Abstract
The gabbroic Portrush Sill in Northern Ireland, part of the North Atlantic Igneous Province, intruded Lower Jurassic mudstones and siltstones about 55 Ma ago. We used petrologic observations and geochemical analyses to study how the sill interacted with the sedimentary rocks. Field relationships show that an Upper Sill and numerous associated Minor Intrusions were emplaced in the sedimentary host rocks before intrusion of the Main Sill, some 10 m above its upper contact. Geochemical analyses reveal two magma contamination processes: Nb and Ta anomalies, coupled with incompatible element enrichment, record contamination by deep crustal rocks, whereas Li, Pb and Ba anomalies reveal a superficial contamination through fluid circulation at the contact between magmatic and sedimentary rocks. Analysis of mineral assemblages and geochemical data from the contact aureole demonstrate uniform metamorphic conditions between the two main intrusions and an absence of a thermal gradient. The identification of pyrrhotite by magnetization analyses and of orthopyroxene by microprobe analyses indicates very high temperatures, up to 660 °C. Thermal modelling explains these temperatures as the coupled effects of the Main Sill and the earlier intruded Upper Sill and Minor Intrusions. Even though the chemical composition of the Main Sill suggests another type of parental liquid, all three units were emplaced in a very short time, certainly less than five years.
| Original language | English |
|---|---|
| Pages (from-to) | 67-79 |
| Number of pages | 13 |
| Journal | Geological Magazine |
| Volume | 149 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - Jan 2012 |
| Externally published | Yes |
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Keywords
- contact metamorphism
- magma contamination
- Northern Ireland
- Portrush Sill
- thermal modelling
ASJC Scopus subject areas
- Geology
Cite this
Intrusion history of the Portrush Sill, County Antrim, Northern Ireland : Evidence for rapid emplacement and high-temperature contact metamorphism. / Ledevin, Morgane; Arndt, Nicholas; Cooper, Mark R.; Earls, Garth; Lyle, Paul; Aubourg, Charles; Lewin, Eric.
In: Geological Magazine, Vol. 149, No. 1, 01.2012, p. 67-79.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Intrusion history of the Portrush Sill, County Antrim, Northern Ireland
T2 - Evidence for rapid emplacement and high-temperature contact metamorphism
AU - Ledevin, Morgane
AU - Arndt, Nicholas
AU - Cooper, Mark R.
AU - Earls, Garth
AU - Lyle, Paul
AU - Aubourg, Charles
AU - Lewin, Eric
PY - 2012/1
Y1 - 2012/1
N2 - The gabbroic Portrush Sill in Northern Ireland, part of the North Atlantic Igneous Province, intruded Lower Jurassic mudstones and siltstones about 55 Ma ago. We used petrologic observations and geochemical analyses to study how the sill interacted with the sedimentary rocks. Field relationships show that an Upper Sill and numerous associated Minor Intrusions were emplaced in the sedimentary host rocks before intrusion of the Main Sill, some 10 m above its upper contact. Geochemical analyses reveal two magma contamination processes: Nb and Ta anomalies, coupled with incompatible element enrichment, record contamination by deep crustal rocks, whereas Li, Pb and Ba anomalies reveal a superficial contamination through fluid circulation at the contact between magmatic and sedimentary rocks. Analysis of mineral assemblages and geochemical data from the contact aureole demonstrate uniform metamorphic conditions between the two main intrusions and an absence of a thermal gradient. The identification of pyrrhotite by magnetization analyses and of orthopyroxene by microprobe analyses indicates very high temperatures, up to 660 °C. Thermal modelling explains these temperatures as the coupled effects of the Main Sill and the earlier intruded Upper Sill and Minor Intrusions. Even though the chemical composition of the Main Sill suggests another type of parental liquid, all three units were emplaced in a very short time, certainly less than five years.
AB - The gabbroic Portrush Sill in Northern Ireland, part of the North Atlantic Igneous Province, intruded Lower Jurassic mudstones and siltstones about 55 Ma ago. We used petrologic observations and geochemical analyses to study how the sill interacted with the sedimentary rocks. Field relationships show that an Upper Sill and numerous associated Minor Intrusions were emplaced in the sedimentary host rocks before intrusion of the Main Sill, some 10 m above its upper contact. Geochemical analyses reveal two magma contamination processes: Nb and Ta anomalies, coupled with incompatible element enrichment, record contamination by deep crustal rocks, whereas Li, Pb and Ba anomalies reveal a superficial contamination through fluid circulation at the contact between magmatic and sedimentary rocks. Analysis of mineral assemblages and geochemical data from the contact aureole demonstrate uniform metamorphic conditions between the two main intrusions and an absence of a thermal gradient. The identification of pyrrhotite by magnetization analyses and of orthopyroxene by microprobe analyses indicates very high temperatures, up to 660 °C. Thermal modelling explains these temperatures as the coupled effects of the Main Sill and the earlier intruded Upper Sill and Minor Intrusions. Even though the chemical composition of the Main Sill suggests another type of parental liquid, all three units were emplaced in a very short time, certainly less than five years.
KW - contact metamorphism
KW - magma contamination
KW - Northern Ireland
KW - Portrush Sill
KW - thermal modelling
UR - http://www.scopus.com/inward/record.url?scp=82955168389&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=82955168389&partnerID=8YFLogxK
U2 - 10.1017/S0016756811000537
DO - 10.1017/S0016756811000537
M3 - Article
AN - SCOPUS:82955168389
VL - 149
SP - 67
EP - 79
JO - Geological Magazine
JF - Geological Magazine
SN - 0016-7568
IS - 1
ER -