Rubidium-strontium dating of the trondhjemite of Rio Brazos, New Mexico and of the Kroenke Granodiorite, Colorado

Journal of Research of the U.S. Geological Survey
By: , and 

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Abstract

The quartz-eye trondhjemite and associated hornblendite near Rio Brazos, Brazos Peak quadrangle, New Mexico, and the Kroenke Granodiorite of the Mount Harvard quadrangle and Sawatch Range, Colo., lie on an approximate 1,700-m.y. Rb-Sr isochron. Their initial         8 7Sr/ 8 6Sr ratio is about 0.7026. Six samples of the trondhjemite of Rio Brazos contain 8-43 ppm Rb and 57-194 ppm Sr, and six of the Kroenke intrusive, 53-99 ppm Rb and 314-595 ppm Sr. The Rio Brazos intrusive contains more SiO2 but less Al2O3 and K2O than does the Kroenke intrusive. The hornblendite contains much MgO and CaO but is low in alkalies; two samples show 2.5-3.2 ppm Rb and 288-431 ppm Sr. These rocks are of the same general age as the much more abundant, typically calc-alkaline Boulder Creek Granodiorite and associated intrusives of Colorado and northern New Mexico.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Rubidium-strontium dating of the trondhjemite of Rio Brazos, New Mexico and of the Kroenke Granodiorite, Colorado
Series title Journal of Research of the U.S. Geological Survey
Volume 2
Issue 6
Year Published 1974
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Description 5 p.
First page 705
Last page 709
Country United States
State New Mexico, Colorado
Other Geospatial Rio Brazos, Mount Harvard
Online Only (Y/N) N
Additional Online Files (Y/N) N
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