Peridotite enclaves hosted by Mesoarchaean TTG-suite orthogneisses in the Fiskefjord region of southern West Greenland

Szilas, Kristoffer; Kelemen, P. B.; Bernstein, Stefan

doi:10.1016/j.grj.2015.03.003

Cited by 28 publications

(32 citation statements)

References 105 publications

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“…2.8 Ga Storø Supracrustal Belt cropping out further south (Szilas et al 2014). Supracrustal rocks are also found intercalated with meta-gabbronoritic and ultramafic rocks that may represent layered intrusive complexes (Szilas et al 2015). The supracrustal rocks found in the Akia Terrane are interpreted as remnants of arc-related oceanic crust, a model which has the precursor to the orthogneiss intruded within a convergent plate-tectonic setting (Garde 1990(Garde , 1997Garde et al 2000;Szilas et al 2017).…”

Section: The Akia Terranementioning

confidence: 99%

Building Mesoarchaean crust upon Eoarchaean roots: the Akia Terrane, West Greenland

Gardiner

Kirkland

Hollis

et al. 2019

Contrib Mineral Petrol

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Constraining the source, genesis, and evolution of Archaean felsic crust is key to understanding the growth and stabilization of cratons. The Akia Terrane, part of the North Atlantic Craton, West Greenland, is comprised of Meso-to-Neoarchaean orthogneiss, with associated supracrustal rocks. We report zircon U-Pb and Lu-Hf isotope data, and whole-rock geochemistry, from samples of gneiss and supracrustals from the northern Akia Terrane, including from the Finnefjeld Orthogneiss Complex, which has recently been interpreted as an impact structure. Isotope data record two major episodes of continental crust production at ca. 3.2 and 3.0 Ga. Minor ca. 2.7 and 2.5 Ga magmatic events have more evolved εHf, interpreted as reworking of existing crust perhaps linked to terrane assembly. Felsic rocks from the Finnefjeld Orthogneiss Complex were derived from the same source at the same time as the surrounding tonalites, but from shallower melting, requiring any bolide-driven melting event to have occurred almost simultaneously alongside the production of the surrounding crust. A simpler alternative has the Finnefjeld Complex and surrounding tonalite representing the coeval genesis of evolved crust over a substantial lithospheric depth. Hafnium isotope data from the two major Mesoarchaean crust-forming episodes record a contribution from older mafic Eoarchaean crust. Invoking the involvement of an Eoarchaean root in the growth of younger Mesoarchaean crust puts important constraints on geodynamic models of the formation of the discrete terranes that ultimately assembled to form Earth's cratons.

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Section: The Akia Terranementioning

confidence: 99%

Building Mesoarchaean crust upon Eoarchaean roots: the Akia Terrane, West Greenland

Gardiner

Kirkland

Hollis

et al. 2019

Contrib Mineral Petrol

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“…1. Schematic geological map of southern West Greenland (from Szilas et al, 2015) showing the location of samples (yellow filled triangles). Inset shows Landsat image.…”

Section: Regional Backgroundmentioning

confidence: 99%

Apatite: a U-Pb thermochronometer or geochronometer?

