301-7 Onset of Rodinia Rifting Recorded by Detrital Zircons in the Cheshire Formation

Session: Geochronology (Posters)

Presenting Author:

Authors:

Abstract:

The rifting of eastern Laurentia is recorded by meta-volcanic units associated with rift-clastic successions exposed along the Eastern Seaboard from Alabama to Newfoundland. Although the timing of rifting is inferred by U-Pb dating of zircons from within these meta-volcanic units, in many places these volcanics are non-existent or covered by younger sediments making it difficult to establish the exact timing of rifting. For example, in southern Quebec, New England, and New York, the timing of rifting is constrained by the Tibbit Hill volcanics, the Pinney Hollow Formation, and a handful of intrusions in Quebec, all of which range from ~590-531 Ma. These relatively young ages contrast with evidence for earlier rifting in the southern Appalachians (~760-700 Ma) and maritime Canada (~615 to 550 Ma), raising the question of whether the onset of rifting in New England and Southern Quebec was delayed relative to other parts of the margin. We address this question by dating detrital zircons from the Cambrian-aged Cheshire Quartzite, which was deposited as a mature sandstone blanketing the recently rifted margin of Laurentia. It thus acts as a repository for zircons shed from the landscape during and after rifting, including from rift-related magmas that should provide a relatively complete record of the timing of rifting. Results from 10 samples of the Cheshire Quartzite reveal that roughly 3% of detrital zircons range in age from ~540 to 900 Ma, precluding a source region in the Laurentian basement. A large population of these grain ages are between ~590-900 Ma, suggesting they are derived from rift-related volcanics that are no longer exposed at the surface in southern Quebec, New England, or New York. We argue that these “missing” source rocks are relatively local, suggesting that rifting may predate the commonly accepted time frame of 531 to 590 Ma inferred from dated volcanic deposits currently exposed at the surface.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8732

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.