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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

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DOI: 10.1080/00288306.1991.9514464

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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

Additional Publication Details

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
Number of Pages:
10