Jack Hills Research Articles

New evidence for ~ 4.45 Ga terrestrial crust from zircon xenocrysts in Ordovician ignimbrite in the North Qinling Orogenic Belt, China

Evidence for the earliest known terrestrial crust comes predominantly from Jack Hills in Western Australia, where hafnium isotopic results from >3.8Ga detrital zircons indicate crustal precursors as old as ~4.4–4.5Ga. We present evidence from magmatic cores in >3.9Ga xenocrystic zircons from a felsic volcanic rock in the North Qinling Orogenic Belt, China, of similar Hf crustal model ages up to 4.45Ga. These lie on the same Lu/Hf trajectory as the least disturbed Jack Hills and Apollo 14 zircons, therefore providing only the second example of the earliest known generation of continental crust on Earth. In addition, the rims of two zircon grains record later growth at 3.7Ga and, when combined with the fact that the grains are incorporated in Paleozoic volcanic rocks, imply long-lived crustal residence within the basement of the North China Craton. These results therefore establish the wider distribution and survival of the most ancient crustal material on the Earth and highlight the possibility for the further discovery of ancient crustal remnants.

Who’s got the “Reel” power? The problem of female antagonisms in blaxploitation cinema

Between 1973 and 1975, films starring Pam Grier and Tamara Dobson such as Cleopatra Jones (Jack Starrett, 1973), Coffy(Jack Hill, 1973) and Foxy Brown (Hill, 1974) introduced leading black women into the predominantly male blaxploitation scene as aggressive action heroines. Within the cinematic spaces of blaxploitation films which featured women as active agents, a racial and sexual divide exists. These films positioned women either inside or outside of gender tolerability by utilising binary constructions of identity based on race, sex and elementary constructions of good and evil, black and white, straight and gay, and feminine and butch. Popular representations of lesbianism and sisterhood within blaxploitation cinema reflect a dominant social view of American lesbianism as white while straight women are consistently represented as black. However, these spaces also constricted black and white female identities by limiting sexuality and morality to racial boundaries. This article seeks to question the unique solitude of these female heroines and interrogate a patriarchal cinematic world where sisterhood is often prohibited and lesbianism demonised.

Metamorphic replacement of mineral inclusions in detrital zircon from Jack Hills, Australia: Implications for the Hadean Earth: COMMENT

We appreciate that [Rasmussen et al. (2011)][1] have characterized a large number of inclusions in Jack Hills (Australia) detrital zircons, but we find two significant flaws in their paper: one of scholarship and one of omission. With regard to the first, their paper implies discovery of reset

Metamorphic replacement of mineral inclusions in detrital zircon from Jack Hills, Australia: Implications for the Hadean Earth: REPLY

Metamorphic replacement of mineral inclusions in detrital zircon from Jack Hills, Australia: Implications for the Hadean Earth: REPLY

From oppositional readers to positional producers: the making of black female heroism in Coffy

This essay explores the production history and textual relations of Coffy (Jack Hill, 1973), an exploitation film starring Pam Grier about a black female vigilante which briefly topped Variety's chart of highest grossing films in America. The relative simplicity of Coffy's production context – a bottom-line exploitation picture from American International Pictures written and directed by white male hired-hand Jack Hill – combined with the heightened images of sex and race in the film's textual representation, offers a revealing site for exploring the encoding processes of filmic identity politics. Scholarly unease about the film's representational politics has given rise to readings that rely heavily on ‘oppositional gazes’ to account for Coffy's popularity and appeal. This essay, by contrast, examines the film's positional producers, considering the generic, commercial and creative determinants of the film production. In turn, it examines how these determinants fed into the representation of Coffy's heroine, focusing on her class status, fighting heroism and sexuality. I argue that, through her collaboration with Jack Hill, Pam Grier had more agency in the shaping of her own emerging screen image than has previously been acknowledged. By combining established ideas from feminist and black film studies with cultural industries approaches, I argue that compelling narratives like Coffy, about individuals from oppressed groups, are often informed and energized by the unequal, high-stakes conditions of their own determination.

