Displays

A common method used to evaluate dynamic topography amplitudes begins with an estimate of Moho depth, usually from seismic data but sometimes - or also - from the inversion of gravity data. Then the principles of Airy isostasy are applied: surface topography is assumed to be in isostatic equilibrium, buoyantly supported by the displacement of high-density mantle material by the low-density crustal ‘root’ that compensates the surface topographic mass. Hence, the actual relief of the Moho yields an ‘isostatic topography’ which will depart from the actual, observed topography by a component that, in theory, must arise from convective support or subsidence. Notwithstanding the fact that the errors on the seismic Moho may be larger than the topography itself, there is another source of uncertainty, that of the flexural rigidity of the lithosphere. Airy isostasy is essentially an end-member of plate flexure models, one in which the flexural rigidity is zero. However there are very few places on Earth where the flexural rigidity, usually represented by its geometric analogue the effective elastic thickness (Te), is indeed zero. In most environments, the rigidity of the plate will act to resist flexure, with the implication that the ‘Airy isostatic topography’ and therefore the dynamic topography will be in error. Here several scenarios will be presented illustrating these issues, and paths for remediation recommended.

How to cite: Kirby, J.: The influence of plate strength on dynamic topography estimates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2132, https://doi.org/10.5194/egusphere-egu2020-2132, 2020.

Mantle convection is the driving mechanism for plate tectonics and associated geological activities, including earthquakes, surface dynamic uplift and subsidence, and volcanoes. Mantle convection can be regarded as the central framework for linking the sub-disciplines of solid Earth science, e.g., geochemistry, seismology, mineral physics, geodesy and geology.

In theory, it is possible to model mantle convection by integrating the principial conservation equations in time, given a past mantle-state as the starting point. Nonetheless, there remains a fundamental lack of knowledge on any past mantle-states. Without such knowledge any direct comparison of convection models and solid Earth observations is challenging and often impractical. One can, however, pose the problem differently, and obtain a past flow history by minimising ‘a misfit’ functional between observations and models of Earth’s mantle. The recent applications of adjoint method in geodynamics, together with the ever-increasing computational power, has facilitated solutions to such minimisation problems, where a unique flow history in Earth’s mantle can be generated, subject to assumed geodynamic modelling parameters.

Here, we build on previously published adjoint models and present a suite of eight high resolution (11 kms) reconstruction models going back to 50 Ma ago. These models incorporate many improvements. First, we take advantage of the recent advances in surface and body waveform tomography to obtain high resolution images of present-day structures in Earth’s mantle. Our thermodynamic modelling of mantle structures rely on the most recent datasets of mantle mineralogy and account for effects of anelasticity. Furthermore, we assume a wide range of viscosity profiles, including published models consistent with observations of geoid, mantle mineralogy, and post-glacial rebound studies. Finally, we verify these models by comparisons against a range of different geologic observations.

How to cite: Ghelichkhan, S. and Oeser, J.: Global Adjoint Reconstructions of Earth’s Mantle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7446, https://doi.org/10.5194/egusphere-egu2020-7446, 2020.

For a comprehensive link between seismic tomography and geodynamic models, uncertainties in the seismic model space play a non-negligible role. More specifically, knowledge of the tomographic uncertainties is important for obtaining meaningful estimates of the present-day thermodynamic state of Earth's mantle, which form the basis of retrodictions of past mantle evolution using the geodynamic adjoint method. A standard tool in tomographic-geodynamic model comparisons nowadays is tomographic filtering of mantle circulation models using the resolution operator R associated with the particular seismic inversion of interest. However, in this classical approach it is not possible to consider tomographic uncertainties and their impact on the geodynamic interpretation. 

Here, we present a new method for 'filtering' synthetic Earth models, which makes use of the generalised inverse operator G^†, instead of using R. In our case, G^† is taken from a recent global SOLA Backus–Gilbert S-wave tomography. In contrast to classical tomographic filtering, the 'imaged' model is constructed by computing the Generalised-Inverse Projection (GIP) of synthetic data calculated in an Earth model of choice. This way, it is possible to include the effects of noise in the seismic data and thus to analyse uncertainties in the resulting model parameters. In order to demonstrate the viability of the method, we compute a set of travel times in an existing mantle circulation model, add specific realisations of Gaussian, zero-mean seismic noise to the synthetic data and apply G^†. 
 
Our results show that the resulting GIP model without noise is equivalent to the mean model of all GIP realisations from the suite of synthetic 'noisy' data and also closely resembles the model tomographically filtered using R. Most important, GIP models that include noise in the data show a significant variability of the shape and amplitude of seismic anomalies in the mantle. The significant differences between the various GIP realisations highlight the importance of interpreting and assessing tomographic images in a prudent and cautious manner. With the GIP approach, we can moreover investigate the effect of systematic errors in the data, which we demonstrate by adding an extra term to the noise component that aims at mimicking the effects of uncertain crustal corrections. In our presentation, we will finally discuss ways to construct the model covariance matrix based on the GIP approach and point out possible research directions on how to make use of this information in future geodynamic modelling efforts.

How to cite: Schuberth, B. S. A., Freissler, R., Zaroli, C., and Lambotte, S.: Tomographic filtering of mantle circulation models via the generalised inverse: A way to account for seismic data uncertainty, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9728, https://doi.org/10.5194/egusphere-egu2020-9728, 2020.

The Eifel hotspot is one of the few known active continental hotspots. The evidence is based on volcanism as recent as 11ka and a seismic velocity anomaly that shows a plume-like feature downward to at least the upper transition zone. However, the volcanism lacks a clear space-time progression of activity, and evidence for surface deformation has been ambiguous. Here, we show that the greater area above the Eifel plume shows a distinct and significant surface deformation anomaly not seen anywhere else in intraplate Europe. We use GPS data of thousands of stations in western Europe to image contemporary vertical land motion (VLM) and horizontal strain rates. We show significant surface uplift rates with a maximum of ~1.0 mm/yr (after subtracting the broader-scale VLM predicted by glacial isostatic adjustment) roughly centered on the Eifel Volcanic Field, and above the mantle plume. The same area that uplifts also undergoes significant N-S-oriented extension of ~3 nanostrain/yr, and this area is surrounded by a radial pattern of shortening. River terrace data have revealed tectonic uplift of ~150–250 m of the Eifel since 800 ka, when recent volcanism and uplift reactivated, which would imply an average VLM of 0.1–0.3 mm/yr since that time. Our VLM results suggest that the uplift may have accelerated significantly since Quaternary volcanism commenced. The remarkable superimposition of significant uplift, horizontal extension, and volcanism strongly suggests a causal relationship with the underlying mantle plume. We model the plume buoyancy as a half-space vertical force applied to a bi-modal Gaussian areal distribution exerted on a plane at 50 km depth. Our modelling shows a good regional fit to the long-wavelength aspects of the surface deformation by applying buoyancy forces related to the plume head at the bottom of the lithosphere. From our spatially integrated force and the first-order assumption that the plume has effectively been buoyant since 250 ka (to explain Quaternary uplift) or 800 ka (at today’s rate), we estimate that a 360 km high plume requires density reduction of 57-184 kg m^-3 (i.e., ~0.7-5.6% of a 3300 kg m^-3 dense reference mantle), which is consistent with observed seismic velocity reductions. Finally, we note that the highest extension rates are centred on the Lower Rhine Embayment (LRE), where intraplate seismicity rates are high, and where paleoseismic events increased since 800 ka. We suggest that the surface uplift imposed by the Eifel plume explains the relatively high activity rate on faults along the LRE, particularly since the N-S extension would promote failure on the NW-SE trending faults in the LRE.

