Abstract

Nonlinear unroofing rates from ∼10 to <1 mm/yr following high-pressure Acadian (Devonian) metamorphism have been documented in southwestern New England by using combined petrologic, fluid inclusion, thermochronometric, and thermal modeling techniques. Thermobarometry of pelitic schists from the Rowe-Hawley belt of western Connecticut indicates peak Acadian pressure-temperature conditions of 8.2 kbar and 575°C. Densities of CO2and H2O-rich fluid inclusions require nearly isothermal decompression followed by more isobaric cooling from these conditions. Comparison of this observed path to those generated by thermal models suggests that decompression was characterized by initial rapid upward en bloc velocity (∼1 cm/yr) of brief duration, followed by much slower unroofing rates (≤0.3 mm/yr). Published geochronologic ages in this region constrain the rapid uplift to the Middle Devonian, and uplift slowed dramatically by the end of the Devonian. This differential uplift has major implications for interpretation of Devonian igneous activity and sedimentation in southwestern New England.

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