Neogene regional stress field inferred from the pattern of ore veins in Hokkaido, Japan

Abstract

Neogene stress field in Hokkaido has been analyzed, based on the strikes of ore veins. The ore veins formed during the period from late Middle Miocene to Recent are taken into account. Those of E-W and ENE-WSW directions are predominant in both northeast and southwest Hokkaido.
The major veins of thirteen representative mines are formed in the conjugate shear fractures, that is, E-W or ENE-WSW dextral and NW-SE sinistral. The estimated stress field is NW-SE or WNW-ESE compressional and parallel to the direction of the subducting Pacific Plate, even at ore-forming period. The predominance of E-W and ENE-WSW dextral shears might be related to the oblique subduction of the Pacific Plate.