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Figure 7. Equal-area projection (lower hemisphere) of structures in southern part of Flattop Butte terrane (fig. 4). Measurements are on metasedimentary rocks.

Figure 7 Equal-area projection (lower hemisphere) of structures in southern part of Flattop Butte terrane (fig. 4). Measurements are on metasedimentary rocks.

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Figure 1. Index map of Hartville Uplift showing out- line of Rawhide Buttes West and Rawhide Buttes East quadrangles. Outline of published map I-2567 (Sims and others, 1997) also shown. Detailed geologic mapping (scale 1:24,000) of Precam- brian rocks in the Hartville Uplift, southeastern Wyoming (Day and others, 1994; fig. 1) following earlier regional geologic mapping (scale 1:48,000) by Snyder (1980) has shown that the Late Archean granite and supracrustal rocks (Whalen Group) of the Wyoming province (fig. 2) were deformed during three convergent (tectonic) events in the Early Proterozoic, extending from between ~2.1 Ga to pre-1.7 Ga (table 1). These events are recorded in the Guernsey quadrangle (Sims and others, 1997) (fig. 1) and are expressed in part in this map area. From oldest to brian rocks in the Hartville Uplift, southeastern Wyoming Detailed geologic mapping (scale 1:24,000) of Precam-
Figure 1. Index map of Hartville Uplift showing out- line of Rawhide Buttes West and Rawhide Buttes East quadrangles. Outline of published map I-2567 (Sims and others, 1997) also shown. Detailed geologic mapping (scale 1:24,000) of Precam- brian rocks in the Hartville Uplift, southeastern Wyoming (Day and others, 1994; fig. 1) following earlier regional geologic mapping (scale 1:48,000) by Snyder (1980) has shown that the Late Archean granite and supracrustal rocks (Whalen Group) of the Wyoming province (fig. 2) were deformed during three convergent (tectonic) events in the Early Proterozoic, extending from between ~2.1 Ga to pre-1.7 Ga (table 1). These events are recorded in the Guernsey quadrangle (Sims and others, 1997) (fig. 1) and are expressed in part in this map area. From oldest to brian rocks in the Hartville Uplift, southeastern Wyoming Detailed geologic mapping (scale 1:24,000) of Precam-
figure 2. Precambrian basement map of north-central United States and adjacent Canada. The Hartville Uplift (HU) is at the intersection of the Trans-Hudson and Central Plains orogens, and rocks in the uplift were deformed by both Early Proterozoic orogenies, as well as by an earlier unnamed deformation (D>).
figure 2. Precambrian basement map of north-central United States and adjacent Canada. The Hartville Uplift (HU) is at the intersection of the Trans-Hudson and Central Plains orogens, and rocks in the uplift were deformed by both Early Proterozoic orogenies, as well as by an earlier unnamed deformation (D>).
The map area composes a part of the southeastern mar- gin of the Wyoming Archean craton. An early nappe-forming Figure 3. K-Q-P diagram showing compositions (volume percent) of 2.65-Ga Flattop Butte Granite and 2.66-Ga Rawhide Buttes Granite. These granitic units have comparable compositions.
The map area composes a part of the southeastern mar- gin of the Wyoming Archean craton. An early nappe-forming Figure 3. K-Q-P diagram showing compositions (volume percent) of 2.65-Ga Flattop Butte Granite and 2.66-Ga Rawhide Buttes Granite. These granitic units have comparable compositions.
[able 2. Approximate modes of Rawhide Buttes Granite (percent by volume) ‘fable 3. Approximate modes of Flattop Butte Gran (percent by volume). (Tr. trace amounts present] Deformation Dy has been dated by the Rb-Sr whole- rock method on the Flattop Butte Granite at 1.98 Ga (see section by Peterman and others below). The deformation of the granite was pervasive and strong, and it yielded a tightly controlled Rb-Sr isochron.
[able 2. Approximate modes of Rawhide Buttes Granite (percent by volume) ‘fable 3. Approximate modes of Flattop Butte Gran (percent by volume). (Tr. trace amounts present] Deformation Dy has been dated by the Rb-Sr whole- rock method on the Flattop Butte Granite at 1.98 Ga (see section by Peterman and others below). The deformation of the granite was pervasive and strong, and it yielded a tightly controlled Rb-Sr isochron.
[Tr, trace amounts present] episode of deformation (Dj) affected rocks in the southern part of the Hartville Uplift. Manifestation of D, in the north- ern part of the uplift is difficult to document. However, the entire uplift, at least on the western side, was deformed by an older, unnamed Proterozoic orogeny (D>).
[Tr, trace amounts present] episode of deformation (Dj) affected rocks in the southern part of the Hartville Uplift. Manifestation of D, in the north- ern part of the uplift is difficult to document. However, the entire uplift, at least on the western side, was deformed by an older, unnamed Proterozoic orogeny (D>).
Figure 4. Index to tectonostratigraphic terranes in Rawhide Buttes West and Rawhide Buttes East quadrangles.
Figure 4. Index to tectonostratigraphic terranes in Rawhide Buttes West and Rawhide Buttes East quadrangles.
‘igure 5. Equal-area projections (lower hemisphere) of structures in Rawhide Buttes Granite in Rawhide Buttes terrane (fig. 4). A, poles to S, foliation. B, orientation of L; lineations in the Rawhide Buttes Granite.
‘igure 5. Equal-area projections (lower hemisphere) of structures in Rawhide Buttes Granite in Rawhide Buttes terrane (fig. 4). A, poles to S, foliation. B, orientation of L; lineations in the Rawhide Buttes Granite.
‘igure 6. Equal-area projections (lower hemisphere) of structures in Bald Butte domain of Rawhide Buttes ter- rane (fig. 3). A, poles to foliation; foliations have been largely reoriented by D; doming. B, orientation of linea- tions.
