Joint South-Central and North-Central Sections, both conducting their 41st Annual Meeting (1113 April 2007)
Paper No. 38-6
Presentation Time: 8:40 AM-12:00 PM

CRUSTAL THICKNESS, POISSON'S RATIO, AND MOHO SHARPNESS BENEATH THE MIDCONTINENT RIFT

MOIDAKI, Moikwathai1, GAO, Stephen S.1, LIU, Kelly H.1, and ATEKWANA, Estella2, (1) Geological Sciences and Engineering, University of Missouri-Rolla, 127 McNutt Hall, Rolla, MO 65401, mmnq5@umr.edu, (2) Boone Pickens School of Geology, Oklahoma State University, 105 Noble Research Center, Stillwater, OK 74078

The Mesoproterozoic Midcontinent rift (MCR) in the central US is an approximately 2000 km long, 100 km wide structure from Kansas to Michigan. During the 20-40 million years of rifting, a thick (up to 20 km) layer of basaltic lava was deposited in the rift valleys. Quantifying the effects of the rifting and associated volcanic eruptions on the structure and composition of the crust and mantle beneath the MCR is important for the understanding of the evolution of continental lithosphere. In this study we measure the crustal thickness (H), crustal mean Vp/Vs (which is uniquely related to the better-known Poisson's ratio), and the sharpness of the Moho (R) at about 20 portable and permanent stations in Iowa, Kansas, and South Dakota by stacking P-to-S converted waves (PmS) and their multiples (PPmS and PSmS). Under the assumption that the crustal mean velocity in the study area is the same as the IASP91 earth model, we find a significantly thickened crust beneath the MCR, from about 42 km to about 46 km. The crustal Vp/Vs increases from about 1.80 to as large as 1.95, which corresponds to an increase of Poisson's ratio from 0.28 to 0.32, suggesting a more mafic crust beneath the MCR. The R measurements are spatially variable and are relatively small in the vicinity of the MCR, indicating the disturbance of the original sharp Moho by the rifting and magmatic intrusion and volcanic eruption.

Joint South-Central and North-Central Sections, both conducting their 41st Annual Meeting (1113 April 2007)
General Information for this Meeting
Session No. 38
Geophysics in the Midcontinent (Posters)
Kansas Union, University of Kansas: Ballroom
8:40 AM-12:00 PM, Friday, 13 April 2007

Geological Society of America Abstracts with Programs, Vol. 39, No. 3, p. 71

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