High-resolution X-ray texture goniometry

Abstract

High-resolution X-ray texture goniometry (HRXTG) significantly improves peak/background ratios and allows for the determination of crystallographic preferred fabrics of small regions (2) in heterogeneously deformed rocks. The basic instrument is a commercially available automated single-crystal X-ray diffractometer equipped with a Mo source. A stage for transmission mode was constructed that is driven by the original motors, so the unit is fully computer controlled. Absorption corrections are calculated, which removes the need for generally difficult to obtain empirical corrections. This, combined with equipment optimization, enables us to use small irradiated volumes of rocks with variable compositions. The advantage of HRXTG in heterogeneously deformed rocks is demonstrated in a cleaved mudstone. Analysis of 2 areas in a 2 cm bed showing a gradation from micaceous sandstone to slate reveals that fabric intensity of both mica and chlorite increases significantly (dM from 0.64 to 1.03 and from 0.45 to 0.78, respectively), without appreciable change in the oblate shape (kM) of the fabric. Thus, HRXTG can record a strain state at the mm-scale of heterogeneously deformed rocks.