TY - JOUR
T1 - Late Caledonian transpression and the structural controls on pluton construction
T2 - new insights from the Omey Pluton, western Ireland
AU - Mccarthy, William James
AU - Reavy, Reginald John
AU - Stevenson, Carl
AU - Petronis, Michael S.
PY - 2015/3/1
Y1 - 2015/3/1
N2 - The Galway Granite Complex is unique among the British and Irish Caledonian granitoid terranes, as it records punctuated phases of magmatism from ∼425–380 Ma throughout the latest phase of the Caledonian Orogeny. Remapping of the Omey Pluton, the oldest member of this suite, has constrained the spatial distribution and contact relationships of the pluton's three main facies relative to the nature of the host rock structure. The external contacts of the pluton are mostly concordant to the limbs and hinge of the Connemara Antiform. New AMS data show that a subtle concentric outward dipping foliation is present, and this is interpreted to reflect pluton inflation during continued magma ingress. Combined field, petrographic and AMS data show that two sets of shear zones (NNW–SSE and ENE–WSW) cross-cut the concentric foliation, and that these structures were active during the construction of the pluton. We show that regional sinistral transpression at ∼420 Ma would have caused dilation along the intersection of these two fault sets, and suggest that this facilitated centralised magma ascent. Lateral emplacement was controlled by the symmetry of the Connemara Antiform to ultimately produce a discordant phacolith. We propose that regional sinistral transpression at ∼420 Ma influenced the siting of smaller intrusions over NNW–SSE faults, and that the later onset of regional transtension caused larger volumes of magma to intrude along the E–W Skird Rocks Fault at ∼400 Ma.
AB - The Galway Granite Complex is unique among the British and Irish Caledonian granitoid terranes, as it records punctuated phases of magmatism from ∼425–380 Ma throughout the latest phase of the Caledonian Orogeny. Remapping of the Omey Pluton, the oldest member of this suite, has constrained the spatial distribution and contact relationships of the pluton's three main facies relative to the nature of the host rock structure. The external contacts of the pluton are mostly concordant to the limbs and hinge of the Connemara Antiform. New AMS data show that a subtle concentric outward dipping foliation is present, and this is interpreted to reflect pluton inflation during continued magma ingress. Combined field, petrographic and AMS data show that two sets of shear zones (NNW–SSE and ENE–WSW) cross-cut the concentric foliation, and that these structures were active during the construction of the pluton. We show that regional sinistral transpression at ∼420 Ma would have caused dilation along the intersection of these two fault sets, and suggest that this facilitated centralised magma ascent. Lateral emplacement was controlled by the symmetry of the Connemara Antiform to ultimately produce a discordant phacolith. We propose that regional sinistral transpression at ∼420 Ma influenced the siting of smaller intrusions over NNW–SSE faults, and that the later onset of regional transtension caused larger volumes of magma to intrude along the E–W Skird Rocks Fault at ∼400 Ma.
KW - Anisotropy of magnetic susceptibility
KW - anticline
KW - ascent and emplacement
KW - Caledonian granite
KW - flow
KW - fold
KW - Galway Granite Complex
KW - microstructure
KW - phacolith
KW - transpression
UR - http://journals.cambridge.org/download.php?file=%2F224_88998DBFCFCC069CBE95B4951B009B66_journals__TRE_TRE106_01_S1755691015000201a.pdf&cover=Y&code=edab62b1c94974d900828a47df480146
U2 - 10.1017/S1755691015000201
DO - 10.1017/S1755691015000201
M3 - Article
SN - 1755-6910
VL - 106
SP - 1
EP - 18
JO - Earth and Environmental Science Transactions of the Royal Society of Edinburgh
JF - Earth and Environmental Science Transactions of the Royal Society of Edinburgh
IS - 1
ER -