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Fluid inclusion microthermometric data from five temporally controlled vein sets in the southeastern Piedmont province record changes in fluid composition and deformation conditions during regional exhumation and cooling related to postorogenic Mesozoic rifting. In general, compositions of postmetamorphic fluids are remarkably consistent across the southeastern Piedmont, indicating regional fracture connectivity during fluid-trapping events between the end of the Alleghanian collisional orogeny and the opening of the Atlantic Ocean.

Late Paleozoic P1 and P2 quartz veins associated with post-Alleghanian stress relaxation contain metamorphic CO2-H2O-NaCl fluids that were trapped under fluctuating lithostatic (125–240 MPa) to hydrostatic pressures (20–100 MPa) at burial depths of up to 9.3 km. Maximum depths are similar to emplacement depths of post-kinematic plutons, suggesting a period of rapid isobaric cooling. Fluids trapped in veins in the Modoc fault zone give similar trapping pressures, but significantly higher temperatures, suggesting fluid migration from depth along the zone.

Triassic TR1 quartz veins related to early failed rifting record regional decompression as fracturing above the brittle-to-ductile transition allowed regional pore-fluid pressure to drop to hydrostatic levels. During this time, extensive fluid mobility occurred due to opening of regional fractures associated with initiation of rifting and tapping of deep, hot, saline fluid reservoirs.

Calcite in TR2 veins, which are related to the development of Triassic basins, and later TR3 veins related to initial Jurassic dike emplacement host common H2O inclusions. These inclusions are evidence for complete opening of the hydrologic system and for convective circulation of meteoric water, which resulted in dilution of “in situ” fluids, and ultimately to a pure-H2O system. These fluids continued to be trapped in vein minerals through the Early Cretaceous.

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