- Category: ERC Project
- Project date: 01 January, 2021
- ERC website: https://erc.europa.eu/
- Sample-specific thermochronological predicitions from a thermo-kinematic model (Pecube)
- Development of a Pecube user interface
- Coupling of codes: iSOSIA & Pecube
ERC ProjectThe existence, nature and strength of potential couplings and feedbacks between tectonic processes in the lithosphere and climatic processes in the atmosphere constitute a central overarching question in Earth-Systems research1. The Earth’s surface constitutes the interface across which these couplings occur, primarily through weathering, erosion and associated topographic relief development. Erosion of tectonically uplifted topography enhances weathering and organic-carbon burial, which are the primary processes by which CO2 is drawn down from the atmosphere and stored in the lithosphere on geologic timescales, providing a mechanism for the observed long-term cooling during the Cenozoic2-4. Coupling in the other direction has also been proposed: the cooler and more variable climate of the late Cenozoic may have led to increased relief and erosion rates5,6. If acting simultaneously, these two links should lead to a positive feedback that would act to destabilize the climate-erosion system. The physical nature of the controls of topographic relief and climate on erosion and weathering are thus of prime importance in models of long-term climate evolution7-10 but remain incompletely understood.
An increase in global erosion rates due to late Cenozoic climate change has been invoked from both the sedimentary record6,11 and more recently from modelling of a global thermochronology dataset12, but remains controversial and has been intensely debated for the last 25 years. The proponents of a significant late-Cenozoic increase in global erosion rates argue that it results from a permanent disequilibrium between landscape state and rapidly varying climatic forcing11,13. The opposing view is that landscapes naturally tend towards a steady state in which the incoming tectonic flux is balanced by the outgoing erosional flux; hence, any climatic perturbation of erosion rates must be transient14-16. It has been argued that the inferred global increase of sedimentation rates is an artefact of preservation (known as the “Sadler effect”)16-18. We have recently shown19 that the analysis of a global thermochronology dataset, presented as providing independent support for increased late-Cenozoic erosion rates12, is also flawed because it is affected by a “spatial correlation bias” in which spatial variations in erosion rates were erroneously transformed into temporal increases. To date, the case for a significant late-Cenozoic increase in global erosion rates remains to be made, but traditional thermochronology data provide insufficient temporal resolution to assess if late-Cenozoic climate change has affected global erosion rates19. Considering the pitfalls of a global approach to data analysis that neglects the local context of the data, there is an urgent need for focused case studies, employing novel thermo-chronological methods that allow a breakthrough improvement in spatial and temporal resolution.
Nowhere is the effect of climate change on mountainous relief and erosion more evident than in currently or recently glaciated mountain belts, where late-Cenozoic climate cooling and the onset of glaciations have profoundly altered erosion processes and consequently reshaped the landscape by carving deep glacial valleys. Despite this visually striking impact of glaciation on landscapes, the relative efficiency of glacial versus fluvial erosion has been a subject of continuous debate since the recognition of Quaternary glaciations in the late 19th century. Our current understanding suggests that glacial erosion is not more efficient than fluvial erosion over long (million-year) timescales, at which both fluvial and glacial erosion rates tend to track tectonic-uplift rates20. However, glacial processes strongly modify landscapes by selective erosion, which can be understood from the basic physics of glaciers21-23. Glacial erosion rates are primarily controlled by the basal sliding velocity of glaciers24,25. Because basal sliding requires water, i.e. temperate conditions, climate plays a major role in the efficiency of glacial erosion26. Whereas warm-based glaciers carve their valleys efficiently, cold-based glaciers are non-erosive and may even protect the landscape from erosion26-28. The timing and impact of the transformation from fluvial to glacial landscapes and its relationship to climate remains an open question; estimates vary from the mid-Pleistocene (~1 Ma) in mid-latitude mountains such as the western Alps29-31 to the Eocene-Oligocene (~30 Ma) in high-latitude regions such as Greenland and Antarctica32,33. The glacial response time (i.e. how long it takes to transform a fluvial into a glacial landscape) similarly remains unknown, despite recent theoretical predictions34.
The potential feedbacks between surface erosion and the underlying tectonic driver add further complexity to this coupled system. If erosion can enhance tectonic deformation, climatically controlled increases in erosion will not necessarily be transient. Although this feedback is theoretically well understood and has been predicted to exist for nearly 30 years35,36, clear demonstrations from field data have remained elusive15,37.
Three major research questions thus remain unanswered:
1. To what extent has the switch from fluvial to glacial erosion in mountain belts affected their topographic relief, and has this change substantially increased global erosion rates and sediment fluxes? What is the response time for these modifications?
2. Is the glacial imprint on topography globally synchronous, or does it track spatially and temporally variable conditions that locally allow for efficient glacial erosion? Can latitudinal variations in relief change be demonstrated? Have high-latitude regions gone through an early period of efficient glacial erosion before their current state in which topography is preserved?
3. Are there couplings between tectonic activity and topographic-relief development in response to glaciation? Do tectonic uplift rates modulate the glacial imprint on the landscape? Can feedbacks be demonstrated, whereby glacial erosion affects the tectonic deformation field?
(1) develop new high-resolution, ultra-low temperature thermochronology by setting up a world-leading 4He/3He laboratory;
(2) build new numerical modelling tools that include the latest developments in kinetics of thermochronological systems and make sample-specific model predictions;
(3) couple these tools to glacial landscape-evolution models, enabling the first modelling of real landscapes, with real thermochronology data as constraints;
(4) study potential feedbacks between glacial erosion and tectonic deformation in carefully selected field areas.
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