DETRITAL ZIRCON U-PB GEOCHRONOLOGY OF THE GREATER CENTRAL MAINE BASIN, NEW HAMPSHIRE AND SOUTHWESTERN MAINE

The Central Maine Basin records widespread synorogenic deep-marine sedimentation associated with the Salinic and Acadian orogens of the New England Appalachians. Previous work exploring the detrital zircon U-Pb geochronology of metasedimentary units within the Central Maine Basin provided evidence for distinct source regions, provenance shifts, and anomalously young zircon in some of the examined units. In addition to revisiting some of these anomalous samples, we expand the geographic range of sampled Central Maine Basin units into western and south-central New Hampshire, including providing new laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) detrital zircon U-Pb data from the Littleton, Fitch, Warner, Francestown, Perry Mountain, Clough, and Rangeley formations. We focused our sampling in these units’ type areas and at sites where fossils independently constrain depositional ages. Due to the abundance of metamorphic rims on the examined detrital zircons, we carefully selected spots using cathodoluminescence imaging; moreover, we applied strict filtering criteria to large-N datasets. We also targeted roof pendants of the Littleton Formation (i.e., Interval Clay Slate) in the White Mountains to see if remnants of higher structural levels in the Acadian orogen escaped widespread zircon metamorphic rim crystallization. In addition, we explored if chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) analyses on igneous zircon from adjacent Devonian plutonic rocks could address issues related to metamorphic rim development and/or Pb-loss. The combination of these approaches suggests that some of the anomalously young depositional ages are older and more in keeping with the previous stratigraphic age assignments. The “too-young” zircons do not require stratigraphic revisions. Our study highlights the need to treat detrital zircon U-Pb maximum depositional ages with extreme caution in the New England Appalachians.