Abstracts Category : Other

MODELING ATMOSPHERE-MOUNTAIN INTERACTIONS: IMPLICATIONS FOR STABLE ISOTOPE-BASED PALEOALTIMETRY

by Lauren B Wheeler

The measure of surface uplift can provide an important constraint on the behavior of continental lithosphere and the underlying upper mantle. Isotope-based paleoaltimetry aims to quantitatively estimate the magnitude and timing of surface uplift from records of the isotopic composition of precipitation in order to provide constraints on the tectonic processes driving mountain building. As the surface of a topographic barrier increases in height, along the windward side, -values of precipitation should get progressively more negative, and on the leeside, -values of precipitation should also get progressively more negative based on the presence and development of a topographically-induced rain shadow. If modern precipitation and the isotopic composition of that precipitation are indeed related to the elevation of the mountain range, a record of paleo--values should, in principle, contain a record of the paleoelevation. A deeper understanding of the processes that control the windward and leeside isotopic composition of precipitation will improve interpretations of isotope-based paleoaltimetry records and has the potential to improve the reliability of the technique for constraining the topographic and tectonic evolution of mountain ranges. In this study I focus on the underlying assumptions within isotope-based paleoaltimetry interpretations from windward and leeside studies, for both empirical and theoretical approaches. The research presented here focuses on: (1) the role of atmospheric flow deflection on leeside isotope-based paleoaltimetry records and the subsequent interpretations of those records in the southern Sierra Nevada and the Southern Alps (Chapter 2 and Chapter 4), (2) whether simple models of upslope flow are sufficient for understanding mountain-atmosphere interactions (Chapter 3), and (3) the limitations and opportunities provided by theoretical approaches based on Rayleigh distillation (Chapter 3). Through the comparison of leeside isotope-based paleoaltimetry in the southern Sierra Nevada and the Southern Alps, I conclude that leeside isotope-based paleoaltimetry is best applied in relatively low-lying mountain ranges with simple uplift histories, and where atmospheric flow patterns are primarily two-dimensional (Chapter 2 and Chapter 4). From simulations of windward lapse rates for orographically enhanced precipitation, I find that lapse rates generally steepen with increasing elevation and lapse rates from Rayleigh distillation models are almost always steeper than the simulated lapse rates due to the high precipitation efficiency (Chapter 3). The difference in lapse rates between Rayleigh distillation models and the simulations of orographic precipitation suggests that Rayleigh distillation models may be best used for determining the minimum elevation of a mountain range and the maximum amount of uplift. Advisors/Committee Members: Joseph Galewsky, Brandon Schmandt, Lindsay Lowe Worthington, John Wakabayshi.