Seamount Age Estimates from Paleomagnetism and their Implications for the History of Volcanism on the Pacific Plate

Abstract

Of 100 reliable Pacific seamount paleomagnetic poles, only 36 have ages that also seem to be reliably determined. Nevertheless, it is possible to make age estimates for most of the undated seamounts by comparing their paleomagnetic poles to the Pacific apparent polar wander path. According to their locations along the polar path, seamount paleopoles were divided into four groups: (1) early Tertiary, about 36–45 Ma; (2) Late Cretaceous, 64–79 Ma; (3) mid-Cretaceous, 80 Ma to about 120 Ma, and (4) Early Cretaceous-Jurassic, older than about 120 Ma. The greatest number of paleopoles lie along the mid- to Late Cretaceous portion of the polar wander path, implying a heavy concentration of volcanism of this age in the central and western Pacific. Though there appears to be a significant fraction of seamounts with ages within about 20 Ma of the underlying seafloor throughout this area, many of the seamounts between the western Pacific trenches and the Line Islands in the central Pacific are intraplate volcanoes, formed long after the underlying lithosphere. Moreover, these off-ridge seamounts generally show a trend of decreasing paleomagnetic age toward the southeast, consistent with hypotheses that explain the intraplate volcanism by the northwestward drift of the Pacific plate over mantle plumes presently located in the southeast Pacific.