Multiphase Fracturing, Fluid Evolution, and Geothermal Sustainability in Mesoproterozoic Carbonates of the North China Craton

ABSTRACT Understanding the origin and evolution of fractures is critical for evaluating the long‐term sustainability of geothermal water production from carbonate reservoirs, an emerging low‐carbon energy source aligned with global carbon‐neutrality goals. In this study, we develop a fracture‐fluid evolution model for Mesoproterozoic carbonates of the North China Craton (NCC) by integrating U–Pb dating of fracture‐filling dolomites with petrological, micro‐CT, and multi‐isotopic (C, O, clumped and 87 Sr/ 86 Sr) analyses. Three principal phases were identified at ~1550 to 973 Ma, 669 to 597 Ma, and 106 to 58 Ma. Clumped isotope‐derived temperatures (57.1°C–93.6°C) and calculated burial depths (mostly < 2 km, with few reaching ~2.5 km) indicate predominantly shallow diagenetic conditions. Fluids responsible for Phases I–II fracturing were primarily seawater‐derived, whereas meteoric water dominated Phase III fracturing beginning in the late Mesozoic. Our results demonstrate that high reservoir connectivity—primarily driven by multiphase fracturing—exerts a first‐order control on reservoir quality, while porosity and pore‐throat dimensions play a secondary role. This connectivity, coupled with the absence of large karstic cavities, sustains high hydrostatic pressures and sustained geothermal yields. An estimated ~1.1 × 10 22 J of geothermal energy—derived from meteoric recharge over recent geologic time—underscores the carbon‐neutral potential of these fractured carbonates. The integrated methodology presented here offers a transferable framework for evaluating fractured geothermal systems worldwide.