Kirkland

Yakymchuk

Szilas

et al. 2018

Lithos

127

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Apatite is an accessory mineral that is frequently found in both igneous and clastic sedimentary rocks. It is conventionally considered to be characterized by a closure temperature range between 375 and 600°C and hence has been employed to address mid-temperature thermochronology questions relevant to the reconstruction of thermal events in the middle to lower crust. However, questions remain as to whether apatite faithfully records thermally-activated volume diffusion profiles, or rather is influenced by recrystallization and new growth processes. We present a case study of two apatite samples from the Akia Terrane in Greenland that help chart some of the post magmatic history of this region. Apatite in a tonalitic gneiss has distinct U-enriched rims and its U-Pb apparent ages correlate with Mn chemistry, with a high Mn group yielding an age of c. 2813 Ma. The U-Pb and trace element chemistry and morphology support an interpretation in which these apatite crystals are originally igneous and record cooling after metamorphism, with subsequent generation of discrete new rims. Epidote observed in the sample implies a b600°C fluid infiltration event associated with apatite rims. The second sample, from a granitic leucosome, contains apparently homogeneous apatite, however U-Pb analyses define two distinct discordia arrays with different common Pb components. An older, c. 2490 Ma, component is associated with elevated Sr, whereas a younger, c. 1800 Ma, component has lower Sr concentration. A depth profile reveals an older core with progressively younger ages towards a compositionally discrete late Paleoproterozoic rim. The chemical and age profiles do not directly correspond, implying different diffusion rates between trace elements and U and Pb. The variation in core ages is interpreted to reflect radiogenic-Pb loss from a metamorphic population during new rim growth. The younger, c. 1800 Ma U-Pb age is interpreted to date new apatite growth from a compositionally distinct reservoir driven by tectonothermal and fluid activity, consistent with regional mica Ar-Ar ages. Results from these two samples show that recrystallization, dissolution and regrowth processes likely formed the younger rim overgrowths, and at temperatures below those often considered to be closure temperatures for Pb diffusion in apatite. The results from these samples imply many apatite grains may not record simple thermally activated Pb diffusion profiles and cautions against inversion of apatite U-Pb data to thermal histories without detailed knowledge of the grain growth/alteration processes.

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“…The peridotites occur as large discontinuous lensoid bodies within tonalitic orthogneiss. Exposures of these peridotites can be found in the Miaggoq, Seqi, Ulamertoq, and Amikoq ultramafic bodies, which are also associated with noritic rocks [1] ( Figure 1B). [22]); (C) Geologic map of Ulamertoq peridotite body showing the sampling locations of chromitites with zoned chromites (filled circle) and homogeneous chromites (filled square) (adapted from Garde [21]).…”

Section: Geological Settingmentioning

confidence: 99%

“…The same zonation is not observed with the accessory chromite in the peridotite host, which is characterized by Cr enrichment from core to rim. Fields of the olivine-spinel mantle array (OSMA) [4] and Seqi ultramafic complex [1] are shown for reference; (C) The homogeneous chromites are characterized by higher TiO2 contents compared to the zoned chromites. Fields for Rhum layered complex [29], Ujaragssuit [30], and Fiskenaesset [31] are included for comparison.…”

Section: Chromitementioning

confidence: 99%

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Contrasting Textural and Chemical Signatures of Chromitites in the Mesoarchaean Ulamertoq Peridotite Body, Southern West Greenland

et al. 2018

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Peridotites occur as lensoid bodies within the Mesoarchaean orthogneiss in the Akia terrane of Southern West Greenland. The Ulamertoq peridotite body is the largest of these peridotites hosted within the regional orthogneiss. It consists mainly of olivine, orthopyroxene, and amphibole-rich ultramafic rocks exhibiting metamorphic textural and chemical features. Chromitite layers from different localities in Ulamertoq show contrasting characteristics. In one locality, zoned chromites are hosted in orthopyroxene-amphibole peridotites. Compositional zonation in chromites is evident with decreasing Cr and Fe content from core to rim, while Al and Mg increase. Homogeneous chromites from another locality are fairly uniform and Fe-rich. The mineral chemistry of the major and accessory phases shows metamorphic signatures. Inferred temperature conditions suggest that the zoned chromites, homogeneous chromites, and their hosts are equilibrated at different metamorphic conditions. In this paper, various mechanisms during the cumulus to subsolidus stages are explored in order to understand the origin of the two contrasting types of chromites.

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Peridotite enclaves hosted by Mesoarchaean TTG-suite orthogneisses in the Fiskefjord region of southern West Greenland

Cited by 28 publications

References 105 publications

Building Mesoarchaean crust upon Eoarchaean roots: the Akia Terrane, West Greenland

Building Mesoarchaean crust upon Eoarchaean roots: the Akia Terrane, West Greenland

Apatite: a U-Pb thermochronometer or geochronometer?

Contrasting Textural and Chemical Signatures of Chromitites in the Mesoarchaean Ulamertoq Peridotite Body, Southern West Greenland

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