The Pacific-Antarctic Ridge-Foundation hotspot interaction: a case study of a ridge approaching a hotspot

The Foundation hotspot-Pacific-Antarctic Ridge (PAI) system is the best doc umented case of a fast spreading ridge approaching a hotspot and interactin g with it. The morphology, crustal structure inferred from gravity anomalie s and the chemical composition of the lavas of the axial area of the PAR sh ow evidence of the influence of the hotspot, that is presently located roug hly 35 km west of the spreading ridge axis. Along-axis variation in the Man tle Bouguer anomaly is about 28 mGal, corresponding to a crustal thickening of 1.5 km where the hotspot is nearer to the PAR. Anomalous ridge elevatio n is 650 m and the along-axis width of the chemical anomaly is 200 km. A co mparison of these axial parameters with those derived for other ridge-hotsp ot systems, suggests that the amount of plume material reaching the ridge a xis is smaller for the Foundation-PAR system. This implies a weaker connect ion between the plume and the ridge. Cumulative effects of a fast spreading rate and of a fast ridge-hotspot relative motion can be responsible for th is weak plume-ridge flow. The how from the hotspot may be less efficiently channelled towards the ridge axis when a fast ridge is rapidly moving towar ds a hotspot. (C) 2000 Elsevier Science B.V. All rights reserved.