A DECADE OF DETRITAL ZIRCON GEOCHRONOLOGIC STUDIES

Detrital zircon geochronology has developed into a powerful and widely used research tool during the past decade. Advances that have made this technique feasible include the miniaturization of conventional ID-TIMS techniques to enable analysis of individual zircon grains, and the availability of ion microprobes. ID-TIMS analysis commonly yields ages of high precision, but the analyses are very time consuming (~1 age per hour of mass spectrometer time). Ion microprobes yield ages of lower precision, but are advantageous in that they provide spatial resolution and the analyses can be performed more rapidly (~4 ages per hour). Newly developed excimer-laser-ablation multi-collector ICP mass spectrometers may become the optimal tool for detrital zircon geochronology, as they yield ages of moderate precision (comparable to ion microprobes), with spatial resolution (beam size down to ~10 microns), and are highly efficient (~30 ages per hour).

Examples of research areas that have been enhanced by detrital zircon geochronology are as follows. (1) Recognition of several global-scale events of sediment generation and dispersal (e.g., Grenville and Pan-African orogenies). (2) Elucidation of specific sediment transport systems across continents in rivers and aeolian systems, along continental margins by longshore transport, and in off-shelf basins along continental margins. (3) Analysis of the displacement history of crustal fragments or terranes in various orogenic belts. (4) Reconstruction of thrust belt development by linking foreland basin sequences to specific thrust sheets. (5) Deciphering the temporal evolution of igneous provinces by examining the age spectra of zircons in nearby clastic strata.