Projects within the Earth Dynamics Group

 

Beyond plate tectonics (BPT)

Aim: Integrate Plate Tectonics into Mantle Dynamics

Objectives:

  1. Develop a global absolute plate motion model since Pangea and possible Gondwana assembly
  2. Link surface and deep processes

Rationale: Large-scale convection in the mantle continuously reshapes Earth's surface through horizontal and vertical movements. The horizontal movements cause continents to collide, diverge and slide past one another. The field of plate tectonics attempts to describe this complex, dynamic evolution of the outer shell of the Earth in terms of plates for which the past movements can be traced using geological data. Even though links between mantle activity and plate tectonics are becoming more evident, there is still no generally accepted mechanism that consistently explains plate tectonics in the framework of mantle convection.

The prime aim in this project is to integrate Plate Tectonics into Mantle Dynamics and develop a theory that explains plate motions quantitatively and dynamically. We will develop a new model of plate kinematics that will be linked to the mantle with the aid of a new plate motion reference frame based on moving hotspots and on palaeomagnetic data. A global reference frame will be corrected for True Polar Wander in order to develop a reference frame with respect to the mantle. The resulting plate reconstructions will constitute the input to subduction models that are meant to test the consistency between the reference frame and subduction histories. The final outcome will be a novel global subduction reference frame that will be used to explore links between surface processes such as eruption of large igneous provinces and heterogeneities in the deepest mantle.

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Mantle forcing of Earth surface evolution in Europe and the Mediterranean: From Past to Present (TOPO-4D)

Aim: Absolute plate motions and dynamic topography of Europe

Objectives:

  1. Refine Mediterranean plate tectonic models and construct oceanic paleo-age grids.
  2. Reconstruct Europe (past 100 Myr) in an absolute mantle reference frame.
  3. Test plate tectonic models against seismic tomography models.
  4. Calculate European dynamic topography in the present and past.

Rationale: Surface deformation, in particular topography evolution, results from a complex coupled dynamic system in which mantle processes (e.g. global mantle currents, plate subduction and collision) interact with surface processes (e.g. erosion, sedimentation, sea-level change, or (de)glaciation). The impact of mantle processes on surface deformation is perhaps conceptually well understood but largely lacks thorough quantification. As a result, it is in many cases impossible to discriminate between mantle-induced and surface induced contributions to surface deformation. Valuable observations of vertical surface motions can often not be equivocally interpreted unless basic assumptions, such as isostasy, are being invoked (e.g. observations of glacial isostatic rebound, vertical motions in orogens, in sedimentary basins, and in subduction zones, of large continental regions and of sea level change). Any progress in understanding present-day topography and topography evolution, and progress in making correct interpretations of valuable surface observables requires quantification of real-Earth mantle dynamics and of the surface response. The European-Mediterranean region is a well-studied natural laboratory for which this progress can now be made.

This project is part of a larger European colloborative effort (headed by Prof. W. Spakman) that forms part of Topo-Europe (European Research Council). Our part constitutes a backbone in this collaboration in which novel interpretations of slab remnants at the base of the upper and lower mantle are being used to fix plate reconstructions to the mantle frame. This provides the link between the European plate and underlying mantle through time and allows for realistic dynamic topography evolution calculations based on back-in-time integration of the convection equations starting from mantle structure as imaged by tomography.

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Influence of glacial erosion, isostasy and mass balance on topography

Aim: Understand vertical movements and landform processes along passive margins subjected to glacial erosion.

Objectives:

  1. Quantify the vertical movement caused by interaction of glacial erosion and isostasy
  2. Quantify mass balance between erosion and sedimentation
  3. Develop tools for data processing, numerical calculations and visualization

Rationale: Active erosion not only produces incised topography, but also removes material away from the eroded area, turning on isostatic processes. Whereas the glacial erosion is localized, the isostatic response, stiffened by elastic lithosphere, is outspread. Thus, the areas adjusted to fjords may experience significant, kilometer-scale, uplift.  We analyze this process using ProShell, an in-house developed numerical shell, which quantifies “erosion backward in time” and use a simple elastic plate model for calculations.
We apply this technique to model passive margins of Greenland to explain elevated Mesozoic marine sediments on the east and tilted palaeo-plateau on the west of Greenland. The recent applications involve North Sea realm and concentrated more on the balance between sedimentation and erosion. The project is a collaboration with Ebbe H. Hartz (PGP and Det norske oljeselskap) and with financial support from Det Norske Oljeselskap.

