DETRITAL ZIRCON GEOCHRONOLOGY AND HISTORY OF DEFORMATION OF THE SPOKANE AREAS PRE-NEOGENE ISOLATED BUTTES

Isolated buttes composed of Cambrian to Mesoproterozoic sedimentary rocks of the Spokane, Washington area were previously characterized by hand sample description and stratigraphic correlations. This project uses new detrital zircon (DZ) U/Pb ages and regional detrital zircon data for defensible identification of the isolated buttes. The buttes are composed of material deposited before the separation of the Mawson continent from western Laurentia during the rifting of supercontinent Columbia, the formation and subsequent rifting of supercontinent Rodinia, to the opening of the Iapetus Ocean, preserving information about these major events in the DZ age populations. The initial lack of age data resulted in multiple maps with conflicting units and ages, cross sections that could only explore possible variations of the deformation in eastern Washington. New cross sections with DZ age determination allows for more defensible subsurface interpretations. Ten samples were analyzed by DZ U/Pb age determination resulting in three buttes containing DZ signatures comparable to Cambrian units from previous studies in northeast Washington, two were congruent to known Deer Trail Group samples, and five were closely matching to known Belt-Purcell Supergroup samples. DZ age populations in these 10 samples suggest new aspects to be added to the current model of the rifting of supercontinent Columbia. Later Cretaceous fold and thrust deformation and Eocene uplift is inspected via an updated cross-sectional model and provides insight into factors such as the Latah fault, the Priest River Core Complex, and location of the Jumpoff Joe fault. These age determinations provide useful information about many aspects of the understudied basement rock in the Spokane region.