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MESOPROTEROZOIC BELT BASIN: CRUSTAL-SCALE ANOMALY IN THE NORTHERN ROCKIES J.W. Sears

MESOPROTEROZOIC BELT BASIN: CRUSTAL-SCALE ANOMALY IN THE NORTHERN ROCKIES J.W. Sears University of Montana, Missoula. Belt Supergroup. Calgary. Kimberly. ALBERTA. MONTANA. Libby. Gibbs. Chief Mountain klippe. Belt/Purcell. Upper Cretaceous. Lewis Thrust. Belt Supergroup. Calgary.

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MESOPROTEROZOIC BELT BASIN: CRUSTAL-SCALE ANOMALY IN THE NORTHERN ROCKIES J.W. Sears

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  1. MESOPROTEROZOIC BELT BASIN: CRUSTAL-SCALE ANOMALY IN THE NORTHERN ROCKIES J.W. Sears University of Montana, Missoula

  2. Belt Supergroup Calgary Kimberly ALBERTA MONTANA Libby Gibbs

  3. Chief Mountain klippe Belt/Purcell Upper Cretaceous Lewis Thrust

  4. Belt Supergroup Calgary Kimberly ALBERTA MONTANA Libby Gibbs

  5. Gabbro sill reflectors Cook and Van der Velden, 1995 Km

  6. 130 km 130 km 110 km 80 km 55 km 40 km 35 km

  7. 74 Ma 59 Ma

  8. Dry slab overrides wedge of wet sedimentary rock with high pore pressures in front Strong slab slides on plastic base in rear

  9. Rebound of crustal keel drives Paleogene extension, folds Purcell anticlinorium Restored at 59 Ma Crustal Keel

  10. EARTHSCOPE IMPLICATIONS • Inverted Belt Basin forms crustal-scale structure • Thick, coherent Belt-Purcell Supergroup • constrains upper-crust structure • Mafic sill seismic reflectors constrain middle-crust structure • Good Moho reflectivity to bound lower crust • Strong, well-layered Belt Basin controlled geodynamics of Northern Rockies thrust belt • Post-thrust rebound drove extension, formed Purcell anticlinorium - implications for mantle rheology

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