Ediacaran–Middle Paleozoic Oceanic Voyage of Avalonia from Baltica via Gondwana to Laurentia: Paleomagnetic, Faunal and Geological Constraints

Current Ediacaran–Cambrian, paleogeographic reconstructions place Avalonia, Carolinia and Ganderia (Greater Avalonia) at high paleolatitudes off northwestern Gondwana (NW Africa and/or Amazonia), and locate NW Gondwana at either high or low paleolatitudes. All of these reconstructions are incompatible with 550 Ma Avalonian paleomagnetic data, which indicate a paleolatitude of 20–30ºS for Greater Avalonia and oriented with the present-day southeast margin on the northwest side. Ediacaran, Cambrian and Early Ordovician fauna in Avalonia are mainly endemic, which suggests that Greater Avalonia was an island microcontinent. Except for the degree of Ediacaran deformation, the Neoproterozoic geological records of mildly deformed Greater Avalonia and the intensely deformed Bolshezemel block in the Timanian orogen into eastern Baltica raise the possibility that they were originally along strike from one another, passing from an island microcontinent to an arc-continent collisional zone, respectively. Such a location and orientation is consistent with: (i) Ediacaran (580–550 Ma) ridge-trench collision leading to transform motion along the backarc basin; (ii) the reversed, ocean-to-continent polarity of the Ediacaran cratonic island arc recorded in Greater Avalonia; (iii) derivation of 1–2 Ga and 760–590 Ma detrital zircon grains in Greater Avalonia from Baltica and the Bolshezemel block (NE Timanides); and (iv) the similarity of 840–1760 Ma TDM model ages from detrital zircon in pre-Uralian–Timanian and Nd model ages from Greater Avalonia. During the Cambrian, Greater Avalonia rotated 150º counterclockwise ending up off northwestern Gondwana by the beginning of the Ordovician, after which it migrated orthogonally across Iapetus to amalgamate with eastern Laurentia by the Late Ordovician–Early Silurian. SOMMAIRELes reconstitutions paléogéographiques courantes de l’Édiacarien-Cambrien placent l’Avalonie ,la Carolinia et la Ganderia (Grande Avalonie) à de hautes paléolatitudes au nord-ouest du Gondwana (N-O de l'Afrique et/ou de l'Amazonie), et placent le N-O du Gondwana à de hautes ou de basses paléolatitudes.  Toutes ces reconstitutions sont incompatibles avec des données avaloniennes de 550 Ma, lesquelles indiquent une paléolatitude de 20-30º S pour la Grande Avalonie et orientée à la marge sud-est d’aujourd'hui sur le côté nord-ouest.  Les faunes édicacariennes, cambriennes et de l'Ordovicien précoce dans l’Avalonie sont principalement endémiques, ce qui permet de penser que la Grande Avalonie était une île de microcontinent.  Sauf pour le degré de déformation édiacarienne, les registres géologiques néoprotérozoïques d’une Grande Avalonie légèrement déformée et ceux du bloc intensément déformé de Bolshezemel dans l'orogène Timanian dans l’est de la Baltica soulèvent la possibilité qu'ils aient été à l'origine de même direction,  passant d'une île de microcontinent à une zone de collision d’arc continental, respectivement.  Un tel emplacement et une telle orientation sont compatibles avec: (i) un contexte de collision crête-fosse à l’Édiacarien (580-550 Ma) se changeant en un mouvement de transformation le long du bassin d’arrière-arc; (ii) l’inversion de polarité de marine à continentale, de l’arc insulaire cratonique édicarien observé dans la Grande Avalonie; (iii) la présence de grains de zircons détritiques de 1 à 2 Ga et 760-590 Ma de la Grande Avalonie issus de la Baltica et du bloc Bolshezemel (N-E des Timanides); et (iv) la similarité des âges modèles de 840-1760 Ma TDM de zircons détritiques pré-ourallien-timanien, et des âges modèles Nd de la Grande Avalonie.  Durant le Cambrien, la Grande Avalonie a pivoté de 150° dans le sens antihoraire pour se retrouver au nord-ouest du Gondwana au début de l'Ordovicien, après quoi elle a migré orthogonalement à travers l’océan Iapetus pour s’amalgamer à la bordure est de la Laurentie à la fin de l’Ordovicien-début du Silurien

