Sericitization of plagioclase in the Rosses granite complex, Co. Donegal, Ireland

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Authors:Que, Meideno; Allen, Alistair R.
Author Affiliations:Primary:
University College, Department of Geology, Cork, Ireland
Volume Title:Mineralogical Magazine
Source:Mineralogical Magazine, 60(6), p.927-936. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0026-461X
Publication Date:1996
Note:In English. 34 refs.; 1 table
Summary:Sericitization in three separate pulses of the Rosses Granite Ring Complex, Co. Donegal, Ireland, has been investigated texturally and chemically using electron microscopy, electron microprobe and fluid inclusion thermometry. The sericitization, which is restricted to the cores of plagioclase, is associated with pores which are abundant in the cores, but absent in the margins. Alkali feldspar, although porous, is unaltered. Associated with the sericitization is alteration of the adjacent primary plagioclase within the cores of grains to a more sodic composition. It is postulated that the sericitization resulted from the action of externally derived secondary hydrothermal fluids, which gained access to the pores in the plagioclase via now sealed microfractures, formed either by contraction during cooling of the Rosses Complex, or more likely by hydraulic fracturing by the fluids themselves. Limited fluid/rock ratios restricted the degree of sericitization within the host plagioclase, whilst an absence of alteration in alkali feldspar may have been due to the inaccessibility of pores in the alkali feldspar to the hydrothermal fluids at the time of alteration. Fluid inclusion data suggest that the fluids were of low salinity, and that the sericitization took place at an early stage in the cooling history of the Rosses Complex at temperatures between 400 and 600°C. It is further contended that greisenization in the Rosses Complex predated the sericitization and that the greisenization may have been due solely to volatile-rich latestage magmatic fluids.
Subjects:Feldspar group; Framework silicates; Mica group; Petrography; Plagioclase; Sericite; Sheet silicates; Silicates; Donegal Ireland; Europe; Ireland; Rosses Granite; Western Europe
Abstract Numbers:97M/836
Record ID:1997036774
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland
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