Anisotropy-based inclination correction for the Moenave Formation and Wingate Sandstone: implications for Colorado Plateau rotation

Andrea M Mccall,Kenneth P Kodama

doi:10.3389/feart.2014.00015

Abstract

The ~ 201 Ma paleopole for North America at the Triassic-Jurassic boundary is observed in two widely different locations; one paleopole is determined from the Mesozoic rift basins in eastern North America and the other from the Colorado Plateau in the southwestern United States. A large discrepancy in paleopole positions from these two localities has been attributed to large amounts of clockwise vertical axis rotation of the Colorado Plateau (>10o) combined with inclination shallowing of the paleomagnetism. The sedimentary inclinations of the eastern North American basins have been corrected for shallowing, but the Colorado Plateau inclinations have not. Simple vertical axis rotation of the Colorado Plateau is not enough to bring the two paleopoles into agreement. This study of the Moenave and Wingate Formations was conducted to correct Colorado Plateau inclinations using their high field isothermal remanent anisotropy. The Moenave Formation and laterally equivalent Wingate Sandstone, which span the Triassic-Jurassic boundary, were sampled in southern Utah and northern Arizona. Thermal demagnetization isolated a characteristic remanence carried by hematite from 20 sites. High field (5 T) isothermal remanent anisotropy indicated shallowing of the characteristic remanence with an average flattening factor of f=0.69. An inclination-corrected paleopole for the Moenave and Wingate Formations is located at 62.5˚N 69.9˚E (α95=5.5˚) and is shifted northward by 2.9˚ with respect to the uncorrected paleopole. When the inclination corrected paleopole is rotated counterclockwise 9.7o about an Euler pole local to the Colorado Plateau, it is statistically indistinguishable from the inclination-corrected paleopole from the eastern North American rift basins. Rotation of the uncorrected paleopole does not bring it into statistical agreement with rift basin paleopole, therefore an inclination shallowing correction is necessary to support rotation of the Colorado Plateau and bring

Highlights

The apparent polar wander path (APWP) for North America (NA) during the early Mesozoic has been observed from two widely different locations; in the sedimentary and volcanic rocks of the rift basins in the northeastern United States, and in strata in the American Southwest, on the Colorado Plateau (CP)
Large amounts (>10◦) of vertical axis clockwise rotation of the CP about an Euler pole local to the CP (Steiner and Lucas, 2000), combined with inclination shallowing of the paleomagnetism is suggested to be the reason for the difference between the pole paths (Kent and Olsen, 2008), but structural, geologic, and some paleomagnetic data suggest that the rotation is limited to less than 5◦ (Hamilton, 1981, 1988; Gordon et al, 1984; Bryan and Gordon, 1986, 1990; Cather, 1999; Molina-Garza et al, 2003)
When the characteristic remanent magnetization (ChRM) could not be isolated and the maximum angular deviation (MAD) was greater than 12◦ (Figures 3F,G), the specimen was rejected, leading to a high rejection percentage in some sites, often over 50%

Summary

Introduction

The apparent polar wander path (APWP) for North America (NA) during the early Mesozoic has been observed from two widely different locations; in the sedimentary and volcanic rocks of the rift basins in the northeastern United States, and in strata in the American Southwest, on the Colorado Plateau (CP). Large amounts (>10◦) of vertical axis clockwise rotation of the CP about an Euler pole local to the CP (Steiner and Lucas, 2000), combined with inclination shallowing of the paleomagnetism is suggested to be the reason for the difference between the pole paths (Kent and Olsen, 2008), but structural, geologic, and some paleomagnetic data suggest that the rotation is limited to less than 5◦ (Hamilton, 1981, 1988; Gordon et al, 1984; Bryan and Gordon, 1986, 1990; Cather, 1999; Molina-Garza et al, 2003). Inclination shallowing corrections have been shown to be important for geologically realistic interpretations of paleomagnetic data by many workers, using two different techniques that yield the same result when compared; the anisotropy technique (Kodama and Davi, 1995; Kodama, 1997; Tan and Kodama, 1998, 2002; Vaughn et al, 2005; Bilardello and Kodama, 2009, 2010) and the E/I www.frontiersin.org

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