Abstract:
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.
