This research project has utilized the new scanning electron microscope (SEM) in the Dept. of Geosciences to conduct chemical and crystallography analysis of polymorphs- minerals that have the same chemical formula, but different crystal structure. Specifically, this study explores phase transitions in the Al2SiO5 minerals- kyanite, sillimanite, and andalusite. Aluminous schists in the Goat Mountain area of the Clearwater metamorphic core complex in northern Idaho contain all three of these minerals. Electron backscatter diffraction (EBSD) and energy-dispersive X-Ray spectroscopy (EDS) were the primary techniques that were applied. This report addresses the chemistry and microstructure of these rocks through an integrated mineral chemistry (EDS) and crystallographic (EBSD) study. The primary goal is to gain a better understanding of the tectonic history of the Clearwater area with respect to deformation of these rocks. In preparation for analysis, thin sections were polished using the Buehler VibroMet 2 Vibratory Polisher and carbon coated with the Denton Vacuum Desk V. Sample preparation is extremely critical to get clear results. EDS provides the chemical evaluation of the thin section and element maps were produced. EBSD generates crystal orientation maps and patterns needed to interpret the microstructure. The Clearwater metamorphic core complex consists of mid crust that is exhumed during crustal extension. Based on lithological differences, the complex is categorized into two distinct zones: the internal zone-basement amphibolite, anorthosite, and schist; and the external zone- metamorphosed Middle Proterozoic Belt Supergroup sediments and pre-Belt schist and gneiss. The area of focus was on the unique schists near Goat Mountain and the bounding Jug Rock shear zone to the east. The results will allow us to interpret the processes of the earth with a better understanding and will benefit future research.

Study of the morphology and mineralogy of Mars reveals features that seem to indicate presence of significant liquid water on the surface in the past, including putative dry lakes, valleys, channels, deltas and alluvial fans [1]. This has resulted in theories of a period of global Martian climate change between 3.7 and 3.2 billion years ago, from a wetter, and possibly warmer, environment to the arid one seen today. However, isotope studies and modeling have failed to provide definitive constraints on the early climate of Mars [2]. The study of analog sites on Earth may provide a different avenue to understanding possible changes on Mars during this period. Previous work on this project has sought to link four sites in the Andes of South America to stages of the proposed climate change through comparison of satellite images to features found on Mars. The northern sites on the Chilean and Bolivian Altiplano, with their drying lakes and alluvial fans, resemble a Mars towards the close of the theorized climate change. On the other hand, the southern sites in the High Andes more closely represent the hypothesized early Martian climate, with active deltas and glaciers. Remote sensing climate data from NASA’s Giovanni databases can now be used to study how large a change in atmospheric pressure, temperature, humidity and precipitation might have occurred between the stages of climate change represented by these sites. For example, while there is no significant change in temperature between the northern and the southern sites, the southern sites receive more than 50% more precipitation. Additionally, we can study how quickly these variables are currently changing to place a rate of change on each of the stages.

[1] Kleinhans M. (2010) Earth Surf. Process. Landforms, 35, 102–117.

[2] Cassata W. S. et al. (2001) Icarus, 221, 461.