Constraints on the timing of Scandian deformation and the nature of a buried Grampian terrane under the Caledonides of northwestern Ireland

C. L. Kirkland, G. I. Alsop, J. S. Daly, M. J. Whitehouse, R. Lam, C. Clark

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

In the Caledonides of northwestern Ireland there is little evidence for the crystalline basement to the Dalradian Supergroup, though ascertaining its nature is a critical prerequisite for palaeogeographical reconstructions. In Donegal a lamprophyre intrusion has sampled material with isotopic composition, age and fabrics that permit the investigation of the hidden basement of this region. U–Pb and Lu–Hf isotopes in concert with structural analysis are used to elucidate the origin of three morphologically distinct zircon populations from the lamprophyre. The first of these comprises c. 828 to c. 1660 Ma rounded inherited grains. The second population, of 476 ± 3 Ma large xenocrystic grains, displays oscillatory zoned cores embayed by cross-cutting overgrowths, implying a multi-stage magmatic genesis. The third population, of 437 ± 5 Ma high aspect ratio euhedral grains, is interpreted to date the magmatic crystallization of the lamprophyre. Hf isotopic data from the Silurian and Neo- to Mesoproterozoic zircons yield crustal residence ages of 1.0–2.3 Ga. However, the Ordovician grains have ϵHfi values of c. −20 and model ages of 2.7–2.8 Ga. These data are consistent with the presence of either Archaean crust or an underthrust Ordovician magmatic rock with an Archaean source component, at depth in NW Ireland. Felsic xenoliths, interpreted to be derived from the country rock Dalradian metasediments, exhibit a pre-entrainment foliation and are randomly oriented relative to the foliation within the lamprophyre matrix, indicating deformation prior to c. 437 Ma, probably related to the Grampian orogeny. The host lamprophyre contains a magmatic foliation parallel to a foliation in the country rock, implying synkinematic emplacement during regional NW–SE compression at 437 Ma.
Original languageEnglish
Pages (from-to)615-625
Number of pages11
JournalJournal of the Geological Society
Volume170
Issue number4
Early online date24 May 2013
DOIs
Publication statusPublished - Jul 2013

Fingerprint

lamprophyre
terrane
foliation
Dalradian
country rock
Archean
Ordovician
zircon
metasediment
structural analysis
orogeny
entrainment
Silurian
emplacement
isotopic composition
crystallization
compression
isotope
crust
matrix

Cite this

Constraints on the timing of Scandian deformation and the nature of a buried Grampian terrane under the Caledonides of northwestern Ireland. / Kirkland, C. L.; Alsop, G. I. ; Daly, J. S.; Whitehouse, M. J.; Lam, R.; Clark, C.

In: Journal of the Geological Society , Vol. 170, No. 4, 07.2013, p. 615-625.

Research output: Contribution to journalArticle

@article{2b3411ffc9274fda999ae139b2b1d7be,
title = "Constraints on the timing of Scandian deformation and the nature of a buried Grampian terrane under the Caledonides of northwestern Ireland",
abstract = "In the Caledonides of northwestern Ireland there is little evidence for the crystalline basement to the Dalradian Supergroup, though ascertaining its nature is a critical prerequisite for palaeogeographical reconstructions. In Donegal a lamprophyre intrusion has sampled material with isotopic composition, age and fabrics that permit the investigation of the hidden basement of this region. U–Pb and Lu–Hf isotopes in concert with structural analysis are used to elucidate the origin of three morphologically distinct zircon populations from the lamprophyre. The first of these comprises c. 828 to c. 1660 Ma rounded inherited grains. The second population, of 476 ± 3 Ma large xenocrystic grains, displays oscillatory zoned cores embayed by cross-cutting overgrowths, implying a multi-stage magmatic genesis. The third population, of 437 ± 5 Ma high aspect ratio euhedral grains, is interpreted to date the magmatic crystallization of the lamprophyre. Hf isotopic data from the Silurian and Neo- to Mesoproterozoic zircons yield crustal residence ages of 1.0–2.3 Ga. However, the Ordovician grains have ϵHfi values of c. −20 and model ages of 2.7–2.8 Ga. These data are consistent with the presence of either Archaean crust or an underthrust Ordovician magmatic rock with an Archaean source component, at depth in NW Ireland. Felsic xenoliths, interpreted to be derived from the country rock Dalradian metasediments, exhibit a pre-entrainment foliation and are randomly oriented relative to the foliation within the lamprophyre matrix, indicating deformation prior to c. 437 Ma, probably related to the Grampian orogeny. The host lamprophyre contains a magmatic foliation parallel to a foliation in the country rock, implying synkinematic emplacement during regional NW–SE compression at 437 Ma.",
author = "Kirkland, {C. L.} and Alsop, {G. I.} and Daly, {J. S.} and Whitehouse, {M. J.} and R. Lam and C. Clark",
year = "2013",
month = "7",
doi = "10.1144/jgs2012-106",
language = "English",
volume = "170",
pages = "615--625",
journal = "Journal of the Geological Society",
issn = "0016-7649",
publisher = "Geological Society of London",
number = "4",