A search for thermal excursions from ancient extraterrestrial impacts using Hadean zircon Ti-U-Th-Pb depth profiles

Few terrestrial localities preserve more than a trace lithic record prior to ca. 3.8 Ga greatly limiting our understanding of the first 700 Ma of Earth history, a period inferred to have included a spike in the bolide flux to the inner solar system at ca. 3.85–3.95 Ga (the Late Heavy Bombardment, LHB). An accessible record of this era may be found in Hadean detrital zircons from the Jack Hills, Western Australia, in the form of μm-scale epitaxial overgrowths. By comparing crystallization temperatures of pre-3.8 Ga zircon overgrowths to the archive of zircon temperature spectra, it should, in principle, be possible to identify a distinctive impact signature. We have developed Ti-U-Th-Pb ion microprobe depth profiling to obtain age and temperature information within these zircon overgrowths and undertaken a feasibility study of its possible use in identifying impact events. Of eight grains profiled in this fashion, four have overgrowths of LHB-era age. Age vs. temperature profiles reveal a period between ca. 3.85–3.95 Ga (i.e., LHB era) characterized by significantly higher temperatures (approximately 840–875 °C) than do older or younger zircons or zircon domains (approximately 630–750 °C). However, temperatures approaching 900 °C can result in Pb isotopic exchange rendering interpretation of these profiles nonunique. Coupled age-temperature depth profiling shows promise in this role, and the preliminary data we report could represent the first terrestrial evidence for impact-related heating during the LHB.

Hafnium isotope evidence from Archean granitic rocks for deep-mantle origin of continental crust

Combined whole-rock and zircon MC-ICP-MS Lu–Hf isotope data are reported for a large collection of Archean granitoids belonging to typical tonalite–trondhjemite–granodiorite (TTG) suites. Our data demonstrate that the time-integrated Lu/Hf of the mantle source of TTGs has not significantly changed over the last 4Gy. Continents therefore most likely grew from nearly primordial unfractionated material extracted from the deep mantle via rising plumes that left a depleted melt residue in the upper mantle. The deep mantle could retain its primitive relative element abundances over time because sinking plates are largely stripped barren of their oceanic and continental crust components at subduction zones; this process results in only small proportions (<15–25%) of present-day continental mass getting recycled to great depths. Zircon populations extracted from the analyzed TTGs have Hf isotopic compositions broadly consistent with those of their host whole-rocks, whereas the U–Pb system in the same grains is often disturbed, causing a discrepancy that creates spurious initial εHf values. This problem is endemic to the Archean detrital zircon record and consistent with experimental results bearing on the relative retentivity of Hf vs. U and Pb in zircon. We argue that this behavior biases the Archean zircon record toward negative εHf values, which are at odds with the present TTG data set. If Hadean Jack Hills zircons are considered in light of these results, the mantle source of continents has remained unchanged for the last 4.3Gy.

Processes on the Young Earth and the Habitats of Early Life

Conditions at the surface of the young (Hadean and early Archean) Earth were suitable for the emergence and evolution of life. After an initial hot period, surface temperatures in the late Hadean may have been clement beneath an atmosphere containing greenhouse gases over an ocean-dominated planetary surface. The first crust was mafic and it internally melted repeatedly to produce the felsic rocks that crystallized the Jack Hills zircons. This crust was destabilized during late heavy bombardment. Plate tectonics probably started soon after and had produced voluminous continental crust by the mid Archean, but ocean volumes were sufficient to submerge much of this crust. In the Hadean and early Archean, hydrothermal systems around abundant komatiitic volcanism may have provided suitable sites to host the earliest living communities and for the evolution of key enzymes. Evidence from the Isua Belt, Greenland, suggests life was present by 3.8 Gya, and by the mid-Archean, the geological record both in the Pilbara in Western Australia and the Barberton Greenstone Belt in South Africa shows that microbial life was abundant, probably using anoxygenic photosynthesis. By the late Archean, oxygenic photosynthesis had evolved, transforming the atmosphere and permitting the evolution of eukaryotes.

