Rheological inheritance controls the formation of segmented rifted margins in cratonic lithosphere

Observations from rifted margins reveal that significant structural and crustal variability develops through the process of continental extension and breakup. While a clear link exists between distinct margin structural domains and specific phases of rifting, the origin of strong segmentation along the length of margins remains relatively ambiguous and may reflect multiple competing factors. Given that rifting frequently initiates on heterogenous basements with a complex tectonic history, the role of structural inheritance and shear zone reactivation is frequently examined. However, the link between large-scale variations in lithospheric structure and rheology and 3-D rifted margin geometries remains relatively unconstrained. Here, we use 3-D thermo-mechanical simulations of continental rifting, constrained by observations from the Labrador Sea, to unravel the effects of inherited variable lithospheric properties on margin segmentation. The modelling results demonstrate that variations in the initial crustal and lithospheric thickness, composition, and rheology produce sharp gradients in rifted margin width, the timing of breakup and its magmatic budget, leading to strong margin segmentation

The role of inherited lithospheric heterogeneities in defining the crustal architecture of rifted margins and the magmatic budget during continental breakup

During the final stage of continental rifting, stretching localizes in the future distal domain where lithospheric necking occurs resulting in continental breakup. In magma-poor margins, the lithospheric necking is accompanied by crustal hyperextension, serpentinization and exhumation of mantle lithosphere in the continent-ocean transition domain (COT). In magma-rich margins, the necking is accomplished by the emplacement of large amounts of volcanics in the COT, in the form of seaward dipping wedges of flood basalts (SDRs). This study examines the factors controlling the final crustal architecture observed in rifted margins and the magmatic budget during continental breakup, using observations from the Labrador Sea. The latter shows magma-rich breakup with SDRs documented in the north and magma-poor breakup with a wide domain of exhumed serpentinized mantle recorded in the south. The pre-rift strength of the lithosphere, defined by the inherited thermal structure, composition, and thickness of the lithospheric layers, controls the structural evolution during rifting. While variations in the magmatic budget associated with breakup are controlled primarily by the interaction between the pre-rift inheritance, the timing and the degree of mantle melting, in relation to lithospheric thinning and mantle hydration

New Evidence of 'Anomalous' Vertical Movements along the Hinterland of the Atlantic NW African Margin

Low‐temperature thermochronology studies revealed major exhumation events affecting domains in the hinterland of the Central Atlantic margins, where Palaeozoic and/or Precambrian basement is exposed. Thus, domains traditionally assumed to be stable since at least the Variscan and juxtaposed to subsiding Meso‐Cenozoic basins, appear to be affected by km‐scale vertical movements during the Atlantic rifting and after the Early Jurassic breakup in the Central Atlantic. In this contribution, we investigate the extent and the magnitude of these motions along the NW African margin by presenting the first low‐temperature thermochronology data from west Mauritania. The analysed 22 samples were collected along the Mauritanides, N‐S trending Variscan Belt separating the cratonic Taoudeni Basin in the east from the Atlantic coastal basin in the west. The obtained apatite fission track (AFT) ages range between 236 and 90 Ma, with mean track lengths between 11.22 and 12.81 μm and Dpar comprised between 1.6 and 2.1 μm. The uncorrected (U‐Th‐Sm)/He (AHe) ages vary between 261 and 33 Ma. Inverse thermal modelling of the AFT and AHe data indicates that the hinterland of the Mauritanian Atlantic margin experienced (i) burial between the Permian and the Late Triassic, (ii) km‐scale exhumation during Middle‐Late Jurassic and Early Cretaceous, (iii) burial during the Palaeogene‐‐early Miocene, and (iv) exhumation between mid‐Miocene and present‐day. We argue that these vertical movements are primarily driven by the tectonic evolution of the Atlantic rift and the subsequent geodynamic evolution of the Central Atlantic Ocean and the African plate

Anticline growth by shortening during crustal exhumation of the Moroccan Atlantic margin

It is unclear how the crustal-scale erosional exhumation of continental domains of the Moroccan Atlantic margin and the excessive subsidence of its rifted domains affected the Late Jurassic-Early Cretaceous post-rift evolution of the margin. To constrain the km-scale exhumation, we study the structural evolution of the Jbel Amsittene. This anticline is located on the coastal plain of the Moroccan Atlantic margin, and is classically considered to have been developed initially in the Late Cretaceous by halokinesis, and by contraction during the Neogene. Contrarily, our structural analysis indicates that the anticline is a fault-propagation fold verging north with Triassic salts at its core and that it formed by shortening shortly after continental breakup of the Central Atlantic. The anticline grew by NNW-SSE to NNE-SSW contraction, as shown by syn-tectonic wedges, regional kinematic indicators and synsedimentary structures in Upper Jurassic to Lower Cretaceous rocks. It grew further and tightened during the Cenozoic, presumably in relation to the Atlas/Alpine contraction. Thus, our data and interpretation suggest that “tectonic-drives-salt” in the anticline early growth, which is coeval with the growth of other anticlines along the Moroccan Atlantic margin and widespread km-scale exhumation farther onshore. Anticline growth due to shortening argues for intraplate far-field stresses potentially linked to the geodynamic evolution of the African, American and European plates

