Chapter 11 - Mesozoic tectogenesis: development and deformation of ‘Newark’ rift zones in the Appalachians (with special emphasis on the Hartford basin, Connecticut)

Abstract

Mesozoic tectogenesis in the Appalachians was dominated by deformation along pre-existing zones of weakness. NW-SE extension in the Late Triassic and Early Jurassic resulted in dip-slip motion along grain-parallel faults, and development of extensive rift systems (rifting phase). Subsidence was followed by isostatic uplift and differential tilting. In the Middle Jurassic the NE-trending structures became loci for subhorizontal sinistral shearing. This event is referred to as the shifting phase. The shearing implies major changes in the spreading configuration that may have been brought about by independent motion of the African and North American plates or by a change in the absolute motion direction of North America. The drifting phase began in the Late Jurassic. Strain release in this period predominantly occurred along the same NE trending (grain-parallel) structures and involved both normal dip-slip (extension) and reverse-slip motion or thrusting often with a dextral strike-slip component (compression). The responsible compressive stress may have originated from processes related to basal drag of the North American continent. Strain appears to have decreased with time and to have become less penetrative.