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Ordovician and Siluro-Lower Devonian magmatic rocks in the northern Appalachians south of the Iapetus suture are currently interpreted as distinct belts composed of multiple, small, peri-Gondwanan terranes that amalgamated during the sequential closures of Iapetus (latest Ordovician), the Tetagouche backarc basin (early Silurian), the Acadian seaway (Siluro-Devonian), and the Rheic Ocean (Devono-Carbonferous) (multiple terrane model). Here, the Siluro-Lower Devonian magmatic belts are shown to have slab failure affinities and together with the Ordovician arcs form paired belts parallel to the Iapetus suture, which suggests that they were emplaced along the common, peri-Avalonian margin during pre- and post-collisional processes. The Iapetan suture and the paired belts are inferred to repeat in Atlantic Canada due to dextral, strike-slip processes of mid-Late Devonian or younger age (terrane wreck model). In Newfoundland, the repetition is inferred to be the result of oblique, dextral offset of ca. 250 km. In the Quebec Embayment, the Iapetan paired magmatic belts are repeated twice in the limbs of a Z-shaped orocline related to oblique, dextral offsets of ca. 1200 km of the southern limb. Limited Siluro-Devonian paleomagnetic data indicate no paleolatitudinal differences across the Iapetus suture, however ca. 100[degrees] post-mid Silurian clockwise rotation is indicated for the middle fold limb; these data favour the terrane wreck model. The terrane wreck model results in a simple tectonic scenario of southerly subduction of Iapetus beneath a single ribbon continent (Avalonia sensu lato) that was subsequently deformed. Key words: Appalachians, Ordovician arcs, Silurian--Lower Devonian slab failure, palinspastics, oroclines, Ganderia, terrane wreck. Desrochesmagmatiques d'age ordovicien et silurien-devonien inferieur dans le nord des Appalaches au sud de la suture de Iapetus sont actuellement interpretees comme representant des ceintures distinctes composees de multiples petits terranes perigondwaniens qui se sont amalgames durant les fermetures successives de Iapetus (Ordovicien terminal), du bassin d'arriere-arc de Tetagouche (Silurien precoce), du bras de mer acadien (Silurien--Devonien) et de l'ocean Rheique (Devonien--Carbonifere) (le << modele des terranes multiples >>). Nous demontrons que les ceintures magmatiques d'age silurien--devonien inferieur presentent des affinites de rupture de plaque et que, avec les arcs ordoviciens, elles forment des ceintures jumelees paralleles a la suture de Iapetus, ce qui indiquerait qu'elles ont ete mises en place le long de la marge periavalonienne commune durant des processus pre- et post-collision. Nous inferons que la suture de Iapetus et les ceintures jumelees se repetent au Canada atlantique en raison de processus de decrochement dextre actifs au milieu du Devonien tardif ou apres (le << modele d'empilement de terranes >>). A Terre-Neuve, nous inferons que la repetition est le resultat d'une translation dextre oblique sur environ 250 km. Dans le rentrant de Quebec, les ceintures magmatiques jumelees iapetennes sont repetees deux fois dans les flancs d'un oroclinal en Z associe a des translations dextres obliques d'environ 1200 km du flanc sud. Si des donnees paleomagnetiques limitees pour le Silurien--Devonien ne revelent aucune difference de paleolatitude de part et d'autre de la suture de Iapetus, quelque 100[degrees] de rotation horaire apres le Silurien moyen sont indiques pour le flanc median du pli; ces donnees favorisent le modele d'empilement de terranes. Ce modele se traduit par un scenario tectonique simple de subduction vers le sud de Iapetus sous un seul continental rubane (l'Avalonie au sens large) qui a par la suite ete deforme. [Traduit par la Redaction] Mots-cles : Appalaches, arcs ordoviciens, rupture de plaque au Silurien--Devonien inferieur, palinspatique, oroclinaux, Ganderie, empilement de terranes., Introduction The formation and deformation of orogenic belts is fundamental to plate tectonics and informs our evolving understanding of convergent margin processes. A convergent margin preserves a combination of evidence [...]

