Crustal growth and crustal recycling in the Nagssugtoqidian orogen of West Greenland:: Constraints from radiogenic isotope systematics and U–Pb zircon geochronology

doi:10.1016/S0301-9268(98)00058-8

Precambrian Research

Volume 91, Issues 3–4, 31 August 1998, Pages 365-381

https://doi.org/10.1016/S0301-9268(98)00058-8 Get rights and content

Abstract

We present Sr–Nd–Pb whole-rock isotopic data for regionally collected samples of late Archean to Paleoproterozoic gneisses and granitoids from the Nagssugtoqidian orogen of West Greenland, together with U–Pb zircon (SHRIMP) geochronological data for Paleoproterozoic granitoids. These data are used, together with additional published geochronological data, to place constraints upon late Archean (>2.7 Ga) crustal growth, and subsequent Paleoproterozoic (ca. 1.92 to 1.76 Ga) crustal growth and recycling in the Nagssugtoqidian. Nd-isotope data suggests that the oldest recognisable components dated at ca. 2.85 Ga contain varying amounts of older (>3.1 Ga?) light rare earth element enriched (continental crustal) component(s) as well as juvenile ca. 2.85 crust. The behaviour of Sr- and Pb-isotope systematics during Paleoproterozoic Nagssugtoqidian metamorphism is dependent upon both the grade of this event (granulite or amphibolite) and the original (i.e. Archean) grade of metamorphism. Juvenile Paleoproterozoic magmatic additions to the Nagssugtoqidian crust are represented by the Arfersiorfik quartz diorite and Sisimiut charnockite, which are shown to be contemporaneous by SHRIMP U–Pb dating. Variations in isotopic composition from these two units are related to moderate degrees of crustal contamination or extraction from a heterogeneous mantle source, probably in a magmatic arc which varied from oceanic (Arfersiorfik; minimal interaction with pre-existing continental crust) to continental (Sisimiut) in character respectively. Late granite sheets (Paleoproterozoic) throughout the Nagssugtoqidian orogen generally have a local late Archean protolith.

Introduction

The investigation and characterisation of complex polyphase Precambrian gneiss terranes is critically dependent upon isotope and trace-element geochemical and geochronological data. In particular, the development of high-precision U–Pb zircon geochronology (by ion-probe or conventional methods) means that whole-rock isotopic data (Pb, Nd, Sr) from a single dated sample may be evaluated in a carefully constructed age framework to yield information about the relative contributions of different geochemical and isotopic reservoirs to overall crustal evolution and geochemical behaviour during metamorphic events.

The present study is part of an ongoing investigation by the Danish Lithosphere Centre (DLC) of the Paleoproterozoic Nagssugtoqidian orogen of West Greenland, where Proterozoic tectonothermal events obscure the relationship between Archean and Proterozoic orthogneisses and granitoids. Samples collected for this work have been dated in a reconnaissance manner using ion-probe U–Pb zircon methods by Kalsbeek and Nutman (1996), providing a broad geochronologic framework for the Nagssugtoqidian. Our interpretation of whole-rock isotope systematics presented in this paper is closely based upon this framework and is used to place isotope constraints upon late Archean crustal growth in the Nagssugtoqidian orogen, as well as to demonstrate the juvenile nature of many of the Proterozoic lithologies. Furthermore we use these data to investigate the response of Archean rocks to Paleoproterozoic metamorphism (granulite and amphibolite facies) and anatexis.

Section snippets

Geological setting of the Nagssugtoqidian orogen

The Nagssugtoqidian orogen is an east–west trending ca. 150 km wide belt, north of the Archean craton of Greenland which has been affected by Paleoproterozoic tectonothermal activity (Ramberg, 1949). The orogen consists mainly of Archean (2.85–2.70 Ga) and Paleoproterozoic (1.95–1.90 Ga) orthogneisses, both strongly affected by deformation and metamorphism around 1.85 Ga as well as during somewhat later events (Connelly and Mengel, 1996; Kalsbeek and Nutman, 1996; Kalsbeek et al., 1987; Taylor and

