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Full-Text Articles in Physical Sciences and Mathematics
Advances In The Geology Of The Tobacco Root Mountains, Montana, And Their Implications For The History Of The Northern Wyoming Province, Tekla A. Harms, John B. Brady, H. Robert Burger, John T. Cheney
Advances In The Geology Of The Tobacco Root Mountains, Montana, And Their Implications For The History Of The Northern Wyoming Province, Tekla A. Harms, John B. Brady, H. Robert Burger, John T. Cheney
Geosciences: Faculty Publications
Integrated studies by Keck Geology Consortium participants have generated many new insights into the Precambrian geology of the Tobacco Root Mountains. We have clarified the tectonic setting and origin of two suites of metamorphic rocks: (1) a quartzofeldspathic gneiss complex with associated metasupracrustal rocks (the combined Indian Creek and Pony–Middle Mountain Metamorphic Suites) that originated in a continental arc setting between 3.35 and 3.2 Ga with subsequent sedimentation and (2) mafic metavolcanic rocks with intercalated metasedimentary rocks (the Spuhler Peak Metamorphic Suite) from a suprasubduction zone ophiolite or backarc basin possibly of Proterozoic age. A poorly preserved metamorphic event at …
40Ar/ 39Ar Ages Of Metamorphic Rocks From The Tobacco Root Mountains Region, Montana, John B. Brady, Dana N. Kovaric, John T. Cheney, Lisa J. Jacob, J. Toby King
40Ar/ 39Ar Ages Of Metamorphic Rocks From The Tobacco Root Mountains Region, Montana, John B. Brady, Dana N. Kovaric, John T. Cheney, Lisa J. Jacob, J. Toby King
Geosciences: Faculty Publications
Measurements of 60 single-grain, UV laser microprobe 40Ar/39Ar total gas ages for hornblende from metamorphic rocks of the Tobacco Root Mountains in southwest Montana yield a mean age of 1.71 ± 0.02 Ga. Measurements of 40Ar/39Ar step-heating plateau ages of three bulk hornblende samples from the Tobacco Root Mountains metamorphic rocks average 1.70 ± 0.02 Ga. We believe that these and the K/Ar or 40Ar/39Ar ages reported by previous workers are cooling ages from a 1.78 to 1.72 Ga, upper-amphibolite to granulite facies, regional metamorphism (Big Sky orogeny) that affected the northwestern portion of the Wyoming province, including the Tobacco …
General Geology And Geochemistry Of Metamorphosed Proterozoic Mafic Dikes And Sills, Tobacco Root Mountains, Montana, John B. Brady, Heidi K. Mohlman, Caroline Harris, Sarah K. Carmichael, Lisa J. Jacob, Wilfredo R. Chaparro
General Geology And Geochemistry Of Metamorphosed Proterozoic Mafic Dikes And Sills, Tobacco Root Mountains, Montana, John B. Brady, Heidi K. Mohlman, Caroline Harris, Sarah K. Carmichael, Lisa J. Jacob, Wilfredo R. Chaparro
Geosciences: Faculty Publications
Just over two billion years ago, basaltic magma intruded rocks of the Pony– Middle Mountain Metamorphic Suite and the Indian Creek Metamorphic Suite that now crop out in the Tobacco Root Mountains of Montana near the northwestern margin of the Wyoming province. Numerous examples can be found of mafic dikes that crosscut layering and gneissic banding, demonstrating that the host rocks were metamorphosed to form the gneissic texture prior to intrusion of the dikes. Although many of the intrusions appear to be sills that followed compositional layering, close inspection reveals low-angle discordance in nearly every case, consistent with rotation of …