How to cite: Kreemer, C., Blewitt, G., and Davis, P.: A Buoyant Eifel Mantle Plume Revealed by GPS-Derived Large-Scale 3D Surface Deformation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12058, https://doi.org/10.5194/egusphere-egu2020-12058, 2020.

Sustainable development and transition to a clean-energy economy is placing ever-increasing demand on global supplies of base metals (copper, lead, zinc and nickel). Consumption over the next ~25 years is set to exceed the total produced in human history to date, and it is a growing concern that the rate of exploitation of existing reserves is outstripping discovery of new deposits. Therefore, improvements in the effectiveness of exploration are required to reverse this worrying trend and maintain growth in global living standards.

Approximately 70% of known lead, 55% of zinc and 20% of copper has been deposited between 2 Ga and recent by low temperature hydrothermal circulation in shallow sedimentary basins. These basins are formed by extension and rifting, which are key manifestations of the plate-mode of tectonics. Despite 150 years of research, the relationship between deposit locations and local geological structure is enigmatic and there remains no accurate technique for predicting their distribution at continental scales.

Here, we show that modern surface wave tomography and recent parameterisations for anelasticity at seismic frequencies can be used to map lithospheric structure, and that sediment-hosted base metal deposits occur exclusively along the edges of thick lithosphere. Approximately 90% of the world's sediment-hosted copper, lead and zinc resources lie within 200 km of these boundaries, including all giant deposits (>10 megatonnes of metal). Incorporation of higher resolution regional seismic studies into global lithospheric thickness models further enhances the robustness of this relationship. 

This observation implies that lithospheric architecture imparted by the plate-mode of tectonics is stable over billion-year timescales, and that there is a genetic link between lithospheric scale  processes and near-surface hydrothermal mineral systems. Our new maps provide an unprecedented global means to identify fertile regions for targeted mineral exploration, and provide a clear economic justification for funding targeted seismic arrays, theoretical advances in imaging techniques, and geodynamic studies that improve our understanding of deep-time plate tectonics.

How to cite: Hoggard, M., Czarnota, K., Richards, F., Huston, D., Jaques, L., and Ghelichkhan, S.: Treasure maps, sustainable development, and the billion-year stability of cratonic lithosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7105, https://doi.org/10.5194/egusphere-egu2020-7105, 2020.

 Hotspots are thermal instabilities that originate in the mantle and manifest themselves on the surface by volcanism, continental breaks or "traces" observed in the oceans. Theirs effects under the continents are still debated: in addition to a phase of activity associated with surface volcanism, a residual thermal anomaly could persist durably under the lithosphere along the trajectory of the hotspot. For a simple model of thermal anomaly (a parallelogram aligned in a fixed direction), we compute the perturbations of the geoid, of the gravity vector and of the associated gravity gradients, and show that in a coordinate system aligned with the parallelogram, the gravity gradients exhibit a characteristic signal, with an order of magnitude of a few hundred mEotvös, well above the current data detection level. Thus considering four real cases :in North Africa (with Hoggar, Tibesti, Darfur and Cameroon hotspots), in Greenland (Iceland), in Australia (Cosgrove) and in Europe (Eifel), we calculate the paleo-positions of the hotspots for 100 Myr in a reference frame linked to the lithospheric plates, and we build maps of the Bouguer gravity gradients filtered on the spatial scale of a few hundred kilometers (the scale of the hotspot) and oriented along the direction of these trajectories. We clearly detect, in the scale-orientation diagrams, signals aligned in the direction of the movement of the plates on spatial scales of a few hundred kilometers. These preliminary results are very enthusiastic: gradiometric data indeed allow us to follow the tracks of hotspots in the continental lithosphere, for at least 20 Myr.

How to cite: Greff-Lefftz, M., Panet, I., and Besse, J.: Continental Hotspots Tracks from Analysis of GOCE Gravity Gradients Data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9142, https://doi.org/10.5194/egusphere-egu2020-9142, 2020.

The seafloor surrounding ocean hotspots is typically 0.5 - 2 km shallower than expected for its age over areas hundreds to >1000 km wide, but the processes generating these bathymetric swells are uncertain. Two end-member models have been proposed to explain swell uplift. The first model, lithospheric thinning, posits that reheating of the lithosphere causes the seafloor to uplift due to the isostatic effect of replacing colder, denser lithosphere with hotter, less dense upper mantle. The second model, dynamic uplift, proposes that swells are supported by upward flow of ascending mantle plumes and/or hot, buoyant plume material ponded beneath the swell lithosphere. If swells are dominantly produced by lithospheric thinning, the resulting thermal subsidence should approximately mimic the subsidence of young ocean lithosphere. This places an upper bound on the rate of seafloor and island subsidence following swell uplift, since conductive cooling of the lithosphere is a gradual process. On the other hand, if swell topography is dominantly produced by dynamic uplift, then seafloor subsidence depends primarily on how rapidly plate motion carries the seafloor off the swell and the spatial extent of the swell.

Because these two models predict different patterns of seafloor and island subsidence, swell morphology and the geologic record of island drowning may reveal which of these mechanisms dominates the process of swell uplift. To test this, we isolated regional swell bathymetry at 14 ocean hotspots. Considering the end-member case of lithospheric thinning, we modeled the thermal evolution of the lithosphere at each hotspot following swell uplift, and we compared the resulting thermal subsidence to observed swell subsidence. We also estimated island residence times atop swell bathymetry (swell length/plate velocity), and we compared this residence time to the age at which islands typically drown in each hotspot island chain. We found that observed swell subsidence significantly outpaces thermal subsidence. Moreover, island drowning ages match swell residence times, suggesting that islands and the seafloor subside as tectonic plate motion transports them past mantle sources of swell uplift. This correspondence argues strongly for dynamic uplift of the lithosphere at ocean hotspots. Our results also explain global variations in island lifespan on fast- and slow-moving tectonic plates (e.g. drowned islands in the Galápagos <4 million years (Ma) old versus islands >20 Ma above sea level in the Canary Islands), which profoundly influence island topography, biodiversity, and climate.

How to cite: Huppert, K., Perron, J. T., and Royden, L.: Hotspot swells and the lifespan of volcanic ocean islands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15208, https://doi.org/10.5194/egusphere-egu2020-15208, 2020.

