STATISTICAL META-ANALYSIS OF DETRITAL ZIRCON AGE SPECTRA: GEOLOGICAL IMPLICATIONS OF SHAPE AND DISPERSION PARAMETERS OF DATED GRAINS

Zircon age dates from freely accessible published data repositories were compiled into a standardized meta-analytical database. Data include samples of individually dated zircon grains extracted from sedimentary rocks representing a wide range of tectonic settings, paleoclimatic regimes, geographic regions and stratigraphic ages. For each sample of dated grains, values for tectonic setting, climatic conditions, and minimum/maximum age of the stratigraphic unit of interest were assigned based on review of the relevant literature. The resulting database of samples (age spectra) was then analyzed in terms of basic descriptive univariate parameters (skewness, kurtosis, mean, standard deviation, and related variables) using the software package SAS and SAS/IML programming languague.

Preliminary results suggest that the distribution of age spectra for a given sample of dated grains is independent of both geologic age of the strata and of climatic conditions during deposition of the rock unit from which that sample was derived. Standard deviation and skewness values do not change in any notable manner throughout the late Proterozoic and the Phanerozoic (the time intervals encompassed by our data). However, zircon age spectra appear to be dependent on tectonic setting. Samples from active margin settings (forearc, backarc, and foreland basins) tend to display age spectra that vary from symmetrical to strongly right skewed distributions, whereas samples from passive margins exhibit age spectra that are either close to symmetrical or slightly left skewed. These statistical trends suggest that the shape of age spectra of individually dated detrital zircon grains may provide independent insights into tectonic regimes of ancient sedimentary basins. In addition, the relation between the sample size (number of grains dated) and the age range suggest that a minimum of 60 zircons is necessary to reliably use the age spectra of detrital samples for dating sedimentary rocks; this is consistent with sample size recommendations reported in some recent studies of detrital zircons.