Mechanisms of Continental Crust Growth

This chapter focuses on several themes that are related to the mechanism of continental crust growth. We first outline several questions that emerge from the numerous studies on the structure and composition of continental crust. Then, we describe the main views on the modes of continental growth (e.g., the steady state versus episodic growth, expressed by the Armstrong-Moorbath debate). We focus on the topic of the apparent fast rate of several major segments of continental crust (the Reymer and Schubert dilemma), and describe various solutions to this dilemma (e.g., plume-arc accretion vs arc-tectonic models). The plume-related growth models involve the production of oceanic plateau, development of subduction margins, and accretion of juvenile terranes. The arc-tectonic model suggests 'normal' arc development and accretion by lateral movements. We discuss the 'anomalous' seismic velocities in the mantle-derived plateaus sections (e.g., the 'Ontong Java paradox') in light of magmatic processes that are involved in the transformation of juvenile oceanic terranes to continental crust. We emphasize the importance of water in post-Archean crustal magmatism and the relation to plate-tectonic and subduction processes (the 'water, plate tectonic, granite, continental crust' connection). Finally, we bring short descriptions of the histories of several major orogenic events that constructed over geological time the Earth's continental crust (e.g., the Sumozero-Kenozero, Superior, Birimian, Arabian-Nubian Shield), and outline the similar geological histories of these orogenic cycles: they commenced with production of thick tholeiitic (plume-plateau related?) basaltic sequences, followed by development and long-time (∼200. My) activity of arcs (and calc-alkaline magmatism), followed by intracrustal melting and production of calc-alkaline granites, and terminating by production of relatively small volumes of alkaline magmas.