Reconnaissance U–Pb dating and age–lithology definitions

All of the samples analysed for whole-rock Sr, Nd, and Pb isotopes in this study have been dated using U–Pb zircon ion-probe methods (SHRIMP). Most of these dates were obtained as part of a reconnaissance analytical program (Kalsbeek and Nutman, 1996) in which a small number of zircon grains (three to five) were dated from 90 samples distributed throughout the Nagssugtoqidian orogen in order to provide an estimate of crystallisation or metamorphic age that in most cases is precise to better

Whole-rock isotopic evolution: methodology

Before the advent of routine high-precision dating of the kind now possible by ion-probe and single crystal U–Pb zircon methods, whole-rock isotopic studies were largely used to provide age information via multiple sample isochron or single sample model age determinations. In many cases, geochronological information obtained in this way yields sensible age information where other methods fail (e.g. Whitehouse et al., 1996), highlighting the continued applicability of isochron methodology. In

Archean biotite gneisses; Proterozoic metamorphism at amphibolite facies or lower

Neodymium isotopic data for eight Archean biotite gneisses are shown in a Nd-isotope evolution diagram (Fig. 4). Six of these have initial Nd-isotopic compositions between contemporaneous chondritic [ε_Nd(t)=0] and depleted mantle [ε_Nd(t)=+3] reservoirs, which we interpret as indicating that they represent relatively juvenile late Archean crustal generation with little or no contribution from ancient (mid-early Archean) crust. Depleted mantle model ages (t_DM) for these six samples, calculated

Archean crustal development in the Nagssugtoqidian

SHRIMP U–Pb zircon dating (Kalsbeek and Nutman, 1996; this paper) permits division of the rocks of the Nagssugtoqidian orogen into the following age categories: (1) Archean rocks, 2.70–2.85 Ga; (2) juvenile Paleoproterozoic rocks, the Sisimiut charnockite and the Arfersiorfik association, both ca. 1.92 Ga; and (3) late granitic rocks, formed from Archean protoliths ca. 1.765–1.84 Ga.

The Archean rocks have been variably affected by Paleoproterozoic metamorphism and deformation. This, together with

Acknowledgements

Stephen Moorbath has generously given encouragement and isotopic inspiration to the authors over many years. We are grateful to the Nagssugtoqidian group at the Danish Lithosphere Centre, in particular Mogens Marker, Flemming Mengel, and Jeroen van Gool, for their support and encouragement of this work. MJW acknowledges support from the Royal Society of London (via a University Research Fellowship). Roy Goodwin and John Arden are thanked for their assistance with the isotopic analyses in

References (34)

G. Gruau et al.
Resetting of Sm–Nd systematics during metamorphism of 3.7-Ga rocks: implications for isotopic models of early Earth differentiation
Chem. Geol.
(1996)
P.J. Hamilton et al.
Sm–Nd studies of Archaean metasediments and metavolcanics from West Greenland and their implications for the Earth's earliest history
Earth Planet. Sci. Lett.
(1983)
F. Kalsbeek et al.
Nagssugtoqidian mobile belt of West Greenland: cryptic 1850 Ma suture between two Archaean continents — chemical and isotopic evidence
Earth Planet. Sci. Lett.
(1987)
S. Moorbath et al.
Extreme Nd-isotopic heterogeneity in the early Archaean — fact or fiction? Case histories from northern Canada and West Greenland
Chem. Geol.
(1997)
R.H. Steiger et al.
Subcommission on geochronology: Convention on the use of decay constants in geo- and cosmochronology
Earth Planet. Sci. Lett.
(1977)
P.N. Taylor et al.
Dating the metamorphism of Precambrian marbles: Examples from Proterozoic mobile belts in Greenland
Chem. Geol. (Isotope Geosci. Sect.)
(1990)
M.J. Whitehouse et al.
Conflicting mineral and whole-rock isochron ages from the late Archean Lewisian Complex of northwest Scotland: implications for geochronology in polymetamorphic high-grade terrains
Geochim. Cosmochim. Acta
(1996)
D. Bridgwater et al.
Geological reconnaissance of the Precambrian rocks of South-East Greenland
Rapp. Grønlands Geol. Unders.
(1969)
D. Bridgwater et al.
The Proterozoic Nagssugtoqidian mobile belt of southeast Greenland: A link between the eastern Canadian and Baltic shields
Geosci. Canada
(1990)
B. Chadwick et al.
The Proterozoic mobile belt in the Ammassalik region, South-East Greenland (Ammassalik mobile belt): an introduction and re-appraisal
Rapp. Grønlands Geol. Unders.
(1989)

Claoué-Long, J.C., Compston, W., Roberts, J., Fanning, C.M., 1995. Two carboniferous ages: A comparison of SHRIMP...

