Abstract
Orientation, filling minerals and surface morphology of fractures observed in the integrated data of boring cores and borehole TV images of Late Cretaceous Toki granite in central Japan were analyzed at the interval between 51-1, 012m of vertical hole drilled in Toki City, Gifu Prefecture. Orientation of the fractures are grouped into NNW, NS and NE-ENE trends with steep-dips and horizontal attitude. The steeply dipping fractures change their strikes from NNW to NNE and ENE to EW with depth. Fracture surface morphologies are classified into the planar type with rough surface (Pr), with flat surface (Pf), with striations (Ps), and irregular type with rough surface (Wr). The Ps fractures trending NNW-SSE and dipping steeply at the depth about 340m were formed by the horizontal shear. Most of the Pr, Pf and Ps fractures are dipping steeply, and are considered to form as shear fractures on the basis of their morphologies. Part of the horizontal Wr fractures observed near the unconformity with the overlying Cenozoic formation are interpreted as sheeting joints, whereas the steeply dipping Wr and rest of the horizontal Wr seem to be cooling joints. The filling minerals include clay minerals, chlorite, epidote, quartz and calcite.
