A zircon population from an Archean tonalite sample from southern West Greenland has been used as a source analogue in order to test common methods and approaches applied to ancient detrital zircon populations. Measurements of U-Th-Pb, oxygen and Lu-Hf isotopes as well as rare earth element and Ti concentrations were made in these zircon crystals and, where possible, in multiple areas within a single grain. The population is dominated by oscillatory zoned cores aged 3.82 Ga with an isotopically and compositionally distinct rim that formed at 3.59 Ga. We demonstrate that multiple age components may be erroneously inferred from within these oscillatory zoned zircon cores, both from the total population and within individual grains. This has bearing on other zircon-hosted geochemical systems, as temporal correlations may be incorrectly assigned. Oxygen and Lu-Hf isotope compositions are relatively consistent through the population with only a small number of outliers. Ranges in rare earth element and Ti abundances are evident from the total population, from which apparent inverse cooling trends may be inferred. Additionally, we show that even with enhanced filtering of Ti concentrations using light rare earth element abundances, crystallisation temperatures derived from zircon grains of a single, hand sample sized rock can yield both wide and bimodal results. Since even simple, single “source rock” zircon populations may, without careful scrutiny, portray artificially complex results, particular care must be taken in the interpretation of complex ancient detrital zircon populations.

Our understanding of the Early Earth and the processes that have shaped its evolution have spawned predominantly from the geochemical and isotopic signatures of a small number of zircon populations around the world. Studies of trace element distributions, Hf and O isotope systematics as well as mineral inclusion chemistry in detrital zircon are combined with U-Pb chronology in order to constrain source rock characteristics. However, previous research has highlighted the potential for primary isotopic and geochemical signatures to be modified after deposition, enhanced by self-induced radiation damage and crystal-plastic deformation. Further complications arise when an unknown number of source rocks contribute to the detrital sediments, or when the source rocks are absent as is the case for Hadean detrital zircon. 

In this thesis, a range of analytical methods are applied to relatively uncharted ancient detrital zircon populations, in addition to a systematic investigation into the behaviour of titanium, rare earth elements, U-Th-Pb, Lu-Hf and O isotopes in a magmatic source-rock analogue to such ancient detrital zircon suites. Three localities are studied: Mt. Alfred, within the Yilgarn Craton of Western Australia (detrital study); the Saglek Block, the western-most extent of the North Atlantic Craton in northern Labrador (detrital study); and a locality south of Isua in southern West Greenland (analogue study). We have utilised a CAMECA ims 1280 Secondary Ion Mass Spectrometer (SIMS) for its high spatial resolution and small volume sampling, except for the Lu-Hf analyses which were carried out using a Laser Ablation Multicollector Inductively Coupled Plasma Mass Spectrometer (LA-MC-ICP-MS).

The main outcomes of this study are threefold. 1) Heavily discordant, ancient detrital zircon populations require extensive data filtering in order to produce reliable data for age comparison. Further, age estimations of pervasive Pb loss even in metamict detrital zircon may be achieved using intragrain discordia intercept ages. Applying this in a regional sense reveals that detrital zircon from Mt. Alfred, Western Australia have a distinct provenance in comparison to other metasedimentary units of the Youanmi Terrane, and bear resemblance to the Mt. Narryer metasediments of the Narryer Terrane. 2) Detrital zircon from metasedimentary rocks exposed to high grade metamorphism in the Saglek Block, Northern Labrador yield predominantly Mesoarchaean age signatures, along with a minor Eoarchaean aged component. Lu-Hf isotope data from these zircon reveal up to five near-chondritic populations. U-Pb-Hf data from two samples of metapelite (L1407 and L1408) suggest that a previous re-assignment of deposition age for this unit to >3.95 Ga is unsubstantiated, undermining later studies based on that interpretation. 3) Geochemical complexities in zircon from an Eoarchaean meta-tonalite, taken as a source analogue to ancient detrital zircon, challenge the assumptions and interpretations drawn from detrital zircon studies. Lu-Hf and O isotope systems display mostly homogenous compositions, despite recognised U-Pb disturbance. Petrogenetic trace element proxies such as REE and Ti yield heterogeneous results, even within individual grains. Discerning magmatic signals from detrital zircon populations can therefore, without careful scrutiny, portray artificially complex results and consequently, lead to false interpretations.

