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A composite spessartite–appinite intrusion from Port‐na‐Blagh, County Donegal, Ireland
Author(s) -
Elsdon R.,
Todd S. P.
Publication year - 1989
Publication title -
geological journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.721
H-Index - 54
eISSN - 1099-1034
pISSN - 0072-1050
DOI - 10.1002/gj.3350240203
Subject(s) - geology , magma , geochemistry , layered intrusion , intrusion , felsic , amphibole , pyroxene , mafic , petrology , outcrop , sorting , quartz , olivine , paleontology , volcano , computer science , programming language
A sheet‐like appinite from Breaghy Head, North Donegal, is closely associated with a spessartite intrusion. Field, mineralogical, and geochemical similarities indicate that the parent magmas were very similar, and the appinite magma may have been derived from the spessartite by small degrees of crystal fractionation. The appinite is divided into an amphibole‐rich lower part and a felsic upper part; the mineralogical contrast between the two is best explained by two‐pulse intrusion of a batch of spessartitic magma within which amphibole and pyroxene had already segregated due to crystal settling or flow sorting. Unlike other Caledonian appinites, the Breaghy Head intrusion is not one of a cluster, and appears to be an isolated development. Possible reasons for its location are discussed.