T42B-05:
Mid-Continent Rift: Rift, LIP, or Both?
Thursday, 18 December 2014: 11:20 AM
Carol A Stein1, Seth A Stein2, Jonas Kley3, David Hindle3 and G Randy Keller Jr4, (1)University of Illinois at Chicago, Chicago, IL, United States, (2)Northwestern University, Evanston, IL, United States, (3)Georg-August-Universitaet Goettingen, Goettingen, Germany, (4)University of Oklahoma, Norman, OK, United States
Abstract:
North America’s Midcontinent Rift (MCR) is traditionally considered to have formed by midplate extension and volcanism ~1.1 Ga that ended due to compression from the Grenville orogeny, the ~1.3 - ~0.98 Ga assembly of Amazonia (Precambrian northeast South America), Laurentia (Precambrian North America), and other continents into the supercontinent of Rodinia. We find that a more plausible scenario is that it formed as part of the rifting of Amazonia from Laurentia and became inactive once seafloor spreading was established. The MCR has aspects both of a continental rift - a segmented linear depression filled with sedimentary and igneous rocks - and a large igneous province (LIP). Comparison of areas and volumes for a range of continental LIPS shows that the MCR volcanic rocks are significantly thicker than the others. The MCR flood basalts have steeper dips and thicker overlying sediments than other continental flood basalts, and were deposited in a subsiding basin after most extension ended, indicating that they are better viewed as post-rift than syn-rift rocks. Hence we view the MCR as a LIP deposited in crust weakened by rifting, and thus first a rift and then a LIP.
