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Source controls on mineralisation: Regional geology and magmatic evolution of Fiji

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journal contribution
posted on 2022-11-07, 16:32 authored by Rose Hannah Clarke, Daniel Smith, Jonathan Naden

 There is a well-established link between world-class gold telluride mineral deposits and alkalic magmatic host rocks, often emplaced post-subduction in arc terranes. Fiji is home to two such deposits, and provides an ideal location to study the relationship between the alkalic (shoshonitic) host rocks, their geodynamic context, and potential roles in metal enrichment. A total of 93 new geochemical analyses of magmatic rocks from across Fiji are presented, alongside detailed petrography and mineralogy and a new compilation of literature data. Despite relatively similar mineralogy across syn- and post-subduction samples, there are geochemical differences between them, with the latter displaying elevated concentrations of Ba (<2137 ppm), Rb (<218 ppm), Sr (<2648 ppm) and K2O (<10.18 wt%), and depletions in Nb and Ta. Multi-element trends suggest exaggerations of ‘typical’ arc patterns in post-subduction shoshonites. Geochemical data suggest that whilst the fluxing of fluids and sediment melts from a subducted slab may play a role in producing the distinctive post-subduction magmas, they are likely insufficient to drive such strong trends. Instead, biotite or possibly phlogopite in the lithosphere are suggested as being a key ‘ingredient’. Earlier subduction can modify the lithosphere through the addition of hydrous phases, both by metasomatism of the lithospheric mantle, or by the formation of residual minerals during fractional crystallisation. Remelting of these phases could liberate trace elements and metals. Biotite in particular could facilitate some of the observed large ion lithophile elements (LILE) enrichments and the alkali-rich (potassic) nature of the magmas. 

Funding

The Central England NERC Training Alliance 2 (CENTA2)

Natural Environment Research Council

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BGS University Funding Initiative (Project S392)

Tellurium and Selenium Cycling and Supply

Natural Environment Research Council

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History

Author affiliation

School of Geography, Geology and Environment, University of Leicester

Version

  • VoR (Version of Record)

Published in

Lithos

Volume

423-433

Publisher

Elsevier

issn

0024-4937

Copyright date

2022

Available date

2022-11-07

Language

en

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