PENNSYLVANIAN TO PERMIAN LATERAL ESCAPE OF THE BRONSON HILL ARC AND CENTRAL MAINE BASIN IN SOUTHERN NEW ENGLAND: SIGNIFICANCE OF SINISTRAL KINEMATICS ALONG THE WESTERN BRONSON HILL SHEAR SYSTEM

Over a decade of research, founded on mapping, structural and kinematic analyses, evaluation of mineral parageneses, zircon and monazite geochronology, and synthesis with existing studies, has provided a new understanding that the post-Acadian played a significant role in the tectonic development of southern New England. Our work shows that plutons and stratified rocks of the Bronson Hill arc and Central Maine basin in Massachusetts record the cumulative effects of progressive partitioned dextral transpression throughout the Carboniferous. In contrast, the western half of the Bronson Hill throughout Connecticut, Massachusetts, and New Hampshire is characterized by sinistral/top-to-south deformation, including sinistral fabrics and kinematics in the Mt. Dumplin high strain zone and Bolton syncline, sinistral tectonites in the Glastonbury gneiss, top-to-south deformation associated with the Pelham dome, and sinistral deformation along the Westminster West fault. All of these structures have been subjected to various methods of geochronology, which all show that deformation was contemporaneous in the Upper Pennsylvanian-Permian. The timing coincides with dextral transpression to the east in the eastern Bronson Hill and Central Maine, and dextral strike-slip motion along the Norumbega fault system. Sinistral deformation is not expected within a model of dextral oblique convergence, however, all of the structures were temporally linked. The data can be reconciled within a model of lateral escape, where a crustal block was displaced northward, facilitated by conjugate strike-slip systems – the sinistral western Bronson Hill shear system in the west and the dextral Norumbega fault system in the east. Our data support and extend the original hypothesis by McWilliams et al. (2013). We further submit that this model can explain an assortment of enigmatic features in New England, including contrasting kinematics, differential exhumation, and the Pelham dome. We now know that much of the tectonometamorphic effects in southern New England are attributed to a period of oblique convergence and lateral escape in the Mississippian, rather than the Lower-Middle Devonian Acadian orogeny. This model may not be viable along the length of the Northern Appalachians due to the local geometric framework of convergence.