Vår kunskap om jordens tidigaste historia och processerna som har format dess utveckling kommer företrädesvis från geokemiska och isotopkemiska signaturer hos ett fåtal zirkonpopulationer från olika delar av världen. Studier av spårelementsfördelning, Hf- och O-isotopsystematik samt kemidata från mineralinklusioner i detritiska zirkoner kan kombineras med U-Pb kronologi för att bestämma ursprungsbergarternas karaktär. Tidigare forskning har emellertid fäst uppmärksamhet på att primära geokemiska och isotopkemiska signaturer kan modifieras efter depositionen, förstärkt av interna strålningsskador och kristall-plastisk deformation. Ytterligare komplikationer uppstår när ett okänt antal ursprungsbergarter bidrar till detritiska sediment eller när ursprungsbergarterna saknas, vilket är fallet för hadeiska detritiska zirkoner.

I denna avhandling har ett antal analysmetoder tillämpats på relativt outforskade detritiska zirkonpopulationer, tillsammans med systematiska undersökningar av titans, sällsynta jordartselements, U-Th-Pb, Lu-Hf och O-isotopers beteende i en magmatisk ursprungsbergart analog med sådana tidiga detritiska zirkonsviter. Tre lokaler har studerats: Mt. Alfred i Yilgarn-kratonen i västra Australien (detritisk studie); Saglek Block, den västligaste utlöparen av den nordatlantiska kratonen i norra Labrador (detritisk studie); och en lokal söder om Isua i sydvästra Grönland (jämförelsestudie). Vi har använt oss av en CAMECA ims 1280 jonmikrosond (SIMS) för dess höga rumsliga upplösning och goda förmåga att analysera små provvolymer, med undantag av Lu-Hf analyserna, vilka utfördes med laserablation (Laser Ablation Multicollector Inductively Coupled Mass Spectrometer, LA-MC-ICP-MS).

De främsta resultaten från denna studie är följande tre: 1) Starkt diskordanta zirkonpopulationer av hög ålder fordrar omfattande datafiltrering för att generera data som är tillförlitliga för ålderskorrelation. Vidare, åldersuppskattningar av genomgripande blyförlust, även i metamikta, detritiska zirkoner, kan erhållas genom beräkning av diskordia-intercept-åldrar inom enskilda kristaller. När detta tillämpas i ett regionalt perspektiv framkommer det att detritiska zirkoner från Mt. Alfred, Western Australia har en distinkt provenans jämfört med andra metasedimentära enheter i Youanmi Terraine och uppvisar likheter med Mt. Narryer metasediment i Narryer Terraine. 2) Detritiska zirkoner från metasediment som utsatts för höggradig metamorfos i Saglek Block, norra Labrador ger företrädesvis mesoarkeiska ålderssignaturer, tillsammans med en mindre eoarkeisk komponent. Lu-Hf isotopdata från dessa zirkoner visar på upp till fem populationer med nära-kondritisk sammansättning. U-Pb-Hf data från två prover av metapelit (L1407 och L1408) tyder på att en tidigare omtolkning av depositionsåldern för denna enhet till >3.95 Ga är ogrundad, vilket undergräver senare studier baserade på denna tolkning. 3) Geokemisk komplexitet i zirkoner från en eoarkeisk metatonalit, ansedd som en motsvarighet beträffande ursprung till äldre detritiska zirkoner, ifrågasätter antaganden och tolkningar baserade på studier av detritiska zirkoner. Lu-Hf och O-isotopsystem uppvisar mestadels homogena sammansättningar, trots uppvisad U-Pb störning. Petrogenetiska spårelement proxies såsom REE och Ti ger heterogena resultat, även inom enskilda korn. Påvisande av magmatiska signaler från detritiska zirkonpopulationer kan därför, utan noggrann granskning, visa på konstgjort komplexa resultat som följaktligen kan leda till felaktiga tolkningar.

