Granitic magmatism by melting of juvenile continental crust: new constraints on the source of Palaeoproterozoic granitoids
in Fennoscandia from Hf isotopes in zircon
Tom Andersen
Ulf Bertil Andersson
Stuart Graham
Göran Åberg
Siri L. Simonsen
10.6084/m9.figshare.3454589.v1
https://geolsoc.figshare.com/articles/dataset/Granitic_magmatism_by_melting_of_juvenile_continental_crust_new_constraints_on_the_source_of_Palaeoproterozoic_granitoids___in_Fennoscandia_from_Hf_isotopes_in_zircon/3454589
<p>Zircons from nine Palaeoproterozoic granitoid intrusions within the southern part of the Fennoscandian Shield have been studied
by laser ablation inductively coupled plasma source mass spectrometry to obtain U–Pb ages (in the range 1.88–1.68 Ga) and
Hf isotope compositions. Six granitoids are from the 1.85–1.65 Ga Transscandinavian Igneous Belt; during that period more
than 10<sup>6 </sup>km<sup>3</sup> of granitoid magma intruded the pre-existing crust. The large majority of magmatic zircons from the nine granitoids have
a limited initial range, <sup>176</sup>Hf/<sup>177</sup>Hf = 0.2816–0.2818, and define an evolutionary trend given by an initial value of ε<sub>Hf(1.88Ga)</sub> ≈ +2 ± 3 at an average <sup>176</sup>Lu/<sup>177</sup>Hf = 0.015. These data show that a geographically extensive, long-lived, relatively homogeneous, and dominant magma source
resided within 2.1–1.86 Ga Svecofennian juvenile crust between 1.88 and 1.68 Ga. Zircon xenocrysts (1.91–1.98 Ga) with initial
ε<sub>Hf</sub> = +0 to +2.5 from one of the intrusions provide additional evidence for such a long-lived crustal source of granitic magmas
in central Fennoscandia. The granitoids were emplaced during a period of active mafic underplating that supplied heat to the
anatectic zone in the lower–middle crust, but little or no mantle-derived Hf to the granitic magmas, in contrast to many mixed
intermediate rocks.
</p>
2016-06-21 12:13:43
10 6 km 3
granitic magmas
Palaeoproterozoic granitoid intrusions
Hf isotope compositions
laser ablation inductively
crust
plasma source mass spectrometry
Ga
Geology