Compston, W., Williams, I.S., Meyer, C., 1984. U–Pb geochronology of zircons from lunar breccia 73217 using a sensitive...

Connelly, J.N., Mengel, F.C., 1996. Archean and Paleoproterozoic magmatism and metamorphism in the Nagssugtoqidian...

F. Corfu et al.

Polymetamorphic evolution of the Lewisian Complex, NW Scotland, as recorded by U–Pb isotopic compositions of zircon, titanite and rutile

Contrib. Mineral. Petrol.

(1994)

D.J. DePaolo et al.

The continental crustal age distribution: methods of determining mantle separation ages from Sm–Nd isotopic data and application to the southwestern United States

J. Geophys. Res.

(1991)

C.R.L. Friend et al.

New evidence for protolith ages of Lewisian granulites, northwest Scotland

Geology

(1995)

Ireland, T.R., 1995. Ion microprobe mass spectrometry: Techniques and application in cosmochemistry, geochemistry and...

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Extent and age of Mesoarchean components in the Nagssugtoqidian orogen, West Greenland: Implications for tectonic environments and crust building in cratonic orogenic belts
2021, Lithos
Citation Excerpt :
4) Rifting at 2045 Ma to produce an inter-cratonic basin (Kalsbeek and Manatschal, 1999; Mayborn and Lesher, 2006; van Gool et al., 2002). 5) Minor Paleoproterozoic crustal building from 1950 to 1870 Ma (Connelly et al., 2000; Kalsbeek and Nutman, 1996; Whitehouse et al., 1998). 6) Final reassembly of the rifted Archean segments during continental collision between 1873 and 1775 Ma – i.e. the Nagssugtoqidian orogeny (Connelly et al., 2000; van Gool et al., 2002).
The Nagssugtoqidian orogen (NO), which forms the northern margin of the North Atlantic craton in West Greenland, is largely comprised of ~2870 to 2720 Ma juvenile continental crust reworked during Paleoproterozoic orogenic events. Sparse evidence of components older than 3100 Ma in the area (U–Pb zircon ages and bulk-rock Sm–Nd isotopes) have hinted at a unit called the Qorlortoq gneiss but were not substantiated by regional studies. Here we report the “rediscovery” of the Qorlortoq gneiss, documented through a new geochemical and geochronological dataset of this orthogneiss and related components, which include ultramafic cumulate enclaves and late basaltic dykes. Laser Ablation Split Stream (LASS) U-Pb/Lu-Hf isotopic analyses of zircon from the gneiss give a U–Pb concordia upper-intercept age of 3177 ± 12 Ma and weighted mean εHf(t) of 1.7 ± 0.5, indicating a juvenile protolith extracted from a depleted mantle source.
Ultramafic enclaves of cumulate origin make up a key component of the Qorlortoq gneiss. Their trace element systematics indicate a parental melt with tholeiitic affinities, sourced from depleted mantle beneath relatively thin lithosphere (<80 km), that was subsequently contaminated by crustal assimilation. Re–Os isotope systematics of the cumulates and their relationship with the younger Qorlortoq dykes place the age of these cumulates close to that of the Qorlortoq gneiss.
The age of the Qorlortoq gneiss makes it the oldest known component in the NO by ~300 Ma. The extended timescale between episodes of crustal production in this area, could indicate a geodynamic environment characterized by stagnant-lid or episodic mobile-lid tectonics, at least on a regional scale. These constraints provide important information about the diversity and nature of Archean geodynamic environments.
The Archean Victoria Fjord terrane of northernmost Greenland and geodynamic interpretation of Precambrian crust in and surrounding the Arctic Ocean
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In far North Greenland at the head of Victoria Fjord (∼81°30′N), a ∼1000 km² exposure of Precambrian crystalline basement rocks is a window through the region's extensive latest Neoproterozoic and Paleozoic Arctic Platform sedimentary cover sequence. These basement rocks, named here the Victoria Fjord terrane, are dominated by weakly-foliated granodioritic orthogneisses, with lesser amounts of migmatite. These are intercalated with strips of supracrustal rocks dominated by paragneisses. This poorly-exposed Archean terrane at Greenland's northern tip is succeeded to the south by the extensive east-west trending Paleoproterozoic Inglefield Mobile Belt of juvenile arc rocks.
The Victoria Fjord terrane granodiorites have zircon U-Pb ages from 3292 ± 14 Ma to ∼3260 Ma. Reconnaissance U-Pb dating on schlieric migmatite zircons yielded ages of ∼3280, 3400 and 3500 Ma. Paragneiss detrital zircons have ages of mostly ∼2710 Ma, with a minority of 3000–2900 Ma grains. This demonstrates that these sedimentary rocks were not derived from the local basement. Post- Archean magmatic or metamorphic zircon was not detected in any of the samples.
