ABSTRACT

A high-energy, tightly focused laser beam can be used to "ablate" tiny areas on the surface of a solid, liberating submicroscopic fragments for analysis by plasma-source mass spectrometers to determine isotopic ratios and elemental compositions at trace levels. This micro-sampling technique produces geochronological and geochemical measurements at high spatial resolution with great efficiency. Recent advances in laser technology have led to the development of short-wavelength solid-state laser systems that significantly improve the accuracy, precision, and resolution of these measurements. In this project, a modern 193-nm laser-ablation system will be integrated into existing mass-spectrometry facilities at the University of Texas at Austin to bring this powerful technology to bear on a range of earth-science investigations.

Geochronological applications will center upon determining the ages of large numbers of individual grains of zircon trapped in sedimentary rocks from localities around the world. This will permit investigators to constrain the ages of sediment accumulation, the sources of the sediments, and the degree of correlation of potentially related sedimentary packages; these results in turn will permit testing of tectonic and sedimentological hypotheses for the rocks' origins. Similar applications to basement rocks will allow rapid screening of ages of lithospheric blocks and discrimination of isotopic reservoirs in ancient orogens.

Geochemical applications will focus on spatially resolved trace-element and isotopic measurements to address scientific questions as diverse as volatile recycling in the mantle, the dynamics of volcanic magma mixing and crystallization, rates of solid-state diffusion in geologic materials, and optimal sampling of cave deposits for paleoclimate studies.

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