Experimental calibration of garnet- and pyroxene-diffusion-chronometry and -thermometry for applications to terrestrial and planetary samples

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There is an increasing recognition that many geological processes occur in pulses, or are too short to be captured by long-lived radiogenic isotopes. Moreover, thermal histories in many high temperature settings in the Earth (e.g. metamorphic, plutonic and volcanic systems) as well as in planetary systems such as asteroid parent bodies or the lunar or Martian interior often follow non-linear paths. These require tools that can monitor processes continuously and over a range of different timescales. Diffusion chronometry is one such tool that is being increasingly used to address these issues. In spite of the rapid developments, there remain critical experimental parameters that are needed for the determination of timescales in all of the above settings that could not be collected so far because of experimental limitations. New experimental developments now make it possible to determine these critical parameters. In this project we wish to use these novel experimental advances to determine diffusion coefficients and partition coefficients (required as geothermometers for use as boundary conditions in diffusion models) in the garnet- orthopyroxene-clinopyroxene system, which can be widely used in all of the above settings. Therefore, results from this study would considerably expand the scope of diffusion chronometry. An added advantage of studying this system is that compositions of these phases are used to determine pressures, temperatures and fluid activities. Thus, timescales obtained from diffusion chronometry with these minerals can be directly related to specific processes and conditions that a rock experienced during its evolution.