Geology and Environmental Change Science Center

Isotopic ages for Proterozoic rocks in the Estes Park and Denver West quadrangles

geologic map of Denver West and Estes Park

Proterozoic Intrusive Rocks
(pale green shows extent of Proterozoic metamorphic rocks)

a pinkish box represents the Pikes Peak Granite on the map Yp--Pikes Peak Granite (approx. 1080 Ma)
a brown box represents the Middle Proterozoic granitic rocks on the map Yg--Middle Proterozoic granitic rocks (approx. 1400 Ma)
a green box represents the Early Proterozoic granitic rocks on the map Xg--Early Proterozoic granitic rocks (approx. 1700 Ma)

Proterozoic dikes

green lines represent dikes on the map Yam--Middle Proterozoic dikes (approx. 1400 and 1300 Ma)

Ages in Millions of years
(open symbols indicate vague or inexact locations)

40Ar/39Ar ages
dot indicating 40Ar/39Ar ages 540 to 1500 million years ago 540 to 1,500 (15)
dot indicating 40Ar/39Ar ages 1500 to 1900 million years ago 1,500 to 1,900 (4)
Rb/Sr ages
polygon indicating Rb/Sr ages 540 to 1500 million years ago 540 to 1,500 (12)
polygon indicating Rb/Sr ages 1500 to 1900 million years ago 1,500 to 1,900 (0)
K-Ar ages
star indicating K-Ar ages 540 to 1500 million years ago 540 to 1,500 (5)
star indicating K-Ar ages 1500 to 1900 million years ago 1,500 to 1,900 (0)
U/Pb ages
square indicating U/Pb ages 540 to 1500 million years ago 540 to 1,500 (4)
square indicating U/Pb ages 1500 to 1900 million years ago 1,500 to 1,900 (4)

gray lines represent 7 and one-half minute quad map boundary 7 1/2' quadrangle boundary
heavy black lines represent 30 by 60 minute quad map boundary 30' x 60' quadrangle boundary

A map has also been compiled for all Phanerozoic rocks, which include mostly Late Cretaceous and Tertiary intrusives. Similar maps have been created for the Bailey and Fort Collins quadrangles. All data, including references, given dates and uncertainties, and locations, are on a spreadsheet and will soon be available as a USGS publication.


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