Excess hafnium‐176 in meteorites and the early Earth zircon record

The long‐lived176Lu‐to‐176Hf decay system is a powerful tool to understand ancient chemical fractionation events associated with planetary differentiation. Detrital Hadean zircons (&gt;3.8 Gyr) from the Jack Hills metasedimentary belt of Western Australia record extremely enriched Hf‐isotope signals suggesting early extraction of a continental crust (&gt;4.5 Gyr) but fail to identify a prevalent complementary depleted mantle reservoir, suggesting that crust formation processes in the early Earth were fundamentally distinct from today. However, this conclusion assumes that the Hf‐isotope composition of bulk chondrite meteorites can be used to estimate the composition of Earth prior to its differentiation into major silicate reservoirs, namely the bulk silicate Earth (BSE). We report a176Lu‐176Hf internal mineral isochron age of 4869 ± 34 Myr for the pristine SAH99555 angrite meteorite. This age is ∼300 Myr older than the age of the Solar System, confirming the existence of an energetic process yielding excess 176Hf in affected early formed Solar System objects through the production of the 176Lu isomer (t1/2 ∼3.9 hours). Thus, chondrite meteorites contain excess 176Hf and their present‐day composition cannot be used to infer the Lu‐Hf parameters of BSE. Using a revised BSE estimate based on the SAH99555 isochron, we show that Earth's oldest zircons preserve a record of coexisting enriched and depleted hafnium reservoirs as early as ∼4.3 Gyr in Earth's history, with little evidence for the existence of continental crust prior to ∼4.4 Gyr. This new view suggests continuous juvenile crustal growth and recycling throughout the Hadean and Archean eras, perhaps analogous to modern plate tectonics.

Metamorphic replacement of mineral inclusions in detrital zircon from Jack Hills, Australia: Implications for the Hadean Earth

The Hadean (before 4.0 Ga) crust has long been considered to comprise mainly primitive mafic and ultramafic rocks. However, mineral inclusions in detrital zircons as old as 4.4 Ga from Jack Hills, Australia, have been interpreted to be magmatic and to provide evidence for extensive granitic crust. In situ U-Pb dating of monazite and xenotime inclusions in 4.25–3.35 Ga detrital zircons from Jack Hills shows that these inclusions are not magmatic, but formed during metamorphism at either 2.68 Ga or 0.8 Ga. Monazite-xenotime thermometry of intergrowths in the inclusions and the quartz-muscovite rock matrix constrain temperatures to between 420–475 °C, corresponding with conditions during peak regional metamorphism. Petrography and U-Pb geochronology of zircon inclusions from other localities show that the replacement of primary inclusions may commence in the igneous host rock and continue through weathering, sedimentation, and diagenesis. With increasing metamorphic grade, the inclusion assemblage increasingly reflects the composition of the rock matrix. In Jack Hills, most of the inclusions have the same composition and abundances as the metamorphic matrix, consistent with their formation during metamorphism. The titanium content of quartz inclusions indicates formation temperatures of 350–490 °C, supporting a metamorphic origin. Several lines of evidence indicate that at least some of the muscovite inclusions are also secondary. The lack of apatite inclusions in zircons from Jack Hills, relative to zircon in common granitic rocks, suggests that secondary minerals may have replaced primary apatite. Thus, detrital zircon may not be impermeable to post-depositional fluids, raising doubts about the use of the mineral inclusions they contain to infer initial magma chemistry. These results call for a reassessment of the source melts of the Hadean zircons and the composition of the earliest crust.

