THE YIN AND YANG OF MAKING AND DESTROYING CONTINENTAL CRUST AND SHAPING THE ARCHITECTURE OF NORTH AMERICA BASEMENT ROCK

INTRODUCTION: Tectonic processes both create and destroy continental crust. Since at least ~1.0 Ga, the balance between the yin of making and the yang of destruction has been effected primarily by plate tectonic processes operating at subduction zones. At subduction zones arc magmatism adds juvenile melts from the mantle at the same time as sediment subduction and subduction erosion return continental crust to the mantle. Crust is also created and destroyed by processes unrelated to plate tectonics, for example additions from hotspot magmatism and losses by the foundering or delamination of lower crustal material.

ESTIMATED GAINS AND LOSSES: Based on the study of modern, Cenozoic, and Mesozoic subduction zones, we estimate for the Phanerozoic an average global rate of creation and destruction of continental crust that has either been in rough balance at ∼3.2 km3/year (i.e., 3.2 Armstrong Units, AU) or that more crust has being destroyed than created (Stern and Scholl, 2010, International Geology Review, v. 52, p. 1-31). This uncertainty comes from unsure estimates of losses by continent subduction at collision zones and foundering of lower continental crust.

THE SUPERCONTINENT CYCLE: The yin-yang, creation–destruction balance (whether positive or negative), changes over a supercontinent cycle, with crustal growth greatest during supercontinent break-up owing to high magmatic flux above newly created subduction zones, and crustal destruction peaking during supercontinent amalgamation (collision) when continental margins are deeply subducted and high mountains shed more sediment into subduction zones.

IMPLICATIONS: If the global volume of the un-estimated crustal loss by delamination is significant (i.e., 0.2-0.3 AU), and/or the recycling loss at suturing collision zones is underestimated (presently 0.7 AU—see Stern and Scholl, 2010), it is likely that Earth’s inventory of continental crust has been decreasing and perhaps during much of Phanerozoic time. This conclusion challenges the widely held view that the volume of continental crust has progressively increased over time. No matter, destruction of continental crust must have importantly contributed to shaping the architectural fabric of North America basement rock and also to the composition of its underlying mantle.