Apparent Polar Wander of the Pacific Plate and Pacific Hotspots: Implications for True Polar Wander and Hotspot Fixity
Abstract
Whether the apparent polar wander (APW) path of the Indo-Atlantic hotspots is a record of true polar wander could be tested from a detailed APW path of the Pacific plate, the motion of which can be estimated relative to the hotpots independently of reconstructions in the Atlantic and Indian Ocean basins. Such an APW path has previously been lacking because of the difficulty in obtaining fully oriented paleomagnetic samples from oceanic plates. We present an APW path for the Pacific plate and for the hotspots of the Pacific basin. Our Pacific plate APW path from 125 Ma to the present is based mainly on the analysis of the skewness of marine magnetic anomalies due to seafloor spreading and is determined with better accuracy and resolution from 32 Ma to 81 Ma than is the APW path of any continent. Our path is defined by eleven paleomagnetic poles from non-overlapping age windows. Nine of these poles, those with ages from 32 Ma to 81 Ma, are determined from skewness analysis of 1563 crossings of marine magnetic anomalies due to seafloor spreading. They reveal the APW of the Pacific plate over this time interval with an accuracy and age-resolution far superior to other data sets. The skewness-only portion of the path indicates northward motion of the Pacific plate with 3 main swings in declination, clockwise from 81 Ma to 68 Ma, counterclockwise from 68 Ma to 40 Ma, and clockwise from 40 Ma to the present. The older two poles are from combinations of data types. There is no significant motion of the pole from 125 Ma to 88 Ma, but there is a sudden large counterclockwise shift of the pole in the brief interval from 88 to 81 Ma. This large and rapid shift of the pole is strongly supported by paleocolatitude data from azimuthally unoriented vertical cores of igneous rock obtained by deep sea drilling. In a reference frame attached to the Pacific hotspots, the spin axis lay near 80°N, 160°E during mid-Cenozoic time (32-40 Ma), near 80°N, 210°E during early Cenozoic time (55-68 Ma), and near 75°N, 170°E during Campanian and early Maastrichtian time (73-81 Ma). Thus, there was modest motion of the spin axis from 81 Ma to 32 Ma (or younger) with larger swings before and after. The most recent shift, sometime during the past 32 Myr, has been about 10° in arc length. A bigger shift of about 20° arc length occurred from 88 to 81 Ma, near the end of the Cretaceous normal polarity superchron. The largest difference between Pacific hotspot APW and Atlantic hotspot APW occurs for 73 to 81 Ma. The poles available from this time interval for the continents are highly scattered and some are likely biased. Overall there is good agreement between the two sets of curves, with the Indo-Atlantic hotspot APW path resembling a smoothed version of the Pacific hotspot APW path. The substantial overlap of confidence regions for the 125 Ma poles indicates no significant net motion between Pacific hotspots and Indo-Atlantic hotspots for the past 125 Ma. Within uncertainties, however, such motion could be as much as 9 mm/yr for the combined effect of the two paleomagnetically observable degrees of freedom. These results indicate that motion between Pacific and Indo-Atlantic hotspots is small enough that the hotspot reference frame is useful for estimating true polar wander.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2004
- Bibcode:
- 2004AGUSM.U52A..04G
- Keywords:
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- 1500 GEOMAGNETISM AND PALEOMAGNETISM;
- 8155 Plate motions: general