MAL23

TS 2020/2021 Stephan Mueller Medal Lectures, 2021 Arne Richter Award for Outstanding ECS Lecture & 2020 Division Outstanding ECS Award Lecture
Conveners: Claudio Rosenberg, Paola Vannucchi
Presentations
| Fri, 23 Apr, 10:30–12:30 (CEST)

Presentations: Fri, 23 Apr

Chairpersons: Claudio Rosenberg, Paola Vannucchi
10:30–11:10
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EGU21-9351
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Stephan Mueller Medal Lecture 2021
Dietmar Müller

Over the last 25 years the theory of plate tectonics and a growing set of geo-databases have been used to develop global plate models with increasing sophistication, enabled by open-source plate reconstruction software, particularly GPlates. Today’s editable open-access community models include networks of evolving plate boundaries and deforming regions, reflecting the fact that tectonic plates are not always rigid. The theory of plate tectonics was originally developed primarily based on magnetic anomaly and fracture zone data from the ocean basins. As a consequence there has been a focus on applying plate tectonics to modelling the Jurassic to present-day evolution of the Earth based on the record of preserved seafloor, or only modelling the motions of continents at earlier times. Modern plate models are addressing this shortcoming with recently developed technologies built upon the pyGPlates python library, utilising evolving plate boundary topologies to reconstruct entirely destroyed seafloor for the entire Phanerozoic. Uncertainties in these reconstructions are large and can represented with end-member scenarios. These models are paving the way for a multitude of applications aimed at better understanding Earth system evolution, connecting surface processes with the Earth’s mantle via plate tectonics. These models allow us to address questions such as: What are the causes of major perturbations in the interplay between tectonic plate motion and Earth’s deep interior? How do lithospheric deformation, mantle convection driven dynamic topography and climate change together drive regional changes in erosion and sedimentation? How are major perturbations of the plate-mantle system connected to environmental change, biological extinctions and species radiation?

How to cite: Müller, D.: Plate tectonics and Earth System Science, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9351, https://doi.org/10.5194/egusphere-egu21-9351, 2021.

11:10–11:50
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EGU21-5340
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Stephan Mueller Medal Lecture 2020
Mathilde Cannat

The availability of magma is a key to understand mid-ocean ridge tectonics, and specifically the distribution of the two contrasted spreading modes displayed at slow and ultraslow ridges (volcanically-dominated, and detachment fault-dominated). The part of the plate divergence that is not accommodated by magma emplaced as gabbros or basaltic dikes is taken up by normal faults that exhume upper mantle rocks, in many instances all the way to the seafloor. 

Magma is, however, more than just a material that is, or is not, available to fill the gap between two diverging plates. It is the principal carrier of heat into the axial region and as such it may contribute to thin the axial lithosphere, hence diminishing the volume of new plate material formed at each increment of plate separation. Magma as a heat carrier may also, however, if emplaced in the more permeable upper lithosphere, attract and fuel vigorous hydrothermal circulation and contribute instead to overcooling the newly formed upper plate (Cochran and Buck, JGR 2001). 

Magma is also a powerful agent for strain localization in the axial region: magma and melt-crystal mushes are weak; gabbros that crystallize from these melts are weaker than peridotites because they contain abundant plagioclase; and hydrothermally-altered gabbros, and gabbro-peridotite mixtures, are weaker than serpentinites because of minerals such as chlorite and talc. As a result, detachment-dominated ridge regions that receive very little magma probably have a stronger axial lithosphere than detachment-dominated ridge regions that receive a little more magma. 

Because magma has this triple role (building material, heat carrier, and strain localization agent), and because it is highly mobile (through porosity, along permeability barriers, in fractures and dikes), it is likely that variations in magma supply to the ridge, in time and space, and variations in where this magma gets emplaced in the axial plate, cause a greater diversity of spreading modes, and of the resulting slow and ultraslow lithosphere composition and structure, than suggested by the first order dichotomy between volcanically-dominated and detachment-dominated spreading. 

In this talk I illustrate these points using results of recent studies at the Mid-Atlantic and Southwest Indian ridges.

How to cite: Cannat, M.: On magma supply and spreading modes at slow and ultraslow mid-ocean ridges, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5340, https://doi.org/10.5194/egusphere-egu21-5340, 2021.

