GEOCHEMISTRY OF UPPER PROTEROZOIC RIFT-RELATED VOLCANICS, NORTHERN UTAH AND SOUTHEASTERN IDAHO

Mafic volcanic rocks associated with Upper Proterozoic diamictites are widespread in western North America. A continental rift setting has been proposed for their origin. Trace-element and REE geochemistry for these volcanic rocks from N Utah and SE Idaho is reported. The analysed samples are high-Ti within-plate basalts, and they vary from transitional tholeiitic-alkaline in the S to alkaline in the N. The geochemistry, together with the geological setting of the volcanic rocks, indicates a rift setting, but the timing of the rifting and its relationship to final continental separation are still unsettled. -L.C.H.