Palaeomagnetic constraints on the evolution of the Caledonian-Appalachian orogen

Abstract

Late Proterozoic and Palaeozoic (pre-Permian) palaeomagnetic data from all regions involved in, or adjacent to, the Caledonian-Appalachian orogenic belt are reviewed. Between about 1100 and about 800 Ma the Laurentian and Baltic shields were close together, prior to the opening phase of the Caledonian-Appalachian Wilson cycle. The problems of tectonic interpretation of Palaeozoic palaeomagnetic data from within and around the belt derive mostly from differences of typically 10°-20 ° between the pole positions. These can variously be interpreted in terms of (i) relative displacements between different continents or terranes, (ii) differences in ages of remanence and (iii) aberrations due to inadequacy of data or geomagnetic complexity, and it is not always easy to discriminate between these alternatives. If the Pangaea A2 reassembly of continents around the northern and central Atlantic is taken as the end-product of Caledonian-Appalachian orogenesis, the following conclusions can be drawn.

Geomorphology of an Exhumed Carboniferous Paleosurface in the Southern Gaspé Peninsula, Québec: Paleoenvironmental and Tectonic Implications

“…All these structural zones were involved in the Middle Devonian Acadian orogeny, which evolved from purely compressive to transpressive tectonics (Béland, 1982;Kirkwood et al, 1995) as the Iapetus ocean closed (Kent and Opdyke, 1985;Briden et al, 1988;Kent and Keppie, 1988). The resulting structures are a set of open folds which are oriented nearly parallel, or at low angle, to major dextral strike-slip faults (Malo and Béland, 1989;Brisebois et al, 1992;Bourque et al, 1993;Kirkwood et al, 1995).…”

Tectonostratigraphie du carbonifère de la Gaspésie Québec Canada

“…They form a small inlier unconformably overlain by a succession of Siluro-Devonian rocks that occupies most of the southern half of the Gaspé Peninsula. Both sets of rocks were involved in the mid-Devonian Acadian orogeny, which is related to the final closure of the Iapetus Ocean Briden et al, 1988;Kent and Keppie, 1988).…”

“…They are related to regional shear at the level of the Iapetan suture while the Theic Ocean, southern extension of the then-already-closed Iapetus Keppie, 1985Keppie, , 1992Briden et al, 1988;Kent and Keppie, 1988;Reed et al, 1993), was still in the process of closing Barr, 1984;Fyffe and Barr, 1986;Waldron et al, 1989;Pe-Piper et al, 1991;MacDonald et al, 1992;Piper et al, 1993;Kontak, 1994). They are interpreted as horst structures induced by plutonic activity and would have served as intermittent sources for clastic sedimentation during Late Devonian and Mississipian times (St. Peter, 1993).…”

Geophysical framework and the Appalachian-Caledonide connection

“…Although details of the palaeomagnetically derived movements of crustal blocks within the Appalachian-Caledonide orogen are presented elsewhere (Briden et al 1988), a brief mention cannot be avoided in this introduction or its companion paper (Lefort et al 1987).…”

“…Most geophysical techniques (palaeomagnetism and geochronology are the prime exceptions) do not yield data that can be interpreted to give the timing of tectonic activity. Since palaeomagnetism is also dealt with in a companion paper (Briden et al 1988) and the chronological development of the orogen as a whole is the objective of the rest of this volume, interpretative remarks on these subjects will be kept to a minimum.…”