A PETROLOGICAL AND GEOCHEMICAL INVESTIGATION OF THE AMPHIBOLITES AND GREENSTONES IN THE CONNECTICUT VALLEY SYNCLINORIUM

Diverse lithologic and tectonic settings inferred through petrographic and geochemical analysis suggest that two bands of the Ordovician Oronoque member of the Derby Hill Schist should be considered individual lithologic units. In the west the Oronoque member is associated with the Derby Hill Schist and the Wepawaug Schist and may have been a product of shearing along the East Derby Shear Zone. In the east the unit is intercalated between the Maltby Lakes Metavolcanics and may be a low-grade metamorphosed volcanogenic sediment.

Geochemical XRF analyses of amphibolites associated with these two bands of the Oronoque member show a higher degree of affinity with the local country rocks then with each other. This suggests that these rocks may not correlate across a regional syncline as previously suggested (Fritts, USGS, 1965) but may have been sediments on opposite sides of a closing basin with a passive margin in the west and a volcanic arc in the east. The sediments were juxtaposed and folded against a rigid backstop during the Acadian orogeny and reworked during the Alleganian to form their current exposure pattern.