The Foundation Seamount chain: a first survey and sampling

The Foundation Seamounts form a 1400 km-long chain on the Pacific plate from 32 °S, 127 °W to the Pacific-Antarctic spreading axis at 38 °S, 111 °W. Previously only known from sparse single-beam echosoundings and satellite altimetry, we present here the first multibeam bathymetric survey and geological sampling results. We confirm that the submarine topography correlates with the altimetry, and that the chain is volcanic rather than tectonic or microcontinental in origin. The chain can be divided up morphologically and geochemically into three section: (1) west of 125 °W large flat-topped volcanoes composed of incompatible-element depleted lavas ( Nb Zr N ≈ 1) of a near-ridge origin with little or no plume influence, (2) between 125 and 115 °W true intraplate volcanoes with incompatible element enrichment ( Nb Zr N > 1.9) generated over the Foundation plume, (3) east of 115 °W E-W-trending volcanic ridges with compositions ( Nb Zr N 2.0-0.3) suggestive of interaction between the plume and the Pacific-Antarctic spreading axis. On the spreading axis moderate incompatible element enrichments ( Nb Zr N ≈0.8, cf. ≈ 0.3 outside the Foundation area) also suggest plume influence. It appears that the activity of the Foundation plume in the last few million years has (1) significantly waned and (2) become wholly channeled towards the spreading axis. The Foundation plume may be in the process of “dying”.