Metamorphic pressure and the changing thickness of orogenic crust through time

Despite abundant geochemical data spanning 4.4 billion years, first-order secular changes in the characteristics of continental crust including its volume and thickness are poorly constrained. Estimates of crustal thickness using the compositions of magmatic rocks and minerals are variably sensitive to source composition, differentiation, and alteration. Excluding samples subducted to mantle depths, the highest pressures (P) recorded by orogenic metamorphic rocks provide a primary proxy for the maximum attainable thickness of orogenic crust through time that is independent of composition and other extensive variables. A global compilation of metamorphic P reveals secular changes in orogenic crustal thickness that are consistent with independent constraints. The data chart thickening of orogenic crust during the late Archean likely related to the stabilization and strengthening of cratonic lithosphere and the formation of supercratons. By the dawn of the Paleoproterozoic, continental crust had reached a thickness (up to ∼70 km) close to that at the present day with subsequent variations tracking the assembly and breakup of supercontinents.