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The LITHOPROBE Experience:

Learn about the LITHOPROBE project and how active-source seismology is essential for understanding tectonic evolution. Discover the goals, techniques, and results of this multidisciplinary research, which images the internal structure of the Earth's lithosphere.

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The LITHOPROBE Experience:

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  1. The LITHOPROBE Experience: Active-source Seismology and Other Earth Science – An Essential Combination for Understanding Tectonic Evolution Ron Clowes University of British Columbia, Vancouver, BC EarthScope Workshop, Bozeman, MT, Sept. 16-18/05

  2. My main points are … • For most geologists to participate meaningfully in the EarthScope program, multichannel reflection and refraction/wide-angle reflection seismology must be part of the scientific program • The active-source seismology program must be directed at geological targets that have fundamental significance for understanding tectonic evolution • The active-source seismology program must be coordinated with geological studies and Flexible Array

  3. LITHOPROBE is … • A national earth science research project • To investigate the three-dimensional structure and evolution of Canada’s landmass and continental margins • By probing the lithosphere, Earth’s relatively cold, strong, rigid outer shell which is typically 100 km or more thick

  4. WhyLITHOPROBE ? • To gain a basic understanding of the continent on which we live, from which we derive resources and which generates natural hazards • To obtain regional background information useful to mining and petroleum industries

  5. How does LITHOPROBE work? • Multidisciplinary • Collaboration • Partnerships • Decentralized research

  6. GEOPHYSICS REGIONAL INFORMATION LITHOSPHERIC STRUCTURE FOR INDUSTRY & TECTONIC PROCESSES DETAILED STUDIES WITH INDUSTRY

  7. How did LITHOPROBE select fundamental geological features? • Call for integrated, multidisciplinary proposals from a New Transects Subcommittee • Peer-review nationally and internationally • Internal review by 3 disciplinary subcommittees [seismic, em, geology] and the senior Scientific Ctte • Review of evaluations by New Transects Subctte • Recommendation to Sci. Ctte. and LITHOPROBE Board of Directors

  8. How does LITHOPROBE image internal structure? • Seismic reflection – best resolution; crust and upper mantle structure • Seismic refraction – medium resolution; P-wave velocity and composition of crust & upper mantle • Teleseismic studies – lower resolution; S-wave velocity and structure from crust to transition zone • Magnetotellurics – conductivity, fluids • Magnetics & gravity – tie with geology and general structure

  9. Seismic Reflection and Refraction

  10. 6-12 km 0 km 40 km >500 km Near-vertical reflection • Refraction and • wide-angle reflection • Goals: • image the velocity structure • also image major • differences in rock types • provide compositional and • thermal constraints • Goals: • image differences between rock types and subsurface structures: • mapping the detailed • “structural fabric” • limited compositional information

  11. Models • inversion for simplest • structure • imaging using deconvolution, • stacking, and migration • techniques Resolution Upper crust 1 km 3-20 km < 0.1 km/s 0.2 km/s Moho 1.5-2 km 20-50 km 0.1 km/s • Upper crust • 10 m < 0.5 km • Moho • 200 m < 2.5 km INTRO RESULTS CONCLUSIONS TECHNIQUES Near-vertical reflection • Refraction and • wide-angle reflection • velocity structure • & large impedance contrasts • compositional and thermal • constraints • impedance contrasts • structural fabric Primary Goals 10-80 Hz 2–12 Hz

  12. Archean Proterozoic Phanerozoic 4Ga 3Ga 2Ga 1Ga 0Ga Tectonic Ages

  13. Paleoproterozoic Trans-Hudson Orogenin Saskatchewan and Manitoba

  14. Ashton et al., CJES, v. 42, 2005

  15. Mylonites from Pelican Thrust Zone Strain gradient around tectonic inclusion of granodiorite-tonalite Sheath fold defined by attenuated mafic dyke in mylonite Δ-winged porphyroclasts in mylonitic granodiorite-tonalite – Shows dextral shear component Δ-winged porphyroclasts in mylonitic pelitic migmatite – Shows low-angle reverse shear Ashton et al., CJES, v. 42, 2005

  16. Concordia diagrams: the need for dating structures and rocks Ashton et al., CJES, v. 42, 2005

  17. Ashton et al., CJES, v. 42, 2005

  18. L10 L9

  19. Line 10 Line 9 east

  20. Lines 9 and 10 Extensive Crustal Reflectivity Limited mantle reflectivity

  21. Lines 9 and 10 PT PT PT Sask Paleoprot Paleoprot Archean Archean

  22. LS2b L9

  23. Line 9 PT Paleoproterozoic PT Sask Archean Hajnal et al., CJES, v. 42, 2005

  24. Line S2b Sask PT Paleoproterozoic Archean Hajnal et al., CJES, v. 42, 2005

  25. C C` C C` Hajnal et al., CJES, v. 42, 2005

  26. Archean Slave craton and Paleoproterozoic Wopmay Orogenin Northwest Territories

  27. Corridor 1, west half: migrated reflection section and interpretation Fort Simpson Terrane upper crust (upthrust) Fort Simpson lower crust (delaminated) Cook et al., Tectonics, v. 18, 1999

  28. Corridor 1, east half: migrated reflection section and interpretation 0 5 10 Time (s) 15 20 25 30 0 15 Hottah lower crust Slave lower crust 30 Approx Depth (km) 50 Hottah mantle (Archean &/or Proterozoic) Archean Mantle 70 Deformed mantle Proterozoic (?) 90 110 Cook et al., Tectonics, v. 18, 1999

  29. Van der Velden & Cook, CJES, v. 38, 2002

  30. Van der Velden & Cook, CJES, v. 38, 2002 km 0 20 40

  31. Van der Velden & Cook, CJES, v. 38, 2002

  32. Strong crustal reflectivity; related to surface geology Strong mantle reflections . to depths of ~100 km . lateral continuity for 100s of km Crustal delamination during continental collision Deformation within the lithospheric mantle Possibly some Proterozoic mantle beneath Archean Slave craton RESULTS

  33. 1100 1101 Yellowknife array 1112 1113

  34. Offset distance (km)

  35. SNORCLE Line 11, Northwest Territories 1111 1101 H2 H1 J 1113 1100 P-Velocity (km/s)

  36. WA reflections correlate with NVI reflections WA reflection at 180 km depth probably corresponds to base of lithosphere Support for model of delamination, subduction and Proterozoic mantle below Archean Slave craton RESULTS

  37. Integration of seismic reflection and teleseismic results Bostock, JGR, v. 103, 1998

  38. Slave craton teleseismic study Straub et al., CGU-AGU, Montreal, 2004

  39. Impulse responses show mantle stratigraphy Teleseismic images correspond to interpretations of MCS and R/WAR data Support for assembly of proto-Slave craton by processes of shallow subduction; and for subduction of Proterozoic lithosphere below Archean Slave Low velocity anomaly at ~350 km depth centered to the south of the Lac de Gras kimberlite field RESULTS

  40. Summary • In order: • To maximize the scientific and infrastructure investment in EarthScope • To involve the geological and geochemical community in a meaningful way • To develop a true 4-D understanding of lithospheric development • Focused studies within EarthScope should include active-source seismology integrated with all other Solid Earth Science studies

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