Zircon Essay

Detrital-zircon geochronology is an up and coming method to provide information on sedimentary rock provenance. Zircon is used for this method because of its resilience against chemical and physical weathering; in other words zircon is an indicator that is ubiquitous within sedimentary rocks. Zircon also tends to concentrate uranium and thorium (to a lesser extent) and excludes lead. Two parallel uranium-lead decay routes exist, 238U to 206Pb with a half-life of 4.47 billion years and 235U to 207Pb with a half-life of 707 million years. These ratios can be plotted against each other in a Concordia curve to produce a Concordia diagram which are useful in defining the age of a rock. If ratios plotted for a sample fall below the concordant age
Depositional environment and the degree of homogenization of detrital zircon is directly related, where abrupt lateral and vertical variations in detrital zircon composition may record tectonic events in the source region. For example, the nonsystematic variations in the Winthrop Formation detrital zircon age signature suggest that these strata accumulated in a depositional setting characterized by abrupt changes in detrital input. This abrupt change could have been caused by a combination of active tectonism, heterogeneous source region, or limited mixing of a sediment derived from different areas within the source region. One downfall that accompanies zircon dating is the larger the heterogeneity of the zircon composition, the larger the uncertainty for determining accurate fine-scale characterization of the evolution of source regions. Grain structure of zircons also provides valuable information such that large grains that show no visual evidence of older cores but show well developed oscillatory zoning are characteristic of magmatic growth. Overall, one of the major benefits of analyzing the population of detrital zircon is the ability to link the basin to its source