New perspectives on the tectonic evolution of the early Earth driven by advances in geochronology and thermodynamic modelling: examples from Greenland

Archean cratons record complex geological histories with multiple episodes of magmatic and metamorphic events that overprint and obscure the oldest crustal remnants. Fieldwork still forms the cornerstone of geological research, enabling direct observation of rocks in their natural context to unravel Earth's complex history. However, the polymetamorphic nature of craton formation commonly results in strong deformation, metamorphism, and metasomatism, which complicates field relations and the tectonic interpretation of the cratonic nuclei.

In Greenland, the oldest component of the North Atlantic Craton consists of the Eoarchean Itsaq Gneiss Complex (IGC), including the >3.7 Ga Isua Supracrustal Belt (ISB). Until recently it was believed that highly deformed mafic and ultramafic enclaves within the IGC predate the main tonalitic continental crust of the region, and that some of these could potentially be Hadean.

However, recent research has shown these enclaves at Ujaragssuit to be roughly 900 million years younger than first proposed. Furthermore, purported anorthosite sheets associated with these enclaves are in fact metasomatized ultramafic rocks, which together with thermodynamic evidence for Eoarchean granulite facies metamorphism, has obvious tectonic implications.

Likewise, claims of preserved mantle fabrics at ISB have turned out to be found within deserpentinized rocks of cumulate origin. Finally, the supposed oldest evidence for life on Earth is found in the form of graphite inclusions within garnet, which have turned out to be one billion years younger than initially assumed.

Such corrections of our understanding of the early Earth are a natural part of the scientific process and are to be expected as our analytical capabilities increase. However, the above examples demonstrate that a more modest approach should be adopted within the early Earth research community.

Faster progress could be made by relying on careful and conservative interpretations in an incremental manner, rather than making outrageous claims as encouraged by many journals and the media. We should keep Brandolini's law in mind and avoid pushing our models beyond what the data supports.