FORELAND BASIN DEVELOPMENT AND TECTONICS ON THE NORTHWEST MARGIN OF EASTERN AVALONIA

The early Palaeozoic convergence of Avalonia and Laurentia created a f oreland basin at the suture zone of the former Iapetus Ocean. Sediment ological and stratigraphic evidence of shallowing and contemporaneous shortening suggests that the southern part of the basin (the Windermer e Group) became detached from its basement in the late Ludlow, and beg an to invert. The detachment beneath the basin rooted into a northwest -dipping n-mid-crustal thrust system. Contemporaneous uplift to the no rth of the late Silurian basin involved shortening of the Avalonian fo reland basement by thrusting. Basin inversion occurred ahead of a sout heastward-advancing mountain front. We postulate a foreland (southeast ) prograding sequence of thrusting through the Ludlow in the Lake Dist rict. The basin continued to migrate onto the Avalonian foreland throu gh the early Devonian, ahead of an advancing orogenic wedge, finally c oming to a stop in the Emsian.