TY - JOUR
T1 - The Ardara pluton, Ireland
T2 - deflating an expanded intrusion
AU - Vernon, R. H.
AU - Paterson, S. R.
PY - 1993
Y1 - 1993
N2 - The Ardara pluton, north-western Ireland, is a circular monzodiorite-granodiorite intrusion with a "tail." It has been regarded as a typical example of a pluton emplaced entirely by expansion ("balloning") after initial intrusion. Most of the foliation in the pluton is magmatic, with weak superimposed solid-state features, apart from a thin rind of strong solid-state deformation. The solid-state deformation in the pluton appears to be largely, if not entirely, of post-intrusive, tectonic origin. Flattened microgranitoid enclaves, a concentric magmatic flow foliation and compositional zoning in the pluton are consistent with some expansion of magma prior to crystallization. However, strains in the wall rocks indicate that only a small amount (25%-38%) of the volume of the pluton can be ascribed to ballooning. This relatively small amount of expansion could account for (a) observed structural concordance and strong syn-metamorphic deformation in the aureole, (b) flattening of microgranitoid enclaves (magma globules) in the pluton and possibly (c) a small amount of solid-state deformation in the pluton during "lock-up" of magmatic flow. Evidence of solid-state deformation superimposed on a strong magmatic flow foliation in the tail of the pluton implies that a fault was active during emplacement and may have assisted the intrusion. Further space for the pluton may have been made by a complex interaction of processes, many of which cannot be constrained from a two-dimensional cross-section through the area. These possibilities highlight the limitations of attempting to constrain emplacement mechanisms on the sole basis of structures adjacent to plutons.
AB - The Ardara pluton, north-western Ireland, is a circular monzodiorite-granodiorite intrusion with a "tail." It has been regarded as a typical example of a pluton emplaced entirely by expansion ("balloning") after initial intrusion. Most of the foliation in the pluton is magmatic, with weak superimposed solid-state features, apart from a thin rind of strong solid-state deformation. The solid-state deformation in the pluton appears to be largely, if not entirely, of post-intrusive, tectonic origin. Flattened microgranitoid enclaves, a concentric magmatic flow foliation and compositional zoning in the pluton are consistent with some expansion of magma prior to crystallization. However, strains in the wall rocks indicate that only a small amount (25%-38%) of the volume of the pluton can be ascribed to ballooning. This relatively small amount of expansion could account for (a) observed structural concordance and strong syn-metamorphic deformation in the aureole, (b) flattening of microgranitoid enclaves (magma globules) in the pluton and possibly (c) a small amount of solid-state deformation in the pluton during "lock-up" of magmatic flow. Evidence of solid-state deformation superimposed on a strong magmatic flow foliation in the tail of the pluton implies that a fault was active during emplacement and may have assisted the intrusion. Further space for the pluton may have been made by a complex interaction of processes, many of which cannot be constrained from a two-dimensional cross-section through the area. These possibilities highlight the limitations of attempting to constrain emplacement mechanisms on the sole basis of structures adjacent to plutons.
UR - http://www.scopus.com/inward/record.url?scp=0027884371&partnerID=8YFLogxK
U2 - 10.1016/0024-4937(93)90030-G
DO - 10.1016/0024-4937(93)90030-G
M3 - Article
AN - SCOPUS:0027884371
VL - 31
SP - 17
EP - 32
JO - Lithos
JF - Lithos
SN - 0024-4937
IS - 1-2
ER -