Detrital Zircon Double Dating Reconstructs the Missing Grenville Foreland and Great Unconformity Exhumation

Abstract

The c. 1090–980 Ma Grenville Orogeny that resulted in final amalgamation of the supercontinent Rodinia is not associated with extensive preserved foreland basins common in other convergent margins, which has generated controversy about why these basins are absent and the nature of Meso‐Neoproterozoic orogenesis. The c. 993 Ma Jacobsville Sandstone and correlative units preserved in the North America Midcontinent region are the only known syntectonic units associated with the final stage of Grenville orogenesis. In this study, we apply U‐Pb geochronology and (U‐Th)/He thermochronology “double dating” to detrital zircon in the Jacobsville Sandstone and determine the former extent of foreland sediments that once buried this unit. Our interpreted (U‐Th)/He data set ( n  = 66) includes dates ranging from 375 ± 13 Ma to 1618 ± 47 Ma. The dates younger than depositional age c. 993 Ma indicate that the Jacobsville was buried hot enough to reset the (U‐Th)/He system in a subset of grains. This burial must have occurred in the Neoproterozoic, because maximum Phanerozoic temperatures are too cool to account for partial resetting. A novel inverse thermal history modeling approach helps constrain maximum temperatures of 130–200°C between c. 993 and 700 Ma. This corresponds to 3.4–6.3 km of sedimentary burial, substantially thicker than estimates from previous investigations west of our study area. Collectively, available data support Jacobsville deposition and burial in a broken foreland basin system with variable sedimentary thickness. Most of this foreland basin was removed in the late Neoproterozoic by exhumation that generated the Great Unconformity.