LATE PALEOZOIC TRANSPRESSION, EXTRUSION, AND LATERAL ESCAPE IN THE APPALACHIAN OROGEN OF SOUTHERN NEW ENGLAND, USA: THE INFLUENCE OF PROMONTORIES AND EMBAYMENTS ON AN OBLIQUE MARGIN

Bedrock mapping, structural analysis, documentation of kinematics and petrofabrics, and zircon and monazite geochronology are the basis for a new interpretation of the late Paleozoic (post-Acadian) tectonic evolution of south-central New England.

Early fabrics in the Central Maine and eastern Bronson Hill zones are characterized by planar foliations, subhorizontal to shallow-plunging lineations, and dextral kinematic indicators. As deformation progressed, structures and fabrics reflected an increased component of shortening, marked by tightening of west-dipping foliations, development of closed to isoclinal folds, reverse high strain zones, and reverse top-to-east kinematics. Syntectonic mineral assemblages that overprint peak regional high-grade assemblages show that cooling attended deformation, consistent with vertical exhumation attending deformation. New and published geochronology show that dextral transpression is immediately preceded by 355-360 Ma diorite and granite plutonism, and then progressed continually for ~50 Ma. The style of dextral transpression changes along strike, increasing in intensity and metamorphic grade to the south, while decreasing to the north.

In contrast, the western Bronson Hill is characterized by regional sinistral top-to-south deformation from Connecticut to southern New Hampshire, including two regional sinistral shear zones. This deformation preceded ~330-320 Ma staurolite-grade metamorphism and continued to ~295 Ma as shown by syntectonic monazite and an abundance of published data.

Dextral transpression was spatially and temporally linked to sinistral deformation, indicating that the dominant fabrics, structures, and mineral assemblages exposed in this area of New England were driven by progressive dextral transpression and north-directed lateral escape of a crustal block in the Carboniferous. These features are attributed to a period of oblique convergence between Laurentia and Avalon/Meguma in the Mississippian, rather than the Early to Middle Devonian Acadian Orogeny as has long been proposed. The geographic location between the northern edge of the New York Promontory and Quebec Embayment provided a mechanism for lateral escape of the crustal block and the lateral variation of the style of dextral transpression.