Detrital zircon age structure within ca. 3 Ga metasedimentary rocks, Yilgarn Craton: Elucidation of Hadean source terranes by principal component analysis

A multivariate approach using a similarity matrix derived from >5500 U–Pb zircon analyses was used to investigate the complex and overlapping detrital zircon age structure within ca. 3Ga metasedimentary rocks from the Yilgarn Craton, Western Australia. Detrital zircon analyses were grouped by their 207Pb/206Pb dates using a robust Chi-square grouping method which produced 74 Yilgarn-wide age groups from a pool of >3500 analyses and that were correlated between different metasedimentary rocks. Principal component analysis (PCA) was then used on a calculated similarity matrix of >65 samples which contained these age groups. PCA indicates that the main age populations of the detrital zircons in the ca. 3Ga metasedimentary rocks were derived in varying portions from the Narryer and Yarlarweelor Gneiss Complexes. Differences between the age structure of >3.9Ga zircon populations within the Mt. Alfred metasedimentary rocks with those from Mt. Narryer, Jack Hills and Maynard Hills localities is best explained by their derivation from two Hadean terranes which were joined by ca. 3.7Ga.

Li isotopes and trace elements as a petrogenetic tracer in zircon: insights from Archean TTGs and sanukitoids

We report d 7 Li, Li abundance ((Li)), and other trace elements measured by ion probe in igneous zircons from TTG (tonalite, trondhjemite, and granodiorite) and sanukitoid plutons from the Superior Province (Canada) in order to characterize Li in zircons from typical Archean continental crust. These data are compared with detrital zircons from the Jack Hills (Western Australia) with U-Pb ages greater than 3.9 Ga for which parent rock type is not known. Most of the TTG and sanukitoid zircon domains preserve typical igneous REE patterns and CL zoning. (Li) ranges from 0.5 to 79 ppm, typical of (Li) in continental zircons. Atomic ratios of (Y ? REE)/(Li ? P) average 1.0 ± 0.7 (2SD) for zircons with magmatic composition preserved, supporting the hypothesis that Li is interstitial and charge compensates substitution of trivalent cations. This substitution results in a relatively slow rate of Li diffusion. The d 7 Li and trace element data constrain the genesis of TTGs and sanukitoids. (Li) in zircons from granitoids is significantly higher than from zircons in primitive magmas in oceanic crust. TTG zircons have d 7 Li (3 ± 8%) and d 18 O in the range of primitive mantle- derived magmas. Sanukitoid zircons have average d 7 Li (7 ± 8%) and d 18 O higher than those of TTGs supporting genesis by melting of fluid-metasomatized mantle wedge. The Li systematics in sanukitoid and TTG zircons indicate that high (Li) in pre-3.9-Ga Jack Hills detrital zircons is a primary igneous composition and suggests the growth in proto-continental crust in magmas similar to Archean granitoids.

Tracing the provenance and recrystallization processes of the Earth's oldest detritus at Mt. Narryer and Jack Hills, Western Australia: An in situ Sm–Nd isotopic study of monazite

Mount Narryer and Jack Hills metasedimentary rocks in the Narryer Gneiss Complex of the Yilgarn Craton, Western Australia, contain zircons with ages up to 4.4 Ga, the oldest known crustal materials on Earth, and monazites up to 3.6 Ga. In this study, we have investigated 147Sm– 143Nd systematics of detrital and metamorphic monazites from these metasedimentary rocks using laser ablation-multicollector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS). All detrital monazites have negative initial εNd(t) values, indicating that their parental magmas formed by remelting of older crustal materials. A comparison between the initial εNd(t) values of the detrital monazites and granitoids in the Narryer Gneiss Complex indicates that the Mt. Narryer and Jack Hills sediments were partly derived from the most isotopically enriched surrounding granitoids with ages of ca. 3.6 and 3.3 Ga. The metamorphic monazites generally have lower initial εNd(t) values when compared to the detrital monazites. However, the detrital and metamorphic monazites show similar distributions of εNd(t) at the ages of sediment deposition (3.28 Ga for Mt. Narryer and 3.05 Ga for Jack Hills). In addition, multiple analyses on single monazite grains having core-rim structures reveal that the cores and the recrystallized rims had identical Nd isotopic compositions at the time of recrystallization. These findings indicate that older monazites are source of light rare earth elements for younger metamorphic monazite formation and, therefore, that monazite can inherit its primary Sm–Nd isotopic signature during the recrystallization processes. We calculated the Nd model ages for all analyzed monazites to estimate crustal residence time of their source materials. We find that no igneous monazites older than 4.0 Ga were recrystallized to form the monazites. This implies that the lack of Hadean monazites is not due to recrystallization of ancient monazites during later metamorphism, but due to high-Ca compositions of the parental magmas of Hadean detritus, which prevent growth of magmatic monazite.

