STRATIGRAPHIC, TECTONIC, AND PALEOGEOGRAPHIC CONSTRAINTS ON THE ACADIAN OROGENY FROM DETRITAL AND IGNEOUS ZIRCON DATING OF ROCKS FROM THE CONNECTICUT VALLEY-GASPE BASIN IN MASSACHUSETTS AND VERMONT

The Connecticut Valley-Gaspe basin (CVGB) is one of several basins in the northern Appalachians filled by Silurian and Devonian rocks. New U-Pb LA-ICPMS and CA-IDTIMS zircon dates indicate that Silurian rocks are restricted to thin discontinuous quartzite lenses on the western margin of the basin (Russel Mtn. Fm. in MA, Shaw Mtn. Fm. in VT). A large time gap separated deposition of the Silurian quartz arenite from Lower Devonian marine deposits of the Waits River, Gile Mtn., and Northfield (VT)/Goshen (MA) Fms., which were deposited ca. 419 to 405 Ma. Dates from meta-rhyolites in the Goshen Fm. (405 ± 4 Ma; 408.6 ± 0.1 Ma) and the Meetinghouse Slate Mbr. of the Gile Mtn. Fm. (407 ± 3 Ma; Rankin and Tucker, 2009) indicate that the youngest rocks occur on the western and eastern margin of the basin. Detrital zircon populations in all units show sediment contribution from both Laurentia and Gondwanan-derived terranes.

The paucity of Silurian rocks in the basin suggest that the region was a positive topographic feature before ca. 420 Ma when loading on the continental margin by the arrival of Avalon initiated basin development and marine deposition. It is noteworthy that no evidence for a foreland basin recording the Late Ordovician to Silurian arrival of Ganderia is preserved in western New England.

Silurian and Devonian rocks from the Catskill (CB) basin in NY contain detrital zircon populations dominated by Laurentian, particularly Grenvillian grains; they did not receive significant Ordovician and Silurian zircon until Middle Devonian and did not receive Gondwanan detritus until the Late Devonian (Selleck et al., 2016). The evolution of detrital zircon populations in the CB has been attributed to protracted erosional or tectonic unroofing of Gondwanan-derived crust in the Acadian hinterland, but the abundance of Gondwanan detritus in the CVGB suggests that a topographic barrier separating the CVGB and CB is a better explanation. We suggest that Acadian deformation in the hinterland created a critical taper that reactivated the Taconic thrust system creating a highland between the CVGB and CB. Erosion of Taconic thrust sheets and underlying Grenville basement produced the eastern Laurentian source for detritus to the CB, and erosional transfer of rock helped maintain the critical taper in the Acadian orogenic wedge.