Based on a high-resolution Rayleigh-wave tomography of the Mediterranean region, shallow asthenospheric volumes are identified characterized by low S-wave velocities between about 70 km and 250 km depth. We distinguish between five major shallow asthenospheric volumes in the Circum-Mediterranean: the Middle East, the Anatolian-Aegean, the Pannonian, the Central European, and the Western Mediterranean Asthenospheres. Remarkably, they form an almost closed circular belt of asthenospheres interrupted only by thick Triassic oceanic lithosphere in the eastern Mediterranean. Shallow asthenosphere beneath the Rhone and Rhine Grabens connects the Western Mediterranean with the Central European Asthenosphere. Beneath the Serbian and Rhodope Mountains shallow asthenosphere forms a link between the Pannonian and the Anatolian-Aegean Asthenosphere.

Cenozoic intraplate volcanic fields are found above all areas underlain by shallow asthenosphere, and is absent in areas of thick lithosphere. Thus, anorogenic intraplate volcanism in the circum-Mediterranean appears to be associated with shallow asthenospheric volumes. Specifically, this applies to volcanic fields in the central Apennines and Sicily underlain by the Western Mediterranean Asthenosphere. Regions without significant tectonic extension above shallow asthenosphere are characterized by elevated topography. Examples are the Anatolian Plateau, the Western Carpathians, the Atlas Mountains and the low mountain ranges in Central Europe and Iberia. In back-arc regions like the Aegean and Pannonian Basins, and the western Mediterranean, strong tectonic extension leads to low topography above shallow asthenosphere. High continental shoulders are present in transition regions towards thinner lithosphere. Examples are the Levantine coast, the Moesian platform and the Bohemian Massif or the southern Atlas Mountains. We further note that in regions of past volcanism continental lithosphere is thickening by long-term cooling. The showcase for this is the North-German Basin where sedimentation and an about 100 km thick lithosphere developed after extensive Permian volcanism. These observations hint at considerable  variability in time of the continental lithosphere-asthenosphere boundary: Thinning of continental lithosphere may be caused by extension and/or thermal erosion whereas cooling may lead to thickening of continental lithosphere as is evident from the Mesozoic evolution of continental lithosphere in central Europe.  

How to cite: Meier, T., El-Sharkawy, A., Lebedev, S., and Behrmann, J.: Shallow Asthenospheric Volumes in the Circum-Mediterranean and their Relation to Intraplate Volcanism and Topography, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11532, https://doi.org/10.5194/egusphere-egu2020-11532, 2020.

Extensive geophysical studies on gravity anomalies and seismic structure of the Pannonian Basin have determined that this extensional sedimentary basin is more elevated than predicted by Airy-type isostatic compensation models. European regional models assuming a two-layered lithosphere containing a uniform crust and a lithospheric mantle estimated ca. 750-1000 meters difference between the actual and calculated isostatic topography for the Pannonian region.

We have revisited this early finding and calculated a refined residual topography map of the Pannonian Basin that also takes into account the low-density sedimentary fill. We show that the actual residual topography of the eastern part of the region is much lower than previously thought and ca. 4-500 meters of positive residual topography characterizes the central and western part of the Pannonian Basin.

In order to interpret the observed residual topography of the basin we carried out a series of elasto-visco-plastic thermo-mechanical numerical models. Our simulation of the last 9Myr covering the classical  “post-rift” phase of the Pannonian Basin analyzes forcing factors, such as asthenospheric-scale mantle convection, elastic flexure of the lithosphere due to increased external stress and sediment re-distribution, and ductile lower crustal deformation. The large-scale positive residual topography is dominantly controlled by mantle dynamics.

Finally, 3D stratigraphic numerical forward modelling has been carried out by DionisosFlow, constrained by our previously calculated tectonic scenario. We analyzed the substantial reorganization of the main sedimentary transport routes in the Pannonian Basin mainly controlled by the development of the observed positive dynamic topography of the basin. Our preliminary model results are in good agreement with geological records, such as the ca. 200 km Pliocene eastward migration of the Paleo-Danube drainage network.

How to cite: Balázs, A., Kovács, Á., Sztanó, O., Matenco, L., Fodor, L., Kovács, A., Granjeon, D., and Gerya, T.: Isostatic and dynamic controls on neotectonic differential vertical movements and sediment transport reorganization of the Pannonian Basin, Central Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17900, https://doi.org/10.5194/egusphere-egu2020-17900, 2020.

The French Massif Central is a portion of the Variscan belt that exhibits a present-day high topography associated with a potential Cenozoic rejuvenation. Despite other Variscan massifs in Central Europe, such as the Bohemian, Rhenish and Vosges/Black Forest Massifs, show similar topography, the French Massif Central is higher, wider and with evidence of more intense late Cenozoic volcanism. Deep-seated processes controlled by mantle upwelling are generally invoked for the origin of Cenozoic uplift, although the timing and quantification of the relief formation remain unclear. Here we present

a thermochronological study based on new apatite (U-Th)/He and fission-track data that have been integrated with published data (Barbarand et al., 2001; Gautheron et al., 2009) to reconstruct the exhumation history of the eastern margin of the massif. Apatite (U-Th)/He and fission-track data show Cretaceous ages from the high elevation samples and Eocene ages from the lower samples. Although the thermochronological ages do not allow to clearly constrain the onset of Cenozoic exhumation, the regional distribution of the mean track length is essential for the interpretation of the eastern margin evolution: mean track length-elevation relationships show a complex and non-linear trend consisting in a general decrease of MTL from high elevation/old age toward intermediate elevations and then a slight increase for the lowermost and youngest samples. We integrated inverse and forward modelling approach to test different hypothesis of margin evolution. The best fit between observed and predicted data is obtained with a Cretaceous cooling followed by a phase of thermal stability around 40°C and a renewed (lower amplitude) cooling during late Cenozoic. These two cooling events represent two main tectonic phases, the first in the Cretaceous and a minor one in late Cenozoic.

The limited amount of erosion coupled with the occurrence of Cretaceous deposits on top of the massif and in the Rhône river valley floor and no evidence for faulting suggest a long-wavelength flexure of the lithosphere, which has produced a margin topography characterized by a broad monocline with a very low gradient. This topography is consistent with a surface growth induced by mantle upwelling.

How to cite: Olivetti, V., Balestrieri, M. L., Godard, V., Bellier, O., Gautheron, C., Valla, P., Zattin, M., Faccenna, C., Pinna-Jamme, R., and Manchuel, K.: Late Cenozoic exhumation of the French Massif Central: constraints to long wavelength uplift from thermochronology analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20743, https://doi.org/10.5194/egusphere-egu2020-20743, 2020.

