8:45am - 9:00amTopics: 3.24 Shaping divergent plate boundaries and associated georesources through tectonic, magmatic and hydrothermal processes
Geodynamic modelling of the Wilson-cycle: investigating the interplay of structural and thermal inheritance
1Helmholtz Centre Potsdam – GFZ German Research Centre for Geosciences, Potsdam, Germany; 2RWTH Aachen University, Tectonics and Geodynamics, Aachen, Germany; 3Geological Survey of Norway, Trondheim, Norway
Many rifted margins are thought to have formed in areas that have previously experienced subduction and orogenesis. Yet, our understanding of how structural and thermal inheritance from preceding convergence affects rifting is still incomplete. We use 2D thermo-mechanical numerical models to investigate how the size of a collisional orogen affects the style of subsequent continental rifting. Our models build an orogen through subduction and collision before the onset of rifting. We focus on the deformation style of the resulting rifted margins and the degree in which inheritance is utilized.
We find that the style of extension changes with the size of the orogen. A narrow orogen produces a narrow margin on the side of the overriding plate with core-complex-style reactivation of the subduction interface while a large amount of oceanic material is preserved in the conjugate margin. In contrast, wide orogens localize rifting away from the subduction interface: the subduction interface is temporarily reactivated, but deformation quickly shifts to the thick orogenic assembly resulting in wide rifted margins. Ductile deformation in the lower crust promotes localization of simultaneously active conjugate shear-zones in the brittle crust above. Rifting in these experiments occurs within the subducting plate.
Our results demonstrate a wide range of features that can form in the presence of inherited compressional structures and emphasise the importance of taking the deformation history into account when trying to understand the evolution of continental rifting.
9:00am - 9:15amTopics: 3.24 Shaping divergent plate boundaries and associated georesources through tectonic, magmatic and hydrothermal processes
Inherited structures and their impact on rift evolution: A numerical study of the South China Sea
1The Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, Germany; 2Institute of Geological Sciences, Freie Universität Berlin, Berlin, Germany; 3Institute of Geosciences, University of Potsdam, Potsdam-Golm, Germany; 4Department of Earth Sciences, ETH Zürich, Zurich, Switzerland; 5CY Cergy Paris Université, GEC, 95000 Neuville sur Oise, France
The South China Sea experienced Cenozoic rifting in a region that was previously part of a Mesozoic Andean-type orogeny, which presumably had resulted in structural, compositional, and thermal inheritance. Recent studies using seismic profiles, drill cores, and geochronological analysis have revealed evidence for such heterogeneous pre-rift lithosphere in the South China Sea (Fan et al., 2017). Here, we further investigate the impact of orogenic inheritance on rift evolution using a numerical forward model that integrates both geodynamic and landscape evolution software (Neuharth et al., 2022). By varying our velocity boundary conditions over time, the model encompasses first continental collision, followed by post-orogenic collapse, continental rifting, and final lithospheric breakup. The model is constrained by observed crustal thicknesses, cooling history, and lithosphere-asthenosphere boundary depth, and successfully reproduces realistic orogenic topography, thrust fault distribution, and rifted margin of the SCS.We find that during orogeny, crustal thickening leads to the development of inherited weaknesses in the modelled crust. From orogenic collapse to continental rifting, pre-existing thrust faults are reactivated and serve as nucleation sites for normal faults, which interact with later rift-related normal faults to modify the regional stress field. The modeling results demonstrate that pre-existing thrust faults and a ductile lower crust play a crucial role in shaping the wide rifted margin of the SCS. We infer from our results that the location of crustal breakup is often influenced by these inherited structures. These regions have typically undergone thermal weakening, which further facilitates the process of crustal breakup during rifting.
9:15am - 9:30amTopics: 3.24 Shaping divergent plate boundaries and associated georesources through tectonic, magmatic and hydrothermal processes
Geodynamic controls on sediment-hosted metal deposits in continental rifts
1GFZ German Research Centre for Geosciences, Potsdam, Germany, Germany; 2University of Potsdam, Potsdam, Germany; 3Freie Universität, Berlin, Germany
Many large sediment-hosted clastic-dominated (CD) base metal deposits occur in failed continental rifts and the passive margins of successful rifts, e.g., in the MacArthur Basin, Australia, and in the Selwyn Basin in Canada. Continental rifts and their margins provide a specific mix of higher temperatures and heat flows, fault networks facilitating fluid flow, sediment input from the generated topography, and ocean water contributing pelagic sediments and sulfates. The large-scale geodynamics thus provide the necessary ingredients for metal leaching, with metal deposition then occurring on much smaller spatial and temporal scales.
