Abstract

Observations in the central Pacific suggest that older seamounts are uplifted if plate motion carries them over mantle hot spots. A depth-anomaly map of the area reveals several volcanic chains now located on younger hot-spot swells. Uplift is estimated by comparing the observed depth of a seamount summit or the observed stratigraphic section in an atoll with that predicted assuming standard subsidence of the sea floor after the seamount formed. Cretaceous seamounts on the margin of the Hawaiian Swell have standard summit depths, whereas those on the crest of the swell are at least 1,100 m shallower. Summit depth correlates with sea-floor depth anomaly, implying that the Hawaiian Swell has caused the uplift. Eocene fossils are exposed at the surface in the Tuamotu Atolls, whereas, according to the standard subsidence relation, Eocene deposits should be covered by 1,000 to 2,000 m of more recent material. The inferred uplift is consistent with the atoll's present position atop the Society Swell. Possible evidence for 600 m of uplift in the Southern Cook Islands, however, is unexplained by swell height. The observed uplifts of the Cretaceous seamounts near Hawaii and of the Tuamotu Atolls put a limit on when the Hawaiian and Society Swells formed at their present locations of maximum elevation. The swells must have developed within the past several million years and probably formed at the same time as did the younger volcanic edifices on their summits.

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