‘igure 6. Equal-area projections (lower hemisphere) of structures in Bald Butte domain of Rawhide Buttes ter- rane (fig. 3). A, poles to foliation; foliations have been largely reoriented by D; doming. B, orientation of linea- tions.
igure 8. Equal-area projections (lower hemisphere) of D, structures in Flattop Butte Granite. A, individual plots of poles to S, schistosity. B, orientation of L2 lineation, contoured; rare folds are oriented similarly to lineations.
igure 8. Equal-area projections (lower hemisphere) of D, structures in Flattop Butte Granite. A, individual plots of poles to S, schistosity. B, orientation of L2 lineation, contoured; rare folds are oriented similarly to lineations.
re 9. Map showing localities of geochronology samples.
re 9. Map showing localities of geochronology samples.
[Suffix letters refer to type of sample: WR, whole rock; Mi, microcline; and Bi, biotite. Analytical uncertainties based on replicate analyses of Precambrian granitic rocks: + 1.75 percent for 87Rb/*Sr and + 0.025 percent for 8751/§6Sr at the 95 confidence level. do, ditto]
[Suffix letters refer to type of sample: WR, whole rock; Mi, microcline; and Bi, biotite. Analytical uncertainties based on replicate analyses of Precambrian granitic rocks: + 1.75 percent for 87Rb/*Sr and + 0.025 percent for 8751/§6Sr at the 95 confidence level. do, ditto]
Instrumental neutron activation analyses for Sm and Nd. All others are by isotope dilution. [Sm and Nd concentrations are precise to + 1.5 percent (2 sigma). Uncertainties for '3Na/!4Nd are given as plus and minus values of the last one or two fig ures of the ratio. go is [(!3Nd/!44Nd-0.512636)/0.512636]x10*. T,, (model age in 10° yrs) is (1/6.54x10~!7)[14+!8Na/!4Nd-0.512636)/(!47Sm/!44Nd) where 6.54x107!? is the decay constant for '47Sm in yr, --, not determined]
Instrumental neutron activation analyses for Sm and Nd. All others are by isotope dilution. [Sm and Nd concentrations are precise to + 1.5 percent (2 sigma). Uncertainties for '3Na/!4Nd are given as plus and minus values of the last one or two fig ures of the ratio. go is [(!3Nd/!44Nd-0.512636)/0.512636]x10*. T,, (model age in 10° yrs) is (1/6.54x10~!7)[14+!8Na/!4Nd-0.512636)/(!47Sm/!44Nd) where 6.54x107!? is the decay constant for '47Sm in yr, --, not determined]
igure 10. Rubidium-strontium isochron diagram for whole-rock samples of the Flattop Butte Granite. Isochron: 1.98+0.10 Ga and IR=0.767+0.016. Interpreted as age of metamorphism (D, deformation). Analytical data given in table 4.
igure 10. Rubidium-strontium isochron diagram for whole-rock samples of the Flattop Butte Granite. Isochron: 1.98+0.10 Ga and IR=0.767+0.016. Interpreted as age of metamorphism (D, deformation). Analytical data given in table 4.
Table 6. Uranium, thorium, and lead data for zircons from the Flattop Butte Granite and gneiss at Cassa anticline. {Numbers in parentheses below atom ratios, ages in millions of years. Numbers in parentheses after sample numbers are screen sizes of the zircons] igure 11. Uranium-lead concordia diagram for the zircons from the gneiss at Cassa anticline (HU—16, open symbols) and the Flattop Butte Granite (HU-27A, filled symbols). Numbers in parentheses are mesh size of zircon fractions. Suffix R identifies leached zircon; suffix L is leachate. The chord through the two points for HU-—27A intersects concordia at 0.37+0.47 Ga and 2.80+0.17 Ga. The chord through the three points for HU-16 intersects concordia at 0.06+0.13 Ga and 2.36+0.17 Ga. igure 12. Rubidium-strontium isochron diagram for Rawhide Buttes Granite. Nine whole-rock sample data points were used in the regression: T=2.66+0.12 Ga and TR=0.696+0.009. Suffix letter abbreviations are the same as in table 4. The data point for HU-1 Bi is off scale, having coordinates at 516.4 and 10.566. The dot-dashed line is an isochron through HU-—1 Bi, HU-1 Mi, HU-1 Wk; T=1.32 Ga, IR=0.820. Analytical data given in table 4.
Table 6. Uranium, thorium, and lead data for zircons from the Flattop Butte Granite and gneiss at Cassa anticline. {Numbers in parentheses below atom ratios, ages in millions of years. Numbers in parentheses after sample numbers are screen sizes of the zircons] igure 11. Uranium-lead concordia diagram for the zircons from the gneiss at Cassa anticline (HU—16, open symbols) and the Flattop Butte Granite (HU-27A, filled symbols). Numbers in parentheses are mesh size of zircon fractions. Suffix R identifies leached zircon; suffix L is leachate. The chord through the two points for HU-—27A intersects concordia at 0.37+0.47 Ga and 2.80+0.17 Ga. The chord through the three points for HU-16 intersects concordia at 0.06+0.13 Ga and 2.36+0.17 Ga. igure 12. Rubidium-strontium isochron diagram for Rawhide Buttes Granite. Nine whole-rock sample data points were used in the regression: T=2.66+0.12 Ga and TR=0.696+0.009. Suffix letter abbreviations are the same as in table 4. The data point for HU-1 Bi is off scale, having coordinates at 516.4 and 10.566. The dot-dashed line is an isochron through HU-—1 Bi, HU-1 Mi, HU-1 Wk; T=1.32 Ga, IR=0.820. Analytical data given in table 4.
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