Gondwana break-up related magmatism in the Falkland Islands
M. J. Hole
R. M. Ellam
D. I. M. Macdonald
S. P. Kelley
10.6084/m9.figshare.3454094.v1
https://geolsoc.figshare.com/articles/dataset/Gondwana_break-up_related_magmatism_in_the_Falkland_Islands/3454094
<p>Jurassic dykes (<em>c</em>. 182 Ma) are widespread across the Falkland Islands and exhibit considerable geochemical variability. Orthopyroxene-bearing
NW–SE-oriented quartz-tholeiite dykes underwent fractional crystallization at >1 GPa, and major element constraints suggest
that they were derived by melting of a pyroxenite-rich source. They have εNd<sub>182</sub> in the range −6 to −11 and <sup>87</sup>Sr/<sup>86</sup>Sr<sub>182</sub> >0.710 and therefore require an old lithospheric component in their source. A suite of basaltic-andesites and andesites exhibit
geochemical compositions transitional between Ferrar and Karoo magma types, and are similar to those seen in the KwaZulu-Natal
region of southern Africa and the Theron Mountains of Antarctica. Olivine-phyric intrusions equilibrated at <0.5 GPa, and
have isotopic compositions (εNd<sub>182</sub> 1.6–3.6 and <sup>87</sup>Sr/<sup>86</sup>Sr<sub>182</sub> 0.7036–0.7058) that require limited interaction with old continental lithosphere. A suite of plagioclase-phyric intrusions
with <sup>87</sup>Sr/<sup>86</sup>Sr<sub>182</sub> <em>c</em>. 0.7035 and εNd<sub>182</sub> <em>c</em>. +4, and low Th/Ta and La/Ta ratios (<em>c</em>. 1 and <em>c</em>. 15, respectively) also largely escaped interaction with the lithosphere. These isotopically depleted intrusions were probably
emplaced synchronously with Gondwana fragmentation and the formation of new oceanic lithosphere. Estimates of mantle potential
temperature from olivine equilibration temperatures do not provide unequivocal evidence for the presence of a plume thermal
anomaly beneath the Falkland Islands at 182 Ma.
</p>
2016-06-21 11:53:48
Falkland Islands
olivine equilibration temperatures
lithosphere
Nd
Falkland Islands Jurassic dykes
NW
Karoo magma types
Sr
andesites exhibit geochemical compositions
intrusion
Geology