Other
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusmgp21a..01g&link_type=abstract
American Geophysical Union, Spring Meeting 2005, abstract #GP21A-01
Other
1525 Paleomagnetism Applied To Tectonics (Regional, Global), 3040 Plate Tectonics (8150, 8155, 8157, 8158), 8157 Plate Motions: Past (3040), 8450 Planetary Volcanism (5480)
Scientific paper
Except for young volcanic islands, the Pacific plate is largely lacking outcrop amenable to traditional paleomagnetic analysis. As a result, a wide variety of alternative methods have been developed for estimating pole positions including analysis of the magnetic anomalies over seamounts ("seamount poles"), shape analysis of magnetic anomalies due to seafloor spreading ("skewness poles"), analysis of the amplitudes of magnetic anomalies due to seafloor spreading, analysis of azimuthally unoriented piston cores and deep-sea drilling cores in both sedimentary and igneous rocks, and analysis of equatorial sediment facies. In the 1970s, studies of seamount poles, of skewness, and of equatorial sediment facies all provided strong evidence for northward motion of the Pacific plate, in general agreement with the northward motion of the Pacific plate predicted if it is assumed that the hotspots are fixed relative to the spin axis. Beginning in about 1980, however, strong evidence was obtained that the northward motion of the Pacific plate relative to the spin axis was less than its northward motion relative to the Hawaiian and other hotspots, implying a southward drift of the Hawaiian hotspot. Results from DSDP Leg 55 first demonstrated southward motion of the Hawaiian hotspot [Kono 1980, Jackson, Koizumi et al. 1980]. Morgan [1981] showed that paleomagnetic poles and hotspot tracks from the Indian and Atlantic Oceans (and bordering continents) predicted this southward motion if the Pacific hotspots are fixed relative to those in the Indo-Atlantic, while both move together relative to the spin axis. This coherent motion of global hotspots can be interpreted as the result of true polar wander. Gordon & Cape [1981] and Gordon [1982] analyzed equatorial sediment facies, published piston core paleomagnetic data, and skewness data. They showed that the data were mutually consistent and indicated southward motion of the Hawaiian hotspot relative to the spin axis consistent with Morgan's predictions. Since then, the apparent polar wander of the Pacific plate has been elaborated in considerably greater detail. Here I concentrate on the results from skewness. Because the ages of the magnetic anomalies analyzed are unambiguous and automatically known to the nearest polarity chron, the ages of skewness poles are precisely known. The geometry of spreading on the Pacific plate during Cenozoic and Late Cretaceous time enables the estimation of poles with very compact confidence regions. Poles have been determined for many different anomalies and give a detailed, but far from complete, view of Pacific plate apparent polar wander since 83 Ma. In contrast, results from igneous rocks obtained by deep sea drilling are far sparser, less accurate, and give only paleolatitudes and not unique poles. The data are nevertheless useful, especially for time intervals lacking magnetic reversals (i.e., the Cretaceous Normal Polarity Superchron) and to provide an independent test of the results from skewness and other approaches. These independent tests reveal a high level of consistency with skewness results, strongly supporting the usefulness and reliability of skewness analysis.
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