GP43A-3633:
Advancing Late Mesoproterozoic Paleogeography With New Constraints From The Keweenawan Rift And The Umkondo Large Igneous Province
Thursday, 18 December 2014
Nicholas Swanson-Hysell1, Taylor M Kilian1,2, Samuel A Bowring3, Richard E Hanson4, Seth D Burgess3 and Jahandar Ramezani3, (1)University of California Berkeley, Earth and Planetary Science, Berkeley, CA, United States, (2)Yale University, New Haven, CT, United States, (3)MIT-EAPS, Cambridge, MA, United States, (4)Texas Christian University, Fort Worth, TX, United States
Abstract:
Laurentia and Kalahari are currently interpreted as independently moving continents ca. 1110 million years ago that subsequently became conjoined in the supercontinent Rodinia. Their relative positions and orientations are dependent both on the directional comparison of paleomagnetic poles and geomagnetic polarity choices for those poles. In this contribution, we use newly developed and existing paleomagnetic and geochronological data from both the ca. 1110-1085 Ma Midcontinent Rift of Laurentia and the ca. 1109 Ma Umkondo Large Igneous Province (LIP) of Kalahari to present improved constraints on relations between the two continents. Previous mean poles for the Umkondo LIP have been either calculated by taking the mean of regional submeans or at the site level which is problematic given the preponderance of multiple sites from single individual cooling units. We report a new Umkondo grand mean pole that is the mean of the virtual geomagnetic poles (VGPs) of individual cooling units and is reinforced with new data from ~20 previously unstudied Umkondo sills from Botswana. This approach yields a pole whose position and uncertainty are the most robust calculated to date. The portion of Laurentia’s Mesoproterozoic apparent polar wander path (APWP) known as the Logan Loop and Keweenawan Track partially overlaps in age with the Umkondo pole and is of central importance in efforts to reconstruct late Mesoproterozoic paleogeography. Ongoing debates as to the geometry and timing of Rodinia assembly critically hinge on the comparison of paleomagnetic poles from other continents to the Keweenawan record. We present an updated compilation for the Keweenawan Track APWP using an improved chronostratigraphic context enabled by new geochronological and paleomagnetic data. Ongoing improvements and time-calibration of this record further constrains the rate of Laurentia’s motion and provides opportunities for increased rigor in the determination of relative paleogeographic positions such as between Laurentia and Kalahari.
