TRANSPRESSION, EXTRUSION, AND LATERAL ESCAPE IN SOUTHERN NEW ENGLAND AND SCALE-DEPENDENT RESPONSE OF STRAIN PARTITIONING

Dextral transpression was a consequence of oblique convergence in the northern Appalachians during the middle to late Paleozoic, and has been documented from the Canadian Maritimes into Maine. It seems intuitive to infer that dextral transpression likely continues further south along strike of the orogen. Structures and fabrics in the Bronson Hill zone of southern New England record a wide range of states of finite strain, from contraction to local constriction, along with shear zones of conjugate kinematics. Structural relationships and geochronology indicate that this phase of heterogeneous deformation was contemporaneous at 330-300 Ma. At the multi-kilometer scale of the entire study area, strike-slip deformation has been largely partitioned into relatively thin zones of metastratified rocks, while contraction has been predominantly accommodated in relatively wide, intervening zone of granitic orthogneiss. These structures reflect partitioned dextral transpression and vertical exhumation, coeval with lateral escape of the orthogneiss, facilitated by bounding conjugate shear zones. At this scale, partitioning is thought to be the result of the pre-existing lithologic architecture, which created rheological contrasts/mechanical instabilities. Strain hardening associated with higher degrees of coaxial strains in the orthogneiss may also have assisted with syn-tectonic partitioning. Within these individual regional structures, structural subdomains (up to 1 km) reflect quasi-homogeneous transpression that exist between the resolvable scale of effects of partitioning at the multi-kilometer (regional) and meter scales (outcrop). Any incompatibilities between laterally adjacent homogeneous subdomains could have been maintained by partitioning at the meter-scale, which would explain the range of outcrop-scale structures not related to lithologic variations.