The Carboniferous to Palaeogene Wandel Sea Basin of North Greenland is an important piece in the puzzle of Arctic geology, particularly for understanding how the Paleocene–Eocene movement of the Greenland Plate relates to the compressional tectonics in the High Arctic; e.g. Eurekan Orogeny (arctic Canada), West Spitzbergen Orogeny (Svalbard) and Kronprins Christian Land Orogeny (North Greenland). We will refer collectively to these manifestations related to the movement of the Greenland Plate as the Eurekan Orogeny. Here, we present apatite fission-track analysis (AFTA) and vitrinite reflectance (VR) data combined with observations from the stratigraphic record to place constraints on the timing of key tectonic events.

Our study reveals a long history of episodic burial and exhumation since the collapse of the Palaeozoic fold belts along the east and north coasts of Greenland. Our results provide evidence for pre-Cenozoic phases of uplift and erosion in Early Permian, Late Triassic, Late Jurassic and mid-Cretaceous times, all of which involved removal of sedimentary covers that were 2 km thick or more.

Paleocene cooling and exhumation affected the major fault zones of the Wandel Sea Basin. The Paleocene episode thus defines the timing of the compressional event that caused folding and thrusting of Upper Cretaceous and older sediments along these fault zones. We conclude that the Paleocene inversion of the fault zones took place in the initial phase of the Eurekan Orogeny after the onset of seafloor spreading west of Greenland

Regional cooling, reflecting exhumation of the Wandel Sea Basin and surrounding regions, began at the end of the Eocene. Prior to the onset of exhumation, a cover of about 2.5 km of Paleocene–Eocene sediments had accumulated across a wide area. Northern Peary Land, north of the Harder Fjord Fault Zone, was uplifted about 1 km more than the area south of the fault zone during this episode. Regional denudation and reverse faulting that began at the end of the Eocene took place after the end of sea-floor spreading in the Labrador Sea and thus represent a post-Eurekan tectonic phase. A major plate reorganisation in the NE Atlantic and regional exhumation of West and East Greenland and adjacent Arctic regions took place at the same time, coinciding with a minimum of spreading rates in the NE Atlantic followed by expansion of the Iceland Plume.

Cooling from mid-late Miocene palaeotemperatures at sea level correspond to burial below a rock column about 1.8 km thick.

The preserved sedimentary sequences of the Wandel Sea Basin represent remnants of thicker strata, much of which was subsequently removed during multiple episodes of uplift and erosion. The thickness of these sedimentary covers implies that they must have extended substantially beyond the present-day outline of the basin, and thus that it at times was coherent with the sedimentary basins in the Arctic, as has been suggested from stratigraphic correlations.

How to cite: Japsen, P., Green, P. F., and Chalmers, J. A.: Thermo-tectonic development of the Wandel Sea Basin, North Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17188, https://doi.org/10.5194/egusphere-egu2020-17188, 2020.

During the last decade, the study of the south Patagonian Andes and Antarctic area have demonstrated the occurrence of a complex mantle setup during the pre-Atlantic opening (200-140 Ma) with the formation and disappearance of an anomalous flat slab (~1000 km long), combined with the Karoo Plume development and western migration. In the Patagonian foreland, this period is characterized by plutons emplacement distant from the arc, flowed by a major volcanic income, the Chon Aike Large Igneous Province (~180 Ma to ~160 Ma). These markers are mostly seen in the Deseado Massif (~47 ° to ~48 ° S. Lat), a 350 x 200 km topographically high (between 500 and 1000 m elevation) area surrounded by Cretaceous and Cenozoic basins. The evolution of the Deseado Massif remains poorly constrained, although it is believed to be at this high topographic level since the end of the Chon Aike event.

In order to understand the pre-Atlantic opening evolution of the Deseado Massif and its potential long-term stability, we used a low temperature thermochronological approach. For this purpose, we sampled the Chon Aike deposits (rhyolite and ignimbrite) and basement rocks (~450 Ma to ~200 Ma plutons) across the Deseado Massif. The thermal history was reconstructed using new apatite (U-Th)/He data and published apatite fission tracks data. These thermochronometers are sensitive to temperature ranges from 120 ° and 40 °C, allowing to reconstitute rocks cooling and reheating history in the last kilometers of the crust. The thermal models reveal a significant Jurassic reheating event (post Chon Aike event) followed by a last cooling phase before ~100 Ma. The origin of this heating-cooling event will be discussed in relation with potential deposit accumulation/erosion, a change in the regional geothermal gradient, and finally, the eventual controls produced by the regional mantle setup.

How to cite: Derycke, A., Gautheron, C., Genge, M., Zattin, M., Mazzoli, S., Witt, C., and Marquez, M.: Patagonian Foreland burial and exhumation during Mesozoic revealed by low temperature thermochronology: a response to mantle processes?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3618, https://doi.org/10.5194/egusphere-egu2020-3618, 2020.

The Rio Grande Rise (RGR) consists of an aseismic, basaltic plateau currently submerged in the southwestern side of the South Atlantic Ocean. Its origin is still a matter of considerable debate, ranging from a microcontinent formed by fragmentation of the South American plate (1) to a basaltic ridge formed by expressive intra-plate magmatism triggered by the arrival of the Tristan da Cunha plume in the Cretaceous (2). The western portion of the RGR (WRGR) is crossed by a major rift-like structure known as the Cruzeiro do Sul Lineament (CSL) interpreted as tectonically active mainly from Upper Cretaceous to Middle Eocene (3). So far, understanding the development of the CSL is central to deciphering the thermo-tectonic history of the RGR with implications for the understanding of opening of the South Atlantic Ocean and the evolution of associated lithospheric plate margins. For this purpose, basaltic rocks from the northern and southern flanks of the CSL dredged during the Rio Grande Rise Project expedition (PROERG) carried out by the Geological Survey of Brazil (CPRM) were analysed for apatite (U-Th-Sm)/He (AHe) thermochronology. Thermal histories for these rocks (time-temperature paths) were obtained by the QTQt software (4). Single-grain AHe ages vary from ~ 5 to 65 Ma and the thermal histories indicate a phase of cooling at the southern flank in the Eocene, and three phases of cooling at the northern flank: in the Eocene, Miocene, and Pliocene, respectively. Based on published seismic and stratigraphic data (3,5,6), the Eocene cooling is mainly interpreted in terms of magmatic cooling and basement uplift and erosion, whereas the Miocene and the Pliocene cooling probably reflect tectonic driven basement uplift and erosion. The preliminary AHe data suggest that the CSL was tectonically active at least until the Pliocene. Plumes evolution also must be considered to explain these reactivations and uplifts.  

