An evaluation of continental growth and early Earth tectonics: Observations and models

Abstract

The generation of sialic continental crust on a planetary scale requires specific conditions for global tectonics because, unlike the oceanic crust, it requires more than a single stage melting of the mantle. The close relationship between continental growth and global tectonics has prompted extensive research in recent decades. However, this research has led to disparate estimates with different implications for global tectonics in the early Earth. The study of continental growth, however, has also been unnecessarily confusing because existing estimates are typically assumed to be similarly valid. It is crucial to recognize that various types of purported continental growth models have their own strengths and weaknesses. After categorizing classic growth models and identifying major difficulties in understanding continental growth, recent developments of crustal evolution and crust–mantle differentiation research are reviewed for tectonic background, crustal growth models, and the secular evolution of continental crust composition. While there exists increasing support for substantial continental growth during the Hadean Era, identifying more direct proxies on the mode of early tectonics continues to be challenging. We posit that the global databases of detrital zircons, at least in the ways that they have been studied, do not yield an estimate on net continental growth. To advance our understanding, we propose that improving our understanding of how the geological manifestation of plate tectonics would evolve with the secular cooling of the mantle.