The basis for the distinction between the Eastern and Western Acadian events lies in the contrasting styles of metamorphism accompanying each. Evidence for contrasting metamorphic styles consists of (1) estimated metamorphic field gradients (MFGs) based on thermobarometric studies, and (2) petrological evidence for contrasting P-T trajectories. West of the Acadian metamorphic front, the Taconian zone has an MFG in which peak temperatures of 400-600-degrees-C were reached at pressures of about 4-6 kbar, with both P and T increasing to the east. Near its western edge, the Western Acadian metamorphic overprint has a similar MFG to the Taconian, and is mainly discriminated by 40Ar/39Ar dating and microtextural evidence. East of this narrow zone, the Western Acadian overprint is characterized by progressively higher temperatures (600-725-degrees-C) and pressures (6.5-10 kbar, or more) to the east, yielding an overall MFG that lies along, or slightly above, the kyanite-sillimanite boundary on a P-T diagram. There is little or no plutonism accompanying Western Acadian metamorphism. The basis for the distinction between the Eastern and Western Acadian events lies in the contrasting styles of metamorphism accompanying each. Evidence for contrasting metamorphic styles consists of (1) estimated metamorphic field gradients (MFGs) based on thermobarometric studies, and (2) petrological evidence for contrasting P-T trajectories. West of the Acadian metamorphic front, the Taconian zone has an MFG in which peak temperatures of 400-600-degrees-C were reached at pressures of about 4-6 kbar, with both P and T increasing to the east. Near its western edge, the Western Acadian metamorphic overprint has a similar MFG to the Taconian, and is mainly discriminated by 40Ar/39Ar dating and microtextural evidence. East of this narrow zone, the Western Acadian overprint is characterized by progressively higher temperatures (600-725-degrees-C) and pressures (6.5-10 kbar, or more) to the east, yielding an overall MFG that lies along, or slightly above, the kyanite-sillimanite boundary on a P-T diagram. There is little or no plutonism accompanying Western Acadian metamorphism. The basis for the distinction between the Eastern and Western Acadian events lies in the contrasting styles of metamorphism accompanying each. Evidence for contrasting metamorphic styles consists of (1) estimated metamorphic field gradients (MFGs) based on thermobarometric studies, and (2) petrological evidence for contrasting P-T trajectories. West of the Acadian metamorphic front, the Taconian zone has an MFG in which peak temperatures of 400-600-degrees-C were reached at pressures of about 4-6 kbar, with both P and T increasing to the east. Near its western edge, the Western Acadian metamorphic overprint has a similar MFG to the Taconian, and is mainly discriminated by 40Ar/39Ar dating and microtextural evidence. East of this narrow zone, the Western Acadian overprint is characterized by progressively higher temperatures (600-725-degrees-C) and pressures (6.5-10 kbar, or more) to the east, yielding an overall MFG that lies along, or slightly above, the kyanite-sillimanite boundary on a P-T diagram. There is little or no plutonism accompanying Western Acadian metamorphism. The basis for the distinction between the Eastern and Western Acadian events lies in the contrasting styles of metamorphism accompanying each. Evidence for contrasting metamorphic styles consists of (1) estimated metamorphic field gradients (MFGs) based on thermobarometric studies, and (2) petrological evidence for contrasting P-T trajectories. West of the Acadian metamorphic front, the Taconian zone has an MFG in which peak temperatures of 400-600-degrees-C were reached at pressures of about 4-6 kbar, with both P and T increasing to the east. Near its western edge, the Western Acadian metamorphic overprint has a similar MFG to the Taconian, and is mainly discriminated by 40Ar/39Ar dating and microtextural evidence. East of this narrow zone, the Western Acadian overprint is characterized by progressively higher temperatures (600-725-degrees-C) and pressures (6.5-10 kbar, or more) to the east, yielding an overall MFG that lies along, or slightly above, the kyanite-sillimanite boundary on a P-T diagram. There is little or no plutonism accompanying Western Acadian metamorphism.