Early Archean crustal evolution of the Jack Hills Zircon source terrane inferred from Lu–Hf, 207Pb/ 206Pb, and δ 18O systematics of Jack Hills zircons

Several lines of isotopic evidence – the most direct of which is from Hadean Jack Hills zircons – suggest a very early history of crust formation on Earth that began by about 4.5 Ga. To constrain both the fate of the reservoir for this crust and the nature of crustal evolution in the sediment source region of the Jack Hills, Western Australia, during the early Archean, we report here initial 176Hf/ 177Hf ratios and δ 18O systematics for <4 Ga Jack Hills zircons. In contrast to the significant number of Hadean zircons which contain highly unradiogenic 176Hf/ 177Hf requiring a near-zero Lu/Hf reservoir to have separated from the Earth’s mantle by 4.5 Ga, Jack Hills zircons younger than ca. 3.6 Ga are more radiogenic than –13ε (CHUR) at 3.4 Ga in contrast to projected values at 3.4 Ga of –20ε for the unradiogenic Hadean reservoir indicating that some later juvenile addition to the crust is required to explain the more radiogenic younger zircons. The shift in the Lu–Hf systematics together with a narrow range of mostly mantle-like δ 18O values among the <3.6 Ga zircons (in contrast to the spread towards sedimentary δ 18O among Hadean samples) suggests a period of transition between 3.6 and 4 Ga in which the magmatic setting of zircon formation changed and the highly unradiogenic low Lu/Hf Hadean crust ceased to be available for intracrustal reworking. Constraining the nature of this transition provides important insights into the processes of crustal reworking and recycling of the Earth’s Hadean crust as well as early Archean crustal evolution.

The age distribution of detrital zircons in quartzites from the Toodyay-Lake Grace Domain, Western Australia: Implications for the early evolution of the Yilgarn Craton

Evidence for the early history of the Archean Yilgarn Craton has been largely obliterated by the craton-wide emplacement of granitic rocks at ca. 2650 Ma. However, detrital zircons from rare, ca. 3.1 Ga quartz-rich metasediments preserved in the Yilgarn Craton provide an opportunity to investigate the age structure and composition of the pre-existing basement and therefore provide a valuable record of the early history of crustal components that combined to form the Yilgarn Craton. In this report we present the results of an ion microprobe (SHRIMP) U-Pb geochronological study of detrital zircons from six samples of quartzites from the Toodyay-Lake Grace Domain (TLGD) in the South West Terrane of the Yilgarn Craton. Consistent features in the detrital zircon age spectra in all samples demonstrate a basic uniformity in the composition of the source rocks. The results suggest a provenance dominated by ca. 3350 to 3200 Ma granitic rocks with an age peak at ca. 3265 Ma. No granites of this age have so far been identified in the south-western part of the Yilgarn Craton, although ca. 3280 Ma granites occur in the Narryer Terrane in the northwestern corner of the craton. A second consistent zircon age component suggests an earlier episode of granite emplacement at ca. 3500 to 3400 Ma. A minor component of material contributed zircons as old as 3850 Ma to the pre-2650 Ma basement of the proto-Yilgarn Craton. Our zircon age results suggest that the provenance of the TLGD was different from that of the ca. 3.1 Ga quartzites and metaconglomerates from Mt Narryer and the Jack Hills in the Narryer Terrane and from the Maynard Hills greenstone belt in the Southern Cross Domain. Although the zircon age spectra are not consistent with an origin from presently exposed gneisses from the Narryer Terrane, the presence of granite and pegmatite in the Narryer Terrane close in age to the main zircon age peak in the TLGD sediments suggests a possible connection. Some detrital zircons in the TLGD have been altered hydrothermally or overgrown by zircon rims during the ca. 2650 Ma sillimanite-grade metamorphism that affected the southern part of the TLGD.

