50-4 Measuring the changing tempo of burial, exhumation, and deformation during the rift-drift transition along the Eastern Border fault of the Mesozoic Hartford Basin, southern Connecticut, USA.

Session: Latest Research Advances in Structural Geology and Tectonics

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Abstract:

The Hartford (Connecticut Valley) basin is one of a series of rift basins preserved on and offshore along the eastern margin of North America. The basin preserves uppermost Triassic and Lower Jurassic terrestrial rift sedimentary strata interlayered with basalts of the 201.5 Ma Central Atlantic Magmatic province. These layers are tilted gently to moderately eastward, warped into several 10-25-km-scale transverse folds along the Easter Border fault, and cut by subparallel and branching faults with apparent normal offset. The timing of this late-stage deformation and its relation to rifting vs post rift (drifting) processes has long been a topic of debate. We combine apatite and zircon (U-Th)/He thermochronology and thermal history modeling with new geologic mapping and cross section construction to develop a 4D model of burial, exhumation, and deformation in the southern Hartford Basin.

Zircon and apatite were analyzed from six samples spanning the Eastern Border fault. Thermal histories were modeled using HeFTy with additional constraints provided by depositional ages and existing ⁴⁰Ar/³⁹Ar cooling ages. The northernmost two footwall samples are consistent with nearly monotonic cooling from high-grade conditions during the Permian Alleghanian orogeny to <100 °C by the Early Jurassic, followed by slower cooling to temperatures of <40 °C by ~140 Ma. The southernmost sample located ~5 km from the present-day limit of the basin cooled more slowly from ~300 °C in the Middle Triassic to temperatures <150 °C by ~130 Ma. Results from the northernmost and southernmost basin samples agree and show between 50–200 °C of post-depositional heating, peaking at ~165 Ma, followed by cooling to <50 °C by ~130–120 Ma. These samples are from locations where >700 m of strata are preserved within adjacent synclines (Middletown and Saltonstall). The third basin sample, where <200 m of overlying strata are preserved (Totoket syncline), is consistent with only 25-75 °C of post-depositional heating. Variations in preserved thickness are thus broadly consistent with the thermochronology data. Furthermore, lower Jurassic strata, preserved between lava flows within the Totoket syncline, are thinner than the same section within the neighboring Saltonstall syncline. Thermal history modeling and geologic observations are thus consistent with a model where deformation, including transverse folding, initiates during the rift phase, but continues into the post-rift phase, spanning 70-80 million years.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7371

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