Abstract:
We use global paleomagnetic data to construct an apparent polar wander path (APWP) for India than spans the past 75 m.y. The total uncertainties for each paleomagnetic pole include not only those uncertainties related to the determination of the pole, but also those related to reconstruction uncertainties that accumulate as these poles are rotated into the Indian plate reference frame. Comparison of poles from the rest of the globe with paleomagnetic data from the Indian plate, which are comprised of one paleomagnetic pole from the Deccan Traps and 44 paleocolatitude data from DSDP and ODP drill sites, show good agreement. As apparent in past compilations, this new APWP indicates that India has moved progressively northward since the Late Cretaceous, with the rate of motion being more rapid in the Late Cretaceous and Paleogene than before or after this period. The preferred South Pole APWP for India during the Cenozoic roughly follows the 100 degrees E meridian, west of that shown in other recent compilations. Because the paleomagnetic data indicate that the trend of the APWP has been fairly constant over tens of millions of years, we investigate fitting the data to a small-circle track as defined by the paleomagnetic Euler pole (PEP) model. A single PEP track spanning the interval from about 20 to 75 Ma can be found that is consistent with 18 out of 19 of the reconstructed paleomagnetic poles and the Deccan Traps pole. The location of the preferred PEP is at 14 degrees S, 186 degrees E, defining a small-circle South Pole APWP that is 77.8 degrees angular distance away. The location of the PEP is consistent with the position of the reconstruction (stage) pole that describes the motion of the hotspots relative to India for the interval from 80 to 20 Ma. Furthermore, extrapolation of the PEP track back in time shows that it also provides an excellent fit to paleomagnetic data back to 120 Ma. At its young end, the track passes to within 2 degrees of the South Pole. Hence, one small-circle track fits paleomagnetic data for a period spanning the past 120 m.y. Using a maximum likelihood algorithm and the 25-73 Ma paleomagnetic data, we estimate that the rate of APW along the track must have had an abrupt decrease at 57+ or -3 Ma, which is thought to correspond to when the collision or suturing of India with Eurasia began to impede India's northward progression. Overall, the rate of APW along the PEP track can be well modeled with three rate changes--73, 57, and 20 Ma--over the 120 m.y. interval. Estimated rates are 0.6 degrees /m.y. (66 km/m.y.) for the interval from 120 to 73 Ma; 1.9 degrees /m.y. (211 km/m.y.) for the interval from 73 to 57 Ma; 0.9 degrees /m.y. (95 km/m.y.) for the interval from 57 to 20 Ma; and 0.1 degrees /m.y. (11 km/m.y.) for the interval from 20 Ma to the present. Given these rates along the PEP track, the reconstructed global paleomagnetic poles are on average within 4.7 degrees of the coeval paleomagnetic pole predicted by the preferred PEP. Correction of the global paleomagnetic poles for a 5% geocentric axial quadrupole component reduces this average distance to 4.6 degrees , illustrating the robust nature of an APWP derived from global data and the good fit of the PEP model to these data. Finally, reconstruction of mean global poles and the PEP derived APWP into the hotspot reference frame allows for generalizations to be drawn concerning true polar wander (TPW). First, over the past 75 m.y., TPW as constrained by the hotspot APWP can be divided into three intervals (75-40, 40-20, and 20-0 Ma) defining small-circle tracks separated by cusps. Second, the rate of TPW appears to be particularly slow from 55 to 40 Ma, averaging 0.15 degrees /m.y. (17 km/m.y.), whereas the rate varies little in other intervals, averaging a nearly constant rate of 0.40 degrees /m.y. (44 km/m.y.). The accuracy of such generalizations concerning TPW is hampered, however, by the relatively large uncertainties associated with hotspot reconstructions and paleomagnetic data in relation to the slow rate of TPW. Within these uncertainties, TPW may have been small and perhaps negligible since the Late Cretaceous.