OIINK
OZARKS | ILLINOIS | INDIANA | KENTUCKY
unraveling the secrets of North America's continental interior
Origin and Evolu:on of Cratonic Illinois Basin: Ini:al Results from the EarthScope OIINK Experiment Xiaotao Yang ([email protected])1, Gary L. Pavlis1, Michael W. Hamburger1, Hersh Gilbert2, Chen Chen2, Stephen Marshak3, Timothy H. Larson4 1. Department of Geological Sciences, Indiana University; 2. Department of Earth, Atmospheric, and Planetary Sciences, Purdue University; 3. School of Earth, Society, and Environment, University of Illinois at Urbana-­‐Champaign; 4. Illinois State Geological Survey, University of Illinois at Urbana-­‐Champaign • 
• 
Key Points High-­‐resolu;on lithospheric velocity discon;nui;es are imaged for Illinois basin Strong varia;on of crustal thickness provides new evidence of complicated, 3-­‐D subsidence history of the Illinois basin Indiana University 4. CCP Stacking Image Volume The 3-­‐D image volume of the CCP stack produced from the receiver func;on data is shown on the right. P-­‐to-­‐S amplitudes are shown a?er applying Z1.5 gain with depth. Green spheres are sta;ons used in this study. The figure below it shows major structures surrounding the Illinois basin (shaded ellip;cal area). Structural units include Ste. Genevieve fault zone (SGFZ), the Ozark dome (OD), the Reelfoot ri? (RR), the Rough Creak graben (RCG), and the Wabash Valley fault system (WVFS). The Mississippi embayment is outlined by the dashed curve around the Reelfoot ri?. ê Loca;on of the cross-­‐
sec;ons (ver;cal profiles) analyzed in this study. 1. Geological Background of the Illinois Basin çGeology of eastern US Major structures of central US è 1) Illinois Basin is a intracratonic basin in central U.S; 2) It was ini;ated about 500 m.a. with forma;on of Reelfoot ri? to the south; 3) It is surrounded by a series of intracratonic upli?s including arches and domes. North-­‐dipping Moho is observed. Summary 5. Crustal Thickness 1’ 1 2’ 2 •  The Moho is dipping northward with thickening lower crust •  Sinuous Moho topography is observed 6. Forma:on & Subsidence of the Illinois Basin Top depth of Precambrian basement around Illinois basin é 2. Network Design The Ozark, Illinois, Indiana, Kentucky (OIINK) experiment consists of 140 Flexible Array seismic sta;ons covering the southern Illinois basin area. Other networks such as USArray TA, GSN, CNMSN are used in improving the coverage. OIINK array covers most of the major structures in southern Illinois basin area. Ozark Dome Illinois Basin Sparta Shelf Moho depth map from this study ç 3’ 3 Top depth of Precambrian basement in central US and profile loca;ons ç Ozark Dome Wabash Valley Fairfield Fault Sub-­‐basin System Ozark Ste. Dome Genevieve Fault Sparta Zone Shelf Illinois Basin Sparta Shelf 4’ 4 Illinois Basin Wabash Valley Fault System Rough Creek Graben Rough Creek Graben Before ri?ing Ri?ing (Thinning + Hea;ng) Post-­‐ri?ing (Subsidence + Compression + Cooling) Profiles across major structures (See the Precambrian depth map on the le? for profile loca;ons) ç Subsidence surrounded by upli?s (1)  Northwest-­‐Southeast direc;on (cartoons on the right). 3. Data & Method 1)  Receiver func;ons were es;mated for 213 sta;ons based on 85547 teleseismic records from events 30-­‐95 degrees away with magnitude >=5.0; 2)  Generalized Itera;ve Deconvolu;on method (Wang and Pavlis, in review) was used in es;ma;ng receiver func;ons; 3)  Computer program RFeditor was used in selec;ng high quality receiver func;ons (Yang and Pavlis, in prepara;on); 4)  Standard Common Conversion Point (CCP) stacking method was used in imaging/migra;on process. Bouguer gravity anomaly (mGal) in central US ç
Summary •  Crust thins toward the southeastern basin in general •  The Du Quoin Monocline, separa;ng the Sparta Shelf and the Fairfield Sub-­‐basin, is a crustal-­‐scale boundary •  Wabash Valley Fault System offsets the whole crust •  Prominent crustal thinning occurred in Ozark Dome region • Star;ng from the failed ri? (Rough Creek Graben), sediments deposited mostly in southeastern Illinois basin. • The depocenter migrated to the north with further subsidence of the basin. • Post-­‐ri?ing compressional events accelerated basin subsidence and the upli? of surrounding highlands. (2) East-­‐West direc;on. •  A?er ini;a;on of the basin, flexural deforma;on of the basin lithosphere occurred due to compressional stresses in E-­‐W direc;on.