T14 Innovative Techniques and Applications for Detrital Thermo- and Geochronologic Data

Sunday, 31 October 2010
8:00 AM - 12:00 PM
Room 207

CONSTRAINTS ON THE AGE OF THE HOST SEDIMENT: EMPIRICAL ESTIMATES FROM THE GLOBAL DETRITAL ZIRCON DATABASE

Paper number: T14-14
Program: Technical Sessions
Time: 11:30 AM – 11:45 AM

Authors

Abstract

Previous work exploring adequate sample size needed for reliable detrital zircon geochronology used theoretical approaches to estimate the minimum required number of grains to sample a certain age fraction or fractions (Dodson et al. 1988; Vermeesch, 2004). Our approach is to use a large database of published detrital zircons to empirically estimate the error in age estimates of the host sediment in relation to sample size. A global database of ~270,000 detrital zircons representing ~5300 age distributions provides an opportunity to elucidate the effectiveness of constraining host rock age as a function of number of dated grains per sample. Detrital zircons should be as old as or older than the host sediment, and so these ages constrain the maximum age of host sediment deposition. A new metric was created to look at the offset between the maximum estimate of the host sediment age and the youngest grain age in the sample. The average offset was then calculated for samples consisting of varying numbers of individually dated grains.

The minimum sample size that constrained the average offset between the youngest detrital zircon age (Ma) and the maximum age of deposition of the host sediment (independent of the geological age of the sampled unit and regardless of tectonic setting) was ~50 detrital zircons. However, the characteristics of individual host sediments play a significant role in whether or not detrital zircon geochronology can potentially constrain the age of sedimentation with reasonable accuracy (i.e. drainage basin characteristics such as source terranes in the catchment area, most recent pulse of magmatism in the region of the host sediment, etc.). Another important caveat is that the lowest average offset (as a function of sample size) observed was on the order of 50 Ma, which limits the effectiveness of using this approach to estimate the age of the host sediment, except for Archean and early-to-mid Proterozoic rocks.