Deformable plate tectonic models of the southern North Atlantic

Significant, poly-phase deformation occurred prior to, simultaneous with, and after the opening of the North Atlantic Ocean. Understanding this deformation history is essential for understanding the regional development and the mechanisms controlling rifting and subsequent failure or breakup. Here, we primarily use published constraints to construct deformable plate tectonic models for the southern North Atlantic from 200 Ma to present using GPlates. The aim of this work is to test both the capability of the GPlates deformable modelling approach and the reliability of published plate reconstructions. Overall, modelled crustal thickness values at 0 Ma produced from the deformable models show general, regional-scale, similarities with values derived from the inversion of gravity data for crustal thickness. However, the deformable models typically underestimate thinning in marginal basins and overestimate crustal thickness in continental fragments compared to values from gravity inversion. This is possibly due to: 1) thinning occurring earlier than the 200 Ma start time modelled, 2) variations in the original crustal thickness, 3) depth-dependent stretching, 4) rigid blocks undergoing some degree of thinning, and 5) variations in the mesh density of the models. The results demonstrate that inclusion of micro-continental fragments, and locally defined limits of continental crust, generally produce results more akin to observations. One exception is the Grand Banks where global GPlates models produce more realistic deformation, likely due to the inclusion of the exhumed domains continent-ward of the transition zone boundary. Results also indicate that Flemish Cap rotation is required to provide a reasonable fit between North America and Iberia, with the palaeo-position of the Flemish Cap likely to be the proto-Orphan sub-basins. Moreover, the East and West Orphan sub-basins formed separately due to the respective rotations of the Flemish Cap and the Orphan Knoll, which was likely associated with other continental fragments that subsequently contributed to the thicker crust forming the boundary between the East and West Orphan basins. The results also suggest a link between tectonic and magmatic processes. For example, the inclusion of an Orphan Knoll micro-continental block results in greater extension (higher beta factors) in the northern West Orphan Basin near the termination of the Charlie-Gibbs Fracture Zone, and the site of the Charlie-Gibbs Volcanic Province (CGVP). Thus, we infer that the CGVP was likely influenced by plate tectonic processes through the concentration of strain resulting from interaction in proximity to the transform system. Finally, marginal basins that were considered to be conjugate and thus related, may only appear conjugate through later rotation of micro-continental blocks, and thus their genesis is not directly related

Kinematics and extent of the Piemont–Liguria Basin – implications for subduction processes in the Alps

Assessing the size of a former ocean of which only remnants are found in mountain belts is challenging but crucial to understanding subduction and exhumation processes. Here we present new constraints on the opening and width of the Piemont–Liguria (PL) Ocean, known as the Alpine Tethys together with the Valais Basin. We use a regional tectonic reconstruction of the Western Mediterranean–Alpine area, implemented into a global plate motion model with lithospheric deformation, and 2D thermo-mechanical modeling of the rifting phase to test our kinematic reconstructions for geodynamic consistency. Our model fits well with independent datasets (i.e., ages of syn-rift sediments, rift-related fault activity, and mafic rocks) and shows that, between Europe and northern Adria, the PL Basin opened in four stages: (1) rifting of the proximal continental margin in the Early Jurassic (200–180 Ma), (2) hyper-extension of the distal margin in the Early to Middle Jurassic (180–165 Ma), (3) ocean–continent transition (OCT) formation with mantle exhumation and MORB-type magmatism in the Middle–Late Jurassic (165–154 Ma), and (4) breakup and mature oceanic spreading mostly in the Late Jurassic (154–145 Ma). Spreading was slow to ultra-slow (max. 22 mm yr−1, full rate) and decreased to ∼5 mm yr−1 after 145 Ma while completely ceasing at about 130 Ma due to the motion of Iberia relative to Europe during the opening of the North Atlantic. The final width of the PL mature (“true”) oceanic crust reached a maximum of 250 km along a NW–SE transect between Europe and northwestern Adria. Plate convergence along that same transect has reached 680 km since 84 Ma (420 km between 84–35 Ma, 260 km between 35–0 Ma), which greatly exceeds the width of the ocean. We suggest that at least 63 % of the subducted and accreted material was highly thinned continental lithosphere and most of the Alpine Tethys units exhumed today derived from OCT zones. Our work highlights the significant proportion of distal rifted continental margins involved in subduction and exhumation processes and provides quantitative estimates for future geodynamic modeling and a better understanding of the Alpine Orogeny

Late Cretaceous-Cenozoic basin inversion and palaeostress fields in the North Atlantic-western Alpine-Tethys realm : implications for intraplate tectonics

The authors wish to acknowledge the feedback of two anonymous reviewers, whose comments and suggestions have led to a substantially improved manuscript. CS's (now at Uppsala University, Sweden) postdoctoral fellowship at Durham University was financed by the Carlsberg Foundation. AP's (now at McMaster University, Canada) postdoctoral fellowship at Memorial University of Newfoundland was funded by the Hibernia project geophysics support fund. SJ's postdoctoral fellowship at the University of Calgary is funded by Natural Sciences and Engineering Research Council of Canada.Peer reviewedPostprin

Space Geodetic Constraints on Plate Rigidity and Global Plate Motions.

