Constraints on Miocene Uplift of the Central Cascade Range, Oregon

University Of South Carolina At Columbia, Columbia SC

Investigators

Abstract

ABSTRACT 9909568 Kohn Topographic uplift of mountain ranges and plateaus is intimately related to lithospheric density changes caused by various tectonic processes. In the Cascade Ranges of Oregon existing interpretations of topographic history since the Miocene are in conflict, with one concluding that uplift was progressive between 20 Ma until Late Miocene and the other concluding that uplift did not start until the Late Miocene. The corresponding tectonic inferences are that subduction-related density changes, acting over tens of millions of years was the responsible process or that a short-term forcing factor such as detachment faulting was the cause, respectively. This project will test these hypotheses by using an oxygen isotopic proxy for elevation - isotopic ratio variation associated with mountain rain shadow effect as recorded in mammalian herbivores. The intended data should be able to differentiate between the strong differences in model predictions of the competing hypotheses. Results will be important to the tectonic history of the Cascades and the methodology will likely be applicable elsewhere.