The geoheritage significance of crystals

Crystals are very common and, aside from regions of its molten interior, the Earth can be considered to be a crystalline planet with many types of crystals, expressed as thousands of mineral varieties, occurring in diverse environments. Some of these crystals (and minerals) are of geoheritage significance because of their size, composition, shape, zoning, reaction rims, mineral inclusions, fluid and gas inclusions, twinning, dislocations, exsolution, the unusual occurrence or rarity of a crystal attribute, and their form of aggregation, such as desert roses, or druses. If macroscale geological features are assessed as important in unravelling Earth history, and afforded geoheritage significance, then importance should also be given to crystals where similar principles and patterns are present. Some notable crystals of geoheritage significance are the giant gypsum in Mexico and in Spain, the zircon crystals of Jack Hills (the oldest crystals on Earth), the large well‐formed pyrite in Spain, snowball garnets from various locations, and Iceland spar from its type locality.

Constraints on Hadean geodynamics from mineral inclusions in > 4 Ga zircons

The inclusion mineralogy of 1450 zircons over 4 billion years in age from the Jack Hills, Western Australia, was characterized for composition and phase assemblage. Results confirm that the inclusion population of these largely igneous zircons is dominated by muscovite and quartz (~ 75%). If the inclusions are original to the igneous zircons, this observation alone restricts the host melts to formation at pressure–temperature ( P– T) conditions of ~ 650–800 °C and > 4 kbar. Several lines of evidence support the view that most of the analyzed mineral inclusions are primary, including their lack of association with cracks, magmatic crystal forms, and lack of exchange with fuchsitic (Cr-rich) micas in the host conglomerate. The application of Ti-in-zircon thermometry, and phengite, Ti-in-quartz, and Al-in-hornblende barometry to these inclusion assemblages yields estimates of magmatic P–T conditions from 5 to > 12 kbar and 700 ± 40 °C. These data indicate zircon formation along geotherms of ≤ 60 °C/km and imply conductive near-surface heat flow of < 40 to 85 mW/m 2— a range that is substantially lower than most estimates of global Hadean heat flow. Of the possible environments capable of generating melting under such locally low heat flow early in Earth history, underthrusting, possibly in a manner similar to modern convergent margins, appears most consistent with numerous other geochemical constraints derived from investigation of Hadean zircons.

The Hadean protocrust of the Earth: Formation model and probable composition

1003 Despite the unavailability of Hadean rocks, the problems related to the formation of the Earth’s crust (protocrust) at this stage, i.e., after the cessation of the Earth’s accretion (since 4.44 [1] until 3.9 Ga ago), are at present highly debatable. The indirect evidence for magmatic activity of the Earth in the Hadean is pro� vided by finds of corresponding detrital and xenogenic zircons in younger metasedimentary and metaigneous rocks [2, 3, and others]. During the last decade, several studies were dedicated to detrital Hadean zircons aged 3.9–4.4 Ga from Upper Archean ( ~3 Ga) metaterrig� enous rocks of the Jack Hills and Mount Narrier areas in the Yilgarn Craton of Australia. They include the analysis of their geochemical and geochemical isotope composition and similar data on their mineral inclu� sions. These data are used for interpreting the crust formation at the Hadean stage of the Earth’s evolution [2, 4, and others].

