HR: 0830h
AN: ED41C-1185    [PDF]
TI: Employing Fluid Inclusions as an Application of Phase Diagrams and an Introduction to Geothermobarometry
AU: * Farver, J R
EM: jfarver@bgnet.bgsu.edu
AF: Bowling Green State University, Department of Geology, Bowling Green, OH 43403-0218 United States
AU: Onasch, C M
AF: Bowling Green State University, Department of Geology, Bowling Green, OH 43403-0218 United States
AB: One of the ongoing challenges in petrology course development is designing meaningful student learning activities that promote understanding of phase diagrams and their application to relevant geologic processes. In addition, an important component of a modern petrology course is to provide a foundation in the methods employed to establish temperature and pressure conditions during geologic events. We have developed a laboratory exercise wherein students analyze fluid inclusions (water + NaCl) in natural samples of quartz or fluorite. Using a USGS-type fluid inclusion stage, the students observe the heating and cooling behavior of the fluid inclusions and measure the temperatures of homogenization, last ice melting, and the eutectic. In this fashion, students can attach a physical meaning to the phase diagram of water + NaCl that they determined in a previous laboratory exercise (after Brady, 1992, JGE, v.40, p.116-118). Each student collects a set of data that they then combine with the data of their colleagues to produce histograms that they must interpret. The second component of the exercise is to fix the trapping temperature and pressure of the fluid inclusions. Using the data they collect, students calculate the isochore and plot it on a P-T diagram. They also plot the lithostatic and hydrostatic pressure gradients for a given geothermal gradient on the P-T diagram. At this point, additional information on the geologic/tectonic setting of the sample can be provided so that students can consider the overall P-T history of the sample/region. We typically use samples containing both primary and secondary inclusions to illustrate the utility of fluid inclusions to fix P-T conditions during mineral growth as well as later tectonic events. This leads to a general discussion of geothermometric/barometric systems and the requisite assumptions and limitations of the different techniques currently employed. In addition to providing students with a hands-on opportunity to develop a more meaningful understanding of phase diagrams and their application to geologic processes, this exercise provides numerous potential extension activities. In particular, discussions of the important role of fluids in the crust and applications of the phase diagram to economic vein deposits have proved very rewarding.
DE: 6605 Education
SC: Education and Human Resources [ED]
MN: 2003 Fall Meeting