Paleomagnetic results from Upper Triassic and Middle Jurassic strata of east-central New Mexico, and implication for North American apparent polar wander path

Abstract

Two apparent polar wander (APWP) paths for North America (NA) diverge during the Jurassic. The path based on paleomagnetic results from igneous rocks of eastern NA, well-dated Ontario kimberlites, and carbonates and radiolarites of Adria (northern Italy - transformed to NA coordinates) has a large gap at high latitude, which could document rapid plate motion or True Polar Wander. The APWP from coeval NA sedimentary rocks define a lower-latitude, more continuous path. The discrepancy between the two paths has been attributed to inclination error (IE) from deposition and compaction of the sediments.New paleomagnetic results from Upper Triassic (Garita Creek, Trujillo, and Redonda Formations) and Middle Jurassic (Entrada, Summerville, and Lower Morrison Formations) sedimentary units of east-central New Mexico have positive reversal and fold tests, which indicate their magnetization, mostly carried by detrital hematite, is primary. Interpretation of noisy and non-linear demagnetization paths was facilitated by a smoothing scheme, which did not bias the mean directions. Using sample-level directions from line fits, IE was estimated ~20° for the Jurassic units, but is negligible for the Triassic units because mean directions are horizontal. Mean paleomagnetic poles for the ~223 Ma (Garita Creek and Trujillo) and ~214 Ma Redonda Formations are 55.7°N/78.7°E/A95 = 3.2° and 59.7°N/81.0°E/A95 = 4.0°; those for the ~163 Ma Summerville and ~155 Ma Morrison Formations are 59.3°N/138.1°E/A95 = 6.5° and 48.7°N/151.8°E/A95 = 7.8°.Simulated ~163 Ma paleomagnetic poles based on Summerville results and a wide range of IE show that no amount of IE correction to the Summerville directions would produce poles consistent with the high-latitude Jurassic APWP. Furthermore, paleomagnetic poles for Trujillo, Redonda, Summerville, and Lower Morrison Formations of east-central New Mexico, even with IE-correction, streak approximately along the 60° parallel (present coordinates) for most of late Triassic and Jurassic, which validates the lower-latitude APWP. Another explanation for the APWP discrepancy is required.