Singularity analysis of global zircon U-Pb age series and implication of continental crust evolution

Abstract

Recently compiled global databases of igneous and detrital zircon U-Pb ages have been integrated with other types of isotope data (e.g., neodymium, hafnium, and oxygen) to characterize the episodic growth of the continental crust and the development of supercontinents. However, to what extent do the age peaks reflect the rate of continent crust growth or the differential preservation due to supercontinent settings is a long-standing question. Instead of analyzing amplitudes and periodicity of the age series, here, the analysis focuses on shapes of the individual age peaks described by a power law model for measuring the scale invariant fractality and singularity of time-series records. The results indicate that zircon age distributions around peaks follow power law distribution, regardless of the bin-size used to measure the age distribution. Based on the commonly accepted mechanisms (phase transition, self-organized criticality and multiplicative cascade processes) for generation of power law distributions one can relate the nonlinearity of the age peaks to short spurts of accelerated magmatic activities due to “avalanches” (superplumes, slab breakoff etc.) occurred during episodic convection of the mantle. The exponents of the power law age distributions estimated from the age peaks can be used as an index to quantify the intensity of a singularity. The values of exponents calculated at all major age peaks from five global databases exhibit an episodic nature, with a mean duration of approximately 600–800Myr. Both intensity of the zircon episodes and their duration for the interval from 3Ga to 0.5Ga depict a descending trend, which may signify mantle cooling.