A new paleomagnetic pole for the Neoproterozoic Uinta Mountain supergroup, Central Rocky Mountain States, USA

Abstract

Hematite-cemented strata of the Neoproterozoic age (∼800–750 Ma) Uinta Mountain Group (UMG) provide a new well-defined mid-Neoproterozoic paleomagnetic pole for Laurentia. Thermal demagnetization results and rock magnetic experiments reveal the presence of two discrete magnetizations in UMG rocks. Both magnetizations are carried by hematite. The dominant characteristic remanent magnetization (ChRM) is an east-directed (or antipode) shallow, positive to negative inclination magnetization that is typically unblocked over a narrow range of high laboratory temperatures between 660 and 680 °C. The second magnetization, exclusively of normal polarity, is north to northeast-directed and has a moderate to steep, positive inclination and probably represents a recent or modern day viscous remanent magnetization. The response of UMG samples to thermal and chemical demagnetization, comparison with previously obtained data from UMG rocks in the area, results from rock magnetic experiments, and the inferred, low-latitude of Laurentia during UMG deposition in the Neoproterozoic are all consistent with the interpretation that the west or east-directed, shallow magnetization is a near primary remanence. The presence of dual polarities of the ChRM, with the west-directed remanence inferred to be of normal polarity and the east-directed of reverse polarity, suggests that magnetization acquisition in the UMG rocks took place over a sufficient amount of time to average secular variation of the geomagnetic field. The mean paleomagnetic pole derived from the inferred primary magnetizations from UMG strata (0.8°N, 161.3°E, α 95 = 4.6°, N = 9 sampling localities consisting of 79 sites) is fully consistent with recently reported results from rocks of mid-Neoproterozoic age for southwest Laurentia, which define a tight counterclockwise loop, located in the south Pacific, in the apparent polar wander path for Laurentia during the Neoproterozoic.