27-6 Measuring the Magnitude and Timing of Burial, Exhumation, and Deformation During the Rift-Drift Transition Along the Eastern Border Fault of the Mesozoic Hartford Basin, Southern Connecticut, USA.

Session: Recent Work in Mesozoic East Coast Rift Basins: Structure, Sedimentology, Paleontology, Mapping, and More!

Presenting Author:

Phillip Resor

Authors:

Resor, Phillip G.¹, Kennedy, Rebekah², Klang, Zachary J.³, Fosdick, Julie⁴, Wintsch, Robert P.⁵

(1) Wesleyan University, Middletown, , (2) Montana State University, Bozeman, , (3) Wesleyan University, Middletown, , (4) University of Connecticut, Storrs, , (5) Wesleyan University, Haddam, ,

Abstract:

The southernmost Hartford basin in south-central Connecticut preserves uppermost Triassic and Lower Jurassic terrestrial rift sediments 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 a series of subparallel and branching faults with apparent normal offset. The timing of this late-stage deformation and its relation to rifting versus post rift processes remains 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 sample pairs spanning the Eastern Border fault. Inverse thermal histories were modeled using additional constraints from depositional ages and existing footwall ⁴⁰Ar/³⁹Ar amphibole and muscovite cooling ages. The central footwall sample shows monotonic cooling from high-grade conditions during the Alleghanian orogeny to <60°C by the Early Jurassic (~180 Ma). The southernmost Branford sample cooled more slowly from ~300°C in the Middle Triassic (~240 Ma) to ~200°C by the Late Jurassic (~160 Ma) and then experienced rapid cooling to < 150°C by the Early Cretaceous (~140 Ma). Results from the northernmost and southernmost basin samples largely agree and show between 50–180°C of post-depositional heating, peaking ca. Early Jurassic (~185 Ma), followed by cooling to <50°C by the Early Cretaceous (~130–120 Ma). The inclusion of previously published apatite fission track ages leads to models with greater basin heating and longer residence times at intermediate temperatures. 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 compatible with <60°C of post-depositional heating. Variations in preserved thickness are thus broadly consistent with the thermochronology data. 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 Myr.

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

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