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Global plate models for Gplates and computational geodynamics

Aim: Integrating plate reconstructions with geodynamic and climate models

Objectives:

  1. Refine rotation engine and global plate polygons back to 1.1 Ga.
  2. Palaeogeographic maps (Atlas) for the entire Phanerozoic with land, shelf and deep oceans
  3. Construct global oceanic crust age models and sedimentary thickness maps
  4. On-the-fly net rotation and poloidal/toroidal partitioning calculations of plate motions, plate velocities, convergence/divergence rates, length of subduction and ridges and true-polar-wander.
  5. Joint 4D interpretation of seismic tomography/plate reconstructions for improved slab-fitting.

Rationale: Sequential plate reconstructions enable analysis and interpretation of biologic, geologic, palaeoclimatic and palaeogeographic data in time and space. For this task, digital databases and complementary software are needed in order to integrate plate reconstructions objectively with numerical models (climate, lithosphere & mantle) and observations at the surface (palaeomagnetic, volcanism, fauna & facies) and the Earth’s interior (seismic tomography).
GPlates (www.gplates.org) is a reconstruction software with a goal of uniting algorithms for plate reconstruction and geodynamic modelling in one application (founded by Müller, Gurnis & Torsvik). This software is unique and a well-established foundation for an open-source Virtual Geological Laboratory. It has a significant international uptake and provides a unique capability for reconstructing a variety of geo-data in a plate tectonic framework, making use of a temporally-aware information model, combined with flexible data importing, processing, visualisation and interaction.

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Siberian flood basalts and the end-Permian extinction

Aim: Integrating plate reconstructions with geodynamic and climate models

Objectives:

  1. Define Siberia's drift and rotational history during the Late Paleozoic and Early Mesozoic
  2. Explore links between the Siberian flood basalts (reconstructed) and deep mantle heterogeneities (Large Low Shear-wave Velocity Provinces)
  3. Develop a global Late Permian-Early Mesozoic reconstruction (ca. 250 Ma) with modeled oceanic crust age and palaeo bathymetry as input for climate modelling.

Rationale: The Siberian flood basalt province is the largest terrestrial flood basalt in the rock record, and the end-Permian extinction is the largest extinction in Earth history. As better data is gathered, evidence for a temporal relationship between the Siberian flood basalts and the end-Permian extinction is growing stronger. Their apparent coincidence in time strongly suggests that the two are related.  Our ignorance of possible extinction mechanisms, however, underscores the importance of studying connections between basalt geochemistry, tectonics, mantle processes, and life. Deconvolving extinctions and their causes in the past allows a better understanding of current climate change issues, and the Siberian flood basalts and end-Permian extinction is an ideal laboratory for this study.

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Comparative planetology

Aim: To understand similarities and differences between the Earth and the other terrestrial planets

Objectives:

  1. Re-determine crater size frequency distributions for the terrestrial planets, and test the coherence of planetary evolution among the planets and with respect to new orbital evolution models of the projectile populations.
  2. A new generalized time frame for (terrestrial) planetary evolution.
  3. Compare observations and models of gravity and geoid anomalies and dynamic topography in space and spectral domain.
  4. Adapt rheological models developed for Earth to other planets and test whether they are compatible with e.g. large-scale geoid anomalies being caused by density anomalies in the lower mantle.

Rationale: Geological evidence of Earth's accretion and earliest evolution is almost non-existent because of volcanic, erosional and plate tectonic processes that have obliterated most of the rock record from the first 500-800 Ma of Earth history. The record of early history is much better preserved on other planets and moons, and a better understanding of the evolutionary history of planets and small bodies in our solar system therefore directly enhances the understanding of Earth's evolution.

Common planetary geological processes are volcanism, tectonics and impact cratering but only Earth and Mars have water as a surface modifying agent and developed surface morphologies interpreted as fluvial erosion patterns. Earth is currently the only terrestrial planet in our solar system with ongoing plate tectonics, and a surface hydrosphere continually feeding hydrogen into the mantle by subduction is perhaps a fundamental factor enabling Earth-like plate tectonics. Time-scales on planetary bodies beyond Earth are derived from crater frequencies, extrapolated from the Moon to other inner solar system objects. Interplanetary comparison needs improved crater scaling laws which relate observed crater dimensions and projectile sizes. Cratering statistics provide relative sequences of events, and for a given cratering rate model also absolute time frames for planetary evolution. This is based on morphologic features that remain recorded on the planetary surfaces. Re-calibrating time scales is essential for unravelling temporal evolution of volcanism.

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