1. Kumar, N., 1979. Origin of “paired” aseismic rises: Ceará and Sierra Leone rises in the equatorial, and the Rio Grande Rise and Walvis Ridge in the South Atlantic. Mar. Geol. 30, 175–191. https://doi.org/10.1016/0025-3227(79)90014-8
2. O’Connor, J.M., Duncan, R.A., 1990. Evolution of the Walvis Ridge-Rio Grande Rise Hot Spot System: Implications for African and South American Plate motions over plumes. J. Geophys. Res. 95, 17475. https://doi.org/10.1029/JB095iB11p17475
3. Praxedes AGP, Castro DL, Torres LC, et al., 2019. New insights of the tectonic and sedimentary evolution of the Rio Grande Rise, South Atlantic Ocean. Marine and Petroleum Geology. https://doi.org/10.1016/j.marpetgeo.2019.07.035
4. Gallagher K., 2012. Transdimensional inverse thermal history modeling for quantitative thermochronology. Journal of Geophysical Research: Solid Earth 117:1–16. https://doi.org/10.1029/2011JB008825
5. Barker, P.F., 1983. Tectonic evolution and subsidence history of the Rio Grande Rise. In: Barker, P.F., Carlson, R.L., et al. (Eds.), Initial Reports of the Deep Sea Drilling Project, vol 72. US Government Printing Office, Washington, DC, pp. 953-976.

6. Mohriak, W.U., Nobrega, M., Odegard, M.E., Gomes, B.S., Dickson, W.G., 2010. Geological and geophysical interpretation of the Rio Grande Rise, south-eastern Brazilian margin: extensional tectonics and rifting of continental and oceanic crusts. Pet. Geosci. 16, 231–245. https://doi.org/10.1144/1354-079309-910

How to cite: Hackspacher, P. C., Venancio da Silva, B., Glasmacher, U. A., and Soldado Peres, G.: Contributions to thermo-tectonic history of the Rio Grande Rise (South Atlantic Ocean) as revealed by apatite (U-Th-Sm)/He thermochronology , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22294, https://doi.org/10.5194/egusphere-egu2020-22294, 2020.

Earth’s topography is mainly controlled by the structures associated with density differences of the lithosphere and the crust. This is related to isostatic topographic processes which work in association with mantle-induced deformation that together leads to dynamic topography. In this study, the dynamic topographic model of Rubey et al. (2017) has been used. The model links sedimentary basin evolution with plate tectonics and mantle convection to deliver a quantitative framework to understand the combined roles of mantle convection and subduction processes in time and space. Dynamic topography is different from surface topographic variations and this difference can be used to explain past deformation. In the Bengal basin, sedimentation began in a deep basin and shelf region that endured continuous subsidence, and then became involved with crustal adjustments due to collision and uplift of the Himalayas and later on the Indo-Burmese Ranges (IBR). In this study, the dynamic topographic changes have been used to understand the past deformational history and plate dynamics beneath the Bengal Basin and IBR. The model has been run in a cloud-computing environment using the global mantle convection code TERRA along with the plate reconstruction Gplates software to reproduce dynamic topographic variations. In such conditions the shelf zones are the dynamic topographic representation. The results for Bengal basin region, 22.5° to 24.5°N latitude and 91.5° to 93.5° E longitude for the past 20Ma, showed that high sedimentation in the subducting basinal setting caused rising dynamic topography from 20 to 5 Ma continuously. A negative trend (i.e. subsidence) is seen for the past 5Ma. Moreover, when total change in subsidence in the last 5Ma is considered, it has been observed that the northern front of the Bengal Basin steeply plunged towards the north at a time when the Shillong Plateau was uplifted. While there has been overall subsidence of the region both the Shillong Plateau and IBR rose. Present day seismic tomographic study indicates the presence of denser magmatic mass beneath Shillong Plateau which might also be linked with Indian oceanic plate subduction. The Dynamic Topo-Tomographic Model suggests that slab bending associated with subduction caused detachment of the denser material zones and change in the slab setting above which the thick sedimentary column is stacked. The rise of the rigid Shillong Plateau caused a deformational front in the sedimentary zone, south of the Plateau, resulting in a steep plunging dynamic topography. 

How to cite: Rakshit, R., Wasson, R. J., and Bezbaruah, D.: Slab deformation in the Bengal basin due to uplift of the Shillong Plateau and the Indo-Burmese Ranges since the Pliocene, constrained by a Dynamic Topo-Tomographic technique, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-188, https://doi.org/10.5194/egusphere-egu2020-188, 2020.

Comparison of predicted mantle dynamic topography with observed residual topography shows that the amplitude of predicted dynamic topography is too great (Cowie & Kusznir, EPSL, 2018). This over prediction of dynamic topography amplitude most probably arises from uncertainties in the conversion of seismic velocity anomalies from mantle tomography into density anomalies and uncertainties in upper and lower mantle viscosity structure, both of which are required to compute predicted dynamic topography.

Dynamic topography renormalisation, consisting of its rescaling and shifting, is determined by comparing predicted dynamic topography with observed residual topography for “normal” oceanic crust where observations are less prone to errors than for continents, margins and oceanic plateaus. Renormalisation is then applied globally to generate an improved map of dynamic topography for the continents, other remaining oceanic areas, and the Antarctic and Arctic polar regions. An important caveat is that the renormalisation can only be calibrated for oceanic regions, and we assume that the same rescaling of predicted mantle dynamic topography can be applied to the continents.

We present and examine a new global map of mantle dynamic topography produced by renormalising the predicted dynamic topography of Steinberger et al. (2017) which includes seismic tomography above 220 km depth to determine shallow upper mantle densities.

Renormalised maximum amplitudes of mantle dynamic topography uplift for East Africa, the S.W. Pacific and Iceland are 1000, 750 and 750 m respectively. For mantle dynamic subsidence in the Argentine Basin of the S. Atlantic, the maximum amplitude is -750 m. Elongated regions of mantle dynamic uplift are predicted for the Western Cordillera of North America and West Antarctica with maximum values of 500 and 750 m respectively.

How to cite: Kusznir, N. and Cowie, L.: A Global Map of Renormalised Mantle Dynamic Topography , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12062, https://doi.org/10.5194/egusphere-egu2020-12062, 2020.

How to cite: Ghelichkhan, S. and Bunge, H.-P.: The adjoint equations for thermochemical compressible mantle convection: derivation and verification by twin experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7400, https://doi.org/10.5194/egusphere-egu2020-7400, 2020.

A crucial goal in geodynamics is the development of time-dependent earth models so that poorly known mantle convection parameters can be tested against observables gleaned from the geologic record. To this end one must construct model trajectories to link estimates of the current heterogeneity state to future or past flow structures via forward or inverse mantle convection models. Unfortunately, the current heterogeneity state which is derived from seismic imaging methods is subject to substantial uncertainty due to the finite resolution of seismic tomography. These uncertainties are likely to considerably affect the computed flow trajectory, in what is known as the butterfly effect. Here we study mantle convection models to assess the effects of varying initial conditions on the evolution of mantle flow. We compute convection calculations with identical flow parameters but different initial temperature fields. A base temperature field is generated by allowing a mantle convection calculation to evolve until a statistical steady state is reached. This temperature field is then used to initialize our reference case. We proceed to modify this reference temperature field in three different forms to reflect tomographic choices of damping and smoothing: in the first case, we apply a radial averaging to the reference temperature field. In the second case, we truncate a spherical harmonic expansion of the reference field at degree 20. In the final case, we apply an S20RTS filter to the reference field. In all cases we track the divergence of the perturbed models from the reference model. Furthermore, we test the efficiency of surface velocity assimilation, following from the work of Colli et al(2015), in locking two convecting systems and driving their divergence to a minimum. We find in all experiments that the divergence grows exponentially before hitting a maximum value, within 4 transit times, at which point it ceases to grow. In addition, surface velocity assimilation leads either to a reduction of the divergence or prevention of its further growth and within 3 transit times, the maximum possible convergence between reference and perturbed models is reached for all cases, further confirming the results seen in Colli et al(2015).

