TerraneChron : delivering a competitive edge in exploration

erraneChron is GEMOC’s unique methodology for studying crustal evolution and evaluating the metallogenic potential of terranes. It is based on the integrated in situ analysis of zircons for U-Pb age, Hf-isotopic composition and trace-element composition using GEMOC’s laser-ablation-microprobe (LAM) ICPMS, LAM-Multi-Collector (MC) ICPMS and electron microprobe (EMP). The method can be applied to zircons separated from single rocks or to zircons picked from drainage samples judiciously collected within a defined catchment (on scales of 10 1000 km depending on the objective). The use of drainage samples has many advantages: nature has separated and concentrated a statistically more meaningful sample than is achievable by conventional single rock sampling and methods, and this can provide a more comprehensive coverage of rock types from the drainage region. For a meaningful analysis, a sample should comprise 50 70 randomly selected grains as well as non-random grains judged to be representative of minor and/or potentially important detrital populations (T. Andersen, in prep.). The U-Pb analyses provide rapid and cost-effective age determinations with precision comparable to the ion microprobe. The Hf-isotopic data provide information on the source of the magmatic parent rock to each zircon; they tell whether the relevant tectonic event was accompanied by young mantle-derived magmatic input (“juvenile” source), if only pre-existing crust was involved (ie crustal reworking), or a combination of these processes. The trace elements provide information about the composition of the magmatic rock that precipitated the zircon. Thus the TerraneChron approach provides more layers of information than the conventional U-Pb age-spectrum approach.