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MESOPROTEROZOIC BELT BASIN:
CRUSTAL-SCALE ANOMALY IN THE NORTHERN ROCKIES J.W. Sears University of Montana, Missoula
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Belt Supergroup Calgary Kimberly ALBERTA MONTANA Libby Gibbs
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Chief Mountain klippe Belt/Purcell Upper Cretaceous Lewis Thrust
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Belt Supergroup Calgary Kimberly ALBERTA MONTANA Libby Gibbs
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Gabbro sill reflectors
Cook and Van der Velden, 1995 Km
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130 km 130 km 110 km 80 km 55 km 40 km 35 km
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74 Ma 59 Ma
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Dry slab overrides wedge of wet sedimentary rock
with high pore pressures in front Strong slab slides on plastic base in rear
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Rebound of crustal keel drives Paleogene extension,
folds Purcell anticlinorium Restored at 59 Ma Crustal Keel
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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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