}

TY - JOUR

T1 - Constraints on the timing of Scandian deformation and the nature of a buried Grampian terrane under the Caledonides of northwestern Ireland

AU - Kirkland, C. L.

AU - Alsop, G. I.

AU - Daly, J. S.

AU - Whitehouse, M. J.

AU - Lam, R.

AU - Clark, C.

PY - 2013/7

Y1 - 2013/7

N2 - In the Caledonides of northwestern Ireland there is little evidence for the crystalline basement to the Dalradian Supergroup, though ascertaining its nature is a critical prerequisite for palaeogeographical reconstructions. In Donegal a lamprophyre intrusion has sampled material with isotopic composition, age and fabrics that permit the investigation of the hidden basement of this region. U–Pb and Lu–Hf isotopes in concert with structural analysis are used to elucidate the origin of three morphologically distinct zircon populations from the lamprophyre. The first of these comprises c. 828 to c. 1660 Ma rounded inherited grains. The second population, of 476 ± 3 Ma large xenocrystic grains, displays oscillatory zoned cores embayed by cross-cutting overgrowths, implying a multi-stage magmatic genesis. The third population, of 437 ± 5 Ma high aspect ratio euhedral grains, is interpreted to date the magmatic crystallization of the lamprophyre. Hf isotopic data from the Silurian and Neo- to Mesoproterozoic zircons yield crustal residence ages of 1.0–2.3 Ga. However, the Ordovician grains have ϵHfi values of c. −20 and model ages of 2.7–2.8 Ga. These data are consistent with the presence of either Archaean crust or an underthrust Ordovician magmatic rock with an Archaean source component, at depth in NW Ireland. Felsic xenoliths, interpreted to be derived from the country rock Dalradian metasediments, exhibit a pre-entrainment foliation and are randomly oriented relative to the foliation within the lamprophyre matrix, indicating deformation prior to c. 437 Ma, probably related to the Grampian orogeny. The host lamprophyre contains a magmatic foliation parallel to a foliation in the country rock, implying synkinematic emplacement during regional NW–SE compression at 437 Ma.

AB - In the Caledonides of northwestern Ireland there is little evidence for the crystalline basement to the Dalradian Supergroup, though ascertaining its nature is a critical prerequisite for palaeogeographical reconstructions. In Donegal a lamprophyre intrusion has sampled material with isotopic composition, age and fabrics that permit the investigation of the hidden basement of this region. U–Pb and Lu–Hf isotopes in concert with structural analysis are used to elucidate the origin of three morphologically distinct zircon populations from the lamprophyre. The first of these comprises c. 828 to c. 1660 Ma rounded inherited grains. The second population, of 476 ± 3 Ma large xenocrystic grains, displays oscillatory zoned cores embayed by cross-cutting overgrowths, implying a multi-stage magmatic genesis. The third population, of 437 ± 5 Ma high aspect ratio euhedral grains, is interpreted to date the magmatic crystallization of the lamprophyre. Hf isotopic data from the Silurian and Neo- to Mesoproterozoic zircons yield crustal residence ages of 1.0–2.3 Ga. However, the Ordovician grains have ϵHfi values of c. −20 and model ages of 2.7–2.8 Ga. These data are consistent with the presence of either Archaean crust or an underthrust Ordovician magmatic rock with an Archaean source component, at depth in NW Ireland. Felsic xenoliths, interpreted to be derived from the country rock Dalradian metasediments, exhibit a pre-entrainment foliation and are randomly oriented relative to the foliation within the lamprophyre matrix, indicating deformation prior to c. 437 Ma, probably related to the Grampian orogeny. The host lamprophyre contains a magmatic foliation parallel to a foliation in the country rock, implying synkinematic emplacement during regional NW–SE compression at 437 Ma.

U2 - 10.1144/jgs2012-106

DO - 10.1144/jgs2012-106

M3 - Article

VL - 170

SP - 615

EP - 625

JO - Journal of the Geological Society

JF - Journal of the Geological Society

SN - 0016-7649

IS - 4

ER -