ON THE NEED FOR GEOPHYSICAL TRANSECTS INVESTIGATING CRUST AND LITHOSPHERE FROM THE NORTH AMERICAN CRATON TO THE GULF OF MEXICO

Modern geophysical surveys are increasingly important for understanding crustal and lithospheric structure, particularly in regions such as the US mid-continent where basement exposures are rare. Understanding basement geology is also essential for reconstructing basin evolution, thermal history, and other petroleum system elements, all natural concerns of the hydrocarbon industry. It is the responsibility of the academic geoscientific community (supported by the National Science Foundation, mostly as a result of Earthscope, MARGINS, and Continental Dynamics) to identify the important crustal and lithospheric evolution problems for this area. These questions include the nature, location and evolution of the following fundamental lithospheric structures: 1) The Late Mesoproterozoic Grenville suture that trends NE-SW through Texas and into Oklahoma; 2) The Neoproterozoic-Cambrian rifts of Texas and Oklahoma; 3) The Pennsylvanian fold-and-thrust belt and associated foreland basins of Arkansas, Oklahoma, and Texas; and 4) The crustal transition between Jurassic oceanic crust of the Gulf of Mexico and Mesoproterozoic continental crust of Texas and Oklahoma and associated Mesozoic rifts of E. Texas, S. Arkansas, and Louisiana. Targeting these features would also require an offshore geophysical component.

NSF-EarthScope's USArray of passive seismometers is a transportable array migrating across the country with 18-24 month deployments at each site. It is scheduled to be deployed in the central USA in FY09-10. This array uses earthquake data to resolve crustal and upper mantle structure on the order of tens of kilometers and increase resolution of structures in the lower mantle and at the core-mantle boundary. The USArray's second component is a pool of ~2100 instruments (200 broadband, 200 short-period, and 1700 high-frequency) that are deployed using flexible source-receiver geometries. These additional portable instruments permit high-density, short-term observations of key targets within the footprint of the larger transportable array using both natural and active sources. The south-central GSA scientific community should move aggressively to develop collaborations with industry to ensure that important geologic problems are considered for study as this major national initiative moves through our region