Quantifying the evolution of the continental and oceanic crust
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A better understanding of how zircon ages vary with time requires sophisticated statistical analysis of U/Pb isotopic ages from both bedrock and detrital zircon databases. Researchers mostly interpret variation in the preserved zircon age distribution as representing periods of enhanced production of continental crust coupled with recycling of older crust. Yet, estimates from several global databases show considerable variation, which suggests the need for standardizing sampling and statistical analysis methods. Grid-area sampling and modern sediment sampling are proposed for future database development with the goal of producing statistically consistent estimates of zircon age distributions at four scales – global, continental, regional, and intra-basin. Application of these sampling methods and detailed statistical analysis (time-series, spectral, correlation, and polynomial and exponential fitting) indicates possible relationships among continental and oceanic crust formation, large igneous province (LIP) events, the supercontinent cycle, geomagnetic polarity and geomagnetic intensity. Results show a strong correlation of zircon and LIP age spectra with major peaks at 2700, 2500–2400, 2200, 1900–1850, 1650–1600, 1100, 800, 600, and 250 Ma, with a pronounced cyclicity in both events of about 274 million years. Cross-correlation analysis indicates that LIP peaks precede zircon peaks by 10–40 million years. Furthermore, oceanic crust age peaks at 170–155, 135–125, 115–100, 80–70, 55–45 and 33–15 Ma correspond to zircon-LIP peaks. Also correlation analysis indicates a link between the zircon-LIP events and geomagnetic reversal frequency, as well as a possible link between geomagnetic polarity and paleointensity. Improved quantification of geological and geochemical measurements should help solve lingering questions about why time-series records of continental and oceanic crust, the supercontinent cycle, and global LIP events indicate evolution in quasi-periodic episodes.
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