TEXTURAL DEVELOPMENT IN AMPHIBOLITES OF THE SOUTHBURY AND NEWTOWN QUADRANGLES, WESTERN CONNECTICUT

This petrographic study examines amphibolites in central western Connecticut in the staurolite-kyanite zone of the Acadian orogeny. The amphibolites from the Southbury and Newtown quadrangles are dominantly schistose, containing moderately well foliated and lineated amphibole needles. Preliminary x-ray diffraction analysis is consistent with these amphiboles being hornblende. Rietveld refinements show that the amphibolites contain primarily plagioclase and amphibole, the latter between 20 and 80 wt. %. Some of the samples preserve crenulations showing that the dominant foliation (Sn) is predated by an earlier strong fabric Sn-1. This stage of fabric development also involved the growth of amphibole porphyroblasts. Both Sn-1 and porphyroblasts are pervasively overprinted by the dominant Sn foliation. Truncations of Sn-1 amphiboles by subhedral Sn amphiboles shows that the Sn fabric developed by a dissolution-precipitation creep mechanism. Sn fabrics are in turn overprinted by another generation of amphibole porphyroblasts but only in the southern Southbury quadrangle. Here the heat associated with the deformation that formed the foliation outlasted the strain, whereas in the north the deformation continued apparently into the lower amphibolite facies, coinciding with D4 of Scott (1974).