To identify the specific geodynamic conditions conducive to large CD-type deposit formation, we numerically model 2D rift systems from inception to break-up with the geodynamic code ASPECT (Heister et al. 2017) coupled to the landscape evolution model FastScape (Braun and Willett 2013; Neuharth et al. 2022). With high-resolution (~300 m) simulations, we investigate how rift type (e.g., wide versus narrow), the presence of a craton, and the efficiency of erosional and depositional processes affect the formation of potential source and host rock domains. We subsequently analyse the optimal alignment of these regions where metals are leached and deposited, respectively, with faulting events providing fluid pathways between them. For these favorable co-occurrences, we estimate the potential size of metal deposits and identify those conditions that predict the largest deposits.
Braun and Willett. 2013. Geomorphology 180–181. 10.1016/j.geomorph.2012.10.008.
Heister et al. 2017. Geophys. J. Int. 210 (2): 833–51. 10.1093/gji/ggx195.
Neuharth et al. 2022. Tectonics 41 (3): e2021TC007166. 10.1029/2021TC007166.
9:30am - 9:45amTopics: 3.24 Shaping divergent plate boundaries and associated georesources through tectonic, magmatic and hydrothermal processes
Spatio-temporal Dynamics of Hydrothermal Circulation over 10 million years of Ultraslow- Rifting and Spreading
MARUM/Bremen Universität, Germany
Present spatiotemporal variations of hydrothermal fluxes in the modern and recent ocean provide an observational snapshot of the dynamic interaction between the tectonics of ocean basins and submarine hydrothermal systems. In order to support the understanding of feedbacks between tectonics and the life cycle of hydrothermal systems, we discuss the mechanical, fluid flow and heat flux patterns in a coupled ThermoHydroMechanical model at the ocean basin scale. The case study is an ultra-slow spreading basin, evolving from the initial rifting stages up to the ridge formation. Heat release by plastic deformation at fractures and faults, exothermic serpentinization reactions, sensible and latent crystallization heat from magmatic emplacement and radiogenic heat provide different energy-source signatures promoting hydrothermal activity. The large basin-scale domain allows us to navigate through the evolution of the modelled concurrent hydrothermal systems, emerging and decaying in consonance with the tectonics and the energy-sources. We discuss how the evolving permeability field in crust and sediments exerts a strong control on the hydrothermal circulation, and describe the dynamics of reorganization patterns in fluid flow in response to the mechanical strains and heat sources.
9:45am - 10:00amTopics: 3.24 Shaping divergent plate boundaries and associated georesources through tectonic, magmatic and hydrothermal processes
Quantitative analysis of normal fault network evolution
1Geodynamic Modelling Section, GFZ Potsdam, Germany; 2Institute of Geosciences, University of Potsdam, Germany; 3Department of Earth Sciences, ETH Zürich, Switzerland; 4Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, NM, USA
Understanding how normal fault networks initiate and evolve is important for quantifying plate boundary deformation, assessing seismic hazard and finding natural resources. State-of-the-art numerical forward models treat faults as finite-width shear zones, not as discrete entities. To better understand fault system dynamics over geological scales, we develop workflows to isolate individual faults and their role in shaping the fault network.
We present 3D numerical rift models of moderately oblique extension using the ASPECT software. These models reproduce the thermo-mechanical behavior of Earth's lithosphere and simulate fault system dynamics from inception to breakup accounting for visco-plastic rheology, strain softening and surface processes. We extract surficial fault systems as a hierarchical, time-dependent 2D network of nodes, edges and components representing individual faults.
We find that the initial fault network forms through rapid fault growth and linkage, followed by competition between neighboring faults that leads to their coalescence into a stable network. At this point, modelled normal faults continue to accumulate displacement but do not grow any longer. As deformation localizes towards the center of the rift, the initial border faults shrink and disintegrate, being replaced by new faults in the center of the rift. The longevity of faulting is thereby controlled by crustal rheology and surface process efficiency. Quantitative analysis of fault evolution allows us to deduce fault growth and linkage as well as fault tip retreat and disintegration in unprecedented detail.