29-5 Spatio-Temporal Controls on Orogenic Thermal Structure and Evolution in the Southern New England Appalachians

Session: Rates, Dates, and Plates: Petrochronological Approaches to Unraveling Tectonometamorphic Histories (Posters)

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The thermal structure and evolution of orogenic crust exerts a fundamental control on lithospheric rheology and the geodynamic processes that shape mountain belts. While orogenic thermal architecture is often constrained from geodynamic models, xenolith petrography, or seismic imaging, few studies reconstruct large-scale orogenic thermal evolution directly from field-based structural, petrographic, and geochronologic datasets. The New England Appalachians expose a broad section of the middle to lower orogenic crust which formed during late Paleozoic orogenesis on the margin of Laurentia. This crustal section preserves evidence of high- to ultrahigh-temperature (UHT) metamorphism, high pressure granulite (HPG) metamorphism, intense ductile deformation, and widespread fluid-mediated mineral reactions across scales ranging from grains to regions. However, the relationships among these processes and the ultimate effect on orogenic rheology through the Late Paleozoic is not well understood. We present new whole rock and mineral geochemistry, monazite and zircon petrochronology, and phase equilibria modelling of samples from central Massachusetts and eastern Connecticut showcasing the spatio-temporal distribution of metamorphic conditions during the Acadian-Neoacadian (Devonian-early Carboniferous) and Alleghanian (Carboniferous-Permian) orogenies in the New England Appalachians. Our results, integrated with existing regional datasets, corroborate early studies that delineate the orogen into two distinct metamorphic belts (broadly corresponding to the extents of the Connecticut Valley Gaspé Trough and Central Maine Terrane). The metamorphic style to the east of the Bronson Hill Anticlinorium is characterized by much higher metamorphic temperatures until widespread cooling begins in the late Carboniferous and Early Permian. Moreover, for the same region, we find that high to ultra-high temperature (>700 °C) metamorphic domains are commonly separated or truncated by lower amphibolite to greenschist facies moderate-temperature (< 650-700 °C) zones, often representing tight to isoclinal, upright synforms and increasingly localized strain during Late Devonian and Carboniferous deformation. By binning metamorphic conditions by the age of metamorphism, we reconstruct the evolving thermal architecture of the southern New England orogen from ~400–300 Ma, with implications for crustal rheology, strain localization, and the feedbacks between heat, deformation, and fluid flow during collisional orogenesis.

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