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Open-File Report 2006–1051

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Isotopic Ages of Rocks in the Northern Front Range, Colorado

By Anna B. Wilson and Bruce Bryant

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Map Sheet 1
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These maps, and the tables that accompany them, are a compilation of isotopic age determinations of rocks and minerals in four 1:100,000-scale quadrangles in the northern and central Front Range, Colorado. Phanerozoic (primarily Tertiary and Cretaceous) age data are shown on one map; Proterozoic data are on the other (sheet 1). A sample location map (sheet 2) is included for ease of matching specific localities and data in the tables to the maps. Several records in the tables were not included in the maps because either there were ambiguous dates or lack of location precluded accurate plotting.

To illustrate the geological setting for the samples, the plutonic rocks are shown on the maps. The boundaries of the plutons are from the Geologic Map of Colorado with a few modifications. For ease of reference, we labeled each of the larger (and some of the smaller) plutons with a generally accepted name from the literature. As a convenience in using the data, we have informally named some plutons based on geographic features on or near those plutons. Those names are shown in parentheses.

The maps show the type of age determination by symbol and age subdivisions by color. Seven different methods, each shown with a different symbol, were used to determine Phanerozoic ages:...>>MORE

Version 1.0

Posted March 2006

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