Initial ε_Hf of 3290–3260 Ma granodiorite and granite zircons ranges from −4 to +2, and the magmatic protoliths are interpreted as sourced from the melting of somewhat older (3500–3400 Ma) Paleoarchean crust, represented by paleosome in the migmatites. The paragneiss 3000–2900 Ma detrital zircons were derived from juvenile felsic crust of that age. The ∼2710 Ma group show negative correlation of Th/U and initial ε_Hf, such that those with high Th/U up to >2.0 have ε_Hf values of −6 to −10. The ∼2710 zircons were sourced from mafic rocks formed by melting of much older (Paleoarchean?) enriched mantle which was variably contaminated by 3000–2900 Ma crust during its ascent.
The Victoria terrane is unique amongst the Archean basement terranes in Greenland because it is dominated by 3500–3260 Ma crust. However, the Arctic basin contains detrital zircons of that age, and rocks of that age also occur in eastern Siberia and northwestern Canada. Implications for high Arctic early Precambrian geodynamics are discussed.
Constraining a Precambrian Wilson Cycle lifespan: An example from the ca. 1.8 Ga Nagssugtoqidian Orogen, Southeastern Greenland
2018, Lithos
In the Phanerozoic, plate tectonic processes involve the fragmentation of the continental mass, extension and spreading of oceanic domains, subduction of the oceanic lithosphere and lateral shortening that culminate with continental collision (i.e. Wilson cycle). Unlike modern orogenic settings and despite the collection of evidence in the geological record, we lack information to identify such a sequence of events in the Precambrian. This is why it is particularly difficult to track plate tectonics back to 2.0 Ga and beyond. In this study, we aim to show that a multidisciplinary approach on a selected set of samples from a given orogeny can be used to place constraints on crustal evolution within a P-T-t-d-X space. We combine field geology, petrological observations, thermodynamic modelling (Theriak-Domino) and radiogenic (U-Pb, Lu-Hf) and stable isotopes (δ¹⁸O) to quantify the duration of the different steps of a Wilson cycle. For the purpose of this study, we focus on the Proterozoic Nagssugtoqidian Orogenic Belt (NOB), in the Tasiilaq area, South-East Greenland.
Our study reveals that the Nagssugtoqidian Orogen was the result of a complete three stages juvenile crust production (X_juv) – recycling/reworking sequence: (I) During the 2.60–2.95 Ga period, the Neoarchean Skjoldungen Orogen remobilised basement lithologies formed at T_DM 2.91 Ga with progressive increase of the discharge of reworked material (X_juv from 75% to 50%; δ¹⁸O: 4–8.5‰). (II) After a period of crustal stabilization (2.35–2.60 Ga), discrete juvenile material inputs (δ¹⁸O: 5–6‰) at T_DM 2.35 Ga argue for the formation of an oceanic lithosphere and seafloor spreading over a period of ~ 0.2 Ga (X_juv from < 25% to 70%). Lateral shortening is set to have started at ca. 2.05 Ga with the accretion of volcanic/magmatic arcs (i.e. Ammassalik Intrusive Complex) and by subduction of small oceanic domains (M1: 520 ± 60 °C at 6.6 ± 1.4 kbar). (III) Continental collision between the North Atlantic Craton and the Rae Craton occurred at 1.84–1.89 Ga. Crustal thickening of ~ 25 km was accompanied by regional metamorphism M2 (690 ± 20 °C at 6.25 ± 0.25 kbar) and remobilization of pre-existing supracrustal lithologies (X_juv ~ 40%; δ¹⁸O: 5–10.5‰).
Rates and durations obtained for seafloor spreading (175 ± 25 Ma), subduction (125 ± 75 Ma) and continental collision (ca. 60 Ma) are similar to those observed in Phanerozoic Wilson Cycle but differ from what was estimated for Archean terrains. Therefore, timespans of the different steps of a Wilson cycle might have progressively changed over time as a response to the progressive cratonization of the lithosphere.
The Laurentia – West Greenland connection at 1.9 Ga: New insights from the Rinkian fold belt
2017, Gondwana Research
Citation Excerpt :
Thrane et al. (2005) favoured formation of the Prøven Igneous Complex via partial melting of depleted ca. 3.0–2.8 Ga lower crust that was contaminated to varying degrees by pelitic sedimentary rocks from the Karrat Group, on the basis of their Sm-Nd and Lu-Hf isotopic data and geochemical A-type signature. Emplacement of the Prøven Igneous Complex between ca. 1900 and 1876 Ma overlaps in time with calc-alkaline magmatism in the central Nagssugtoqidian Orogen to the south (Fig. 2a), where dioritic rocks of the Arfersiorfik igneous suite are dated between ca. 1921 and 1885 Ma, and charnockitic rocks of the Sisimiut suite (Fig. 2a) are dated between ca. 1912 and 1873 Ma (Kalsbeek et al., 1987; Kalsbeek and Nutman, 1996; Whitehouse et al., 1998; Connelly et al., 2000). In contrast to the Prøven suite, Sm-Nd isotopic compositions and geochemistry from the Arfersiorfik and Sisimiut suites are largely juvenile and interpreted to reflect subduction-related ocean-island and continental arc magmatism, respectively (Kalsbeek and Nutman, 1996; Whitehouse et al., 1998; van Gool et al., 2002).
