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From richer to poorer: zircon inheritance in Pomona Island Granite, New Zealand.

Authors :
Scott, J.
Palin, J.
Cooper, A.
Sagar, M.
Allibone, A.
Tulloch, A.
Source :
Contributions to Mineralogy & Petrology; May2011, Vol. 161 Issue 5, p667-681, 15p, 1 Color Photograph, 1 Black and White Photograph, 2 Charts, 4 Graphs, 2 Maps
Publication Year :
2011

Abstract

Previous U-Pb zircon dating of the Pomona Island Granite (PIG) pluton (South Island, New Zealand) yielded either Permo-Carboniferous or Late Jurassic ages for five samples essentially indistinguishable in their field, petrographic, and geochemical characteristics. Detailed cathodoluminescence imaging and LA-ICP-MS dating of zircon in new and previously dated samples reveal that portions of the pluton contain either delicately oscillatory-zoned Late Jurassic zircon grains with rare Permo-Carboniferous cores, or Permo-Carboniferous grains with ubiquitous but thin Late Jurassic rims. Based on zircon dissolution-overgrowth textures, zircon rim and core trace element compositions, and the limited extent of sub-solidus rock recrystallisation textures, the bipartite age distribution is unlikely to reflect variable Pb-loss or metamorphic re-equilibration. Magmatic Zr-saturation temperatures were ≥851°C for samples dominated by Jurassic zircon and ≤809°C for samples with a predominance of Permo-Carboniferous zircon. Together, these data are consistent with PIG magmas having been derived from partial melting of a Permo-Carboniferous felsic igneous source at variable temperature wholly in the Late Jurassic (157 ± 3 Ma). The lowest temperature melts would have been incapable of dissolving significant amounts of pre-existing zircon and consequently generated inheritance-rich magmas, with the very thin rims on the pre-existing zircon grains the only evidence of the Late Jurassic magmatic age. As the partial melting temperature increased and nearly all pre-existing zircon grains dissolved into the magma, an inheritance-poor batch of melt was generated, which precipitated new zircon grains upon crystallisation. Concentrations of major and many trace elements in both magma batches may have been buffered by retention of residual quartz and feldspar in the source, which would explain the limited geochemical differences between inheritance-rich and inheritance-poor portions. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
00107999
Volume :
161
Issue :
5
Database :
Complementary Index
Journal :
Contributions to Mineralogy & Petrology
Publication Type :
Academic Journal
Accession number :
59834491
Full Text :
https://doi.org/10.1007/s00410-010-0556-5