1350 km and the volcanoes are clustered within a 180 km wide band, trending approximately N70W, which is the direction of absolute motion of the Pacific plate over a fixed reference system. Some of these volcanoes are so shallow that they may have emerged above the sea surface at an earlier time. No dates are known for the seamounts. Surrounding the Foundation Seamounts chain, the tectonic setting is that of the Pacific plate at the time when the strike of the spreading ridge changed from a northwesterly direction to the present northeasterly one. This episode of spreading reorganization involved the existence of a short-lived microplate. West of the Pacific Antarctic ridge, a captured segment of Nazca plate accounts for the large discrepancies in the magnetic anomalies offsets along the Agassiz fracture zone. Large propagators like the Adventure and Kurchatov troughs are described. The newly discovered western segment of the Chile fracture zone is the Pacific plate match of the Chile fracture zone on the Nazca plate.