Predominance of Grenvillian Magmatism Recorded in Detrital Zircons from Modern Appalachian Rivers

Abstract

Detrital zircons from six modern rivers draining the Appalachian Mountains were dated using U-Pb isotopes measured by excimer laser ablation induction coupled plasma-mass spectrometry (ELA-ICP-MS). Of the 905 grains analyzed, 736 were acceptable for age determination and 524 (71%) of these yielded ages between 950 and 1250 Ma, defining a continuous Grenvillian tectonomagmatic event that peaked around 1020-1050 Ma. Of the remaining zircons, 20% (n = 149) have Paleozoic ages corresponding mainly with the Taconian (430-500 Ma) and Acadian (350-400 Ma) orogenies. The overwhelming dominance of Grenvillian 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 are a measure of the intensity of crustal melting associated with an orogeny, the Grenvillian dwarfs the collective Paleozoic orogenies in the Appalachians and therefore was the most important tectonomagmatic event to affect eastern North America.