How to cite: Taiwo, A. and Bunge, H.-P.: Mantle Flow Trajectories in the Presence of Poorly Constrained Initial Conditions: Analysis of an Ensemble of Models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2624, https://doi.org/10.5194/egusphere-egu2020-2624, 2020.

 Our results suggest that geologic maps yield geodynamically-relevant quantities, allowing one to constrain mantle-induced surface deflections of the lithosphere related to past dynamic topography.

How to cite: Vilacís Baurier, B., Hayek Valencia, J. N., Bunge, H.-P., Friedrich, A. M., and Carena, S.: Hiatus Mapping at a Continental Scale for Cretaceous and Cenozoic time, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4170, https://doi.org/10.5194/egusphere-egu2020-4170, 2020.

The late Mesozoic and Cenozoic plate tectonic evolution of the broad Asian region is associated with the northwestward subductions of the Pacific and Philippine Sea plates in the east and the collision and convergence of the Indo-Australian with the Eurasian plates along the Tethys tectonic belt in the southwest. To better understand the subsurface behavior of subducting slabs and their effects on the tectonic evolution of the overriding plates, we are conducting a multiscale full seismic waveform inversion at the period from 30 to 120 s based on spectral-element and adjoint methods. This is intended to provide a high-resolution seismic model of the crust and mantle down to ~2000 km depth under China and adjacent regions.

For the forward and adjoint simulations we use the newly developed spectral-element solver Salvus (Afanasiev et al., 2019), which allows us to simulate the 3D visco-elastic wavefield in highly heterogeneous, attenuating and anisotropic media, while respecting surface topography and internal discontinuities. We compare observed and synthetic waveforms based on time-frequency phase misfits, and compute sensitivity kernels with respect to the vertically and horizontally propagating/polarized P and S velocities (V_PH , V_PV , V_SH , V_SV) and density (ρ). Finally, we take advantage of the iterative solution of the nonlinear inverse problem with the help of the L-BFGS algorithm to update the structural model.

For this study we selected 386 earthquakes in the moment-magnitude range 5.0 ≤ Mw ≤ 6.8 that occurred in the region between 2009 and 2018. Our final dataset contains 1,281,216 three-component recordings from the above events recorded at 2,426 unique stations. To reduce the risk of convergence towards a local minimum, we divide the whole inversion procedure into three successively broadened period bands (70-120 s, 50-120 s, 30-120 s). The starting model is extracted from the Collaborative Seismic Earth Model (Fichtner et al., 2018) and we will conduct the inversion from longer to shorter period. The primary goal of this ongoing study is to probe into the Mesozoic and Cenozoic plate tectonics and mantle dynamics of the Asian continent setting in two unique tectonic systems (Indo-Australia-Eurasia and Western-Pacific Subduction Zones) with a holistic viewpoint, rather than discuss several hot topics in isolation.

References

Modular and flexible spectral-element waveform modelling in two and three dimensions. Geophys. J. Int., 2019, 216(3), 1675–1692. https://doi.org/10.1093/gji/ggy469.

The Collaborative Seismic Earth Model: Generation 1. Geophys. Res. Lett., 2018,

How to cite: Ma, J., Thrastarson, S., van Herwaarden, D.-P., Fichtner, A., and Bunge, H.-P.: Multiscale Seismic Full-waveform Tomography of the Crust and Mantle beneath China and adjacent regions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2967, https://doi.org/10.5194/egusphere-egu2020-2967, 2020.

We present a suite of four ancient buried landscapes that occur beneath the southeastern flank of the Faroe-Shetland basin on the fringes of the North Atlantic Ocean. These landscapes have been mapped on a calibrated three-dimensional seismic reflection survey. They are manifest as regional unconformities, representing repeated transient sub-aerial exposure events during Early Paleogene times. Once flattened, decompacted and depth converted, these landscapes equate to minimum transient uplifts of O(200)m.  Buried ephemeral landscapes are excellent natural experiments that develop over geological time on large spatial scales with known lithologies, exposure times and initial topographies. Dendritic drainage patterns recovered from these landscapes are highly disequilibrated and contain multiple knickpoints that are systematically arranged within catchment areas. Applying the stream power law, longitudinal rivers profiles are inverted to calculate spatially and temporally varying uplift histories. These unique landscapes are attributed to laterally advecting pulses of hot material that travel away from the Icelandic plume. They provide valuable insights into the dynamics of flow within an asthenospheric channel associated with a mantle plume. Diachronous V-shaped ridges straddling the Reykjanes Ridge independently record advecting thermal pulses of the Icelandic plume. We combine histories of vertical motions with a compilation of independent observations, including V-shaped ridges, to present a semi-continuous thermal history of Icelandic plume pulses.

How to cite: Conway-Jones, B. and White, N.: Transient Buried Landscapes as Manifestations of Icelandic Plume Activity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-551, https://doi.org/10.5194/egusphere-egu2020-551, 2020.

Deformation patterns of continental interiors cannot be explained by the plate-mode of mantle convection and standard plate-boundary processes. In order to understand the occurrence of spatial and temporal patterns of earthquakes, active deformation, uplift and erosion, diking, rifting, and volcanism, other mechanisms need to be invoked. We explore the role, the plume-mode of mantle convection may play to explain the above mentioned features for the Cenozoic of central Europe. We ask whether geological maps at the continental scale are useful to distinguish between the two basic mantle-flow directions, i.e., vertical versus horizontal flow.  The French Massif Central and the German Eifel are highlands in Central Europe that were characterized by intense volcanic activities during the Cenozoic Era. The origin of the distinctive topographically high and volcanically active regions, and, therefore, the evolution of the Cenozoic geology of Central Europe has been enigmatic. In an effort to address the problem, the Cenozoic geological series of Central Europe as displayed on the geological maps of France and Germany at 1 : 1 000 000 was reconstructed. The plume-mode stratigraphic framework mapping followed the Plume-Event-based Stratigraphic Model proposed by Friedrich et al. (2018) to evaluate the contribution of a mantle plume to the generation of the Central European volcanic province, and the influence of a mantle plume versus asthenospheric flow on the evolution of Cenozoic geology of the region. The resultant plume-stratigraphic map-patterns yields a NE-SW-oriented, narrow (200 - 400 km), elongated (up to c. 1200 km) region of uplift and erosion, from the Massif Central to the Rhenish Massif.  The best fit patterns are obtained by assuming an onset of uplift and erosion some 40 Myrs prior to Miocene volcanism. Given that the temporal resolution of the input maps is restricted to geological series, these numbers carry a large uncertainty and depend on the assumption that the series boundaries relate to geological events, which need not be the case. Future applications of this plume-stratigraphic mapping is promising to reveal mantle-parameters,  particularly once the temporal resolution of the input maps improves from series to stages.

