PETROLOGICAL APPLICATIONS OF THE RAMAN MICROPROBE (RMP): EXAMPLES OF THE CHARACTERIZATION OF MICRON-SIZED MINERALS IN ECLOGITES.

Eclogites are high-pressure metamorphic rocks essentially composed of clinopyroxene and garnet without primary plagioclase. Like other metamorphic rocks, they may have experienced more than one period of recrystallization, and hence they often contain reaction products in the form of oriented or non-oriented intergrowths (symplectites, kelyphites) of two or more minerals of which one or more may be a microphase (1 - 50 mu m wide). Accurate characterization of such microphases is necessary for a proper interpretation of the mineral reactions concerned and for geothermobarometric estimations of the geological history of the rocks. The Raman microprobe (RMP) can provide spectra from microphases below the surface and, when compared with a series of standard spectra from larger known minerals, one can characterize the structure and perhaps the chemistry of such microphases. By identifying crystals difficult or impossible to identify by other means, RMP offers a valuable tool for petrology. Some examples of cases histories and work in progress on diverse eclogites of geodynamical importance are discussed.