Harmonic hierarchy of mantle and lithospheric convective cycles: Time series analysis of hafnium isotopes of zircon

Abstract

Abstract Hafnium isotopes of zircon represent a well-dated proxy for the evolution of magmatic systems through Earth history. Time series analysis on the hafnium isotopes of zircon reveals a hierarchy of statistically significant periodic signals spanning multiple orders of magnitude (106–109\u202fyear\u202fcycles). We attribute the hierarchy of cyclicity to organizing mechanisms of mantle and lithospheric convection at various time scales, ranging from short-term cycles in magmatism and subduction to long-term cycles related to oceans, supercontinents, and superoceans. A ∼600-Myr supercontinent cycle is the strongest signal in the global hafnium database and the phase relationship implies elevated mantle-derived magmatism during supercontinent tenure and elevated crustal reworking during plate reorganization, as expected. A half-supercontinent cycle (Wilson cycle) and a double-supercontinent cycle (superocean cycle) are also present, harmonic with the supercontinent cycle, and related to each other by amplitude modulation. Analysis of local magmatic systems of the circum-Pacific subduction girdle surrounding Pangaea reveal similar significant and harmonic cycles of ∼6 and ∼20\u202fMyr attributed to magmatic cycles and ∼60, ∼120, and ∼240\u202fMyr attributed to subduction cycles. All subduction systems reveal a prevalent ∼60\u202fMyr cycle attributed to an upper mantle convective cycle that has two phase relationships, suggesting that advancing and retreating arc systems can be identified with time series analysis. The harmonic hierarchy of geodynamic cycles identified herein controlled by mantle convection on long time scales and lithospheric convection on short time scales arguably completes the picture of cyclicity in the Earth system, complimenting well-known orbital, oceanic, and astronomical cycles.