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Book Chapter

Some observations on the use of zircon U–Pb geochronology in the study of granitic rocks

By
Ian S. Williams
Ian S. Williams
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Published:
January 01, 1992

In situ, microscale, U–Pb isotopic analyses of zircon using the SHRIMP ion microprobe demonstrate both the potential and the limitations of zircon U–Pb geochronology. Most zircons, whether from igneous or metamorphic rocks, need to be considered as mixed isotopic systems. In simple, young igneous rocks the mixing is principally between isotopically disturbed and undisturbed zircon. In polymetamorphic rocks, several generations of zircon growth can coexist, each with a different pattern of discordance. A similar situation exists for igneous rocks rich in inherited zircon, as these contain both melt-precipitated zircon and inherited components of several different ages. Microscale analysis by ion probe makes it possible to sample the record of provenance, age and metamorphic history commonly preserved within a single zircon population. It also indicates how the interpretation of conventionally-measured bulk zircon isotopic compositions might be improved.

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GSA Special Papers

The Second Hutton Symposium on the Origin of Granites and Related Rocks

P. E. Brown
P. E. Brown
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B. W. Chappell
B. W. Chappell
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Geological Society of America
Volume
272
ISBN print:
9780813722726
Publication date:
January 01, 1992

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