The Eocene Heart Mountain Slide of northwest WY covers an area of as much as 5000 km2 and includes allochthonous Paleozoic carbonate and Eocene volcanic rocks with a run-out distance of as much as 160 km. The slide event is dated at 48.87 +/- 0.21 Ma using U-Pb zircon ages from associated basal layer carbonate ultracataclasite (CUC) and vertical injectites of this material. The emplacement event took place over a period of hours. The triggering event that caused the slide to initiate was the horizontal eruption of diamond-bearing kimberlite that is present as a large, allochthonous dike at White Mountain. The kimberlite has a U-Pb zircon age of 48.65 +/- 0.56, which is within the error of the current estimate of the slide emplacement age from U-Pb injectite zircons. AMS results for the kimberlite preserve a horizontal Kmax flow fabric parallel to the dike (N55°E, 90°). We also performed AF demagnetization on the kimberlite samples and report a paleopole (5°, 29° plunge), which is compatable with the presumed Eocene paleopole. Other remnants of the kimberlite remain to be discovered in areas within the Eocene volcanic succession.
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