Skewness of Magnetic Anomalies M0 to M29 in the Northwestern Pacific

Abstract

M-sequence magnetic anomalies from the Phoenix, Japanese, and Hawaiian lineation patterns in the western Pacific have been analyzed for cross-sectional skewness to determine a paleomagnetic apparent polar wander path for the Pacific plate for the Early Cretaceous and Late Jurassic. Results from magnetic anomalies MO to M29 have been averaged to yield pole locations ranging in age from 122 to 155 Ma both with and without the possibility of anomalous skewness. In either case these results show that the Pacific plate was moving south from 155 to 129 Ma (Kimmeridgian to Hauterivian). The plate then reversed this motion and began to move slowly to the north. The M-sequence skewness data have been combined with younger poles from seamounts to show that this slow northward drift continued until about 82 Ma, when the Pacific plate began moving more rapidly to the north. This northward drift has continued at varying rates since that time.A discrepancy in the skewness of the Phoenix lineations relative to the Hawaiian and Japanese lineations becomes apparent just prior to Ml On time and grows to a maximum at M29 time. This could be due to a yet-undiscovered plate (called here the Stealth plate) that lay between the Pacific plate and the Phoenix lineations from Ml On to M29 time. Alternatively, it could be due to time-varying anomalous skewness resulting, perhaps, from changes in magnetic field strength during normal or reversed polarity intervals, causing the magnetization pattern to differ from the assumed "square-wave" shape. Both interpretations imply similar types of north-south motion for the Pacific plate; however, the anomalous skewness interpretation also implies a large component of clockwise rotation from 145 to 82 Ma.

Magnetic anomaly lineations from Late Jurassic to Early Cretaceous in the west-central Pacific Ocean

“…It is remarkable that the amplitudes from MlON and M I are so large (about 1000 nT). Larson & Sager (1991) indicated a possibility that there is a sequence of lineations from M22 to M25 south of the Mid-Pacific Mountains; this is backwards with respect to our sequence. The reversal sequence was identified by only one track.…”

Synthesis of Drilling Results from the Mid-Pacific Mountains: Regional Context and Implications

“…Revising published poles (Cox and Gordon, 1984;Sager and Pringle, 1988), we derived three poles with mean ages of 126,104, and 92 Ma. To help in bracketing the age range of the MPM, we also used a paleopole for 85 Ma that was constrained mainly by seamountanomaly inversions (Sager and Pringle, 1988) and two anomalyskewness-based poles for the end of the M-series reversals, MO to M5 and M6 to M10N (Larson and Sager, 1992 Duncan and Clague (1985) of Pacific Plate motion relative to the hotspots. Ages of volcanism for each site are from Pringle and Duncan (this volume).…”

“…They are labeled, in italics, by age in millions of years. Filled squares show paleolatitudes determined from the skewness of seafloor magnetic lineations M0 to M5, M6 to M10N, and M10N to M16 (Larson and Sager, 1992). Vertical bars show 95% confidence limits of paleolatitude; horizontal bars show either one standard deviation of error on mean age or on basalt radiometric dates, or age ranges for points having ages constrained by biostratigraphy or magnetostratigraphy.…”

Paleomagnetism of the Joban Seamount Chain: Its origin and tectonic implications for the Pacific plate

“…Poles located a significant distance from the APWP are probably erroneous. [Cox and Gordon, 1984;Sager, 1992;Larson and Sager, 1992]. Seamount D5 also has a pole to the northwest of the old end of the APWP, so together with IW and HT, they may be Early Cretaceous in age.…”

“…Inversion of magnetic anomalies over seamounts [Vacquier, 1962;Parker et al, 1987] is most commonly applied to the Pacific plate because this plate contains plentiful seamounts. Since many of these seamounts have not been dated, paleomagnetic results from these inversions have been used to study volcanism in individual chains as well as over the entire plate [Sager and Keating, 1984;Sager and Pringle, 1987;Sager, 1992;Sager et al, 1993]. In 1990 and 1992 we conducted a systematic geophysical survey of the Joban Seamount Chain (JSC) and nearby Daigo-Kashima (D5) seamount (Figures I and 2) in the northwestern Pacific [Kobayashi, 1991[Kobayashi, , 1993.…”