Collaborative Research: Uplift of the Washington Cascades and Climatic Evolution of Eastern Washington

University Of Washington, Seattle WA

Investigators

Abstract

Montgomery Reiners 0087413 0087318 The Washington Cascades cast one of the largest climatic rain shadows in North America, with mean annual precipitation in some areas on the west side higher than 4 m/yr, and on the east side lower than 0.15 m/yr. We are studying the temporal relationships between mountain-building and climate in this regional setting by using a combined approach of low-temperature apatite (U-Th)/He thermochronometry in the Cascades crystalline rocks themselves, and stable isotope variations in authigenic minerals in clays and carbonates in paleosols of different ages on the dry, east side of the range. In addition, through combined GIS and He dating work, we are examining the relationship between creation of Cascades topographic relief and Pleistocene-to-recent glaciation in the range, and evaluating the role of relatively recent erosional forces on orogenic exhumation. Our preliminary work indicates that He ages record much younger ages than other radiometric systems in the Cascades, suggesting a relatively recent (late Miocene at the earliest) period of exhumation, which is consistent with paleontological evidence from eastern Washington for the lack of a severe climate contrast until this time.