42-1 The Hartland Rift Succession of West Connecticut: Startigraphic and Tectonic Context

Session: Paleozoic Events and Processes: Sedimentary Geology, Paleontology, and Geochemistry (Posters)

Presenting Author:

Author:

Abstract:

Recent mapping in Roxbury and adjacent quadrangles in western CT provides the basis for a stratigraphic and tectonic re-evaluation of the meta-sediments. These poly-deformed rocks originated as a thick pile of medium- to coarse-grained, quartzo-feldspathic meta-sandstones and interlayered meta-mudstones. The thickness of the section is indeterminate but likely on the order of kilometers. Reported detrital zircon analyses from these rocks all show a classic Laurentian age spectra. A distinct mappable belt of amphibolites exists east of and roughly parallel to the structural discontinuity known as Camerons' Line. Age constraints are poor: the section post-dates the youngest detrital zircon (~950 Ma) and pre-dates the oldest intrusion (~450 Ma). Analysis of meta-sandstone samples indicate an abundance of arkosic and sub-arkosic lithologies with no evidence of derivation from anything but an igneous-metamorphic cratonic source, consistent with detrital zircon age data. A fundamental question arises: how do you get such a thick section of Laurentian-derived, feldspar-rich, clastic sediment once the early Paleozoic carbonate margin is established? The answer is you don't. 

These metaseds are interpreted as late Proterozoic-Cambrian rift fill deposited prior to the establishment of the Paleozoic margin. In this paradigm the amphibolites are interpreted as rift-related meta-volcanics. Cameron's Line represents the Hinge Zone of the rifted margin, the boundary between highly extended and weakly extended continental crust, and a feature that became a locus of structural re-activation during the Taconic and Acadian Orogenies. 

This package of rocks exhibits no obvious stratigraphic succession. In notes included with his Roxbury map, Gates (1959) repeatedly mentions how he could not establish a stratigraphic sequence and called the whole package Hartland Formation. However, on the State Bedrock Map, Rodgers (1985), inspired by the stratigraphic framework proposed by Hatch and Stanley (1973), and with a dash of long-distance lithodemic correlation, "shoe-horned" a non-existent stratigraphy with implied chrono-stratigraphic significance on the Hartland section. Now recognized as highly misleading, it is proposed that the term Hartland Formation be restored to be more consistent with current geologic data and interpretation of the section. In this proposal, recent Roxbury mapping (Burton and Devlin, 2021, 2023) that shows areas dominated by either schistose meta-sandstones or meta-mudstones would be identified as lithodemic members of the Hartland Formation.

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