The Origin of Spodumene Pegmatites Associated with the Leinster Granite in Southeast Ireland

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Title: The Origin of Spodumene Pegmatites Associated with the Leinster Granite in Southeast Ireland
Authors: Barros, RenataMenuge, Julian
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Date: 1-Jul-2016
Online since: 2020-09-15T10:33:59Z
Abstract: Rare-element pegmatites have diverse chemical signatures and are important sources of strategic metals such as Li, Cs, and Ta. The two main hypotheses to explain rare-element pegmatite formation are (1) residual magmas from the crystallization of granitic rocks, and (2) partial melts from a relatively rare-element-rich source. In southeast Ireland, spodumene and spodumenefree pegmatite dikes occur along the eastern margin of the S-type Leinster Granite batholith. With indistinguishable emplacement ages around 400 Ma, the origin of the Li-rich pegmatitic fluids has been suggested to have resulted from extreme fractional crystallization of Leinster Granite granodiorite magma. To test this hypothesis, we used whole-rock geochemistry of pegmatite and granodiorite samples from drill cores and geochemical modeling of in situ crystallization and batch melting to investigate which process better explains the formation of the pegmatites. Chemical signatures of the pegmatites and granodiorite do not indicate a direct comagmatic relationship, as the granodiorite has higher concentrations of many incompatible elements than the pegmatites (e.g., concentrations of Zr, Ti, and Y). Concentrations of Li, Rb, Cs, Sr, and Ba show no clear fractionation trends from granodiorite to pegmatite. The in situ crystallization model using the average granodiorite composition as the initial magma generates a range of compositions that does not include pegmatites, so it is unlikely that they represent residual granitic magmas. Modeling of partial melting indicates that the Leinster Granite granodiorite and pegmatite magmas could have formed in separate events and from chemically different source rocks, with the pegmatite magmas presumably formed in a younger event because the pegmatites intrude the granodiorite.
Funding Details: European Commission - European Regional Development Fund
Science Foundation Ireland
Type of material: Journal Article
Publisher: Mineralogical Association of Canada
Journal: Canadian Mineralogist
Volume: 54
Issue: 4
Start page: 847
End page: 862
Copyright (published version): 2016 Mineralogical Association of Canada
Keywords: Spodumene pegmatiteLeinster GraniteGeochemical modelingIn situ crystallizationBatch meltingPetrogenesisPartition CoefficientsLithium PegmatitesBlack hillsAlkali feldsparTrace elementsAplites dikesCrystallizationDakota
DOI: 10.3749/canmin.1600027
Language: en
Status of Item: Peer reviewed
Appears in Collections:Earth Sciences Research Collection
Earth Institute Research Collection
ICRAG Research Collection

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