Zoned garnets in metapelites in western Fiordland, southwest New Zealand: polychronic crystallisation and insight into the nature and extent of early Cretaceous regional metamorphism
New Zealand Journal of Geology and Geophysics
By: J.Y. Bradshaw
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Abstract
Two distinct types of compositional zoning are recognised in idioblastic to subidioblastic garnets in amphibolite facies metapelites in western Fiordland. One type occurs in kyanite (?? sillimanite)-bearing rocks and is characterised by a core to rim increase in CaO content, and a sympathetic decrease in FeO and MgO, with MnO remaining essentially constant, or decreasing slightly near the rim. This zoning pattern formed during garnet growth, and records adjustment of mineral equilibria under conditions of increasing load pressure. A much less common type of zoned garnet occurs in sillimanite + K-feldspar-bearing metapelites and is characterised by a core to rim decrease in CaO and MgO contents and a sympathetic increase in FeO and MnO near the rim. This zoning pattern is interpreted to result from post-growth volume diffusion, and records metamorphism at significantly lower pressures. -from Author
Suggested Citation
Bradshaw, J., 1991, Zoned garnets in metapelites in western Fiordland, southwest New Zealand: polychronic crystallisation and insight into the nature and extent of early Cretaceous regional metamorphism: New Zealand Journal of Geology and Geophysics, v. 34, no. 3, p. 261-270, https://doi.org/10.1080/00288306.1991.9514464.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Zoned garnets in metapelites in western Fiordland, southwest New Zealand: polychronic crystallisation and insight into the nature and extent of early Cretaceous regional metamorphism |
| Series title | New Zealand Journal of Geology and Geophysics |
| DOI | 10.1080/00288306.1991.9514464 |
| Volume | 34 |
| Issue | 3 |
| Year Published | 1991 |
| Language | English |
| Publisher | Taylor and Francis |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | New Zealand Journal of Geology and Geophysics |
| First page | 261 |
| Last page | 270 |