The Global Positioning System (GPS) has emerged over the last 10 years as the premier space geodetic technique for geologic observation with the benefits of both accuracy and economy. GPS data from more than 260 stations were processed utilizing GIPSY-OASIS software, and all available RINEX files for these stations beginning on January 1, 1993. The uniform processing strategy, combined with a rigorous independent error estimate of site velocities and the broad geographical distribution of these sites resulted in a global high-precision surface velocity data set. This data set has been used to: (1) compare the effects of different GPS antenna and monument types on data noise; (2) examine in detail the rigidity of the North America plate; (3) constrain the rate of deformation in the northern Gulf of Mexico; (4) define a model for Recent (Holocene) time global plate motions. The weighted root mean square scatter about the best fit line through the daily position estimates are used to assess the effects of different antenna and monument types on North America. The data set is sensitive to glacial isostatic adjustment as indicated by the decrease in chinu 2 from 1.3 to 1.0 by excluding those sites on rigid North America within a radius of 1,800 km of Hudson Bay. The resulting 64 site solution for the angular velocity of North America give a mean rate residual of 1 mm/yr. GULFNET, a regional GPS network created in 1997 in the northern Gulf Coast to measure strain across this active passive margin is described. Preliminary results suggest that deformation is occurring as predicted by the regional paradigm for deformation, i.e. Gulfward motion along normal faults. A new model for Recent global plate velocities (REVEL) describes the relative velocities of 14 plates. For several plate pairs, statistically significant differences are observed between the geodetically and geologically determined velocities reflecting changes in plate velocity through time. Some of the rate differences reflect gradual slowing associated with convergent plate boundaries, and may reflect increased resistance to subduction or convergence associated with decreased slab pull and/or crustal thickening

Uncertainties and implications of the Late Cretaceous and Tertiary position of North America relative to the Farallon, Kula, and Pacific Plates

We present updated global plate reconstructions and calculated uncertainties of the Pacific, Kula, and Farallon/Vancouver plates relative to North America for selected times since 68 Ma. Improved magnetic data from the Indian Ocean decrease the uncertainties in. the global plate circuit approach; these uncertainties are now considerably smaller than those inherent in equivalent reconstructions based on the assumption of fixed hotspots. Major differences between these results and those of others are due to our use of more detailed Africa-North America reconstructions, separate Vancouver and Farallon plate reconstructions, and the assumption of a rigid Antarctica plate during Cenozoic time. The uncertainties in the relative positions of the Pacific and North America plates since the time of anomaly 7 (26 Ma) range up to ±100 km in position, or from 1 to 3 m.y. in time. If the Mendocino triple junction initiated at about 28.5 Ma, its position would have been at 31.3°N ± 130 km relative to fixed North America. Unacceptable overlap of oceanic crust of the Pacific plate with continental crust of western North America in the anomaly 10 (30 Ma) reconstruction is a minimum of 340±200 km along an azimuth of N60°E and may be accounted for by Basin and Range extension. Pacific-North America displacement in the past 20 Ma is found to be considerably less than that calculated by fixed hotspot reconstructions. Farallon (Vancouver)-North America convergence velocity decreased greatly between the times of anomalies 24 and 21 (56 to 50 Ma), prior to the 43 Ma age of the Hawaiian-Emperor bend and the often quoted 40 Ma “end” of the Laramide orogeny. A change in direction of Farallon-North America convergence occurred sometime between 50 and 42 Ma and also may not correlate with the time of the Hawaiian-Emperor bend. The lack of data from subducted parts of the Farallon and Kula plates permits many possibilities regarding the position of the Kula-Farallon ridge, the age of subducted crust, or the position of oceanic plateaus during the Laramide orogeny, leaving open the question of the relationship between plate tectonic scenarios and tectonic style during Laramide time. Displacements of points on the various oceanic plates along the west coast of an arbitrarily fixed North America during the interval between anomalies 30/31 and 18 (68 to 42 Ma) are found to be: Pacific plate, 1700±200 km northward; Farallon plate, 3200±400 km northeastward; Vancouver plate, 3000±400 km northeastward; Kula plate, if attached to the Pacific plate after A24 time, 2500±400 km northward

Kinematics and Convergent Tectonics of the Northwestern South American Plate During the Cenozoic

