A new analysis of the global detrital zircon record with inferences regarding the growth and rise of the continental crust

Abstract:

The growth of the continental crust on Earth remains a contentious topic in the geosciences. Theorized growth rates broadly fall into two categories, episodic and continuous. The former suggests that periods of Earth history witnessed rapid formation and preservation of continental crust, evidenced by peaks of rock formation ages found in the modern record as well as punctuated mantle formation events. The latter suggests that continental crust was growing throughout history, and modern age distributions are biased by preferential preservation events, likely related to supercontinent formation. An additional, and potentially related, debate surrounds the timing of the rise of continental crust above sea level, leading to important feedbacks with the surface environment.

Here, we use a modern detrital zircon age compilation (Puetz & Condie, 2019) that includes >680,000 individual zircon U-Pb ages. We analyze this data in two ways; first using a novel sample-based strategy that calculates the zircon age distribution statistics from individual sedimentary samples, and secondly using a more conventional approach that divides individual analyses by age group only (Parman, 2015; Spencer, 2020). After filtering for discordance and a minimum number of zircon analyses from each sediment, our analysis interrogates 4,248 samples with depositional ages ranging from 3.4 Ga to modern.

Two main features emerge from our analysis: 1) the continental crust grew in pulses throughout Earth history and is not significantly biased by preservation. Major peaks in crust formation occured at ~2.7 Ga, ~1.9 Ga, ~1.1 Ga, and ~0.6 Ga which are broadly coincident with the super-continent cycles. The age peaks, and troughs between them with fewer zircons formed/preserved, are pronounced throughout geologic time. This suggests that continental crust grew episodically (Parman, 2015) ; 2) mature sediments, defined here as having a diverse zircon age distribution with zircon ages near the age of the Earth at the time of deposition, appear on Earth very soon after sediments are preserved globally, near ~3.0 Ga. In light of existing geologic evidence, we interpret this to be a signature of large-scale continental freeboard increase, with continents becoming globally emergent near 3.0 Ga and rising to modern levels by ~2.4 Ga.