A 57 Ma Pacific plate palaeomagnetic pole determined from a skewness analysis of crossings of marine magnetic anomaly 25r

Abstract

An increase in the accuracy and age resolution of the apparent polar wander path of the Pacific plate could be important for testing reconstructions that relate the motion of Pacific basin plates to other plates, for testing if hotspots in different ocean basins are stationary relative to one another, and for estimating the motion of hotspots relative to the spin axis. With these goals in mind, herein we investigate how accurately a palaeomagnetic pole can be estimated from skewness analysis of many crossings of a single magnetic anomaly on the Pacific plate. Apparent effective remanent inclinations of the sea-floor magnetization were estimated from the skewnesses of 132 useful (out of 149 total) crossings of anomaly 25r (56.5-57.8 Ma) distributed over a distance of more than 11 OOO km across the Pacific plate. These estimates were inverted to obtain a best-fitting palaeomagnetic pole latitude, pole longitude, and anomalous skewness for this single reversed-polarity chron. The best-fitting model gives a pole of 78.2"N, 4.8"E with a 95 per cent confidence ellipse having a 6.4" major semi-axis oriented 93" clockwise of north and a 4.1" minor semi-axis; anomalous skewness is 16.2" f 4.6" (95 per cent confidence limits). We also investigated the effect of the dependence of anomalous skewness on spreading rate by correcting our data using an empirical model. The pole obtained from the inversion of this alternative data set lies a statistically insignificant 0.6" from the pole obtained using no correction. That a pole with usefully compact confidence limits and a narrowly resolved, precisely estimated age can be so determined suggests that an accurate apparent polar wander path with a fine-age resolution can be determined for the Pacific plate by applying the same approach to the shapes of other marine magnetic anomaliks.Comparison of our chron 25r pole with other Pacific palaeomagnetic and palaeoequatorial sediment facies data indicates that the Pacific plate remained nearly stationary relative to the spin axis during the Eocene (-0.05" Myr-' f 0.28" Myr-I), but probably moved rapidly northward during the Paleocene (0.83" Myr-' f 0.46" Myr-I). Comparison of these data to latitudes of dated volcanic edifices along the Hawaiian-Emperor chain indicates that the Hawaiian hotspot drifted southward by 10.2" f 3.4" (95 per cent confidence limits) since 57 Ma, but only by 1.7" f 1.9" since 39 Ma, which gives a southward displacement of 8.5" f 3.9" (95 per cent confidence limits) between 57 and 39Ma, corresponding to a rate of southward motion of 52 f 24 mm yr-'. Incorporation of realistic uncertainties of volcano ages would increase these uncertainties considerably, however. We also examined the distance between the crossings of anomalies 25 and 27 on all the profiles we analysed; along the palaeo-Pacific-Farallon boundary these distances are inconsistent with the joint hypotheses of symmetric spreading and single Pacific and Farallon plates between 62 and 56Ma, indicating that the evidence for a single Pacific plate in early...

Are the Pacific and Indo–Atlantic hotspots fixed? Testing the plate circuit through Antarctica

“…This would seem to preclude separate north and south Pacific plates during the Cenozoic or at least limit the amount of relative motion between them. As a final note on the suggestion of separate north and south Pacific plates, Petronotis et al [26] saw no evidence in their analysis of magnetic anomaly 25r for a north-south Pacific split and they freely incorporated data from north and south of the Eltanin Fracture Zone in determination of their 57 Ma Pacific pole.…”

“…[26]). However, the rate of motion of the Pacific plate over the Hawaiian-Emperor hotspot from the Late Cretaceous through the Cenozoic varies only gradually, without a sense of the implied surges in polar motion (Fig.…”

“…Small degrees of non-uniformity in the magnetization of a seamount, that may be due to secular variation during the period of volcanic extrusion, variations in rock types and their resultant magnetic properties, and structural complexities, can yield sizable errors of 10º or more in mean poles determined assuming uniform seamount magnetization [22]. Paleomagnetic poles have also been derived from the skewness of marine magnetic anomalies on the Pacific plate [20,[24][25][26][27]. [18] global, non-Pacific, synthetic APW path transferred to Antarctica [15] and to the Pacific using Cande et al [8]; NZ 75, [19] ca.…”

“…[18] global, non-Pacific, synthetic APW path transferred to Antarctica [15] and to the Pacific using Cande et al [8]; NZ 75, [19] ca. 75 Ma result from Chatham Islands, south Pacific; Pac 32 through Pac 76v are Pacific anomaly skewness poles; Pac 32, [20]; Pac 57, [26]; Pac 65, [24]; Pac 73, [25]; Pac 76v, [27]; Pac 76s, [23] Pacific seamount-based pole; Pac 81, co-latitude circle from Detroit Seamount [47]. Unfortunately, skewness poles can also be biased to varying degrees by anomalous skewness [28].…”

Pacific Equatorial Age Transect

“…In order to plan site surveys we used the digital age grid of seafloor age from Müller et al (1997;based on Cande and Kent, 1995), heavily modified and improved with additional magnetic anomaly picks from Petronotis (1991) and Petronotis et al (1994), and DSDP/ODP basement ages. For this grid, each point is then backrotated in time to zero age, using the fixed-hotspot stage-poles from Koppers et al (2001) and Engebretson et al (1985) and the paleopole data from Sager and Pringle (1988).…”