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Open AccessArticle

Metasomatic Reactions between Archean Dunite and Trondhjemite at the Seqi Olivine Mine in Greenland

1
Department of Geosciences, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen K, Denmark
2
Geosciences Centre, University of Göttingen, Goldschmidtstraße 1, 37077 Göttingen, Germany
3
Centre for Exploration Targeting—Curtin Node, The Institute for Geoscience Research, School of Earth and Planetary Sciences, Curtin University, Perth 6102, WA, Australia
*
Author to whom correspondence should be addressed.
Minerals 2020, 10(1), 85; https://doi.org/10.3390/min10010085
Received: 29 November 2019 / Revised: 17 January 2020 / Accepted: 19 January 2020 / Published: 20 January 2020
A metasomatic zone formed between the contact of a 2940 ± 5 Ma intrusive trondhjemite sheet in the Archean dunite of the Seqi Ultramafic Complex, SW Greenland, consists of three distinct mineral zones dominated by (1) talc, (2) anthophyllite, and (3) phlogopite. These zones supposedly resulted from a process of dissolution of olivine by silica rich fluid residual from the trondhjemite magma, with crystallization of secondary minerals along a compositional gradient in the fluid phase. A zircon crystal inclusion in a large (4 cm) olivine porphyroblast was dated in situ via LA-ICP-MS U–Pb isotope analysis, yielding a weighted mean 207Pb/206Pb age of 2963 ± 1 Ma, which coincides with granulite facies metamorphism and potential dehydration. Considering phase relations appropriate for the dunite composition, we deduced the talc forming conditions to be at temperatures of 600–650 °C and at a pressure below 1 GPa. This is supported by oxygen isotope data for talc, anthophyllite and phlogopite in the metasomatic zone, which suggests formation in the temperature range of 600–700 °C from fluids that had a δ18O of ~8‰ and a Δ’17O0.528 of about −40 ppm, i.e., from fluids that could have been derived from the late stage trondhjemite sheet. View Full-Text
Keywords: Archaean; Greenland; ultramafic rocks; metasomatism; talc; anthophyllite; phlogopite Archaean; Greenland; ultramafic rocks; metasomatism; talc; anthophyllite; phlogopite
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Whyatt, L.; Peters, S.; Pack, A.; Kirkland, C.L.; Balic-Zunic, T.; Szilas, K. Metasomatic Reactions between Archean Dunite and Trondhjemite at the Seqi Olivine Mine in Greenland. Minerals 2020, 10, 85.

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