Pony-Cherry Creek Age Relations in Southwestern Montana

Reid, Rolland R.

doi:10.1130/0016-7606(1955)66[1315:pcaris]2.0.co;2

Cited by 3 publications

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“…In addition to original differences in the protoliths, the presence of inverted and repeated successions in various outcrop belts of the Montana Precambrian section is bound to have added to the confusion in age relations. Thus, although rocks like those of the Cherry Creek Group have been found underlying rocks like those of the Pony Series (Reid, 1957), the latter are not necessarily younger than the former, a possibility also pointed out by Reid (1957Reid ( , 1966. Therefore, on the basis of present knowledge, the evidence is insuffi cient to justify application of the terms Cherry Creek Group and Pony Series to the sequence of the Archean rocks in the Tobacco Root Mountains.…”

Section: Pony Series-cherry Creek Group Problemmentioning

confidence: 87%

Explanatory text to accompany geologic map of southern Tobacco Root Mountains, Madison County, Montana

Vitaliano¹,

Burger²,

Cordua³

et al. 2004

Precambrian Geology of the Tobacco Root Mountains, Montana

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The core of the Tobacco Root Mountains, a domal uplift of southwestern Montana, is composed of regionally metamorphosed Archean rocks that have been intruded by diabase dikes of late Precambrian age and by igneous rocks of late Mesozoic and Cenozoic age. The Archean rocks, originally a stratiform sequence of epiclastic, volcaniclastic, and carbonate sedimentary rocks, have been metamorphosed to amphibolite-granulite rank with attendant migmatization. The distribution of the metamorphic rocks and the later intrusions is shown on the map.In this report to accompany the map, the nature of the crystalline rocks is described briefl y. Two thermal events affected the area in Precambrian time, one about 2.7 b.y. B.P. and the second at about 1.6 b.y. B.P. A third event may have begun in very late Precambrian time, but is most strongly represented by changes of late Mesozoic age.Because of the structural complexities, correlation of the metamorphic rocks in the Tobacco Root Mountains with Precambrian sequences elsewhere in southwestern Montana is extremely diffi cult.

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Section: Pony Series-cherry Creek Group Problemmentioning

confidence: 87%

Explanatory text to accompany geologic map of southern Tobacco Root Mountains, Madison County, Montana

Vitaliano¹,

Burger²,

Cordua³

et al. 2004

Precambrian Geology of the Tobacco Root Mountains, Montana

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show abstract

“…(1955), who divided the Pre-Cambrian into three groups, the Pony gneiss, the Cherry Creek gneiss, and the Dillon granite. The temporal relations of these rocks are still a matter of dispute (Scholten, 1955;Reid, 1955). All the biotite ages from these rocks fall in the range 1560 to 1660 m.y., regardless of the type of rock from which they come.…”

mentioning

confidence: 99%

Absolute Age of Pre‐cambrian Rocks in Wyoming and Montana*

Giletti

Gast

1961

Annals of the New York Academy of Sciences

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Isotopic ages from southwestern Montana

Giletti¹

1966

J. Geophys. Res.

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Potassium‐argon and rubidium‐strontium age measurements for the southwest Montana basement show that a regional metamorphism occurred 1.6±0.1 gigayears (Gy) ago and was accompanied by igneous intrusion (Dillon granite gneiss). The southeastern margin of this metamorphism is found in the Gravelly Range and the Gallatin River canyon. Rocks to the southeast of the margin yield ages from 2.1 to 3.2 Gy. Some of the gneisses in the 1.6‐Gy terrane may be 3.1 Gy old. The Laramide Boulder and Tobacco Root batholiths sharply reduced the isotopic ages of the Precambrian rocks they intruded in a narrow belt around their contacts. Deposition of the Belt series postdates the 1.6‐Gy age.

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Pony-Cherry Creek Age Relations in Southwestern Montana

Cited by 3 publications

References 0 publications

Explanatory text to accompany geologic map of southern Tobacco Root Mountains, Madison County, Montana

Explanatory text to accompany geologic map of southern Tobacco Root Mountains, Madison County, Montana

Absolute Age of Pre‐cambrian Rocks in Wyoming and Montana*

Isotopic ages from southwestern Montana

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