Reworking of Earth's first crust: Constraints from Hf isotopes in Archean zircons from Mt. Narryer, Australia

Discoveries of >4 Ga old zircon grains in the northwest Yilgarn of Western Australia led to the conclusion that evolved crust formed on the Earth within the first few 100 Ma after accretion. Little is known, however, about the fate of the first crust that shaped early Earth's surface. Here we report combined solution and laser-ablation Lu–Hf–U–Pb isotope analyses of early Archean and Hadean detrital zircon grains from different rocks of the Narryer Gneiss Complex (NGC), Yilgarn Craton, Western Australia. The zircons show two distinct groups with separate evolutionary trends in their Hf isotopes. The majority of the zircon grains point to separation from a depleted mantle reservoir at ∼3.8–3.9 Ga. The second Hf isotope trend implies reworking of older Hadean zircon grains. The major trend starting at 3.8–3.9 Ga defined by the Hf isotopes corresponds to a Lu/Hf that is characteristic for felsic crust and consequently, the primary sources for these zircons presumably had a chemical composition characteristic of continental crust. Reworked Hadean crust appears to have evolved with a similar low Lu/Hf, such that the early crust was probably evolved with respect to Lu–Hf distributions. The co-variation of Hf isotopes vs. age in zircon grains from Mt. Narryer and Jack Hills zircon grains implies a similar crustal source for both sediments in a single, major crustal domain. Age spectra and associated Hf isotopes in the zircon grains strongly argue for ongoing magmatic reworking over hundreds of millions of years of the felsic crustal domain in which the zircon grains formed. Late-stage metamorphic zircon grains from the Meeberrie Gneiss unit yield a mean U–Pb age of 3294.5 ± 3.2 Ma with initial Hf isotopes that correspond to the evolutionary trend defined by older NGC zircon grains and overlap with other detrital zircon grains, proving their genetic relationship. This ‘Meeberrie event’ is interpret here as the last reworking event in the precursor domain before final deposition. The continuous magmatic activity in one crustal domain during the Archean is recorded by the U–Pb ages and Hf isotope systematics of zircon grains and implies reworking of existing crust. We suspect that the most likely driving force for such reworking of crustal material is ongoing crustal collision and subduction. A comparison of Hf isotope signatures of zircon grains from other Archean terranes shows that similar trends are recognised within all sampled Archean domains. This implies either a global trend in crustal growth and reworking, or a genetic connection of Archean terranes in close paleo-proximity to each other. Notably, the Archean Acasta gneiss (Canada) shows a similar reworking patterns to the Yilgarn Craton of Hadean samples implying either a common Hadean source or amalgamation at the Hadean–Archean transition.

Palaeoenvironmental analysis of Archaean siliciclastic sedimentary rocks in the west–central Jack Hills belt, Western Australia with new constraints on ages and correlations

Abstract: Zircons with ages between 3.05 and 4.4 Ga and hosted in conglomerates and associated sandstones in the Jack Hills belt of Western Australia have been the subject of numerous studies but none, to date, has been concerned with understanding the depositional environments of the sedimentary rocks. Intact, 250 and 320 m thick stratigraphical sections include conglomerates and sandstones that are equivalent to those at the W74 discovery site that host the ancient zircons. Facies associations are compatible with a prograding fan delta depositional setting in which alluvial fans were sourced by proximal highlands, were built directly into a lake or sea and were characterized by high gradients and high flow velocities. Locally, the succession is capped by a 20–25 m thick interval of cross-bedded quartz arenite–gritstone with a similar U–Pb detrital zircon age spectrum to the W74 discovery site, suggesting that this facies association is of comparable age and genetically related to the underlying facies associations. The quartz arenite–gritstone facies association is interpreted to record transgressive tidal reworking of the fan delta. Similar sedimentary units, including areally extensive quartz arenite successions, are widely developed elsewhere in Western Australia and on other continents, indicating that stable continental crust was widespread by 3.0 Ga.