The U-Th-Pb isotopic data from detrital zircon grains from five samples of Archean quartzite from the Mt. Alfred area of the Illaara greenstone belt in the Yilgarn Craton of Western Australia are presented in this study. The zircon grains are typically fractured and contain both irregular and oscillatory zoned internal structures as revealed by cathodoluminescence imaging. Concordant ²⁰⁷Pb/²⁰⁶Pb ages range between 3109 ± 17 and 3918 ± 16 Ma (2σ), with three main age peaks at ca. 3640, 3690 and 3760 Ma. Older ²⁰⁷Pb/²⁰⁶Pb ages up to 4067 ± 5 Ma are strongly affected by at least one recent disturbance event, however one single-grain discordia yields an upper intercept age of 4107 ± 12 (MSWD = 1.2). A further sixteen zircon grains with multiple analyses define discordia that suggest U-Pb disturbance events in the Neoarchean and the Mesozoic, the latter as a result of invasive low temperature weathering solutions. The notable lack of grains with ages less than ∼3.6 Ga in the Mt. Alfred detrital zircon population differentiates it from other quartzite samples from both the Illaara Formation and the Eoarchean zircon-bearing metasedimentary rocks of the Narryer Terrane. Also, the limited spread of zircon ages between 3640 and 3760 Ma suggests a relatively uniform and possibly local source region. However, no rocks of this age have been found in the Youanmi Terrane. This implies either the distal transport of similarly aged clastic sediments at 3.1 Ga from the Narryer Gneiss Complex (NGC) to the Mt. Alfred area, or the previous existence of NGC-like rocks near the Illaara greenstone belt that are either not currently recognised or have since been destroyed.

Determining the chronology and quantifying various geochemical reservoirs on planetary bodies is fundamental to understanding planetary accretion, differentiation, and global mass transfer. The Pb isotope compositions of individual minerals in the Martian meteorite Chassigny have been measured by Secondary Ion Mass Spectrometry (SIMS). These measurements indicate that Chassigny has mixed with a Martian reservoir that evolved with a long-term U-238/Pb-204 (mu) value similar to two times higher than those inferred from studies of all other Martian meteorites except 4.428 Ga clasts in NWA7533. Any significant mixing between this and an unradiogenic reservoir produces ambiguous trends in Pb isotope variation diagrams. The trend defined by our new Chassigny data can be used to calculate a crystallization age for Chassigny of 4.526 +/- 0.027 Ga (2 sigma) that is clearly in error as it conflicts with all other isotope systems, which yield a widely accepted age of 1.39 Ga. Similar, trends have also been observed in the Shergottites and have been used to calculate a >4 Ga age or, alternatively, attributed to terrestrial contamination. Our new Chassigny data, however, argue that the radiogenic component is Martian, mixing occurred on the surface of Mars, and is therefore likely present in virtually every Martian meteorite. The presence of this radiogenic reservoir on Mars resolves the paradox between Pb isotope data and all other radiogenic isotope systems in Martian meteorites. Importantly, Chassigny and the Shergottites are likely derived from the northern hemisphere of Mars, while NWA 7533 originated from the Southern hemisphere, implying that the U-rich reservoir, which most likely represents some form of crust, must be widespread. The significant age difference between SNC meteorites and NWA 7533 is also consistent with an absence of tectonic recycling throughout Martian history.

Hadean and Paleo-Eoarchean aged detrital zircon provide a rare glimpse into the nature of the early Earth. Thus, the characterisation of new localities with rocks that host Hadean and Paleo-Eoarchean zircon provide invaluable insight into the Earth’s early crust. We report high spatial resolution SIMS U-Th-Pb data in detrital zircon from five samples of the Mt. Alfred Archean quartzite located in the Illaara Greenstone Belt, Yilgarn Craton in Western Australia. To date, only two studies have published detrital age data for this locality (Wyche et al., 2004; Thern and Nelson, 2012). A total of 487 spots in 450 zircon grains have been analysed for U-Th-Pb and the internal structure of the grains has been studied by cathodoluminescence imaging. Concordant 207Pb/206Pb ages range between 3109 ± 17 and 3918 ± 16 Ma (2σ), with three main age peaks at ca. 3640, 3690 and 3760 Ma. 207Pb/206Pb ages of up to 4067 ± 5 Ma were found, but these were highly discordant. At least two Pb-loss events are evident during the Neoarchean and Permian-Triassic. The Neoarchean event is implied from highly metamict zircon cores producing 207Pb/206Pb ages ca. 2.7-2.8 Ga, younger than a crosscutting quartz-tourmaline vein formed at 2.94 Ga. Single-grain discordia trends define the more recent Pb-loss event, with eight grains producing a weighted average lower intercept age of 224 ± 35 Ma (2σ).We propose that the similarity of ages between the Mt. Alfred detrital zircon age distribution and the Meeberrie gneiss of the Narryer Gneiss Complex (NGC) imply the distal transport of these sediments over ca. 300 km, or the previous existence of NGC-like rocks near the Illaara greenstone belt. The noticeable lack of detrital zircon aged ca. 3.34 Ga as observed in all other detrital populations of the Illaara Formation suggests a different provenance for the Mt. Alfred quartzites.

