geobarometers

Geobarometers are methods and calibrated relations used to estimate the pressure conditions experienced by rocks during geological processes, especially metamorphism. Rather than a single instrument, geobarometry encompasses chemical and thermodynamic approaches that infer pressure from mineral compositions and phase relationships. Geobarometers rely on experimental and natural calibrations that describe how minerals and their assemblages respond to pressure (and temperature). They are used alongside geothermometers to reconstruct pressure–temperature paths in rocks.

Two broad families are common. Mineral-chemical geobarometers exploit pressure-sensitive exchange reactions between minerals, typically Fe–Mg exchanges between garnet and biotite, garnet and orthopyroxene, or plagioclase and calcic minerals. Phase-equilibrium geobarometers use experimentally determined stability fields for mineral assemblages; observed assemblages are compared to pressure–temperature grids or modeled with pseudosections (perple_X, THERMOCALC) to yield pressure estimates at a given temperature.

Procedure and applications: measurements of mineral compositions by electron microprobe feed into calibrations to compute pressure, often with multiple barometers to improve reliability. Geobarometry reconstructs crustal evolution in subduction zones, orogenic belts, and metamorphic terranes, and helps constrain burial and exhumation histories. Limitations include chemical zoning, metasomatism, disequilibrium, and uncertainties in calibrations. Results are typically reported with temperature inputs and associated error estimates.