A fluid inclusion study of fluid pressure and salinity variations in the footwall of the rector branch thrust, North Carolina, U.S.A.

Last melting and homogenization temperatures of fluid inclusions from plastically deformed bedding-parallel quartz veins in the footwall of the Rector Branch thrust, North Carolina, were studied as a function of distance from the thrust. Fluid inclusions and microstructures in mylonitic rocks within the thrust zone were also examined. Fluid inclusions in quartz veins which display evidence for intracrystalline plasticity (e.g. subgrain polygonization) occur along subgrain boundaries and have higher homogenization temperatures (Tn) and a wider range (120–320°C) compared to less deformed samples. Maximum Th values, which approach the temperature of deformation (300 ± 20°C), apparently reflect leakage of inclusions along subgrain boundaries. Minimum Th values (120–160°C), on the other hand, record near lithostatic conditions (2.6 kb) at 300°C.