12-6 Hot orogenic crust and extreme metamorphism: Insights from the Acadian-Neoacadian orogeny in New England, USA

Session: New advances in geological and geophysical research on the Appalachian orogen. (II)

Presenting Author:

Authors:

Abstract:

Ultra-high temperature (UHT) and high-pressure granulites (HPG) provide insights into physicochemical properties and high-grade metamorphic processes within the middle and lower crust. The New England Appalachian region affords a unique opportunity to investigate these high-grade metamorphic conditions (e.g., Ague et al. 2013; Keller and Ague 2018; Ferrero et al. 2021). Here we focus on rocks primarily associated with the Acadian–Neoacadian orogeny. During this time, the region may have undergone extensive crustal thickening leading to a long-lived orogenic plateau between c. 410 and 330 Ma (Hillenbrand et al. 2023). We test the likelihood of reaching UHT and HPG conditions within the proposed time frame by conducting thermal modeling of overthickened crust in concert with Monte Carlo sampling to constrain uncertainties. As part of this effort, we compile compositional data from samples throughout the region to estimate the crustal heat production used in our models. We find that, given the extensive occurrence of metasedimentary and felsic-to-intermediate igneous rocks with high radiogenic heat production, UHT and HPG metamorphism could have been achieved within the crust of the region by c. 360 Ma during the Neoacadian, consistent with regional geochronology. However, extreme metamorphic conditions persist for too long in the model orogen (to ~310 Ma), thus prompting a reconsideration of the exhumation history. We propose an alternative exhumation history with a shorter-lived orogenic plateau that can produce high-grade metamorphism within the observed timescale of Neoacadian peak metamorphism. The results indicate that HPG conditions can be achieved in crustal overthickening scenarios and provide general perspectives on crustal heat production regimes.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2, 2026

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