The interaction of the northern Nazca and southwestern Caribbean oceanic plates with northwestern South America (NWSA) and the collision of the Panama-Choco arc (PCA) have significant implications on the evolution of the northern Andes. Based on a quantitative kinematic reconstruction of the Caribbean and Farallon/Farallon-derived plates, we reconstructed the subducting geometries beneath NWSA and the PCA accretion to the continent. The persistent northeastward migration of the Caribbean plate relative to NWSA in Cenozoic time caused the continuous northward advance of the Farallon-Caribbean plate boundary, which in turn resulted in its progressive concave trench bending against NWSA. The increasing complexity during the Paleogene included the onset of Caribbean shallow subduction, the PCA approaching the continent, and the forced shallow Farallon subduction that ended in the fragmentation of the Farallon Plate into the Nazca and Cocos plates and the Coiba and Malpelo microplates by the late Oligocene. The convergence tectonics after late Oligocene comprised the accretional process of the PCA to NWSA, which evolved from subduction erosion of the forearc to collisional tectonics by the middle Miocene, as well as changes of convergence angle and slab dip of the Farallon-derived plates, and the attachment of the Coiba and Malpelo microplates to the Nazca plate around 9 Ma, resulting in a change of convergence directions. During the Pliocene, the Nazca slab broke at 5.5°N, shaping the modern configuration. Overall, the proposed reconstruction is supported by geophysical data and is well correlated with the magmatic and deformation history of the northern Andes

Buoyancy versus shear forces in building orogenic wedges

International audienceThe dynamics of growing collisional orogens are mainly controlled by buoyancy and shear forces. However, the relative importance of these forces, their temporal evolution and their impact on the tectonic style of orogenic wedges remain elusive. Here, we quantify buoyancy and shear forces during collisional orogeny and investigate their impact on orogenic wedge formation and exhumation of crustal rocks. We leverage two-dimensional petrological–thermomechanical numerical simulations of a long-term (ca. 170 Myr) lithosphere deformation cycle involving subsequent hyperextension, cooling, convergence, subduction and collision. Hyperextension generates a basin with exhumed continental mantle bounded by asymmetric passive margins. Before convergence, we replace the top few kilometres of the exhumed mantle with serpentinite to investigate its role during subduction and collision.We study the impact of three parameters: (1) shear resistance, or strength, of serpentinites, controlling the strength of the evolving subduction interface; (2) strength of the continental upper crust; and (3) density structure of the subducted material. Densities are determined by linearized equations of state or by petrological-phase equilibria calculations. The three parameters control the evolution of the ratio of upward-directed buoyancy force to horizontal driving force, FB/FD=ArF, which controls the mode of orogenic wedge formation: ArF≈0.5 causes thrust-sheet-dominated wedges, ArF≈0.75 causes minor wedge formation due to relamination of subducted crust below the upper plate, and ArF≈1 causes buoyancy-flow- or diapir-dominated wedges involving exhumation of crustal material from great depth (>80 km). Furthermore, employing phase equilibria density models reduces the average topography of wedges by several kilometres.We suggest that during the formation of the Pyrenees ArF⪅0.5 due to the absence of high-grade metamorphic rocks, whereas for the Alps ArF≈1 during exhumation of high-grade rocks and ArF⪅0.5 during the post-collisional stage. In the models, FD increases during wedge growth and subduction and eventually reaches magnitudes (≈18 TN m−1) which are required to initiate subduction. Such an increase in the horizontal force, required to continue driving subduction, might have “choked” the subduction of the European plate below the Adriatic one between 35 and 25 Ma and could have caused the reorganization of plate motion and subduction initiation of the Adriatic plate

Evolution of a microcontinent during continental break-up: re-evaluating the Falklands Plateau

Continental break-up is associated with the formation of complex margins, of which transform margins remain less understood due to their varied crustal architectures. This limits our understanding of the processes that accompany the fragmentation of supercontinents, which impacts the reliability of plate tectonic models. The Falkland Plateau (FP) is an example of a transform margin that developed along one of the most long-lived and long-offset transform faults on Earth. The evolution of the plateau is linked to south-western Gondwana break-up and its present-day morphology has been associated with vertical-axis rotation of an extensive microplate (the Falkland Islands Microplate – FIM). Therefore, the FP represents an ideal example to improve our understanding of transform margin development, block rotation mechanisms, and early stages of Gondwana break-up. Here, the FP architecture and evolution is constrained by integrating seismic reflection and potential field data, and building rigid and deforming plate models. The results support an ~80° Middle-Late Jurassic FIM clockwise rotation. Rapid stress variations affected south western Gondwana before and during the FIM rotation. The rotation was initiated by the East Antarctica southward drift, and resulted in continental crust extension, intrusion, underplating, and oceanic crust generation in the Falkland Plateau Basin. The resulting architecture displays similarities with other transform margins. Furthermore, the FIM structural network supports intra-block deformation during rotation, and shows that current deformation models are applicable to larger scales. This thesis emphasises a need for re-evaluating the deformation interpreted along South America during Gondwana break-up, and disproves recent interpretations of West Antarctic evolution. This study highlights the importance of integrating diverse datasets and methodologies in understanding tectonically complex areas. The updated interpretation of the FP provides more information about transform margin evolution and constraints on the pre-break-up Gondwana configuration, which will inform future research on resource distribution and climate evolution