The production of H2O during metamorphism along active plate boundaries is inferred to contribute to low-frequency tectonic tremor. This study combines predictions from phase equilibria and mechanical modeling of coincident volume changes to investigate links of tremor with hydrofracturing and fluid migration under the actively forming Southern Alps, New Zealand. The posited location of metamorphic fluid production correlates with published geophysical images of inferred permeability enhancement, fluid accumulation and potential fluid flow. As the hanging-wall rocks are translated toward the surface by motion along the Alpine Fault, they can undergo metamorphic reactions that involve positive volume changes. Production of metamorphic fluids leads to hydrofracturing and the development of tremor hypocenters in regions along, and above deep reflectors of the Alpine Fault. The capacity of metamorphic rocks to generate or consume fluid along portions of the pressure–temperature path exerts a fundamental control on the distribution of stresses in the crust.