T24A-06
NORTH AMERICA’S MIDCONTINENT RIFT: WHEN RIFT MET LIP

Tuesday, 15 December 2015: 17:15
306 (Moscone South)
Carol A Stein1, Seth A Stein2, Jonas Kley3, G Randy Keller Jr4, Trevor A Bollmann2, Emily Wolin2, Hao Zhang2, Andrew W Frederiksen5, Kunle Ola5, Michael Edward Wysession6, Douglas Wiens7, Ghassan Alequabi7, Gregory P Waite8, Eunice Blavascunas9, Carol A Engelmann8, Lucy M Flesch10, Tyrone O Rooney11, Robert Moucha12, Eric Brown13 and SPREE Project Team, (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)Self Employed, Washington, DC, United States, (5)University of Manitoba, Winnipeg, MB, Canada, (6)Washington Univ, Saint Louis, MO, United States, (7)Washington University in St Louis, Department of Earth and Planetary Sciences, St. Louis, MO, United States, (8)Michigan Technological University, Geological and Mining Engineering and Sciences, Houghton, MI, United States, (9)Whitman College, Environmental Sciences, Walla Walla, WA, United States, (10)Purdue University, West Lafayette, IN, United States, (11)Michigan State University, East Lansing, MI, United States, (12)Syracuse University, Earth Sciences, Syracuse, NY, United States, (13)Aarhus University, Department of Geoscience, Aarhus, Denmark
Abstract:
Rifts are segmented linear depressions, filled with sedimentary and igneous rocks, that form by extension and often evolve into plate boundaries. Flood basalts, a class of Large Igneous Provinces (LIPs), are broad regions of extensive volcanism due to sublithospheric processes. Typical rifts are not filled with flood basalts, and typical flood basalts are not associated with significant crustal extension and faulting. North America’s Midcontinent Rift (MCR) is an unusual combination. Its 3000-km length formed as part of the 1.1 Ga rifting of Amazonia (Precambrian NE South America) from Laurentia (Precambrian North America) and became inactive once seafloor spreading was established, but contains an enormous volume of igneous rocks. MCR volcanics are significantly thicker than other flood basalts, due to deposition in a narrow rift rather than a broad region, giving a rift geometry but a LIP's magma volume. Structural modeling of seismic reflection data shows an initial rift phase where flood basalts filled a fault-controlled extending basin, and a postrift phase where volcanics and sediments were deposited in a thermally subsiding basin without associated faulting. The crust thinned during rifting and rethickened during the postrift phase and later compression, yielding the present thicker crust. The coincidence of a rift and LIP yielded the world's largest deposit of native copper. This combination arose when a new rift associated with continental breakup interacted with a mantle plume or anomalously hot or fertile upper mantle. Integration of diverse data types and models will give insight into questions including how the magma source was related to the rifting, how their interaction operated over a long period of rapid plate motion, why the lithospheric mantle below the MCR differs only slightly from its surroundings, how and why extension, volcanism, and compression varied along the rift arms, and how successful seafloor spreading ended the rift phase.

Papers, talks, and educational material are available at http://www.earth.northwestern.edu/people/seth/research/mcr.html

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