FINITE STRAIN HETEROGENEITY AND VOLUME LOSS IN SLATES OF THE TACONIC ALLOCHTHON, VERMONT, USA

Slates of the Taconic Allochthon have ellipsoidal reduction spots whic h have been used to determine the finite state of strain at seven site s. The strain is highly heterogeneous at all scales, ranging from seve ral centimeters to many kilometers. Variations in X/Y ratios is small but variations in Y/Z ratios is large and this pattern is seen at all scales. The heterogeneity can be used to determine a strain path, whic h is nearly horizontal on a Flinn diagram. We propose that uniaxial fl attening associated with late stage cleavage development was accommoda ted by volume loss, and that the most highly strained sites have exper ienced an average 55% volume loss, at a minimum. Explaining our result s without volume loss requires a subhorizontal extension and creates s train compatibility problems. Consideration of the strain history of t hese rocks suggests that folding-related strains have been modified by later cleavage-related events, the last of which was uniaxial flatten ing accommodated by volume loss. The finite strains are reflective alm ost exclusively of the latest, cleavage producing strains.