Phanerozoic addition rates to the continental crust and crustal growth

Abstract

Phanerozoic addition rates to the continental crust are calculated by using seismic profiles through magmatic arcs to measure the crustal volumes added during the active lifespans of the arcs. Data for 17 arcs give addition rates per kilometer of arc in the range 20 to 40 km³ km−1 Ma−1. From these data we deduce a world‐wide addition rate of 1.65 km³ a−1 after adding other contributions to the formation of the continental crust, e.g., from hot spot volcanism. We infer a subtraction rate, mainly by subducting sediments, of 0.6 km³ a−1 and arrive at a net crustal growth rate of about 1 km³ a−1. Growth of the continental crust is necessary to maintain approximately constant freeboard, because the secular decline in the heat production of the mantle causes the ocean basins to deepen. An equation for the growth of the continents as a function of the decline in terrestrial heat flow yields approximately constant growth rate since the Archean of 0.9 km³ a−1, in good agreement with the above estimate. On the average, Archean growth rates must have been 3 to 4 times the present rate. Island arc growth rates are inadequate to explain the formation of the Arabian‐Nubian Shield and the Archean granite‐greenstone terrain of the Superior Province, and a captured island chain in Oregon. We confirm the oceanic island origin of the Oregon terrain on the basis of the large growth rates of hotspot islands.

Geochemical Consequences of Melt Percolation: The Upper Mantle as a Chromatographic Column

“…A recent estimate of this rate (Reymer and Schubert 1984) is 30 km 2 /Ma, so for a choice of L = 10 km and Vs = 3 em/year, the critical value is K~rit -0.1. In other words, all elements with Kd > 0.1 will emerge from the mantle column in equilibrium with the initial wedge composition.…”

Feedback between deglaciation, volcanism, and atmospheric CO2

“…Reymer and Schubert (1984) estimate long term crustal production to be 20-40 km 3 per km of arc length per Ma, but this estimate has been criticized as too low by a factor of two (Dimilanta et al, 2002), and any such estimates, which are based on the amount of crust that persists through time, are minima with respect to magma additions because they are the net of production after losses due to erosion. A value of 80 km 3 /km/Ma and 35,000 km total arc length gives a magma production rate of approximately 3 km 3 /yr, in accord with other estimates (Dimilanta et al, 2002).…”

Yin and yang of continental crust creation and destruction by plate tectonic processes

“…Net gain modern processes of crust formation and destruction. Such crust today is mostly generated above subduction zones, with secondary sites associated with rifts, hotspot volcanism, and volcanic rifted margins (Figure 3;Reymer and Schubert 1984;Hawkesworth and Kemp 2006). Subduction zones are also the most important sites of crust removal, by sediment subduction, subduction erosion, and deep subduction of continental crust.…”