How to cite: Friedrich, A. M., Duzingisimana, M. W., and Rieger, S.: Preliminary plume-mode stratigraphic framework maps of Central Europe , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20722, https://doi.org/10.5194/egusphere-egu2020-20722, 2020.

Geological maps contain crucial information to constrain geodynamic models, but they remain underutilized by the geodynamic community. Particularly significant are unconformable geologic contacts at continental scales: what is usually perceived as a lack of data (material eroded or not deposited) becomes instead part of the signal of dynamic topography variation over geologic time.

Here we show how we were able to use geological maps to constrain the dynamic processes in the mantle beneath Africa by understanding its Cenozoic elevation history, and by using it to distinguish between different uplift and subsidence scenarios. This was accomplished by using geological maps at the continent scale to map the spatiotemporal patterns of geological contacts, under the assumption that continental-scale unconformable contacts are proxies for vertical motions and paleotopography.

We found that significant differences exist in interregional-scale hiatus surfaces at the level of geologic series. The total unconformable area at the base of the Miocene expands significantly compared to the base of the Oligocene, strongly suggesting that most of Africa underwent uplift in the Oligocene. In southern Africa there are no marine Oligocene or Pleistocene sediments, suggesting that this region reached a high in the Oligocene, subsided in the Miocene and Pliocene, and has been high again since late Pliocene to Pleistocene. Our results therefore support a dynamic origin for the topography of Africa. Specifically, the time-scale of geologic series (at most a few tens of millions of years) is comparable to the spreading-rate variations in the south Atlantic, which have been linked to African elevation changes through pressure-driven upper mantle flow.

How to cite: Bunge, H.-P., Carena, S., and Friedrich, A. M.: Progress in observational geodynamics from the analysis of geological hiatus surfaces across Africa in the Cenozoic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4094, https://doi.org/10.5194/egusphere-egu2020-4094, 2020.

The topography of the Atlas-Meseta system (Morocco) is the result of Late Cenozoic rejuvenation related to mantle-driven uplift. This recent, large-scale dynamic uplift is testified by the occurrence of uplifted shallow-water marine deposits in the Middle Atlas Mountains and in the Western Meseta, indicating that surface uplift must have started after the Late Miocene (Messinian) at rates of 0.1 to 0.2 mm yr^-1. This recent pulse is still recorded by transient river networks and by the presence of uplifted relict landscape. In particular, in the Anti Atlas and Western Maroccan Meseta, the lack of significant Cenozoic crustal shortening and the occurrence of several hundred of meters of mantle-driven uplift, offers the possibility to investigate magnitude, timing and rates of deep-seated uplift. In this study we have combined geomorphic analysis of stream profiles with in situ-produced cosmogenic concentrations (¹⁰Be, ²⁶Al) in river sediments and bedrock surfaces (corresponding to relict landscape upstream of knickpoints), in order to decipher the uplift history. Our catchment-mean erosion rates allow us to quantitatively constrain the transient state of landscape and hence to unravel the contribution of regional surface uplift on mountain building processes in Morocco during the Plio-Quaternary.

How to cite: Clementucci, R., Siame, L., Ballato, P., Yaaqoub, A., Essaifi, A., Leanni, L., Guillou, V., and Faccenna, C.: Quantifying the dynamic topography through a combination of basin-averaged erosion rates and geomorphic analysis from the Anti Atlas and Western Meseta (Morocco) transient landscape , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11770, https://doi.org/10.5194/egusphere-egu2020-11770, 2020.

Over deep time, mantle flow-induced dynamic topography drives deposition moderated by higher-frequency fluctuations in climate and sea level. The effects of deep mantle convection impact all the segment of the source to sink systems at different wavelengths and over various scales which remains poorly quantified. Field observations and numerical investigations suggest that the long-term stratigraphic record along continental margins contains essential clues on the interactions between dynamic topography and surface processes. However, it remains challenging to isolate the fingerprints of dynamic topography in the geological record.

We use the open-source surface evolution code Badlands (badlands.readthedocs.io), to quantify the impact of different timings and wavelengths of dynamic topography migration on the South African landscape responses.

We test three different dynamic topography scenarios obtained by both backwards advection and forwards modelling of mantle flow. We investigate their influence on landscape dynamics, stratal geometries and depositional patterns of South Africa over the past 40 Ma. We compare the evolution of the drainage organization, sediments flux, and stratigraphy obtained with the models with seismic, geochronological, and thermochronological data. We demonstrate that inland incision, spatial sediment accumulation, and depocenter migration strongly depend on the direction of sediment transport relative to the direction of dynamic topography propagation. It allows to identify realistic evolutions of mantle flow associated with the South African uplift history. Our results suggest that our source-to-sink numerical workflow can be used to explore, in a systematic way, the interplay between dynamic topography and surface processes and can provide insights into recognizing the geomorphic and stratigraphic signals of dynamic topography in the geological record.

How to cite: Mallard, C., Salles, T., Zahirovic, S., and Ding, X.: Dynamic topography controls on source-to-sink systems: Example of the last 40 Ma in South Africa., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20709, https://doi.org/10.5194/egusphere-egu2020-20709, 2020.

How to cite: Holdt, M., White, N., and Stephenson, S.: The Influence of Dynamic Topography on the Great Escarpments , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-696, https://doi.org/10.5194/egusphere-egu2020-696, 2020.

The Jurassic-Cretaceous boundary corresponds to a major step in the Gondwana dispersal. The deformation regime indeed changed from localized, along the incipient ocean (Atlantic Tethys, Somali-Mozambique Ocean), to a highly distributed deformation along several rifts spanning from India to southern South America through Africa including Arabia. The last step of extension is marked by a major unconformity of Late Aptian in age known, since the pioneering work of Edward Suess at the end of the nineteenth century, as the Austrian Unconformity that corresponds to a world-scale plate kinematic reorganization.

We compiled a new map of the Early Cretaceous (Berriasian-Aptian) rifts in Africa and austral South America with a particular emphasis on southern Africa and the Falkland-Malvinas plateau:

At middle wavelength (few tens of kilometers) deformation scale, this Late Aptian event may have stopped the rift regime, corresponding to the transition to a sag setting (Chad and Sudanese rifts), and/or reactivated basement structures (e.g. neoproterozoic faults in the Illizi and Ghadames basins in southern Algeria and Libya). In the central segment of the future South Atlantic Ocean, Late Aptian corresponds to the end of the hyperextension period and the onset of the passive margin coeval with salt deposition.

At a longer wavelength of deformation (several hundreds to thousand of kilometers), the highlighted deformation regime may have changed regional subsidence pattern with for example the overall subsidence of northern Africa and the onset of large marine floodings (e.g. deposition of Nubian sandstones).The Late Aptian unconformity therefore records a major change in the stress within the African plate likely related, considering the scale of deformation, to a reorganization in mantle convection processes.

