A HISTORY OF STABILIZATION AND MODIFICATION OF CRATONIC NORTH AMERICAN CRUST IN SOUTHERN IDAHO USING THERMOCHRONOLOGY OF DEEP CRUSTAL XENOLITHS AND BASEMENT EXPOSURES ALONG THE NORTHERN MARGIN OF THE SNAKE RIVER PLAIN

Granulite xenoliths erupted in Neogene basalts of the Eastern Snake River Plain (ESRP) can be used as windows into the origin and thermal evolution of the lower crust of southern Idaho. Using a combination of LA-ICPMS and ID-TIMS methods, U-bearing accessory minerals in xenoliths from Square Mountain (Fairfield, Idaho) are analyzed to interpret a regional thermochronologic history from the Precambrian through the Tertiary. Overgrowth domains of zircons in the xenoliths are interpreted to identify and date distinct thermal events that affected the lower crust, while intermediate to low closure temperature accessory minerals such as apatite and rutile are analyzed as thermochronometers. These crystallization and cooling ages are compared to similar data derived from Precambrian orthogneisses exposed in the nearby South Fork Boise River drainage (House Mountain). These results will be used as part of a larger study to interpret the thermochonologic history of the crust beneath southern Idaho.