A lower crustal mafic source for the ca. 2550 Ma Qorqut Granite Complex in southern West Greenland

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Naeraa, TomasLund University,Lunds universitet,Berggrundsgeologi,Geologiska institutionen,Naturvetenskapliga fakulteten,Lithosphere and Biosphere Science,Department of Geology,Faculty of Science (author)

A lower crustal mafic source for the ca. 2550 Ma Qorqut Granite Complex in southern West Greenland

Article/chapterEnglish2014

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Elsevier BV,2014

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LIBRIS-ID:oai:lup.lub.lu.se:5e8ff67c-c81b-4119-9a10-0112387b0637
https://lup.lub.lu.se/record/4487324URI
https://doi.org/10.1016/j.lithos.2014.02.013DOI
https://urn.kb.se/resolve?urn=urn:nbn:se:nrm:diva-833URI

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Language:English
Summary in:English

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The late Neoarchaean Qorqut Granite Complex is the youngest large igneous intrusion in the Nuuk region in southern West Greenland, where basement is primarily of Eoarchaean and Mesoarchaean age with a tonalite-trondhjemite-granodiorite (TTG) composition. The Qorqut granite is generally undeformed and it intruded during a prolonged period, starting at ca. 2730 Ma, characterised by crustal reworking, possibly related to syn- or post accretion tectonics or continental collision. We present major and trace element whole rock chemistry and combined U/Pb, Hf and O isotope data from zircon. We obtained a mean zircon U/Pb age of 2547 +/- 4 Ma (MSWD = 0.63). Initial sHf values range from - 12 to -18 requiring a long residence time and a rather homogeneous source. Sample averaged zircon delta O-18 values range from 6.1 +/- 0.2%. to 6.5 +/- 0.3/0.7%o best interpreted with a source region of mainly unweathered mantle derived igneous rocks. Compared to the regional TTG basement, the QGC is characterised by low CaO and Na2O and high K2O, LREE and Rb contents, and a stronger fractionated REE pattern with a negative Eu anomaly. We show that the homogeneous Hf isotope signature of the granite together with its low epsilon value and its pristine oxygen isotope composition are best explained with an Eoarchaean mafic source with a Lu-176/Hf-176 around 0.015-0.019. Trace element modelling confirms that a mafic source in REE and with an eclogitic residue and with plagioclase as a fractionating phase would generate appropriate melt compositions. Modelling requires residual rutile in the source which constrain the pressures to > ca. 13-18 kbar. Zirconium saturation temperatures suggest magma temperatures in the range 750-850 degrees C. The obtained P-T conditions suggest a lower crustal source region in a thickened crustal unit consistent with a post or late continental collisional setting. (C) 2014 Elsevier B.V. All rights reserved.

Subject headings and genre

NATURVETENSKAP Geovetenskap och miljövetenskap Geologi hsv//swe
NATURAL SCIENCES Earth and Related Environmental Sciences Geology hsv//eng
Neoarchaean granite
Greenland
Zircon U/Pb
oxygen and Hf isotopes
trace element modelling
The changing Earth

Added entries (persons, corporate bodies, meetings, titles ...)

Kemp, A. I. S. (author)
Scherstén, AndersLund University,Lunds universitet,Berggrundsgeologi,Geologiska institutionen,Naturvetenskapliga fakulteten,Lithosphere and Biosphere Science,Department of Geology,Faculty of Science(Swepub:lu)geol-aes (author)
Rehnstrom, E. F. (author)
Rosing, M. T. (author)
Whitehouse, K. J. (author)
Whitehouse, Martin J.,1962-Naturhistoriska riksmuseet,Enheten för geovetenskap,Nordsim(Swepub:nrm)martwhit (author)
BerggrundsgeologiGeologiska institutionen (creator_code:org_t)

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In:Lithos: Elsevier BV192, s. 291-3040024-49371872-6143

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NATURAL SCIENCES: NATURAL SCIENCES; and Earth and Relate ...; and Geology

Articles in the publication: Lithos

By the university: Lund University; Swedish Museum of Natural History

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