Evidence of a collision between the Yucatán Block and Mexico in the Miocene

We present the evidence for an anomalous southwest-dipping slab in southern Mexico. The main evidence comes from a clear receiver function image along a seismic line across the Isthmus of Tehuantepec and is also supported by a previous global tomographic model. The slab dips at 35°, is approximately 250 km in length and appears to truncate the Cocos slab at about 120 km depth. We hypothesize that the slab was created by subduction of oceanic lithosphere prior to the collision of the Yucatán Block with Mexico at approximately 12 Ma. This scenario would explain the Chiapas Fold and Thrust Belt as the product of this collision, and its age constrains the date of the event to be in the Miocene

Ediacaran–Middle Paleozoic Oceanic Voyage of Avalonia from Baltica via Gondwana to Laurentia: Paleomagnetic, Faunal and Geological Constraints

Current Ediacaran–Cambrian, paleogeographic reconstructions place Avalonia, Carolinia and Ganderia (Greater Avalonia) at high paleolatitudes off northwestern Gondwana (NW Africa and/or Amazonia), and locate NW Gondwana at either high or low paleolatitudes. All of these reconstructions are incompatible with 550 Ma Avalonian paleomagnetic data, which indicate a paleolatitude of 20–30ºS for Greater Avalonia and oriented with the present-day southeast margin on the northwest side. Ediacaran, Cambrian and Early Ordovician fauna in Avalonia are mainly endemic, which suggests that Greater Avalonia was an island microcontinent. Except for the degree of Ediacaran deformation, the Neoproterozoic geological records of mildly deformed Greater Avalonia and the intensely deformed Bolshezemel block in the Timanian orogen into eastern Baltica raise the possibility that they were originally along strike from one another, passing from an island microcontinent to an arc-continent collisional zone, respectively. Such a location and orientation is consistent with: (i) Ediacaran (580–550 Ma) ridge-trench collision leading to transform motion along the backarc basin; (ii) the reversed, ocean-to-continent polarity of the Ediacaran cratonic island arc recorded in Greater Avalonia; (iii) derivation of 1–2 Ga and 760–590 Ma detrital zircon grains in Greater Avalonia from Baltica and the Bolshezemel block (NE Timanides); and (iv) the similarity of 840–1760 Ma TDM model ages from detrital zircon in pre-Uralian–Timanian and Nd model ages from Greater Avalonia. During the Cambrian, Greater Avalonia rotated 150º counterclockwise ending up off northwestern Gondwana by the beginning of the Ordovician, after which it migrated orthogonally across Iapetus to amalgamate with eastern Laurentia by the Late Ordovician–Early Silurian. SOMMAIRELes reconstitutions paléogéographiques courantes de l’Édiacarien-Cambrien placent l’Avalonie ,la Carolinia et la Ganderia (Grande Avalonie) à de hautes paléolatitudes au nord-ouest du Gondwana (N-O de l'Afrique et/ou de l'Amazonie), et placent le N-O du Gondwana à de hautes ou de basses paléolatitudes.  Toutes ces reconstitutions sont incompatibles avec des données avaloniennes de 550 Ma, lesquelles indiquent une paléolatitude de 20-30º S pour la Grande Avalonie et orientée à la marge sud-est d’aujourd'hui sur le côté nord-ouest.  Les faunes édicacariennes, cambriennes et de l'Ordovicien précoce dans l’Avalonie sont principalement endémiques, ce qui permet de penser que la Grande Avalonie était une île de microcontinent.  Sauf pour le degré de déformation édiacarienne, les registres géologiques néoprotérozoïques d’une Grande Avalonie légèrement déformée et ceux du bloc intensément déformé de Bolshezemel dans l'orogène Timanian dans l’est de la Baltica soulèvent la possibilité qu'ils aient été à l'origine de même direction,  passant d'une île de microcontinent à une zone de collision d’arc continental, respectivement.  Un tel emplacement et une telle orientation sont compatibles avec: (i) un contexte de collision crête-fosse à l’Édiacarien (580-550 Ma) se changeant en un mouvement de transformation le long du bassin d’arrière-arc; (ii) l’inversion de polarité de marine à continentale, de l’arc insulaire cratonique édicarien observé dans la Grande Avalonie; (iii) la présence de grains de zircons détritiques de 1 à 2 Ga et 760-590 Ma de la Grande Avalonie issus de la Baltica et du bloc Bolshezemel (N-E des Timanides); et (iv) la similarité des âges modèles de 840-1760 Ma TDM de zircons détritiques pré-ourallien-timanien, et des âges modèles Nd de la Grande Avalonie.  Durant le Cambrien, la Grande Avalonie a pivoté de 150° dans le sens antihoraire pour se retrouver au nord-ouest du Gondwana au début de l'Ordovicien, après quoi elle a migré orthogonalement à travers l’océan Iapetus pour s’amalgamer à la bordure est de la Laurentie à la fin de l’Ordovicien-début du Silurien