11:50–12:10
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EGU21-6627
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ECS
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Arne Richter Award for Outstanding ECS Lecture 2021
Carolyn Boulton, Catriona Menzies, Virginia Toy, Ludmila Adam, John Townend, and Daniel Faulkner

The central section of the Alpine Fault accommodates a majority (~75%) of the total relative Pacific-Australian plate boundary motion on a single structure. For strain localization to occur to such an extent, the Alpine Fault must accommodate deformation at spatially and temporally averaged work rates that are lower than those required by hanging wall and footwall structures. Exhumation of a complete fault rock sequence (mylonites-cataclasites-gouges) from ~35 km depth in <5 million years provides us with an unparalleled opportunity to identify the weakening mechanisms underpinning the fault’s remarkable efficiency. We summarize the results of experimental, geochemical, geophysical, seismological, and geological research facilitated by the Deep Fault Drilling Project (DFDP).

Three main factors promote crustal-scale weakness on Alpine Fault: (1) high heat flow associated with rapid exhumation results in a shallow frictional-viscous transition at 8-10 km depth. In turn, temperature-sensitive creep (initially crystal-plasticity with an increasing contribution from grain size sensitive mechanisms during exhumation) can accommodate deformation at strain rates on the order of, and episodically higher than, 10–12s–1across a broad portion of the fault zone (from ~8 to 35 km depth). (2) Above the frictional-viscous transition, cataclastic processes associated with quasiperiodic large-magnitude earthquakes have permanently reduced the elastic moduli of damage zone rocks; and (3) cataclastic processes, combined with fluid-rock interactions, have formed low-permeability principal slip zone gouges and cataclasites. The near-ubiquitous presence of juxtaposed, low-permeability fault core gouges and cataclasites promotes dynamic (coseismic) weakening mechanisms such as thermal pressurization.

Clay mineral alteration reactions are commonly thought to result in fault zone weakening through a reduction in the static coefficient of friction, but fluid-rock interactions on the central Alpine Fault largely result in the precipitation of frictionally strong minerals such as calcite and, locally, K-feldspar. Although relatively narrow in down-dip extent, the brittle seismogenic zone of the central Alpine Fault is not misoriented with respect to the maximum principal stress when a full 3D stress analysis is performed. Moreover, the fault comprises frictionally strong gouges and cataclasites that can sustain high differential stresses. Combined, these factors have important implications for estimating dynamic stress drops and the extent to which future earthquake ruptures may propagate beneath the brittle-ductile transition, thereby increasing moment magnitude.

How to cite: Boulton, C., Menzies, C., Toy, V., Adam, L., Townend, J., and Faulkner, D.: Weak at what scale? Insights from a late interseismic interplate fault, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6627, https://doi.org/10.5194/egusphere-egu21-6627, 2021.

12:10–12:30
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EGU21-2490
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TS Division Outstanding ECS Award Lecture 2020
Christoph von Hagke

Understanding the formation of mountain belts requires integrating quantitative insights on multiple scales. While this has long been known, it is now possible to enlarge the scales of observation by exploiting global data sets, making use of data sets covering large regions, or including automated data analysis. At the same time the lower limit of observation is pushed farther, and by now structures can be routinely analyzed at the micro- or even nano-scale over large areas making use of digital imaging techniques.

In this talk I will present results from a variety of geological settings illustrating the use of large data sets for better understanding of mountain belt dynamics. To this end, I will integrate micro-structural work, numerical and analog models, and regional studies of fault geometries and their time evolution constrained by digital field techniques and low-temperature thermochronometry. A particular focus will be laid on the role of mechanical heterogeneity and strain localization through time. It is shown that in some regions geodynamic processes are responsible for local fault geometries, while in others much more local factors such as rheological contrasts of individual layers or even the changes of rheology through time plays a major role. Multiscale studies exploiting digital techniques and including the dimension of time provide an exciting avenue for state of the art and future geological studies.

How to cite: von Hagke, C.: From Structures to Mountain Belt Dynamics – a global and multidisciplinary perspective , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2490, https://doi.org/10.5194/egusphere-egu21-2490, 2021.

Additional speakers/contributors without abstracts

  • Alberto Montanari, University of Bologna, Italy
  • Helen Glaves, British Geological Survey, United Kingdom
  • Sylvie Leroy, CNRS SU, France
  • Nicolas Flament, University of Wollongong, Australia