PROVENANCE ANALYSES OF SEDIMENTARY STRATA IN THE MESOZOIC RIFT BASINS IN CONNECTICUT USING DETRITAL ZIRCON GEOCHRONOLOGY

The provenance for much of the sedimentary fill of the Hartford and Pomperaug rift basins is not well constrained because of discontinuous outcrop, complex paleocurrent patterns and complicated tectonic history of the source areas. Detrital zircon U-Pb geochronology was used to gain a better understanding of provenance. To get a broad representation of the basin fill within the Hartford basin, samples were taken from the Triassic New Haven Arkose (SE basin- North Haven and NW basin- Simsbury), the Jurassic East Berlin Fm (center basin- Berlin), and the Jurassic Portland Fm (NE basin- Manchester and SE basin- Durham). Two samples of the Triassic South Britain Fm (Pierce Hollow and Rattlesnake Members) were collected in the SW Pomperaug basin.

Overall, the samples contain diverse populations of zircons, primarily reflecting sources areas affected by one or more orogeny: Alleghanian (270-320 Ma), Acadian (340-400 Ma), Taconic (420-490 Ma), Peri-Gondwanan (550-640 Ma), and Grenville (900-1300 Ma). Grenville age zircons are found in all but the North Haven sample, with a significant number found in Rattlesnake (53%), Pierce Hollow (14%), East Berlin (21%) and Manchester (11%) samples. Cathodoluminescence imaging revealed that some zircons have distinct core and alteration rim components. “Double-dating”, where age-dates were taken on the core and rims of the same zircon, reveals that some Grenville zircons have Acadian rims, but others are entirely Grenville age. We interpret the Grenville zircons in samples with significant amounts to reflect a western source.

In the Hartford basin, samples from the SE area of the basin near the Eastern Border Fault (EBF) contain 70-80% of combined Taconic and Pan-African zircons reflecting proximity to the Bronson Hill Arc and Avalon terranes. On the western side of the basin, the Simsbury sample is dominated (87%) by Acadian ages and is the only sample to contain less than 10% Taconic zircons (1.5%), suggesting a dominantly western source. The Berlin and Manchester (although taken from near the EBF) samples contain distributions that suggest substantial sediment from both east and west source areas. Pomperaug basin samples also contain subpopulations that reflect eastern and western source areas; most notably the significant number of Grenville zircons from the Rattlesnake Member.