High-temperature silicified zones as potential caprocks of supercritical geothermal reservoirs

•Granite-porphyry systems preserve similar features to those in geothermal systems.•A fossil supercritical geothermal system was observed in tazawako granite complex, NE Japan.•Several quartz filling veinlets were formed under sub- and super-critical states.•Supercritical geothermal system components: a heat source, reservoir, and caprock.•A high-temperature silicified zone is a potential caprock of a supercritical geothermal reservoir.