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

人们越来越认识到，许多地质过程是以脉冲形式发生的，或者太短，不能被长寿命的放射性同位素捕获。此外，地球上许多高温环境(如变质、深成和火山系统)以及小行星母体或月球或火星内部等行星系统的热史往往遵循非线性路径。这些需要能够在一系列不同的时间范围内连续监控流程的工具。扩散比色法就是这样一种工具，正越来越多地被用于解决这些问题。尽管发展迅速，但在上述所有环境中，仍有确定时间尺度所需的关键实验参数，由于实验限制，迄今无法收集到这些参数。现在，新的实验发展使确定这些关键参数成为可能。在这个项目中，我们希望利用这些新的实验进展来确定石榴石-斜方辉石-单斜辉石体系中的扩散系数和分配系数(作为扩散模型中用作边界条件的地温计所需)，该系统可以在上述所有环境中广泛使用。因此，本研究的结果将极大地扩展扩散比色法的研究范围。研究这一体系的另一个好处是，这些相的组成被用来确定压力、温度和流体活动。因此，用这些矿物进行扩散计时获得的时间尺度可以直接与岩石在演化过程中经历的特定过程和条件有关。

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.