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Detrital Zircons in Appalachian rivers: a Record of the Grenvills Superorogeny?

Kenneth Eriksson, Ian Campbell, Michael Palin and Charlotte Allen

Detrital zircons from six rivers draining the Appalachian Mountains were dated using U-Pb isotopes measured by excimer laser ablation (ELA)-ICP-MS. Of the 905 grains analyzed, 726 (80%) yielded ages that were more than 90% concordant. The ages for 72% of the concordant zircons are between 950 and 1250 Ma and define a continuous Grenville tectono-magmatic event that peaked around 1030 Ma. Of the remaining zircons, 19% have Paleozoic ages corresponding with the Taconic (480-420 Ma) and Acadian (400-350 Ma) orogenies. The overwhelming dominance of Grenville-age zircons in rivers draining the Appalachian Mountains implies the former existence of a mountain belt whose detritus has dominated the sedimentary record for the past 1.0 billion years in eastern North America and beyond. In the zircon age spectra, which is a measure of the intensity of crustal melting associated with a tectono-magmatic event, the Grenville dwarfs the collective Paleozoic orogenies in the Appalachians by four times and therefore is called a "superorogeny".