Tectono-stratigraphic evolution and crustal architecture of the Orphan Basin during North Atlantic rifting

The Orphan Basin is located in the deep offshore of the Newfoundland margin, and it is bounded by the continental shelf to the west, the Grand Banks to the south, and the continental blocks of Orphan Knoll and Flemish Cap to the east. The Orphan Basin formed in Mesozoic time during the opening of the North Atlantic Ocean between eastern Canada and western Iberia–Europe. This work, based on well data and regional seismic reflection profiles across the basin, indicates that the continental crust was affected by several extensional episodes between the Jurassic and the Early Cretaceous, separated by events of uplift and erosion. The preserved tectono-stratigraphic sequences in the basin reveal that deformation initiated in the eastern part of the Orphan Basin in the Jurassic and spread towards the west in the Early Cretaceous, resulting in numerous rift structures filled with a Jurassic–Lower Cretaceous syn-rift succession and overlain by thick Upper Cretaceous to Cenozoic post-rift sediments. The seismic data show an extremely thinned crust (4–16 km thick) underneath the eastern and western parts of the Orphan Basin, forming two sub-basins separated by a wide structural high with a relatively thick crust (17 km thick). Quantifying the crustal architecture in the basin highlights the large discrepancy between brittle extension localized in the upper crust and the overall crustal thinning. This suggests that continental deformation in the Orphan Basin involved, in addition to the documented Jurassic and Early Cretaceous rifting, an earlier brittle rift phase which is unidentifiable in seismic data and a depth-dependent thinning of the crust driven by localized lower crust ductile flow

Integrated Multi-Parameter Exploration Footprints of the Canadian Malartic Disseminated Au, McArthur River-Millennium Unconformity U, and Highland Valley Porphyry Cu Deposits: Preliminary Results from the NSERC-CMIC Mineral Exploration Footprints Research Network

Mineral exploration in Canada is increasingly focused on concealed and deeply buried targets, requiring more effective tools to detect large-scale ore-forming systems and to vector from their most distal margins to their high grade cores. A new generation of ore system models is required to achieve this. The Mineral Exploration Footprints Research Network is a consortium of 70 faculty, research associates, and students from 20 Canadian universities working with 30 mining, mineral exploration, and mining service providers to develop new approaches to ore system modelling based on more effective integration and visualization of multi-parameter geological-structural-mineralogical-lithogeochemical-petrophysical-geophysical exploration data. The Network is developing the next generation ore system models and exploration strategies at three sites based on integrated data visualization using self-consistent 3D Common Earth Models and geostatistical/machine learning technologies. Thus far over 60 footprint components and vectors have been identified at the Canadian Malartic stockwork-disseminated Au deposit, 20–30 at the McArthur-Millennium unconformity U deposits, and over 20 in the Highland Valley porphyry Cu system. For the first time, these are being assembled into comprehensive models that will serve as landmark case studies for data integration and analysis in the today’s challenging exploration environment

Kinematic and thermal evolution of the Moroccan rifted continental margin: Doukkala-High Atlas Transect

The Atlantic passive margin of Morocco developed during Mesozoic times in association with the opening of the Central Atlantic and the Alpine Tethys. Extensional basins formed along the future continental margin and in the Atlas rift system. In Alpine times, this system was inverted to form the High and Middle Atlas fold-and-thrust belts. To provide a quantitative kinematic analysis of the evolution of the rifted margin, we present a crustal section crossing the Atlantic margin in the region of the Doukkala Basin, the Meseta and the Atlas system. We construct a post-rift upper crustal section compensating for Tertiary to present vertical movements and horizontal deformations, and we conduct numerical modeling to test quantitative relations between amounts and distribution of thinning and related vertical movements. Rifting along the transect began in the Late Triassic and ended with the appearance of oceanic crust at 175 Ma. Subsidence, possibly related to crustal thinning, continued in the Atlas rift in the Middle Jurassic. The numerical models confirm that the margin experienced a polyphase rifting history. The lithosphere along the transect preserved some strength throughout rifting with the Effective Elastic Thickness corresponding to an isotherm of 450°C. A mid-crustal level of necking of 15 km characterized the pre-rift lithosphere. © 2010 by the American Geophysical Union

Mesozoic Source-to-Sink Systems in NW Africa: Geology of vertical movements during the birth and growth of the Moroccan rifted margin

Cloetingh, S.A.P.L. [Promotor]Hafid, M. [Promotor]Bertotti, G.V. [Copromotor

2-D and 3-D Geodynamic modoelling results: Rheological inheritance and rift segmentation in the Labrador Sea

Here, we use observations from the Labrador Sea to constrain thermal-mechanical simulations of continental rifting. The aimis to investigate the effects of inherited variable lithospheric properties on margin segmentation. These 2-D and 3-D models demonstrate that N-S variations in lithospheric thickness, crustal structure, and rheology within the pre-rift Canadian Shield produce sharp gradients in rifted margin width and the timing of breakup, leading to strong margin segmentation during rifting and continental breakup. See our preprint (DOI) and the peer-reviewed paper (DOI) for more details