STRAIN ANALYSIS IN THE CONTACT AUREOLE OF THE VICTORY PLUTON, NE VERMONT

A number of mechanisms, each predicting different patterns of strain within a pluton's aureole, have been proposed to explain how space is made for plutons in the crust. This study uses the Fry (center-to-center) technique on contact metamorphic porphyroblasts surrounding the Victory Pluton in NE Vermont to test the whether the pattern of strain in the aureole is consistent with any of the proposed mechanisms.

The Victory Pluton is one of a group of plutons intruded in NE Vermont during the late stages of the Acadian Orogeny. Although it appears to cut regional structures, including the Monroe Fault, microstructural and metamorphic evidence suggests that fault movement continued during intrusion. Development of a syn- to post-contact metamorphic crenulation cleavage, pulled-apart andalusite porphyroblasts, flattened fibrolite clumps, and folded granitic veins suggest that deformation occurred away from the fault zone as well as within it.

Sixteen samples were collected from sites around the Victory Pluton. Of those samples, five had a sufficient density of porphyroblasts and were homogeneous enough to apply the Fry method. The orientations of the strain ellipsoids for the samples analyzed are similar in orientation. The long axes of the strain ellipsoids plunge predominantly towards the east, whereas the short axes of the ellipsoids plunge subhorizontally towards the south. There does not appear to be any significant pattern of subvertical elongation or concentric flattening around the pluton, such as should be associated with diapirism or balloon-style emplacement. These results indicate that the majority of syn-intrusion strain in the contact aureole of the Victory Pluton was caused by regional deformation, and that the emplacement mechanism for the pluton is most likely fault-related.