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Host-rock deformation during the emplacement of the Mourne Mountains granite pluton : insights from the regional fracture pattern

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Mattsson_2019_Geosphere_Host_rock_CC.pdf (12.19Mb)
Date
01/02/2020
Author
Mattsson, Tobias
Burchardt, Steffi
Mair, Karen
Place, Joachim
Keywords
QE Geology
Geology
Stratigraphy
DAS
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Abstract
The Mourne Mountains magmatic center in Northern Ireland consists of five successively intruded granites emplaced in the upper crust. The Mourne granite pluton has classically been viewed as a type locality of a magma body emplaced by cauldron subsidence. Cauldron subsidence makes space for magma through the emplacement of ring dikes and floor subsidence. However, the Mourne granites were more recently re-interpreted as laccoliths and bysmaliths. Laccolith intrusions form by inflation and dome their host rock. Here we perform a detailed study of the deformation in the host rock to the Mourne granite pluton in order to test its emplacement mechanism. We use the host-rock fracture pattern as a passive marker and microstructures in the contact-metamorphic aureole to constrain large-scale magma emplacement-related deformation. The dip and azimuth of the fractures are very consistent on the roof of the intrusion and can be separated into four steeply inclined sets dominantly striking SE, S, NE, and E, which rules out pluton-wide doming. In contrast, fracture orientations in the northeastern wall to the granites suggest shear parallel to the contact. Additionally, contact-metamorphic segregations along the northeastern contact are brecciated. Based on the host-rock fracture pattern, the contact aureole deformation, and the north-eastward-inclined granite-granite contacts, we propose that mechanisms involving either asymmetric "trap-door" floor subsidence or laccolith and bysmalith intrusion along an inclined or curved floor accommodated the emplacement of the granites and led to deflection of the northeastern wall of the intrusion.
Citation
Mattsson , T , Burchardt , S , Mair , K & Place , J 2020 , ' Host-rock deformation during the emplacement of the Mourne Mountains granite pluton : insights from the regional fracture pattern ' , Geosphere , vol. 16 , no. 1 , pp. 182-209 . https://doi.org/10.1130/GES02148.1
Publication
Geosphere
Status
Peer reviewed
DOI
https://doi.org/10.1130/GES02148.1
ISSN
1553-040X
Type
Journal article
Rights
Copyright © 2019 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY-NC license
Collections
  • University of St Andrews Research
URI
http://hdl.handle.net/10023/20983

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