 | Du Bray E.A., Petrology of the Crazy Mountains dike swarm and geochronology of associated sills, south-central Montana / Du Bray E.A., Harlan S., Wilson A.B. - Washington: U.S. Geological Survey, 2005. - iii, 21 p. - (U.S. Geological survey. Professional paper; 1715). - ISBN 1-411-306-58-9
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Abstract ........................................................ 1
Introduction .................................................... 1
Acknowledgments ................................................. 5
Geology ......................................................... 5
Analytical Methods .............................................. 5
Petrography ..................................................... 8
Geochronology .................................................. 11
Whole-Rock Chemistry ........................................... 15
Major-Oxide Data ............................................... 15
Trace-Element Data ............................................. 17
Discussion ..................................................... 17
Conclusions .................................................... 19
References Cited ............................................... 19
Figures
1. Maps showing regional geologic setting for the Crazy
Mountains dike swarm ......................................... 2
2. Generalized geologic map of the Big Timber stock ............. 4
3. Total alkali-silica variation diagram showing compositions
of samples from the Crazy Mountains dike swarm ............... 9
4. Graphs showing 40Ar/39Ar age spectra for hornblende and
biotite separates from alkaline intrusive rocks in the
Crazy Mountains ............................................. 12
5. Variation diagrams showing abundances of major oxides
and zirconium in samples from the Crazy Mountains dike
swarm ....................................................... 16
6. Trace-element tectonic setting-discrimination variation
diagram for samples from the Crazy Mountains dike swarm ..... 17
7. Ternary AFM diagram showing compositions of samples
from the Crazy Mountains dike swarm ......................... 18
8. Ternary variation diagram showing the relative
proportions of Rb, K, and Sr in samples from the Crazy
Mountains dike swarm ........................................ 18
Tables
1. Composition of selected samples of the Crazy Mountains
dike swarm ................................................... 6
2. Data for 40Ar/39Ar step heating of samples of alkaline
sills in the Crazy Mountains ................................ 13
3. Summary of isotopic dating results for alkaline sills
in the northern Crazy Mountains ............................. 15
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