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Reconstruction of an Ordovician seafloor volcanohydrothermal system: a case study from the Copper Coast, southeastern Ireland using field, geochemical and fluid inclusion data

Published online by Cambridge University Press:  02 January 2018

C. Breheny*
Affiliation:
Earth and Ocean Sciences, School of Natural Sciences, National University of Ireland, Galway, Ireland.
K. R. Moore
Affiliation:
Camborne School of Mines, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Penryn Campus, Treliver Road, Penryn, Cornwall TR10 9EZ, UK.
A. Costanzo
Affiliation:
Earth and Ocean Sciences, School of Natural Sciences, National University of Ireland, Galway, Ireland.
M. Feely
Affiliation:
Earth and Ocean Sciences, School of Natural Sciences, National University of Ireland, Galway, Ireland.

Abstract

Volcanic rocks in south County Waterford include flow-top hyaloclastite, pillow lavas and peperite, which are formed typically by sub-aqueous eruption or intrusion into unconsolidated sediment. Element mobility in wet sediment during emplacement of volcanic intrusions was reconstructed on a variety of spatial scales using bulk-rock and mineral analysis. Magma-sediment and magma-water interactions enhanced hydrothermal alteration. The chemistry of chlorite was a function of mixing between an Fe-rich magmatic fluid and a Mg-rich meteoric fluid. Chlorite geothermometry yields temperatures of formation between 230 and 388°C compatible with other metamorphic indicators. Fluid inclusion microthermometric data from genetically-related mineralized quartz veins reveal a hydrothermal vein mineralization event that occurred at lower temperatures during the end stage of volcanic activity. A convection driven mixing trend reflects the trapping of co-existing brine with entrained seawater concomitant with, the late stages of emplacement of the Bunmahon Volcano intrusions.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2016

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