Abstract
This study reports the results of paleostress analysis using the three-dimensional orientation and distribution of healed microcracks (HCs) in quartz within granitic bodies. Although the mechanical constraints of a universal stage together with the Terzaghi factor introduce sampling bias to the orientation and distribution of microstructures, few previous studies have taken this bias into consideration. We devised a series of corrections that allow the investigation of the orientation and distribution of HCs within the Ryoke granites, located along the Median Tectonic Line (MTL) in the Chubu region of Japan. Paleostress values were determined by fitting mixed Bingham distributions to the corrected distribution of each sample, resulting in the clustering of HC orientations in each data set into a few groups, which were then inverted to yield a paleostress state. The state corresponding to the group with the maximum number of HCs was considered to be the most significant stress for each individual sample, and the orientation of σ3 of this most significant stress in most samples is roughly perpendicular to the trend of the MTL. However, significant variations in the distribution of σ1 and σ2 were also identified, suggesting that the orientation of σ3 probably reflects the regional stress field, whereas the orientations of σ1 and σ2 are more dependent on the local stress state within the granitic body.