U-Pb data from the Rinkian fold Belt, western Greenland, provide new constraints on provenance and timing of deposition of the Karrat Group, the emplacement interval of the Prøven Igneous Complex, and the tectonic setting of west Greenland during the interval 2.03–1.83 Ga. U-Pb detrital data establish the entire Karrat Group metasedimentary succession as Paleoproterozoic in age, initiated after ca. 2029 Ma (Qeqertarssuaq Formation), with deeper water deposition after 1953 ± 31 Ma and 1905 ± 20 Ma (Nûkavsak Formation). The detrital age profiles highlight a profound change in source region after ca. 1.95 Ga that we attribute to thickening, uplift, and exhumation related to collision of a juvenile magmatic arc with the northwest margin of Rae craton at ca. 1.97–1.95 Ga (Thelon Orogen). Accordingly, the Karrat Group is viewed as having initiated as an extensional rift basin(s) that received ca. 3.00–2.95 Ga detritus from local basement sources, and which evolved into a deeper water foreland-basin succession derived from the north. This foreland basin was intruded by the Prøven Igneous Complex, for which new U-Pb data establish emplacement between 1.90 and 1.87 Ga in a within-(Rae) plate setting. Prøven plutonism is coeval with lower-plate mantle magmatism elsewhere across NE Laurentia which may have been triggered by asthenospheric thinning due to plume-induced extension of lower-plate Rae craton at 1.95–1.92 Ga. Our data refute a direct link between the Prøven Igneous Complex and the voluminous 1.86–1.845 Ga Cumberland Batholith, Baffin Island, long considered its counterpart.
Palaeoproterozoic metamorphism and cooling of the northern Nagssugtoqidian orogen, West Greenland
2012, Precambrian Research
Citation Excerpt :
The latter is commonly termed the Disco craton (e.g., Grocott and Davies, 1999; van Gool et al., 2002; van Kranendonk et al., 1993; Wardle and van Kranendonk, 1996) or the Aasiaat domain (Garde and Hollis, 2010) although it may also represent the southern margin of the Rae Craton (Connelly et al., 2006). The pre-collisional convergence is documented by the occurrence of Palaeoproterozoic calc-alkaline intrusive rocks with supra-subduction geochemical signatures (Kalsbeek et al., 1987), emplaced between 1920 and 1870 Ma (Connelly et al., 2000; Kalsbeek and Nutman, 1996; Whitehouse et al., 1998). These rocks were accreted onto the Nagssugtoqidian orogen at the onset of continental collision soon after the termination of magmatic activity (van Gool et al., 2002).
Lu–Hf and Sm–Nd garnet geochronology combined with geothermobarometric calculations allowed us to gain new insight into the metamorphic evolution of the Northern Nagssugtoqidian orogen (NNO), in West Greenland. Three samples were collected from the southern (SM 310 and SM 316) and northern (SM 339) parts of the NNO. They revealed amphibolite-grade Palaeoproterozoic metamorphism under peak temperature conditions decreasing from c. 810 to 840 °C at 7.5 kbar (SM 310, 316) to c. 690 °C at 10 kbar (SM 339) in the southern and northern part of the NNO, respectively. Our garnet dating defines two episodes: (1) at c. 1780 Ma, determined by Lu–Hf in sample SM 316 and Sm–Nd in sample SM 339, most likely approximating the time of garnet growth, and (2) at c. 1750 Ma defined by the remaining Sm–Nd dates, reflecting time of cooling below isotopic closure. Original garnet growth patterns preserved by HREE (SM 316) and clearly seen zonation of Sm and Nd (SM 339) suggest that the garnets may not have been completely reset and thus, the obtained age of 1780 Ma could be fairly close to the time of garnet crystallisation.
