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Insights into magma histories through silicate-oxide crystal clusters: linking the Hiltaba Suite intrusive rocks to the Gawler Range Volcanics, Gawler Craton, South Australia

Citation

Ferguson, MRM and Ehrig, K and Meffre, S, Insights into magma histories through silicate-oxide crystal clusters: linking the Hiltaba Suite intrusive rocks to the Gawler Range Volcanics, Gawler Craton, South Australia, Precambrian Research, 321 pp. 103-122. ISSN 0301-9268 (2019) [Refereed Article]

Copyright Statement

Copyright 2018 Elsevier B.V.

DOI: doi:10.1016/j.precamres.2018.11.015

Abstract

The Roxby Downs Granite (RDG), host to the supergiant Olympic Dam deposit, and the Gawler Range Volcanics (GRV) in South Australia, both contain clusters of touching silicate and oxide minerals. Here we report on the geochemistry and petrography of these rocks and their contained mineral clusters, before comparing them to similar occurrences elsewhere in the world to gain a better understand of their genesis and the links between the RDG (and other members of the Hiltaba Suite) and the GRV. Crystal clusters in the RDG comprise magnetite + apatite ± titanite ± biotite ± zircon which are typically enveloped in a plagioclase crystal-matrix. In the GRV, crystal clusters comprise pyroxene + titanomagnetite ± plagioclase ± apatite ± zircon, display variably glomeroporphyritic, equigranular, poikilitic, and loosely packed habits, and are enclosed by texturally varied groundmass. Of the GRV lavas studied, pyroxenes and titanomagnetite show systematic trends in major and trace element compositions conformable with the stratigraphic position of their hosts. This suggests the lavas are related through differentiation in the upper crust and represent the inversion of a normally zoned reservoir. There are no compositional contrasts between phenocrysts and crystals in GRV clusters, and Mg# of pyroxenes are consistent with those predicted from whole-rock compositions, implying that all analysed crystals (including those in clusters) were formed within, or were at least equilibrated to, the host lavas’ precursors. Rather than entire histories as isolated crystal clusters entrained by melt flow, intergrowth textures and mafic magmatic enclaves suggest that the majority of GRV crystal clusters were liberated from closely packed crystal masses through magma rejuvenation and associated crystal resorption. Consistent Fe-Ti oxide + apatite + zircon + plagioclase assemblages and textures in both the GRV and RDG suggest a shared genetic scenario, although an extended model is needed to account for the transformation of GRV-type to HS-type crystal clusters. For hot and dry magmas such as those that formed the GRV and RDG, cooling causes pyroxene + Fe-Ti oxide + plagioclase in GRV-type crystal clusters to react with each other and the melt, forming HS-type magnetite + titanite + biotite + feldspar crystal clusters. Rejuvenation events implicated in the liberation of GRV-type crystal clusters may be important drivers of magmatic-hydrothermal iron-oxide deposit formation.

Item Details

Item Type:Refereed Article
Keywords:Hiltaba, Gawler Range volcanics, Roxby Downs granite, Olympic Dam, Crystal cluster, Snake River Plain, San Juan
Research Division:Earth Sciences
Research Group:Geology
Research Field:Igneous and Metamorphic Petrology
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Earth Sciences
UTAS Author:Ferguson, MRM (Mr Matthew Ferguson)
UTAS Author:Meffre, S (Dr Sebastien Meffre)
ID Code:129974
Year Published:2019
Funding Support:Australian Research Council (CE0561595)
Web of Science® Times Cited:3
Deposited By:CODES ARC
Deposited On:2019-01-02
Last Modified:2019-12-10
Downloads:0

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