New Techniques for Noble Gas Geochronometry and Thermochronometry

Citation

Cox, Stephen Ellis (2017) New Techniques for Noble Gas Geochronometry and Thermochronometry. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9V69GKV. https://resolver.caltech.edu/CaltechTHESIS:12212016-095346656

Abstract

Noble gases were among the first species measured by mass spectrometry and interrogated for geochemical information about the solid Earth. The analytical challenge of measuring them has driven technological development in the field, and new applications have in turn followed from new developments. In the first chapter, I present developments that bolster an existing technique, the (U–Th)/Ne system, by verifying the theoretical underpinnings of the method and by exploring its application in several minerals. In the second chapter, I show that the hematite (U–Th)/Ne system is a sound geochronometer for use in the upper crust and a potent thermochronometer for exploring mid-crustal processes. In the third chapter I show significant advances toward using a quadrupole ion trap as a noble gas mass spectrometer, including the first static vacuum measurements. This technique provides new opportunities for low abundance noble gas measurements through its ultra low dark noise time of flight measurement approach and its high resolution, high mass range scanning capabilities. The quadrupole ion trap can measure lower concentrations of rare species like ³He and ²¹Ne on Earth, allowing us to make more precise determinations of cosmogenic exposure ages, and it can measure species with much higher resolution than is currently possible on most spaceflight instruments, allowing us to perform measurements on planetary surfaces and in deep space that are currently reserved to terrestrial laboratories. Finally, in the fourth chapter I demonstrate that an old, largely abandoned technique, (U–Th)/He geochronometry, has useful applications now that we fully understand its limitations.

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