The growth of peak metamorphic mineral assemblages in the southern NNO took place after the end of deformation, as demonstrated by sample SM 316 that was collected from an undeformed mafic dyke cutting across the regional fabric. In contrast, sample SM 339 revealed synkinematic growth of peak metamorphic paragenesis that crystallised in a low angle top-to-SW shear zone overprinted on the pre-existing fabric. Our results are consistent with the interpretation of the NNO as an Archaean crustal block, the Aasiaat domain, that was affected by Palaeoproterozoic metamorphism and localised deformation at 1780 Ma, i.e., 70 Ma after the Nagssugtoqidian collision. This event can be compared to the formation of steep belts (major left-lateral strike-slip shear zones) in the central part of the Nagssugtoqidian orogen. The Aasiaat domain is considered to be an independent microplate separating the Nagssugtoqidian and Rinkian orogens which define respectively its southern and northern margins. The interpretation presented implies the existence of two discrete tectonic sutures to the north and south of the Aasiaat domain.
Formation of the North Atlantic Craton: Timing and mechanisms constrained from Re-Os isotope and PGE data of peridotite xenoliths from S.W. Greenland
2010, Chemical Geology
In this contribution we present platinum-group element (PGE) abundance and Os isotope data of North Atlantic Craton peridotite xenoliths (n = 62) sampled from four major clusters of kimberlite/ultramafic lamprophyre volcanism in W. Greenland. In addition, we analysed olivine separates from selected peridotites.
We find distinct differences in peridotites sampled from the northern (including the reworked Archean Nagssuqtoqidian mobile belt) and southern portions of the W. Greenland fragment of the NAC (WG-NAC). The heavily serpentinized harzburgitic to dunitic peridotites from the northern WG-NAC are typically marked by Os and Ir abundances that are somewhat lower than those of primitive mantle. Pt and Pd abundances are significantly depleted resulting in chondrite-normalized PGE patterns consistent with extensive melt extraction. As a consequence of the melting process, removal of sulphide and possibly a portion of residual PGE-rich alloys is likely. Typically, Os isotopes of these northern samples are unradiogenic (γOs = − 14.2 to − 6.6, average ca.−9.2), with separated olivines being similar in composition. The unradiogenic Os isotope compositions of the northern peridotites result in T_RD^erupt model ages clustering between 2.7 and 3.2 and also at ca. 2.0 Gyr. The grouping of the T_RD^erupt model ages correspond well with the U–Pb zircon ages derived from the trondjemite–tonalite–granodiorite continental crust (∼ 2.8 Gyr) and the tectonic activity associated with the amalgamation and rifting of the WG-NAC and adjacent crust to the WG-NAC (Kangâmiut dykes ∼ 2.0 Gyr; Nagssuqtoqidian ∼ 1.8 Gyr). In detail however, a lack of Eoarchean Re depletion ages has to be recognized in this mantle root although the WG-NAC continental crust clearly preserves magmatic activity from the first 500 Ma of Earth's evolution. This lack of Eoarchean ages in the deep lithosphere may be due to unfortunate bias in the kimberlite eruption sites. Subordinate post-Archean melt extraction and metasomatic enrichment at ca. 2.0 Gyr is evident from the PGE and Os isotope systematics of some of these peridotites and is consistent with prolonged and episodic lithosphere evolution.
The southern WG-NAC peridotites appear to lack the extreme Pd depletion that is endemic in their northern counterparts. Generally the Os isotopes in these samples are more radiogenic (γOs = − 11.5 to + 1.1, average ca. − 7.2) and show a very strong mode of 2.0 Gyr T_RD^erupt model ages. Only a small number of Archean T_RD^erupt model ages can be recognized in this sub-suite of the WG-NAC lithosphere. Despite their relatively depleted major element characteristics, the PGE systematics of the southern peridotites do not preserve evidence of mantle melting and Pd enrichment is evident in a number of samples. Olivine separates from selected southern peridotites typically yield older, Archean, T_RD^erupt model ages relative to the corresponding whole-rock peridotites, although Pd enrichment is evident in the olivine PGE patterns.
The majority of WG-NAC peridotite xenoliths with 2.7 to 3.1 Gyr and 2.0 Gyr T_RD^erupt model depletion ages have normal FeO abundances that are consistent with shallow mantle melting. A significant subset of peridotite xenoliths are enriched in FeO and have 2.3–2.6 Gyr T_RD^erupt model ages that do not align with specific, well-characterized magmatic events, although granulite-facies metamorphism has been proposed during this period. Pronounced PGE over-printing via metasomatism appears to have affected this set of peridotites.
Overall it is apparent that the WG-NAC mantle xenoliths record lithosphere stabilization at the Meso-Neoarchean boundary which was followed by selective modification that has altered and overprinted Os isotope, PGE systematics and FeO abundances in some parts of the lithosphere

