High-Latitude Paleomagnetic Poles from Middle Jurassic Plutons and Moat Volcanics in New England and the Controversy Regarding Jurassic Apparent Polar Wander for North America
A paleomagnetic study of Middle Jurassic plutonic and volcanic rocks in New England (White Mountains Magma Series) yields high-latitude pole positions for North America. High unblocking temperature, moderate to high coercivity magnetizations of normal polarity have been isolated in three plutons (White Mountains batholith, Mount Monadnock, and the Belknap Mountains; mean age ~169 Ma), but the mean pole (88.4°N, 82.1°E, A_95 = 6.1°) is not distinguishable from the geographic axis and therefore the hypothesis that the plutons have been contaminated by recent field overprints can not be rejected. However, a dual polarity, high unblocking temperature, and high coercivity magnetization isolated from the Moat volcanics (169 Ma, Rb-Sr age) was apparently acquired soon after caldera collapse and tilting, at about the time of intrusion and cooling of the Conway granite (reported ages K-Ar biotite, 168 Ma; zircon fission track, 163 Ma). The Moat volcanics pole position (78.7°N, 90.3°E, dp = 7.1°, dm = 10.2°) calculated using the mean magnetization direction of reversed polarity (the Cr component) falls at high latitude but is distinguishable from the spin axis. Moreover, published Middle Jurassic paleomagnetic poles from Gondwana (Africa, Australia, and East Antarctica) transferred to the North American reference frame also suggest a high-latitude Middle Jurassic pole position for North America, in agreement with the Moat volcanics pole. The new evidence for a Middle Jurassic loop to high latitudes in the North American apparent polar wander path conflicts by 15°-20° with some key published Jurassic reference poles (e.g., the Newark Trend N2 and the Corral Canyon poles) used to constrain current paleomagnetic Euler pole (PEP) apparent polar wander paths for the Jurassic. We suggest that a plausible explanation for the discrepancy is that the N2 and Corral Canyon magnetizations are in fact secondary and were acquired after tilting. The hypothesis that the North American apparent polar wander path ventured to high latitude in the Middle Jurassic requires further testing, however the results of this study already suggest that the path may be more complicated than that proposed by recently published PEP studies.
- JB095iB11p17503.pdf application/pdf 1.26 MB Download File
Also Published In
- Journal of Geophysical Research