T153 Detrital Zircon Provenance of Neoproterozoic to Lower Paleozoic Strata of Northern and Western Laurentia

Tuesday, 6 November 2012
8:00 AM - 12:00 PM
203B

DETRITAL ZIRCON AGES FROM THE NEOPROTEROZOIC-CAMBRIAN RIFT-TO DRIFT SEQUENCE OF THE EASTERN US

Paper number: T153-10
Program: Technical Sessions
Time: 10:30 AM – 10:45 AM

Authors

Abstract

Neoproterozoic-Cambrian clastic sedimentary rocks are exposed along the US Appalachian Orogen from Vermont to Georgia. In the north-central part of the orogen units rest nonconformably on Mesoproterozoic metaigneous basement, while in the southern part of the orogen they lie unconformably on Neoproterozoic rift sediments. These rocks were deposited as part of a rift-to drift sequence in response to the break-up of Rodinia and the formation of a passive margin on eastern Laurentia. Previous studies have struggled to constrain the depositional age of these sediments and have mainly relied on analyzing scarce trace fossils or comparing the stratigraphic position of units to those age-constrained by dated volcanics. The goals of this work are to: 1) use detrital zircon to help constrain the age of deposition for the rift-to drift sediments along the entire orogen and 2) use this data to reconstruct the rifting history of eastern Laurentia at this time. As part of this study, 55 different clastic sedimentary rocks were sampled along similar stratigraphic horizons from Vermont to Georgia. Zircon from each sample was dated by LA-MC-ICPMS, producing more than 3,500 U-Pb dates. Along the entire orogen, the dominant detrital populations are 1170 and 1050 Ma, with only a few samples containing zircon with ages close to the estimated time of deposition.

Zircon ages from the southern samples are more variable than those in the north-central. Only one southern sample contains latest Neoproterozoic zircon, others have large secondary populations of 1620, 1470 and 1340 Ma; ages not observed in the north-central dataset. These ages do not correspond to any known local basement, and published detrital zircon data from the underlying Ocoee Supergroup have only a few grains that correspond to these age peaks, suggesting that the Ocoee was not a major source for the overlying Cambrian sediments. It is likely that the southern Cambrian sediments had external, potentially distant, sources that were not exposed in the north-central portion of the orogen during the Neoproterozoic. If the northern and southern Cambrian units are indeed correlative it suggests that portions of the southern Laurentian margin were still rifting in the Cambrian and thus exposing new potential source areas.