Arc duration controls crustal thickness and lava composition: implications for the detrital zircon record

The continental crust was formed predominantly by magmatism at subduction zones. Peaks in the age distribution of detrital zircons derived from the continental crust have been interpreted to indicate that the generation of new crust was a non-steady state process. Here we show that the composition and thickness of subduction zone crust, as well as arc lava compositions, are correlated with arc duration. Older, long-lived arcs have thicker crust than younger arcs, a higher proportion of zircon-bearing felsic middle-upper crust, and erupt lavas with higher (La/Yb)_N and Zr/Yb_6.0 ratios and Zr_6.0 values. The global average crustal thickening rate of active arc segments is 0.12 km/Myr, yielding a present-day global crustal growth rate at arcs of 0.71 – 0.87 km³/yr. Our observations provide a means to estimate the longevity of extinct arc segments from the incompatible trace element ratios of their lavas. Since long-lived arcs with a thick felsic crust component contain a higher proportion of zircon-bearing felsic rocks, and are more resistant to destruction by subduction, variations in the average lifetime of arcs over Earth’s history will influence the detrital zircon record. We propose that the long-lived arcs associated with supercontinents may explain the peaks in detrital zircon age distributions.