THE CHEMICAL-COMPOSITION OF IGNEOUS ZIRCON SUITES - IMPLICATIONS FOR GEOCHEMICAL TRACER STUDIES

Minor and trace element data obtained for ultrapure zircon fractions isolated from a variety of igneous rocks indicate that zircon grains crystallizing in different magmatic environments have unique geochemical signatures. Zircon megacrysts found in kimberlites (mantle zircons?) are characterized by extremely low abundances of U (<30 ppm), Th (<10 ppm), and the REEs, while zircon crystallizing from magmas generated in continental rift settings, such as carbonatite and nepheline syenite magmas, have anomalously low Hf abundances (6000 to 8000 ppm) with correspondingly high Zr/Hf ratios (>60). In addition, zircon crystallizing in mafic magmas have elevated Sc levels (86 to 230 ppm), strongly fractionated REE patterns, and generally high Th/U ratios (> 1) compared to other igneous zircon suites. The presence of diagnostic geochemical signatures in igneous zircon suites indicates that zircon can be used as a geochemical tracer and may be useful for identifying the geochemical nature of source regions in provenance studies of single detrital zircon grains from sedimentary rocks or for deciphering basement rock compositions, if not exposed, from a geochemical study of xenocrystic zircon grains. © 1990.