Peirce John Wentworth

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Peirce
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John Wentworth
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  • Thesis
    The origin of the ninetyeast ridge and the northward motion of India, based on DSDP paleolatitudes
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1977-01) Peirce, John Wentworth
    This thes is is a collection of papers on the paleomagnetics of samples from several Deep Sea Drilling Project (DSDP) sites in the Indian Ocean. These papers present the basic paleomagnetic data, discuss the statistical methods for analyzing such data from DSDP cores, and examine the implications of the paleolatitudes for the origin of the Ninetyeast Ridge and the northward motion of India. Rarely do DSDP paleolatitudes approach the reliability of good continental pole positions. However, the reliability of such paleolatitudes can be markedly improved by using comparisons with paleolatitudes of different ages from the same site, paleolatitudes of similar ages from different sites on the same plate, estimates of paleolatitude from the skewness of marine magnetic anomalies, and continental paleopole. positions. Using such comparisons, a new paleomagnetic pole of upper Cretaceous age has been defined for the Pacific plate. A middle Cretaceous pole has been defined for the Wharton Basin plate, and it suggests that there may have been left lateral motion between Australia and the Wharton Basin. Paleolatitudes from the Ninetyeast Ridge are consistent with the pole position for the Deccan Traps. These data indicate that India and the Ninetyeast Ridge moved northwards with respect to the South Pole at 14.9 ± 4.5 cm/yr from 70 to 40 mybp and at 5.2 ± .8 cm/yr from 40 mybp until the present. However, when this paleomotion is compared to the Australian paleomagnetic data (by removing the relative motion components), a major inconsistency appears between 40 and 50 mybp. The Australian data indicate that India should be 13° further north than the positions implied by the Ninetyeast Ridge data. Basal paleolatitudes on the Ninetyeast Ridge indicate that its volcanic source was approximately fixed in latitude near 50°S, supporting the hypothesis that the ridge is the trace of the Kerguelen hotspot on the northward moving Indian plate. There is considerable geologic evidence in favor of such an hypothesis, and there is none to contradict it.