Application of scanning X-ray analytical microscope to the petrographic characterization of a ductile shear zone: an alternative method to image microstructures

A ductile shear zone within a metasomatic biotite band in the Ryoke granite , Teshima, SW Japan, has been studied using the scanning X-ray analytical m icroscope (SXAM). This enabled the quantitative distributions of major elem ents, such as Si, K, Fe, Al and Ca, to be determined within the shear zone. These element maps were processed to transform them into images showing th e distribution of minerals such as quartz, biotite, plagioclase and K-felds par, which form the major minerals within the biotite band and the granite protolith. Mineral profiles based on these mineral maps compared with the s imple shear strain profile reveal that the shear zone is most intense where quartz and biotite have been substituted for the primary mineral assemblag e of the granite protolith, suggesting that the stresses imposed on the gra nite caused the shear strain to localize along the biotite band to produce the observed shear zone. It appears that the rheological behavior changed a round 50-60% of quartz modal composition. (C) 1999 Elsevier Science B.V. Al l rights reserved.