VARIATIONS IN SLATY CLEAVAGE AND STRETCHING LINEATION ORIENTATION IN THE TACONIC ALLOCHTHON, VERMONT AND NEW YORK

New and previously collected structural data were compiled to produce detailed maps of slaty cleavage (S₂) and stretching lineation (L₂) orientation in the Taconic slate belt. The area of study encompasses a 240 km² region between N43° 43’ and N43° 25’. In total, 1467 measurements of S₂ were compiled, 935 from previous work and 532 in this year’s study. 117 oriented samples were analyzed to determine the orientation of L₂, 57 from previous work and 60 in this year’s study. Contour interval maps of strike, dip, rake, and trend were constructed from these data and were placed as layers onto 1:48000 geologic maps.

The contour interval maps are consistent with two main structural domains previously recognized from changes in the orientation of regional-scale folds. The boundary between the two domains is transitional and located at approximately N43° 34’. In general, the northern domain has more homogenous orientations than the southern domain. In the northern domain the mean orientations of S₂ and L₂ are 013, 29 E and 111, 28, respectively. With the addition of 33 new sites to the original data set of 13 sites, the rake of L₂ on S₂ remained the same. The mean rake is 83° from the south, suggesting that the northern domain records a small component of strike-slip in addition to contractional deformation. In the southern domain, the mean orientations of S₂ and L₂ are 353, 43 E and 126, 37, respectively, and the mean rake of L₂ on S₂ is 59° from the south. The contour interval maps show a correlation between strike of S₂, dip of S₂, and rake of L₂ along strike of the entire study area and also within the southern domain. As S₂ strikes more towards the west, the dip of S₂ becomes increasingly steeper, and L₂ rakes at a smaller angle from the south. The central part of the southern domain shows the most extreme values of strike, dip, rake, and trend. The overall change in S₂ and L₂ orientation from north to south has previously been interpreted as resulting from transport of the southern domain across an Iapetan transform fault and related along-strike variation in orientation of the shear zone in which S₂ and L₂ formed. The new data imply that the shear zone also changes orientation within the southern domain.