New 40Ar/39Ar ages of intrusive rocks from the Henry and La Sal Mountains, Utah (MP 92-2)

MP 922
In stock
General Geology
$5.50
$5.50

By: S. T. Nelson, M. T. Heizler, and J. P. Davidson

Previously published Eocene and late-Oligocene K-Ar ages of intrusive rocks of the Henry and La Sal Mountains are bimodal whereas sphene and zircon fission-track ages are exclusively late Oligocene. The apparent discordance between ages from the two techniques makes it difficult to understand the igneous activity in terms of regional geologic and tectono-magmatic events. Results of new 40Ar/39Ar analyses reported here indicate that intrusive activity spanned several million years during late Oligocene time and forms a time, as well as a spatial, link between magmatism in the San Juan and Reno-Marysvale volcanic fields to the east and west respectively. Eocene K-Ar ages are shown to be the result of two discrete effects. First, excess argon is manifested in some samples by a trapped component of argon with a 40Ar/39Ar ratio that exceeds the atmospheric value. We interpret other apparent Eocene K-Ar ages to result from heterogeneous excess argon, or inherited argon residing in incompletely outgassed hornblende xenocrysts in the rock.

Other Information:
Published: 1992
Pages: 24 p.
Location: Garfield County, Grand County, and San Juan County
Media Type: Paper Publication

The cookie settings on this website are set to 'allow all cookies' to give you the very best experience. Please click Accept Cookies to continue to use the site.
لقد تم اشتراكك بنجاح! | You have successfully subscribed!