Low-Temperature Thermochronology of the Moodus Deep Core, Connecticut: Understanding Spatio-Temporal Patterns of Passive Margin Rejuvenation in New England

Persistent relief, thermochronology and offshore sediment records all suggest that the northeastern United States has experienced one or more periods of tectonic rejuvenation since the opening of the Atlantic Ocean during the Early Jurassic. However, the spatio-temporal patterns and underlying mechanisms of this rejuvenation remain poorly understood. This study constrains the exhumational history of southern Connecticut through (U-Th)/He thermochronology over a vertical transect of the Moodus Deep Core, a 1450 m deep borehole in southern Connecticut. Mean AHe ages for apatite grain groups from each selected depth sample in this crustal section range from 40 Ma at the bottom of the core to 160 Ma at the surface. The AHe dataset is refined by including elemental zoning data obtained from drill holes into the cores of grains through laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS).

Inverse thermal modeling of AHe ages and associated zoning data with the thermal modeling software QTQt indicate the presence of two cooling pulses, one during the Early Cretaceous (125 Ma to 115 Ma) and one during the Paleocene (65 to 55 Ma). The best-fit model suggests accelerated erosion at a rate of 0.2 km/Myr during the Early Cretaceous event followed by 55 Myr of quiescence, then accelerated erosion at a rate of 0.1 km/Myr during the Paleocene event. With the addition of immediate post-rift cooling, this accounts for 1.4 km of total exhumed material from the Moodus region since rifting, significantly less than was concluded from a previous study of exhumation in the White Mountains of New Hampshire (Amidon et al., 2016). The best-fit model suggests a dampened and time-delayed signature of exhumation in southern New England relative to the mountainous uplands, potentially attributable to differential fault architecture in the two regions. The transfer of far-field compressional and tensional stresses from Atlantic spreading regime shifts may be an underlying cause of the rejuvenation events, though additional work is necessary to better understand the correlation between stress regime shifts and unroofing events in New England. Ongoing work will combine apatite (U-Th)/He and apatite fission track ages in a thermal model to better constrain the timing and mechanics of exhumation in southern Connecticut.