Abstract

Reconstructions of the Pacific and Nazca plates suggest that both the Nazca and Tuamotu Ridges originated from a melting anomaly which existed beneath the Pacific-Farallon Ridge during the time interval between anomalies 19 and 11, as would be predicted from the fixed-hotspot hypothesis. The hotspot hypothesis, interpreted according to morphology of the Easter-Sala y Gomez-Nazca trace, would further suggest that the hotspot was located entirely beneath the Nazca plate during the time interval between anomalies 11 and 2′. At the end of this interval, the eastern boundary of the Easter plate formed, centered above the hotspot. According to this scheme, the present location of the hotspot is about 200 km west of Easter Island.

However, the Easter model is incompatible with the hotspot model for the Hawiian-Emperior chain, if the hotspots are fixed relative to one another, as the age of the point on the Tuamotu Ridge which corresponds with the Hawaiian-Emperor bend (53 to 55 m.y.) is significantly greater than the age of the bend (43 m.y.). The fixed-hostpot hypothesis can be satisfied by the two traces only if one or a combination of the following conditions is met: the kinematic age of the Hawaiian-Emperor bend is substantially greater than the isotopically dated age, the magnetic-anomaly time scale is in significant error, and/or magnetic-anomaly identifications in the vicinity of the Tuamotu Ridge are erroneous.

It might appear that other mechanisms for the origin of hotspot traces are preferable to the hotspot hypothesis. The most promising of these involves propagating fractures resulting from intraplate stress. This hypothesis has the advantage of accommodating anomalies in some hotspot traces, such as persistence of igneous activity long after passage of the trace over the hotspot.

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