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
10.6084/m9.figshare.3453317.v1
https://geolsoc.figshare.com/articles/dataset/Constraints_on_the_timing_of_Scandian_deformation_and_the_nature_of_a_buried_Grampian_terrane_under_the_Caledonides_of_northwestern___Ireland/3453317
<p>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 <em>c</em>. 828 to <em>c</em>. 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 ϵHf<sub>i</sub> values of <em>c</em>. −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 <em>c</em>. 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.
</p>
2016-06-21 11:18:34
deformation
Ga
Caledonide
Hf
nature
lamprophyre
country rock Dalradian metasediments
Ireland
crustal residence ages
NW
foliation
Grampian
zircon
aspect ratio euhedral grains
underthrust Ordovician magmatic rock
data
437 Ma
Archaean source component
Geology