Detritiska zirkoner av hadeisk och paleo-eoarkeisk ålder ger en unik inblick i den tidiga jordens beskaffenhet. Undersökning av nya lokaler med bergarter som innehåller hadeiska och paleo-eoarkeiska zirkoner ger därför en ovärderlig inblick i jordskorpans tidigaste historia. Vi rapporterar SIMS U-Th-Pb data med hög rumslig upplösning på detritiska zirkoner från fem prov från den arkeiska Mt. Alfred quartzite belägeni Illaara Greenstone Belt, Yilgarn-kratonen, Western Australia. Hittills har endast två studier publicerat detritiska data från denna lokal (Wycheet al., 2004; Thern and Nelson, 2012). Sammanlagt har 487 punkter i 450 zirkonkristaller analyserats på U-Th-Pb ochde interna strukturerna i kristallerna har studerats med katodluminiscens-avbildning. Konkordanta 207Pb/206Pb-åldrar varierar mellan 3109 ± 17 and 3918 ± 16 Ma (2σ), med tre ålderstoppar vid ca. 3640, 3690 and 3760 Ma. 207Pb/206Pb-åldrar på upp till 4067 ± 5 Ma påträffades men dessa var starkt diskordanta. Minst två blyförlust-episoder kan iakttagas och dessa har neoarkeisk och permisk-triassisk ålder. Den neoarkeiska händelsen kan härledas från starkt metamikta zirkonkärnor som ger 207Pb/206Pb-åldrar på ca. 2.7-2.8 Ga, yngre än en skärande kvarts-turmalin-ådra som bildades vid 2.94 Ga. Diskordialinjer inom samma kristaller definierar en mer recent blyförlust. Åtta kristaller ger ett viktat medelvärde på 224 ± 35 Ma (2σ) för den nedre interceptåldern.Vi hävdar att likheten i åldrar mellan de detritiska zirkonerna från Mt. Alfred och de från Meeberrie gneiss i Narryer Gneiss Complex (NGC) tyder på långväga transport av dessa sediment över ca. 300 km eller tidigare existens av NGC-liknande bergarter nära Illaara greenstone belt. Den tydliga avsaknaden av detritiska zirkoner med åldrar på ca. 3.34 Ga, vilka påträffas i alla andra detritiska populationer i Illaara Formation, tyder på en annan provenans för Mt. Alfred-kvartsiterna.

The Archean metasedimentary rocks of the Saglek Block of the Nain Province, Northern Labrador provide invaluable insight into the Earth’s early evolution. Preliminary mapping campaigns and geochronological studies have indicated the presence of two temporally distinct, yet visually similar supracrustal units, ranging in depositional age from the Eoarchaean Nulliak supracrustal association to the Mesoarchaean Upernavik supracrustal association, potentially equivalent if not older than the oldest exposed supracrustal sequences on Earth to date (Nutman et al. 1989b; Schiøtte et al. 1989b, 1992; Komiya et al. 2015a).We present a comprehensive set of U-Th-Pb-Hf isotope data of detrital zircon from eight metasedimentary rocks of the Saglek Block. The zircon in these samples are younger than or equivalent in age with the local ca. 3.72 Ga Uivak I Gneiss, apart from one inherited core yielding a 207Pb/206Pb age of 3878 ± 20 Ma (2σ). Further, these data indicate deposition ages between ca. 3.2 - 2.8 Ga and 2.7 Ga. Therefore all samples demonstrate affinity with the Upernavik supracrustal association. This finding stands in contrast to the previous assignment of one sample ( L1454; Ryan, 1993; Ryan and Martineau, 2012), and recent reassignment of two samples presented here ( L1407, L1408; Komiya et al., 2017, 2015a) to the Eoarchaean Nulliak supracrustal association.