Abstract
ABSTRACTThe Paleozoic rocks underlying the western third of the New Haven Quadrangle, Connecticut, are mapped at a scale of 1:24,000. This area of ∼41.5 km2, previously mapped only in reconnaissance, contains polymetamorphic argillites and mafic rocks. The northern portion of the mapped area contains the pelitic Wepawaug schist, whereas the southern portion is underlain by the pelitic Savin Schist. Between them lies the Maltby Lakes Complex (MLC) that contains newly identified fault slivers of variably metamorphosed mafic phyllites and amphibolites. Metamorphic foliations in both the MLC and the Savin Schist are truncated by a swarm of basalt dikes: the Allingtown porphyry, which is itself commonly schistose and locally mylonitic. Previous interpretations held that these rocks constitute a conformable, northwest-topping stratigraphic sequence. In contrast, we propose that Ordovician(?) oceanic rocks of the MLC were variably metamorphosed and faulted against the Ordovician(?) Savin Schist. These were intruded by a swarm of stitching Allingtown dikes. This package of rocks was then faulted against Siluro-Devonian(?) Wepawaug forearc sediments. Existing thermochronology indicates a Devonian age of the subsequent regional metamorphism, overprinted by low-grade Permian fabrics associated with dextral transpression and final terrane assembly.
Highlights
Along-strike structural relationships suggest the Orange-Milford Belt (OMB) may correlate with the Connecticut Valley Trough (CVT) in Vermont
Southeastern extent of the Western Highlands. This ‘formation’ included what we presently identify as the Savin Schist, Allingtown porphyry, and Maltby Lakes Complex (MLC)
The metamorphic fabrics preserved in the gneissic amphibolite (Oma) and in the amphibole mylonite (Omm) are evidence of prograde, pre-Acadian, possibly Taconic metamorphism otherwise unknown in this part of Connecticut
Summary
The Orange-Milford Belt (OMB) of mafic and argillitic rocks lies at the southeastern margin of Connecticut’s Western Highlands (Rodgers, 1985). It is bound on the west by the East Derby Shear Zone (EDSZ), a greenschist facies ductile fault (Hatch & Stanley, 1973; Wathen et al, 2015). Just south of the New Haven quadrangle the Eastern Border Fault of the Hartford basin places anatectic rocks of periGondwanan affinity (Aleinikoff et al, 2007) against the OMB. In the absence of independent constraints, some units in New Haven quadrangle are given tentative age assignments based on this correlation, as discussed below (Ages of Map Units)
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