Joint formation in granitic rock of the Sierra Nevada

A single steeply dipping joint set in the Mount Givens Granodiorite was studied. The joints were filled with fluid during formation; these fluids deposited epidote and chlorite within the joints. Relative displacements are normal to the joint surfaces. These observations rule out a shear origin for these joints. The measured extensional strain is 1X10 (super -4) to 5X10 (super -4) . Mineral fillings are sheared, indicating strike-slip motion postdated the jointing. Method developed for estimating the tensile stress responsible for initiating joint growth. Calculations indicate relative tensile stresses of approximately 1 MPa to 40 MPa.--Modified journal abstract.