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Volcanic initiation of the Eocene Heart Mountain Slide, Wyoming, USA.

Malone, David H. and Craddock, John P. and Schmitz, Mark D. and Kenderes, Stuart and Kraushaar, Ben and Murphey, Caelan J. and Nielsen, Stefan and Mitchell, Thomas M. (2017) 'Volcanic initiation of the Eocene Heart Mountain Slide, Wyoming, USA.', The journal of geology., 125 (4). pp. 439-457.

Abstract

The Eocene Heart Mountain slide of northwest Wyoming 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 85 km. Recent geochronologic data indicated that the emplacement of the slide event occurred at ∼48.9 Ma, using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) extracted from U-Pb zircon ages from basal layer and injectite carbonate ultracataclasite (CUC). We now refine that age with U-Pb results from a lamprophyre diatreme that is temporally and spatially related to the CUC injectites. The ages for the lamprophyre zircons are 48.97 ± 0.36 Ma (LA-ICPMS) and 49.19 ±0.02 Ma (chemical abrasion isotope dilution thermal ionization mass spectrometry). Thus, the lamprophyre and CUC zircons are identical in age, and we interpret that the zircons in the CUC were derived from the lamprophyre during slide emplacement. Moreover, the intrusion of the lamprophyre diatreme provided the trigger mechanism for the Heart Mountain slide. Additional structural data are presented for a variety of calcite twinning strains, results from anisotropy of magnetic susceptibility for the lamprophyre and CUC injectites and alternating-field demagnetization on the lamprophyre, to help constrain slide dynamics. These data indicate that White Mountain experienced a rotation about a vertical axis and minimum of 35° of counterclockwise motion during emplacement.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1086/692328
Publisher statement:© 2017 by The University of Chicago
Date accepted:13 March 2017
Date deposited:16 August 2017
Date of first online publication:16 May 2017
Date first made open access:16 May 2018

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