Zircon U–Pb-Hf isotope data in eclogite and metagabbro from southern Sweden reveal a common long-lived evolution and enriched source

ABSTRACT

Several orogenies have shaped the bedrock of southern Sweden. While mafic intrusions represent significant sources of information for reconstructing geodynamics and crustal evolution, the characterization of the various generations of such intrusions in Sweden remains limited. We report in situ zircon U–Pb ages and Hf isotope data from a Fe-Ti eclogite and a coronitic metagabbro from the Eastern Segment in southern Sweden. Crystallisation ages at 1683 ± 17 Ma of the eclogite suggest affiliation with the surrounding 1730–1660 Ma Transscandinavian Igneous Belt intrusions that dominate the Eastern Segment. Secondary zircon growth and Pb-loss in the eclogite sample at 1459 ± 44 Ma and the crystallisation of the metagabbro at 1431 ± 26 Ma overlap and are related to magmatic activity during the Hallandian orogeny. Zircon Hf isotope signatures with chondritic and sub-chondritic values at ~1683 Ma and ~1431 Ma, respectively, correspond to an enriched (or mildly depleted) source in line with a “Mixed Svecofennian Crustal Reservoir”. These isotope signatures are more enriched than those in the surrounding gneisses. Zircon isotope data from the herein analysed zircon grains indicate that the eclogite and metagabbro had an enriched mafic source in the mid to lower crust, or within the subcontinental lithospheric mantle below Fennoscandia.

KEYWORDS:

• Eclogite
• zircon
• lu–Hf
• u–Pb
• eastern Segment
• hallandian
• sveconorwegian

Acknowledgments

Financial support by the Swedish Research Council (grant VR#2016-00261 to A. Petersson) is gratefully acknowledged. C. Möller is acknowledged for providing the thin section for sample LT11074. J. Cutts is thanked for an informal review of this manuscript. Constructive reviews by T. Slagstad and an anonymous reviewer, as well as editorial handling by M. Ripa is greatly appreciated. The Nordsim ion microprobe facility operates as a Swedish national infrastructure partly funded by the Swedish Research Council (grant no. 2017-00671); this is NordSIMS contribution #659.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Additional information

Funding

This work was supported by the Vetenskapsrådet [VR#2016-00261].