Abstract
The Challis-Kamloops arc or belt is a sprawling Eocene igneous province in the northern U.S. and Canadian Cordillera, consisting of a margin-parallel belt in British Columbia and Washington and a west-east belt running from Oregon and Idaho to South Dakota. The Challis magmatic province in Idaho is a key component of the Challis-Kamloops belt, occurring at the intersection between the two geographic trends, and it consists of a volcanic field, a belt of epizonal plutons, and dike swarms. This paper provides a review of the Challis magmatic province, focusing particularly on its geochronology and geochemistry and presenting a large geochemical database including many lesser-known data sources such as theses and state and federal government reports. We also present new geochronological and geochemical data for previously unrecognized alkali basalts west of the main portion of the province. After summarizing data and ideas about the Challis, we present contrasting tectonic models for its formation along with testable predictions to guide future research.