Deformation driven by deep and distant structures : Influence of a mantle lithosphere suture in the Ouachita orogeny, southeastern United States

Heron is grateful for funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement 749664 and a DIFeREns2 COFUND Junior Research Fellowship. We thank the editor, D. Harry, E. Hopper, R. Keller, and anonymous reviewers for their helpful comments. Pysklywec acknowledges support from a Natural Sciences and Engineering Research Council of Canada Discovery Grant and and SciNet HPC Consortium (Loken et al., 2010). We thank the Computational Infrastructure for Geodynamics which is funded by the U.S. National Science Foundation under awards EAR-0949446 and EAR-1550901 for supporting the development of ASPECT. Figure 1A was generated using Generic Mapping Tools (Wessel et al., 2013).Peer reviewedPublisher PD

Penetrative Superplumes in the Mantle of Large Super‐Earth Planets: A Possible Mechanism for Active Tectonics in the Massive Super‐Earths

Abstract Recent theoretical studies suggest that the physical and rheological mantle properties in massive rocky planets fall outside conventional behaviors inferred for mantle properties at the Earth's mantle pressures. The vacancy diffusion occurring at low pressures is assumed to be followed by interstitial diffusion above ∼0.1 TPa resulting in viscosity reduction at higher pressures. In addition, the dissociation transition of MgSiO3 post‐perovskite (pPv) into new phases of minerals at 0.9 and 2.1 TPa, both with large negative Clapeyron slopes, has further impact(s) on the style of circulation in the mantle of super‐Earth planets. Further, the electronic contribution of conductivity increases exponentially with temperature at temperatures ∼5000 K and higher. We employ 3D‐controlled volume spherical convection models to explore the style of mantle circulation in large rocky super‐Earth planets with different core temperatures. Our numerical models resembling a GJ 876 d size super‐Earth reveal that due to the buffering influence of the pPv‐dissociation transition at ∼0.9 TPa, for deep mantle viscosities lower than ∼1022 Pa.s a small‐scale convective layer may develop at the top of the core‐mantle boundary (CMB). Penetrative superplumes originating from deep mantle‐layered regions can maintain the heat flux from the CMB required for the planet's geodynamo, and can survive for billions of years reaching shallow depths of the mantle without significant lateral migration. The strength of the focused penetrative superplumes that can potentially sustain surface volcanism and plate tectonics is enhanced with increasing CMB temperature, but diminished by higher rates of internal heating

Focused Penetrative Plumes: A Possible Consequence of the Dissociation Transition of Post‐Perovskite at ∼0.9 TPa in Massive Rocky Super‐Earths

Abstract Based on the standard view of depth‐increasing viscosity in the mantle of rocky planets, convection in the deep mantle of these planets is expected to become less likely as the size of planet increases. However, a recent theoretical study suggests that above 100 GPa pressure, the mantle viscosity can instead decrease with pressure at higher depths. We explore the potential impact of this type of viscosity structure on the nature of mantle convection in a super‐Earth planet of size GJ 876 d with a mass of ∼7.33 M⊕ (M⊕: Earth's mass). The pressures at the bottom of the mantle of GJ 876 d allow MgSiO3 post‐perovskite to dissociate into magnesium oxide (MgO) and relatively highly oxidized magnesium silicate MgSi2O5 at 0.9 TPa with highly negative Clapeyron slope. Our 3D‐spherical numerical model results suggest that for sufficiently low values of viscosity at the transition depth, a vigorous layered mantle convection may develop at the bottom of GJ 876 d‐size super‐Earth. Focused penetrative plumes originating from the deep mantle layered region can survive and stabilize over very long geological timescales and reach to the surface, which may induce unique circumstances of volcanism and tectonic activity

Small-scale convection at a continental back-arc to craton transition: Application to the southern Canadian Cordillera

A step in the depth of the lithosphere base, associated with lateral variations in the upper mantle temperature structure, can trigger mantle flow that is referred to as edge-driven convection. This paper aims at outlining the implications of such edge-driven flow at a lateral temperature transition from a hot and thin to a cold and thick lithosphere of a continental back-arc. This configuration finds application in the southern Canadian Cordillera, where a hot and thin back-arc is adjacent to the cold and thick North American Craton. A series of geodynamical models tested the thermodynamical behavior of the lithosphere and upper mantle induced by a step in lithosphere thickness. The mantle flow patterns, thickness and heat flow evolution of the lithosphere, and surface topography are examined. We find that the lateral temperature transition shifts cratonward due to the vigorous edge-driven mantle flow that erodes the craton edge, unless the craton has a distinct high viscosity mantle lithosphere. The mantle lithosphere viscosity structure determines the impact of edge-driven flow on crustal deformation and surface heat flow; a dry olivine rheology for the craton prevents the edge from migrating and supports a persistent surface heat flow contrast. These phenomena are well illustrated at the transition from the hot Canadian Cordillera to craton that is supported by a rheological change and that coincides with a lateral change in surface heat flow. Fast seismic wave velocities observed in the upper mantle cratonward of the step can be explained as downwellings induced by the edge-driven flow.Geoscience & EngineeringCivil Engineering and Geoscience

Inherited structure and coupled crust-mantle lithosphere evolution: Numerical models of Central Australia

Continents have a rich tectonic history that have left lasting crustal impressions. In analyzing Central Australian intraplate orogenesis, complex continental features make it difficult to identify the controls of inherited structure. Here the tectonics of two types of inherited structures (e.g., a thermally enhanced or a rheologically strengthened region) are compared in numerical simulations of continental compression with and without “glacial buzzsaw” erosion. We find that although both inherited structures produce deformation in the upper crust that is confined to areas where material contrasts, patterns of deformation in the deep lithosphere differ significantly. Furthermore, our models infer that glacial buzzsaw erosion has little impact at depth. This tectonic isolation of the mantle lithosphere from glacial processes may further assist in the identification of a controlling inherited structure in intraplate orogenesis. Our models are interpreted in the context of Central Australian tectonics (specifically the Petermann and Alice Springs orogenies)

How does the Nazca Ridge subduction influence the modern Amazonian foreland basin?

International audienceThe subduction of an aseismic ridge has important consequences on the dynamics of the overriding upper plate. In the central Andes, the Nazca Ridge subduction imprint can be tracked on the eastern side of the Andes. The Fitzcarrald arch is the long-wavelength topography response of the Nazca Ridge flat subduction, 750 km inboard of the trench. This uplift is responsible for the atypical three-dimensional shape of the Amazonian forelland basin. The Fitzearrald arch uplift is no older than Pliocene as constrained by the study of Neogene sediments and geomorphic markers, according to the kinematics of the Nazca Ridge subduction