Abstract

The presence along the Heart Mountain detachment in Wyoming of microbreccia containing volcanic glass grains with primary shapes and accreted grains equivalent to accretionary and armored lapilli supports the concept that injection of volcanic gases along the fault produced fluidization. The probable source of the volcanic contribution was a fixed feeder pipe, now beneath the Crandall intrusive complex, which left a trail of intrusives akin to a hotspot trace in the moving allochthon. Volcanic gas carrying glass and fluidized microbreccia was injected in sill-like fashion along a bedding horizon near the base of the Ordovician Bighorn Dolomite, resulting in gravitative collapse and spreading, probably catastrophic, of the overlying carbonate and volcanic massif.

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