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Crustal growth and crustal recycling in the Nagssugtoqidian orogen of West Greenland:: Constraints from radiogenic isotope systematics and U–Pb zircon geochronology

Abstract

Introduction

Section snippets

Geological setting of the Nagssugtoqidian orogen

Reconnaissance U–Pb dating and age–lithology definitions

Whole-rock isotopic evolution: methodology

Archean biotite gneisses; Proterozoic metamorphism at amphibolite facies or lower

Archean crustal development in the Nagssugtoqidian

Acknowledgements

Chem. Geol.

Earth Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Chem. Geol.

Earth Planet. Sci. Lett.

Chem. Geol. (Isotope Geosci. Sect.)

Geochim. Cosmochim. Acta

Geological reconnaissance of the Precambrian rocks of South-East Greenland

Rapp. Grønlands Geol. Unders.

The Proterozoic Nagssugtoqidian mobile belt of southeast Greenland: A link between the eastern Canadian and Baltic shields

Geosci. Canada

The Proterozoic mobile belt in the Ammassalik region, South-East Greenland (Ammassalik mobile belt): an introduction and re-appraisal

Rapp. Grønlands Geol. Unders.

Polymetamorphic evolution of the Lewisian Complex, NW Scotland, as recorded by U–Pb isotopic compositions of zircon, titanite and rutile

Contrib. Mineral. Petrol.

The continental crustal age distribution: methods of determining mantle separation ages from Sm–Nd isotopic data and application to the southwestern United States

J. Geophys. Res.

New evidence for protolith ages of Lewisian granulites, northwest Scotland

Geology