Subduction erosion modes: comparing finite element numerical models with the geological record

During subduction erosion, the upper plate is tectonically eroded by the subducting plate and carried into the mantle. The geological record suggests that subduction erosion is a fundamental process at subduction margins; however the underlying causes are not well constrained. Finite-element numerical models of ocean–continent subduction are used to investigate the roles of crustal frictional strength, subduction angle, and convergence rate in subduction erosion processes. Subduction erosion occurs in models in which the plate boundary zone is moderately strong, due to either high frictional strength or shallow angle of subduction. The models exhibit two distinct modes of subduction erosion: (1) steady, with slow trench migration rates (>> 15 km Ma− 1), subsidence at the end of the process, and an increase in the angle of subduction, in which a large block of continental forearc is removed. The unsteady mode is compatible with the sudden migration of the volcanic arc into the continental interior, a concurrent hiatus in arc volcanic production, and geochemical signatures showing crustal (forearc) contamination in the magma source region when arc volcanism renews in its new location. Both modes are inhibited by the presence of a thick sediment layer within the subduction zone, and neither mode requires the presence of topographic asperities on the lower plate. In natural subduction zones, subduction erosion may initially occur through steady erosion at the edge of the continental plate. As material is removed, the subduction angle may gradually decrease, increasing the strength of the plate boundary zone. The increased strength may lead to failure in the continental interior, unsteady removal of a large forearc block and relocation of the subduction zone into the upper plate where the cycle may repeat. The proposed cycle may explain observed patterns in the Andean margin, including steady and unsteady erosion recorded in the geological record and along-strike variation in present-day subduction angles

