CONFIGURATION, TIMING, AND IMPACTS OF THE ARRIVAL OF AVALONIA AND MEGUMA IN THE NORTHERN APPALACHIAN OROGEN

The Silurian-Devonian Acadian orogeny in the northern Appalachian orogen has been generally attributed to the arrival of the Avalonian microcontinent. Avalonia docked against a “Laurentian margin” already much modified from its original rifted shape by earlier Paleozoic events related to the addition of Iapetan continental and oceanic fragments (arcs, backarcs, and oceanic crust) and to the arrival of the Ganderian microcontinent. The docking of Avalonia is generally held responsible for the Acadian orogeny superimposed on that composite Laurentian margin in the Early Devonian. Meguma arrived later in the Devonian during an event provisionally termed the Neoacadian orogeny, although the effects of that event are seen mainly in Meguma itself. The arrival of Meguma was protracted because of the subsequent arrival of the rest of Gondwana during the Carboniferous. This long history of Avalonia-Meguma-Gondwana interactions left a complex pattern of faults, basins/uplifts, and magmatic activity. It also left a legacy in the development of the Maritimes Basin in the Carboniferous-Permian, and in the pattern of subsequent Mesozoic extension when Africa departed. The area experienced a complex interplay of strike-slip, transtensional, transpressional, and salt tectonics. The original promontory-reentrant shape of the Late Neoproterozoic rifted margin of Laurentia in what is now the eastern Canada exerted a strong influence on the pattern of terrane accretion that persisted through the docking of Ganderia, Avalonia, Meguma, and Gondwana.