Middle to late Paleozoic Acadian orogeny in the northern Appalachians: A Laramide-style plume-modified orogeny?

The Laramide orogeny of the western United States is proposed as a modern a nalogue for the Silurian-Devonian Acadian orogeny and subsequent diachronou s, voluminous, short-lived magmatism and basin formation in the northern Ap palachians. Shallowing of the Benioff zone accounts for several enigmatic f eatures associated with plate convergence in the northern Appalachians, inc luding (1) Wenlockian-Ludlovian termination of are-related magmatism in the Avalon terrane followed by a period of relative magmatic quiescence from 3 95 to 380 Ma, and (2) diachronous migration of the Acadian deformation fron t from ca, 415 Ma in the southeast to ca, 370 Ma in the northwest, extendin g more than 600 km into the continental interior. The flattening of the sub duction zone is attributed to overriding of a plume by the convergent margi n, which may explain (1) the abrupt termination of magmatic quiescence by 3 80-370 Ma, and voluminous felsic magmatism and production of plume-related lamprophyres in the southeast (Meguma terrane) as the plume thermally erode d the oceanic lithosphere, causing melting of the lower crust; (2) Late Dev onian regional high-temperature, low-pressure metamorphism in the Meguma te rrane related to the thermal anomalies above a plume; (3) synchronous Devon ian emplacement of Meguma gold deposits and associated siderophile elements , possibly derived from fluid circulation above an ascending plume; (4) rap id Late Devonian uplift and erosion of as much as 10 km due to dynamic upli ft over a plume; (5) migration of magmatism to the north (Avalon terrane, C obequid highlands) so that plume-related Carboniferous magmatism occurred i n and around the Carboniferous-Permian Maritimes basin; (6) the high-densit y lens at the base of the crust beneath the Maritimes basin, the product of plume-derived underplated mafic racks; and (7) a subsidence mechanism for formation of the Maritimes basin by cooling of a decapitated plume head.