Northeastern Section - 36th Annual Meeting (March 12-14, 2001)

Paper No. 10
Presentation Time: 11:50 AM


WALSH, Gregory J., US Geol Survey, PO Box 628, Montpelier, VT 05601-0628,

New 1:24,000 mapping in the New Milford quadrangle spans Cameron's Line in west-central Connecticut. A Lower Paleozoic autochthonous and allochthonous cover sequence overlies Mesoproterozoic basement gneisses exposed in several inliers west of Cameron's Line. The basement contains biotite gneiss, amphibolite, migmatite gneiss, and hornblende gneiss intruded by augen gneiss and granitic gneiss. The augen gneiss and granitic gneiss post-date early Grenville folds yet are deformed by a regionally dominant Grenville foliation. The Cambrian Dalton Formation consists of biotite schist, feldspathic granofels, quartzite, calcite marble, and amphibolite and overlies the basement in the central part of the map. Here, the Cambro-Ordovician Stockbridge Marble overlies the Dalton. In the western part of the quadrangle, near Sherman, basement gneiss is overlain by biotite schist, quartzite, and interbedded marble that is shown as Ordovician Walloomsac Schist on the 1985 State map by Rodgers. These rocks are lithically identical to rocks mapped as Dalton in the central part of the quadrangle below the Stockbridge Marble. The autochthonous cover sequence is overlain by Taconian klippen of Manhattan Schist with interbedded amphibolite. Truncations of amphibolite in the upper plate and marble in the lower plate define a thrust contact at the base of the klippen. Early Taconian S1 foliation and F1 isoclinal folds are the dominant fabric in the Taconian klippen, and these structures are cut by the basal thrust faults. Locally the Grenville fabric and Taconian S1 are overprinted and reoriented by a Taconian S2 foliation. The syn-tectonic (Taconian D2) granite at Candlewood Lake intrudes both basement and cover rocks west of Cameron's Line. East of Cameron's Line, the dominant D2 fabric in the Ratlum Mountain and Rowe Schist dips below the Stockbridge Marble indicating a structural inversion. Fabric associated with movement on Cameron's Line is cryptic, however, as the fault is poorly exposed and the D2 foliation strongly overprints older fabrics. The syn-tectonic (Taconian D2) Brookfield Diorite intrudes all the rocks east of Cameron's Line.