Deep borehole discoveries beneath the Appalachian Basin: Broad Rodinian rift and Neoproterozoic tectonothermal event

Besides a few isolated rift basins along the Neoproterozoic eastern Laurentian margin, the Appalachian Palaeozoic strata rest unconformably on Mesoproterozoic crystalline basement, reflecting a ca. 550+ Ma hiatus. However, a nearly 3 km deep experimental geothermal borehole through the Appalachian basin at Cornell University, New York, unexpectedly encountered deformed Neoproterozoic greenschist facies phyllites and metavolcanics (Cayuta Formation) beneath the Cambrian non‐conformity. Magnetic modelling shows they are in the 5000 km 2 fault‐bounded Ithaca basin, proposed to be associated with Iapetan rifting. The volcanism and metamorphism appear linked to ca. 600–650 Ma thermal events related or unrelated to extension, but requiring uplift and denudation of 5–10 km of rock prior to deposition of the Cambrian Potsdam Group. The Ithaca basin is >350 km inboard of the Laurentian Iapetus margin, indicating a broad Neoproterozoic rift zone for at least the NY and PA portion of eastern Laurentia.