THE TOPOGRAPHIC EVOLUTION OF THE CENOZOIC NORTH AMERICAN PLATEAU AND CORDILLERA RECORDED IN COUPLED BASIN-DETACHMENT SYSTEMS

High-elevation orogenic plateaus and mountain ranges exert a strong control on global climate and precipitation patterns and respond to tectonic processes in the lithosphere and upper mantle. Reconstructing the history of surface elevation thus provides a critical link among erosive, climatic, and tectonic processes. Here we present stable isotope data of lacustrine, fluvial and pedogenic environments as well as core complex-bounding detachment faults that record the Cenozoic isotopic fingerprint of the evolving landscape of the North American Cordillera. Oxygen, hydrogen, carbon, and ⁸⁷Sr/⁸⁶Sr isotope data indicate that between ca. 42 and 39 Ma dramatic changes in topography, atmospheric circulation patterns, and mid- to upper crustal deformation and magmatism characterized the central North American Cordillera (NV/UT/ID). High resolution-dated (⁴⁰Ar/³⁹Ar) sedimentary sequences in the Elko basin (NV) show large negative oxygen isotope shifts in lake water composition that occur contemporaneously with changes in depositional environment and indicate a high elevation landscape undergoing drainage reorganization and development of topography. These rapid events at around 40-39 Ma are contemporaneous with development of extensional detachments in upper-/middle crust that occurred in the presence of low-dD meteoric water (Raft River core complex, UT) as well as vigorous silicic magmatism. The temporal and spatial patterns of areas of extensional (mid-)crustal flow, crustal melting, and landscape reorganization and surface uplift strongly suggest a mantle driving force. Whether lithospheric delamination, change in subduction angle, or mass removal by crustal flow, at ca. 40 Ma the topographic structure of the western United States had reached a critical threshold condition that led to large-scale reorganization of drainage patterns and topography.