40Ar/39Ar Age Determinations for the Carrizo Mountains Laccolith, Navajo Nation, Arizona
Steve C. Semken, William C. McIntosh 1997 New Mexico Geological Society v48 p75-80

This article from the New Mexico Geological Society Guidebook contains information about Late Cretaceous (73.8-70.65 Ma) ages for hornblende separates from the Carrizo Mountains laccolith. Three specimens of diorite porphyry were examined using the 40Ar/39Ar step-heating method and no evidence of excess 40Ar or contamination by older xenocrysts was found. This has called into question some previously published K-Ar ages from the Four Corners area. This article thus confirms that the Carrizo Mountains intrusive center is an Arizona extension of the Laramide-age Colorado mineral belt.

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Subject: Geoscience:Geology:Igneous and Metamorphic Petrology:Igneous Associations and Tectonic Settings, Geoscience:Geology:Tectonics, Structural Geology:Regional Structural/Tectonic Activity
Resource Type: Scientific Resources:Research Results, Journal Article
Topics: Solid Earth:Structural Geology:Regional Structural/Tectonic Activity, Solid Earth:Petrology:Igneous Associations and Tectonic Settings, Solid Earth