NEW CONSTRAINTS ON THE MIDCONTINENT JACOBSVILLE SANDSTONE FROM U-Pb AND (U-Th)/He DOUBLE-DATING

The Proterozoic Keweenawan Supergroup in the Great Lakes region of North America records the c. 1090-980 Ma Grenville Orogeny and final amalgamation of the supercontinent Rodinia. The uppermost sedimentary unit within the Supergroup, the Jacobsville Sandstone, has been interpreted to reflect the last stage of orogenesis and/or post-orogenic events. Thus, the sediment provenance and depositional history of this unit have implications for the timescale of Grenville tectonic subsidence and continental-interior surface processes on Rodinia. To constrain the sediment provenance and exhumation history of an upper horizon within the Jacobsville Sandstone, we acquired zircon U-Pb geochronologic and (U-Th)/He thermochronologic (ZHe) “double-dates.” Double-dating offers a way to maximize the chronologic information available for a sedimentary unit by providing crystallization ages for sediment grains, information related to the exhumation and/or recycling history sediment has undergone prior to final deposition, and information related to the thermal history of the basin itself.

The combined double-dating dataset presented here (n = 68) suggests multiple populations of sediment ultimately sourced primarily from the c. 1400 Ma Grenville Granite Rhyolite Province. ZHe dates for the c. 1400 Ma U-Pb date population (n = 55) range from 0.84 ± 0.02 Ma to 1400 ± 80 Ma. Many zircon lack a significant offset between U-Pb and ZHe dates, suggesting relatively rapid exhumation post-crystallization, as expected for an orogenic setting. Zircon with ZHe dates much younger than U-Pb dates may have been deposited in older Grenville foreland basins and recycled prior to deposition in the Jacobsville basin. Thermal history modeling is consistent with primary sediment contributions from uplifting orogenic sources as well as recycled sedimentary contributions. These data and modeling help validate previous interpretations of Jacobsville Sandstone provenance and provide new constraints on primary sediment exhumation, sediment transport, and the magnitude of subsequent basin heating.