THE EVOLUTION AND GROWTH OF CONTINENTAL CRUST

Knowledge of the areal distribution of continental crust over time is important for understanding the major periods of crust formation. Existing work has suggested that most major landmasses were assembled by approximately 2.5 Ga, but recent work suggests that Laurentia, at least, experienced the largest period of growth during the Proterozoic. This study aims to quantify the rate of continental crust formation from initial formation during the Archean through the assembly of Pangaea. Present day and historic maps of Gondwana and Laurentia are gridded in 1 square-km intervals, with age data binned in 100 m.y. intervals. Plate boundaries are defined as the edge of the continental slope to remove non-tectonic effects, such as changes in sea level. Preliminary results for Laurentia (Ancestral North America) and Australia indicate that paleo-continents varied widely in their crustal growth rates. It was found that that only 33% of present-day Laurentia formed during the Archean, whilst 43% formed during the Proterozoic and 24% during the Phanerozoic. In contrast present-day Australia, formerly part of East-Gondwana, consists of at least 50% Phanerozoic crust with roughly equivalent amounts of Proterozoic (24%) and Archean (26%) crust. This suggests that rates of Archean crustal growth vary widely among continents, and existing estimates for early (e.g. Archean) crustal growth may be overestimated. Testable implications of this research include possible constraints on the rates and mechanics of continental growth as well as constraints on the variability of mantle convection rates through geologic time.