Evolution of the Iapetus Ocean and its borders in pre-Arenig times: a synthesis

Abstract

Summary On the margins of the Laurentian continent the interval c. 800-492 Ma was dominated by (1) rifting involving continental crust and (2) rift sedimentation with or without related volcanicity and plutonism, culminating in (3) the formation of the Iapetus Ocean and succeeded by (4) initial phases of compressional tectonics. The latter involved the approach of volcanic island-arc systems and the partial or complete obduction of ophiolites of the oceanic crust cutting through the slope-rise prism and, at least in some parts of the orogen, being thrust onto the continental-shelf deposits in the Cambrian and Tremadocian. These processes led to the closing of the ocean in the mid-Ordovician Taconian and the Silurian Caledonian orogenies. The earliest and most complete pre-Arenig orogenic movements are recorded in the Finnmarkian orogeny, including obduction of ophiolites in Scandinavia (520–480 Ma). Related sedimentation gaps, preceded by deformation and ophiolite obduction and/or uplift, were accompanied by tectonic melange development and/or volcanicity. These features are recorded widely from northern Britain and Ireland (Grampian orogeny), and from the Appalachians of Newfoundland (Burlington orogenic episode), Maine, USA, and Quebec, Canada (Penobscot orogeny). Movements interpreted as relating to the Penobscotian are now recognized as widespread in the US Appalachians. The Sardic orogenic phase in southern Europe ( c. 510 Ma) is associated with plutonism and metamorphism and may be related to late Cadomian III orogenic movements. In the southeastern landmasses of Gondwanaland (Avalonian-Cadomian-Pan-African) essentially the same time interval ( c. 800–492 Ma) was also dominated initially by rifting of continental crust overlain by late Proterozoic shelf deposits and the obduction and folding of ophiolites (Cadomian I orogeny) and underlying rocks, followed by intrusion of late- to post-tectonic plutons (Bleida). Cadomian II resulted in the deposition of coarse clastics, volcanics and glacigenic sediments (Tiddiline), and folding, erosion and deposition of a thick wedge of late Proterozoic carbonate and clastic rocks with alkaline volcanics (Adoudounian) overlain conformably by lower and middle Cambrian that are overlain disconformably by Tremadocian clastic sediments. During the rifting phase continental fragments drifted away and/or became volcanic arcs with subduction zones and back-arc basins constituting the weakly orogenic Avalonian terrane to the W and the strongly orogenic but discontinuous belt forming a terrane characterized by Cadomian fragments between the Avalonian terrane of the British Isles and the W African craton. Stratigraphic columns and schematic time-slice stratigraphic profiles with interpreted tectonic environments from various parts of the orogen provide comparisons and contrasts in stratigraphic, faunal, structural, volcanic, plutonic and metamorphic evolution.

The Palaeozoic evolution in the Alps: from Gondwana to Pangea

“…Parallels to one of the "transcontinental" palaeotectonic reconstructions (St. Julien and Hubert 1975;Keppie 1977;Rast and Skehan 1983;Stanley and Ratcliffe 1985;Skehan 1988;Lorenz and Nicholls 1984;Keppie and Dallmeyer 1990;Ziegler 1989Ziegler , 1990Matte 1995Matte , 1996Rey et al 1997) and northwestern Africa, an intracontinental evolution appears to apply after the Late Devonian (Piqué and Skehan 1992). Zwart and Dornsiepen (1978) described Acadian (350-400 Ma), Sudetic-Asturian (300-340 Ma), and Alleghenyan (240-270 Ma) stages of tectonic evolution, following more or less an older suture between Laurussia and Gondwana, Le Fort (1989) delineated the chronology of accretion between America, Europe and Africa, and Ziegler (1989Ziegler ( , 1990 presented the accretionary history between Gondwana and Laurussia.…”

Provenance of late Carboniferous sandstones in the Pennine Basin (UK) from combined heavy mineral, garnet geochemistry and palaeocurrent studies

“…Furthermore, zircon age data rule out significant contributions from the Mona Complex, since the westerly derived detritus lacks late Precambrian to early Cambrian zircons that would be associated with derivation from this complex . Possible ultramafic complexes further afield include large masses of ophiolitic material inferred to have been emplaced across Ireland during the Ordovician collision of an oceanic arc with the Laurentian continent (Dewey and Mange, 1999), or similar slices of oceanic crust obducted farther west in Newfoundland, during the same tectonic episode (Skehan, 1988). The detrital zircon age spectrum from the Clifton Rock, one of the western-derived sandstones, indicates that the detritus was derived from a Laurentian-Baltican terrain.…”

Origin and evolution of the Precordillera terrane of western Argentina: A drifted Laurentian orphan

“…At present, studies of the internal architecture and lateral relationships between the Precordilleran units are still limited. Nevertheless, it is reasonable to suggest, on the basis of process-oriented facies analysis, that the Argentine Precordillera is somewhat incompletely preserved (Cañas, 1995a, this volume;Keller, 1996), and it might have been at least 400-500 km wide on the basis of comparisons with the Appalachian carbonate platform (Skehan, 1988;. Hence, what is preserved and exposed of the Precordilleran platform is only part of the original extent.…”