Complementarity of Hf isotopes from detrital and igneous zircon: an example from the Central Gneiss Belt, Grenville Province, Ontario

Abstract

Combined U–Pb and Hf isotopic analysis of detrital and igneous zircon provides information about variations in crustal addition versus reworking through time. However, whereas detrital zircon data from only a few samples can provide information about extended periods of orogenic activity, this approach lacks the geological context that comes with studying igneous zircon and may not record mid- and deep-crustal sources or sources isolated from sites of deposition. Conversely, igneous zircon is likely to miss sources that were removed by later tectonic activity, but which may be preserved in the detrital record. The Central Gneiss Belt of the southwest Grenville Province in Ontario has a relatively well-understood orogenic architecture and records active-margin growth and reworking between ca. 1900 and 1200 Ma. We present U–Pb and Hf isotope data of zircon from 30 orthogneiss samples ranging in age from ca. 1750 to 1250 Ma, covering all tectonostratigraphic levels of the Central Gneiss Belt. As expected, the detrital and igneous datasets display many of the same overall features, such as crustal growth along the southwest Laurentian active margin; however, there are also some distinct differences. In particular, sedimentation appears to have taken place near the active margin, with little or no input from distal inboard sources, thus missing this significant component of reworked crust. This study highlights the need for a combination of detrital and igneous samples to provide the most complete picture of long-lived accretionary orogenic systems.