...Donald R. Lamb; Robert B. Johnson Abstract Natural percussion cones are found on cobbles and boulders of quartzite of the Medicine Peak Quartzite (Precambrian) in Wyoming. Similar cones have been duplicated in the laboratory on cobbles of Medicine Peak Quartzite and on pieces of plate...

... and are characterized by pronounced "knob-and-kettle" topography and tills rich in crystalline constituents. More recent deposits at the base of Medicine Bow Peak, W. of the source of Libby Creek, have been considered by some workers as recent moraines, but are more likely protalus ramparts overlying latest Pinedale...

.... The depositional environment and age of the Bridger Peak quartzite are uncertain ( Houston et al. 1992 ). The Bridger Peak quartzite is correlated with the Conical Peak quartzite of the Medicine Bow Mountains (Fig.  3 ), which is interpreted to be deposited in a fluvial to shallow-marine environment ( Houston et...

...Brainerd Mears Abstract Periglacial polygons, 100 ft. above timberline, are restricted to soil in an alpine meadow on a diorite dike which cuts massive quartzite weathering to felsenmeer. The nets appear inactive because of lichen-covered surface blocks, a distinctive "A" soil horizon, deeply...

... of the Rocky Mountains experiment). 40 Ar/ 39 Ar and U-Pb data define age patterns in the Sierra Madre that are delineated by discrete structures. North of the 1.78-Ga Divide Peak mylonite zone, a foreland structure associated with the Medicine Bow orogeny, 40 Ar/ 39 Ar biotite dates suggest cooling below 300...

... for the Medicine Lodge thrust, suggesting that the thrust cut across a large, pre-thrust fold in Mesoproterozoic quartzites, hence cutting locally down-section in the direction of transport ( Ruppel, 1994 ). Alternatively, the Fritz Creek and Medicine Lodge thrusts may represent two distinct ramps that branch off...

... in the Medicine Bow Mountains of southeastern Wyoming. These shear zones are generally interpreted as a mid-crustal thrust system rotated to its present-day subvertical orientation during late-stage, orogen-scale folding. However, the map geometry, presence of large domains of S tectonites, and vertical mineral...

...John L. Severson ABSTRACT A southeastward-plunging synclinal mountain ridge, capped by Mississippian rocks, rises from a base of Cambrian rocks in the Sunwapta Pass area. Detailed sections involving Silurian and Devonian rocks were studied from the Nigel Peak area on the north southward...

..., and deformation mechanism analyses of the northern mylonite zone of the eastern Medicine Bow Mountains. Mylonites of this zone record a complex deformation history, but the main deformation phase was sinistral/northwest-side-up oblique transpression. Evidence for southeast-side-up, dip-slip motion...

... quartz veins commonly cut the gneiss and Proterozoic quartzite but are unknown in the Phanerozoic rocks of the upper Medicine Lodge Valley, although silicic shear zones and jasperoid are common. The black fine-grained, biotite-rich matrix in sample KT92-153a comprises about 30% of the rock; sample...

... ( Fig. 1 ) as well as a number of small-displacement normal faults northeast of Lima. Fig. 2 —Relation of thickness of (a) Meade Peak and (b) Retort Members of Phosphoria Formation (Permian) to Medicine Lodge, Tendoy, and Snowcrest-Greenhorn thrust-fault systems in southwestern Montana. Isopachs...

... Clapp and Deiss, 1931 Nelson and Dobell, 1961 McNamara Formation Mount Shields Formation McNamaro Formation Red Plume Banner Banner Banner Quartzite Quartzite Quartzite Quartzite Helena Formation Mount Shields Formation Shields Formation Shepard Shepard Shepard Shepard Miller Peak Quartzite Formation...

... suggests that it differs from northern-bounding terranes. Viewed more broadly, the 2.7 Ga and 1.7 Ga age peaks that the Montana metasedimentary terrane shares with the global zircon age spectrum suggest that the drivers of these events in the Montana metasedimentary terrane were common throughout the Earth...

... subprovince, and two Archean terrains that may be allochthonous to the 3.0 Ga craton, (4) the Sierra Madre – Medicine Bow block, and (5) the Black Hills – Hartville block. A thick, fast lower crustal layer, imaged by Deep Probe, corresponds geographically with the Bighorn subprovince and may be an underplate...

.... Downstream, it skirted the southern end of the Carmen culmination and crossed the northern part of the Maiden Peak basement-cored culmination before occupying a longitudinal valley in the footwall of the Medicine Lodge thrust south of segment A. The Hawley Creek paleoriver flowed farther to the south...

... Pennsylvanian age consists of variegated chert-pebble conglomerate, brown quartzite, and minor amounts of gray limestone. Detritus composing this formation was derived from uplands of the Antler orogenic belt in central Nevada. In the Pequop Mountains the Diamond Peak Formation is approximately 1,200 ft (366 m...

... and the Medicine Hat block, why don’t we see ages of magmatism more closely aligned with the record of metamorphism, which presumably reflects crustal thickening during collision? The difference between the 1.86 Ga magmatism and the peak of metamorphism has been previously recognized (e.g., Foster et al...

... and reflect left-lateral, strike-slip displacement. Folds just southeast of the Laramie Peak shear zone, with ages for syndeformational titanite growth in fold hinge areas ranging from 1755–1740 Ma, provide strong evidence for renewed shortening and continuation of the Medicine Bow Orogeny...

... lithosphere appear to be much more fertile for later melting than the adjacent Archean lithosphere, as exemplified by Cretaceous and younger magmatism and mineralization being largely confined to the Great Falls tectonic zone, rather than adjoining Archean lithosphere of either the Medicine Hat block...