Subduction erosion processes with application to southern Mexico

Finite-element numerical models of ocean-continent subduction are used to investigate the roles of crustal frictional strength, subduction angle, and convergence rate in subduction erosion processes. These models exhibit two distinct modes of subduction erosion: (1) slow and steady, removing small blocks of material continually, and (2) fast and non-steady, removing a large forearc block in a single event. The slow mode, called edge-weakening subduction erosion, is enhanced by steeper subduction angles but acts to shallow the subduction angle at crustal depths. The fast mode, called internal-weakening subduction erosion, is enhanced by shallow subduction angles but acts to steepen the subduction angle at crustal depths. The two modes may alternate cyclically in nature and may account, in part, for the variation in subduction angle observed at the modern western American subduction zones. The slow, edge-weakening subduction erosion mode correlates well to subduction erosion processes widely reported for natural subduction zones. The fast, internal-weakening subduction erosion mode has previously been described only for subduction zones involving continental lithosphere on the lower plate. The removal of a 150-250 km wide forearc block from southern Mexico between 27-25 Ma and 21-19 Ma may be a first type example of internal-weakening subduction erosion at an ocean-continent subduction zone. The numerical models showing internal-weakening subduction erosion and the geological record of southern Mexico share the following geological features synchronous with forearc removal: (1) rapid trench migration rates approaching orthogonal plate convergence rates, (2) a step-wise shift in the locus of arc magmatism towards the upper plate, (3) forearc subsidence at the new margin of the upper plate, (4) a zone of crustal unroofing within the upper plate's new forearc region, and (5) a zone of subduction-antitheticDes modéles numériques en éléments finis de subduction océan-continent sont utilisés pour étudier le rôle de la résistance au frottement de la croûte, des angles de subduction et du taux de convergence au cours de la subduction-érosion. Ces modéles mettent en évidence deux régimes distincts: (1) lent et constant, arrachant continuellement de petits blocs de matériel continental, ou (2) rapide et saccadé, arrachant un bloc important d'avant arc en un seul épisode. Le régime lent décrit une subduction-érosion à affaiblissement marginal, favorisée par un fort pendage de la plaque en subduction mais qui tendà diminuer cet angle. A l'inverse le régime rapide décrit une subduction-érosion avec affaiblissement de la zone interne, favorisée par un faible pendage initial de la plaque subduite mais dont l'angle tend à augmenter au cours de la subduction. L'alternance cyclique des deux régimes pourrait expliquer en partie la variabilité du pendage de subduction observée dans les zones de subduction actuelles de la côte ouest américaine.Le régime lent de subduction-érosion (à affaiblissement marginal) est le plus typique de la majorité des cas naturels de subduction-érosion reconnus jusqu'ici. Le régime rapideà affaiblissement de zone interne n'avait été identifié qu'à des zones de subduction où la plaque plongeante est du type continental. L'arrachement d'un bloc d'avant arc substantiel (150à 200 km de largeur) au sud du Mexique, entre 19 à 20 millions d'années (Ma) et 25à 27 Ma, pourrait s'avérer le premier exemple reconnu de subductionà affaiblissement de zone interne dans un contexte de subduction océan-continent. Les modéles numériques qui décrivent un régime de subduction-érosionà affaiblissement de zone interne ont plusieurs traits en commun avec le cas du sud du Mexique: (1) un taux de migration rapide de la fosse de subducti

Subduction erosion modes: comparing finite element numerical models with the geological record

During subduction erosion, the upper plate is tectonically eroded by the subducting plate and carried into the mantle. The geological record suggests that subduction erosion is a fundamental process at subduction margins; however the underlying causes are not well constrained. Finite-element numerical models of ocean–continent subduction are used to investigate the roles of crustal frictional strength, subduction angle, and convergence rate in subduction erosion processes. Subduction erosion occurs in models in which the plate boundary zone is moderately strong, due to either high frictional strength or shallow angle of subduction. The models exhibit two distinct modes of subduction erosion: (1) steady, with slow trench migration rates (>> 15 km Ma− 1), subsidence at the end of the process, and an increase in the angle of subduction, in which a large block of continental forearc is removed. The unsteady mode is compatible with the sudden migration of the volcanic arc into the continental interior, a concurrent hiatus in arc volcanic production, and geochemical signatures showing crustal (forearc) contamination in the magma source region when arc volcanism renews in its new location. Both modes are inhibited by the presence of a thick sediment layer within the subduction zone, and neither mode requires the presence of topographic asperities on the lower plate. In natural subduction zones, subduction erosion may initially occur through steady erosion at the edge of the continental plate. As material is removed, the subduction angle may gradually decrease, increasing the strength of the plate boundary zone. The increased strength may lead to failure in the continental interior, unsteady removal of a large forearc block and relocation of the subduction zone into the upper plate where the cycle may repeat. The proposed cycle may explain observed patterns in the Andean margin, including steady and unsteady erosion recorded in the geological record and along-strike variation in present-day subduction angles