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.