BALancing Craton thickness by self-cOmpression, graiN size evolution and viscous anisotropY

Project Information

Balcony

Grant agreement ID: 101106469

DOI

10.3030/101106469

Project closed

EC signature date 27 April 2023

Start date 1 June 2024

End date 31 May 2026

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 226 751,04

Coordinated by

UNIVERSITETET I OSLO
Norway

Periodic Reporting for period 1 - Balcony (BALancing Craton thickness by self-cOmpression, graiN size evolution and viscous anisotropY)

Reporting period: 2024-06-01 to 2026-05-31

Summary of the context and overall objectives of the project

The MSCA project BALCONY (Balancing craton thickness by self-compression, grain size and viscous anisotropy) investigates the long-term evolution of continental cratons - the oldest and most stable parts of Earth’s continents, many of which have remained intact for more than three billion years. Cratons form the cores of continents and are characterized by thick, cold and mechanically strong lithospheric roots. Their stability has played a fundamental role in preserving continents through Earth’s history, yet the processes that have controlled the growth and stability of these lithospheric roots over geological time remain poorly understood.

BALCONY aims to identify the physical mechanisms that determine the thickness of cratonic lithosphere over billions of years. The project addresses three main scientific objectives. First, it investigates how cratons gradually thicken through long-term cooling of the Earth and tectonic compression associated with mantle convection and supercontinent cycles. Second, it examines the processes responsible for thinning cratonic roots, including viscous deformation caused by mantle flow and the removal of dense lithospheric material through gravitational instabilities (‘drips’). Third, it quantifies the balance between these competing thickening and thinning processes to determine which mechanisms ultimately control craton thickness over geological time.

The project combines numerical modelling with a global compilation of kimberlite occurrences. Kimberlites are rare volcanic rocks that originate at depths greater than approximately 160 km and occur exclusively within cratons. Kimberlites are also economically important because they host around 70% of the world’s diamond resources. The global compilation reveals that kimberlite eruptions were relatively uncommon before approximately 1.5 billion years ago, after which their frequency increased markedly.

BALCONY investigates whether these observations are causally linked through the long-term evolution of cratonic lithosphere. Specifically, the project examines how craton thickness has changed over billions of years and whether progressive lithospheric thickening controlled the temporal distribution of kimberlite magmatism. By integrating numerical simulations with geological observations, the project aims to provide the quantitative framework linking the evolution of cratonic roots with the global record of kimberlite eruptions, thereby improving our understanding of the long-term evolution and stability of Earth’s continental cratons.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

To achieve its objectives, BALCONY developed a suite of high-resolution numerical models that simulate the evolution of continental cratons over the past three billion years. The models were implemented using the open-source geodynamic modelling software ASPECT and incorporate geological and geophysical constraints on the properties of cratons, including initial lithospheric thickness, compositional buoyancy, radiogenic heat production and the long-term cooling of Earth’s mantle. Extensive parameter studies were carried out to generate an ensemble of models exploring the sensitivity of craton evolution to these key physical processes.
To reproduce realistic tectonic conditions, the numerical models include velocity boundary conditions representing three episodes of supercontinent assembly and breakup throughout Earth’s history. These models provide a systematic assessment of how mantle cooling, tectonic compression and gravitational instabilities interact over billion-year timescales to control craton thickness. The modelling results establish a simple conceptual framework in which craton thickness reflects the combined effects of thermal thickening during planetary cooling, additional thickening caused by tectonic compression, and lithospheric thinning through gravitational drip removal. The models demonstrate that cooling and compression become increasingly dominant over time. As cratons cool, the viscosity of their lower boundary increases, making gravitational removal of lithospheric material progressively less efficient. Consequently, thickening mechanisms outpace thinning, leading to a gradual increase in craton thickness over geological time.
Numerical results are supported by a comprehensive global database of kimberlite occurrences from cratons worldwide. This database was used to quantify temporal variations in kimberlite eruption frequency and to assemble an additional dataset relating kimberlite size to eruption age. Statistical analyses were then performed to compare the geological observations with the numerical modelling results.
The combined analyses indicate that many cratons were thinner during the early part of Earth’s history and gradually thickened through cooling and tectonic compression. Around 1.5 billion years ago, an increasing proportion of cratons exceeded the critical lithospheric thickness of ~160 km required to host kimberlite melts. Statistical analyses support this interpretation, showing that although individual cratons followed different evolutionary pathways, the probability of developing lithospheric roots deeper than 160 km increased significantly after this time. These results show that craton thickness exerts a first-order control on the temporal and spatial distribution of kimberlite magmatism, providing a quantitative link between the long-term evolution of continental lithosphere and the geological record of kimberlite eruptions.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

BALCONY provides a new quantitative framework for understanding how continental cratons evolve over billions of years. The project results may be of interest to the mineral exploration sector, as kimberlites are the primary host rocks for most of the world’s diamonds. Improved understanding of the geological evolution of kimberlite magmatism and cratonic lithosphere may help inform future mineral exploration strategies. The project’s findings may also be valuable to science communicators, educators and popular science writers interested in the geological history of continents and the cultural history of diamonds.