Current interpretations of the geology of Cape Breton Island suggest that it exposes a complete cross-section of the Appalachians from Laurentia across Iapetan vestiges to Avalonia. Crucial to this view is the presence of ca. 1 Ga plutons, including anorthosites, which have been regarded as correlatives of Grenvillian basement, a correlation that overlooks the fact that Avalonia is also underlain by a ca. 1 Ga basement. We analyzed zircons from the Red River anorthosite (Blair River Complex, northwestern Cape Breton Island) previously dated as ca. 1.1 Ga: they yielded 421 ± 3 Ma intrusive ages with older ages between 865 ± 18 Ma and 1044 ± 20 Ma inferred to be either xenocrysts derived from the country rock or from the source. Implications of these data suggest that the accompanying low pressure granulite-amphibolite facies metamorphism of the Blair River Complex is either the root of a 440–410 Ma, magmatic belt produced during slab break-off or relict ca. 1 Ga basement. The Blair River Complex occurs in a NNE-SSW, sinistral positive flower structure that progresses upwards from a Neoproterozoic rifted arc through a low grade upper Ordovician-Silurian overstep sequence to amphibolite facies fault slices, capped by the low-pressure, granulite facies rocks (Blair River Complex). The correlation of Neoproterozoic, rifted arc units across most of Cape Breton Island suggests it represents the deformed northwestern margin of Avalonia intruded by a Silurian-Lower Devonian magmatic belt. As the geological record in the Blair River Complex is similar to both Grenvillian and Avalonian basements, its provenance is equivocal, however Pb isotopic data suggest the Blair River Complex has Amazonian (≈Avalonia) affinities. Thus, Cape Breton Island, rather than representing a complete cross-section of the Appalachian orogen, is part of pristine—deformed Avalonia with a positive flower structure exposing a cross-section of Avalonian crust. Unlabelled Image • 420 Ma intrusive age for anorthosite supercedes previous 1 Ga age • Cape Breton Highlands is a +ve flower structure in Silurian magmatic belt. • Pb isotopes confirm Avalonian affinity of entire Cape Breton Island. [ABSTRACT FROM AUTHOR]

Two end-member models have been invoked to accommodate the Mesozoic dispersal of the supercontinent Pangaea. In one end-member, the opening of the Atlantic Ocean is inferred to have been balanced by the closure of the Panthalassan Ocean related to subduction off the western margins of the Americas. In the other end-member model, the opening of the Atlantic Ocean is accommodated by the closure of the paleo-Tethys and Tethys oceans linked to subduction off the southern margins of Eurasia. Here, I re-evaluate global plate circulation data compiled for the middle Mesozoic Era. The present evaluation confirms that closure of the paleo-Tethys and Tethys oceans compensated for the early opening of the central Atlantic and proto-Caribbean oceans. This result implies that the tectonic evolution of the North American Cordillera was independent from the processes governing Pangaea breakup in the Jurassic and Early Cretaceous Periods. As well, the opening Atlantic and closing Tethys realm must have been tectonically connected through the Mediterranean region in terms of a transform fault or point yet to be factored into geological interpretations. Tight geometric and kinematic correlations evident between the opening Atlantic and closing Tethyan domains can be demonstrated, which are most readily explained if the forces causing Pangaea breakup were transmitted from the Tethyan domain into the Atlantic domain, and not vice versa. Thus, slab sinking-based forces produced during the evolution of the Tethyan subduction zones are hypothesized to have controlled the early Atlantic breakup of Pangaea. [ABSTRACT FROM AUTHOR]

Currently, two basic models describe the genesis of the Caribbean Plate: (i) a Pacific model that derives the Caribbean Plate off southern Mexico and (ii) an in situ model. The Pacific model requires the 1100–1400 km sinistral displacement recorded across the Cayman Trough to pass through the Gulf of Tehuantepec into the Middle America Trench, but no evidence of such a connection exists. The in situ model is inconsistent with the 1100–1400 km displacement across the Cayman Trough. A way through this impasse is indicated by the northwestward curvature of active oblique reverse to sinistral transcurrent faulting in southeast Mexico. Extending this potential solution back to ca. 80 Ma forms the basis of the new Pirate model, in which the Caribbean Plate and the Chortis and Chiapas blocks are derived from the northwest by anticlockwise rotation during the latest Cretaceous and Cenozoic. Following passage of the Chortis Block, the northern and southern parts of the Yucatan block collided along the intra-Yucatan suture, producing the 11–9 Ma Chiapas fold-and-thrust belt. The Pirate model accounts for the N-trending segment of the Laramide Sierra Madre Oriental–Zongolica foldbelts by anticlockwise drag, Palaeogene palaeocanyons, the second, 66–40 Ma phase of rifting in the western Gulf of Mexico, and post-10 Ma extension in the Chortis Block (Chortis–Sula rift province). Impingement of the East Pacific Rise on the Middle America Trench led to modification of the Pirate model involving subduction erosion of the ∼200 km-wide, Eocene–Oligocene forearc at ca. 25 Ma, opening of the Gulf of California at ca. 6 Ma, and birth and ESE movement of the Southern Mexico block (<5 Ma) followed by its fragmentation. The Pirate mechanism indicates that the North American Plate is relatively weak and so tears and rotates into the trailing edge of the Caribbean Plate. [ABSTRACT FROM AUTHOR]