How to cite: Dietrich, P., Guillocheau, F., Robin, C., Roche, V., Leroy, S., Rosselo, E., and Révillon, S.: Early Cretaceous extension of Africa and South America: cause and consequences of the Late Aptian intraplate deformation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13826, https://doi.org/10.5194/egusphere-egu2020-13826, 2020.

Since plate tectonics has been linked to material flow in the Earth’s mantle, it is commonly accepted that convective motion in the sublithospheric mantle results in vertical deflections and horizontal plate motion on the Earth’s surface. Those mantle flow-driven vertical deflections are recognized through significant signals and traces in the sedimentary records (unconformities and missing sections). Recently, Friedrich et al. (2018) introduced an event-based plume stratigraphic framework that uses such signals in the stratigraphic record to detect the geological evolution near, and on the Earth’s surface in areas of interregional scale caused by mantle plume movement. Information about these dynamic processes is stored in geological archives, such as (1) stratigraphic records of sedimentary basins and (2) thermochronological data sets of igneous, metamorphic, and sedimentary rocks.

For the first time, this research combines these two geological archives and applies them to the Mesozoic SW Gondwana intraplate environment to retrieve the Paraná-Etendeka plume movement prior to the Paraná-Etendeka LIP. We compiled 18 stratigraphic records of the major continental and marine sedimentary basins and over 35 thermochronological data sets including >1300 apatite fission-track ages surrounding the Paraná-Etendeka Large Igneous Province to test the event-based plume stratigraphic framework and its plume stratigraphic mapping to retrieve the timing and spatial distribution of the Paraná-Etendeka plume.

The plume stratigraphic mapping, using the stratigraphic records is suitable to demark a possible plume center, plume margins and distal regions (Friedrich et al., 2018). Thermochronological data reveal centers of a significant thermal Paraná-Etendeka plume influence. Both archives show significant signals and traces of mantle plume movement well in advance of the flood basalt eruptions. Our LTT data combined with stratigraphic records are modeled successfully with respect to a viable mantle plume driven thermal evolution and therefore, we suggest that thermochronological data, in combination with stratigraphy records have the potential to retrieve the Paraná-Etendeka plume movement.

How to cite: Krob, F., Glasmacher, U. A., Bunge, H.-P., Friedrich, A. M., and Hackspacher, P. C.: Application of stratigraphic frameworks and thermochronological data on the Mesozoic SW Gondwana intraplate environment to retrieve the Paraná-Etendeka plume movement., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2629, https://doi.org/10.5194/egusphere-egu2020-2629, 2020.

We report new results for the topographic evolution of the eastern flank of the South-Central Andes at ~35 S latitude. Our work is based on a piggy-back basin near Malargüe, Argentina, which provides a continuous stratigraphic record from 55 to 10 Ma. We have separated volcanic glass and measured hydrogen isotopes (δD) from 107 samples. Studies over the last several decades show that volcanic glass will take up precipitation water by hydration on a 1 to 10 ka time scale. This reaction is irreversible, and later diffusive exchange is too slow to alter the initial isotopic composition. Thus, we conclude that our data provide a record of the isotopic composition of precipitation for most of the Cenozoic. Empirical and theoretical work indicate that the isotopic composition of precipitation decreases in a linear fashion with increasing orographic lifting. We have calibrated this relationship by isotopic modeling of modern water isotopes (152 samples) at 35 S across Chile and Argentina, and that work indicates a lifting relationship for precipitation δD ~20‰/km.

Our glass isotope record shows a steady decrease in δD through the Cenozoic, which matches well with the isotopic response predicted for global cooling at that time. After correction for this climate effect, our glass isotope record indicates that the Marlargüe region had a steady elevation from 55 to 20 Ma, and then was subjected to a cycle of 1 km of subsidence and an equivalent amount of rebound, between 20 to 0 Ma. 

Ongoing geodynamic modeling provides independent evidence of a large subsidence event in this region of South America as determined from the history of slab age and subduction velocity, both constrained by plate kinematics. This dynamic subsidence would have affected both the Andes and the eastern “retroarc” basin. Previous workers have viewed the subsidence history of the retroarc basin as providing a diagnostic record of the growth and decay of orogenic topography, but our work shows that subduction-induced dynamic topography can produce effects of similar magnitude.

How to cite: Brandon, M., Fennell, L., Hren, M., Hu, J., and Liu, L.: One-Km of Subduction-Induced Subsidence of the Eastern Side of the Southern Andes at 10 Ma, as Measured Using Hydrogen Isotopes in Hydrated Volcanic Glass, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21116, https://doi.org/10.5194/egusphere-egu2020-21116, 2020.

The Borborema Province is a Precambrian domain located in the northeastern corner of the Brazilian Shield. It has experienced a complex tectonic evolution that involves orogenic cycles during Precambrian times as well as continental break-up during Mesozoic times. Thermochronologic studies suggest that this region underwent Late Cretaceous-Cenozoic epeirogenic uplift, which is broadly coeval with basaltic volcanism. This uplift is manifest by marine Albian limestones, which crop out at 700 m altitude within the Araripe Basin, and by emergent Holocene marine terraces along the coastline. Despite its elevation, the Borborema Plateau is underlain by thin (30–35 km) crust and has a long-wavelength (> 700 km) positive free-air gravity anomaly. Both observations imply that some degree of sub-crustal support is required. Offshore, oceanic lithosphere adjacent to the Borborema Province has positive residual depth anomalies with amplitudes of hundreds of meters. We infer that sub-plate mantle convective processes have played a significant role in generating and maintaining plateau elevation. Here, a multi-disciplinary approach is used to analyze the causal relationship between surface topography, crustal thickness and crustal density with a view to constraining the residual topography of the Borborema province and surrounding regions. A combination of legacy active and passive source seismic experiments, comprising receiver function studies and deep seismic refraction profiles, were used to determine crustal velocity structure. The relationship between crustal velocity and density is investigated by analyzing a global compilation of rock physics measurements for a full range of crustal lithologies. In this way, the average density of Borborema crust is calculated and used to estimate residual topography by carrying out an isostatic balance between continental lithosphere and a typical mid-oceanic ridge. Positive residual topographic anomalies are obtained for the entire region that are consistent with the amplitude and sign of off-shore residual depth measurements. The aim of this project is to develop a quantitative understanding of the spatial and temporal evolution of the Borborema Plateau. Future work will focus on analyzing exhumed sedimentary basins that transect the plateau, on modeling the geochemistry of Neogene basalts, on inverting fluvial drainage networks, and on interrogating emergent marine terraces along the adjacent coastline.

How to cite: Santana, P. and White, N.: Dynamic Topography of Borborema Province and Surrounding Regions of Brazil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-741, https://doi.org/10.5194/egusphere-egu2020-741, 2020.