Understanding Pangea breakup requires a robust reconstruction, and this article focuses on the Middle America sector of the supercontinent. Although most Pangean reconstructions locate the Yucatan Block along the southern USA, the Chortis Block is generally placed off southern Mexico (Pacific model), undergoing sinistral relative motion during the Mesozoic and Cenozoic. However, the Pacific model is inconsistent with the absence of a Cenozoic fault linking the Cayman transforms and the Middle America Trench. We present an alternative Pangean reconstruction, where both the Yucatan and Chortis Blocks are placed in the future Gulf of Mexico, moving Mexico westwards along the Mojave–Sonora megashear to accommodate overlap with South America. Subsequent Mesozoic and Cenozoic evolution is inferred to have occurred in two stages: (i) Jurassic clockwise rotation along the Mojave–Sonora and West Florida megashears, followed by (ii) Cenozoic anticlockwise rotation along the Sierra Madre Oriental and East Yucatan megashears. The first stage is linked to the breakup of Pangea where the Gulf of Mexico formed as a pull-apart basin. The second stage is related to the evolution of the Caribbean where the Chortis and Yucatan Blocks rotated into the trailing side of the Caribbean Plate (pirate model). The new reconstruction is consistent with major parameters, such as (i) gravity, magnetic, and palaeomagnetic data; (ii) the westward continuation of the Cayman transform faults through the Chiapas foldbelt and along the N–S front of the Sierra Madre Oriental foldbelt; (iii) the 27–19 Ma removal of the southern Mexican forearc; (iv) offset of the Cretaceous volcanic arc (Guerrero-Suina); (v) the deflection of the Laramide orogen (Sierra Madre Oriental–Zongolica–Colon); and (vi) the continuity of Cretaceous platformal carbonates containing Caribbean fauna across Middle America. In this latter context, the Motagua high-pressure belt is interpreted as a Cretaceous extrusion zone into the upper plate above a subduction zone rather than as an oceanic suture. [ABSTRACT FROM AUTHOR]

Both the timing and mechanism for the removal of a ∼150-250 km wide forearc block from southern Mexico during the Cenozoic are controversial. Principal competing hypotheses are (1) removal due to sinistral strike-slip shear, in which slow, diachronous removal of the Chortis Block throughout the Cenozoic is inferred, and (2) removal due to subduction erosion, in which rapid removal of a large forearc block during the late Oligocene/early Miocene is inferred to be synchronous with the rapid landward migration of the southern Mexican arc. New data indicate northeast-directed back-thrusting in (1) the Chacalapa shear zone west of −96.5°E, with the timing of shear deformation bracketed by a 25.5 ± 0.5 Ma U/Pb zircon age and a 20.7 ± 0.6 Ma Ar/Ar biotite age, and (2) in an unnamed shear zone to the south, with the timing of deformation bracketed by a 27.5 ± 0.5 Ma U/Pb zircon age and a 25.1 ± 0.2 Ma Ar/Ar biotite age. Zircon and biotite ages date the emplacement and cooling of deformed plutons, respectively. The observed back-thrusting is consistent with a model of forearc removal due to subduction-erosion processes because it is evidence for subduction-orthogonal shortening occurring within the upper plate just before the landward migration of the southern Mexican arc. Rapid subduction of the southern Mexican forearc could have recycled continental lithosphere into the upper mantle at a rate up to half the global average rate of subduction erosion during the late Oligocene/early Miocene. [ABSTRACT FROM AUTHOR]