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[Display omitted] • We present new zircon U-Pb, Hf, O isotopes from the Paleoproterozoic Karrat Group. • With provenance analysis of Karrat Group and Rinkian fold belt supracrustal rocks. • Zircon Hf isotopes identify new, abundant ca. 2.15–1.9 Ga juvenile magmatism. • Karrat Group sourced dominantly from orogenies involving the Rae craton. We use zircon U-Pb, Hf and O isotopes to constrain the depositional ages and provenance of metasedimentary rocks of the Paleoproterozoic Karrat Group of West Greenland and to understand the tectonic processes leading to basin development on the eastern Rae craton. An older supracrustal assemblage (Qeqertarssuaq complex) deposited after ca. 2.6 Ga is separated by an unconformity with a younger supracrustal assemblage (the Karrat Group). The Qaarsukassak Formation at the base of the Karrat Group was deposited after ca. 2.0 Ga, with dominantly Archean age modes. The youngest siliciclastic rocks (Nûkavsak and Mârmorilik formations) in the Karrat Group have maximum depositional ages ranging from ca. 1980 to 1950 to 1900 Ma and contain dominant detrital zircon age modes between ca. 2.50 and 1.93 Ga. A ca. 1.92 Ga supracrustal assemblage referred to as the northern domain (Karrat Group, sensu lato) is geographically separated from the Karrat Group (sensu stricto) by the Prøven igneous complex. The stratigraphy and detrital zircon profiles are compared to broadly coeval sedimentary units on the Rae craton and a unifying model of their deposition is presented. The Rae craton is the dominant detritus source; initially these sources were mostly local, changing to a mix of local and distal sources including the western Rae craton. The tectonic setting of the Karrat basin transitioned from extensional to convergent to collisional during its basin evolution, reflecting Wilson cycle phases within an epeiric sea. Accordingly, zircon Hf isotopes in our dataset track the evolution of the opening and closing of the Manikewan Ocean. Detrital zircon Hf isotopes in our dataset reveal a greater proportion of juvenile detritus (especially ca. 2.15–1.95 Ga) than is known from the currently exposed crustal record, pointing to the importance of the detrital zircon record for understanding Paleoproterozoic crustal and tectonic evolution. [ABSTRACT FROM AUTHOR]

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In this paper, we describe an in situ non-destructive technique to identify areas within zircon crystals that have experienced fluid exchange. We show that Raman spectroscopy combined with electron microprobe trace-element analysis can be used to pinpoint areas in altered, complexly zoned, and metamict zircon that record the original magmatic compositions. These techniques are developed on a suite of Paleoproterozoic zircon crystals from the Scourie dike swarm in the Archean gneiss terrane of NW Scotland that are known to be anomalously low in δ18O. We show that zircons from the Scourie dikes record extremely low-δ18O isotopic compositions down to approximately -3‰, which reflect their magmatic values. Zircon populations from the dikes have a range in δ18O from low values (<0‰) up to ~5‰ with no obvious relationship between oxygen isotopic composition and cathodoluminescence. Raman spectra from the zircons show evidence for fluid interaction in some areas of the grains because of partial recrystallization and atypical radiation damage properties. Electron microprobe analysis in the same areas documents high (>1000 ppm) U concentrations and high (>1000 ppm) abundances of non-formula Ca. When the combined Raman and electron microprobe data are used to filter the oxygen isotopic data, the fluid altered areas of the grains show consistently higher δ18O values than the areas without evidence for fluid alteration. The low-δ18O values therefore reflect the original magmatic composition of the grains and indicate that the Scourie dike magmas were low in 18O. We suggest that these non-destructive techniques should be used prior to SIMS analysis of complex zircons to target the least disturbed areas of the grains. [ABSTRACT FROM AUTHOR]

The Columbia River Flood Basalts ( CRB) of the northwestern USA are coeval with eruptions of several thousand km3 of rhyolite. A broad survey of major phenocryst oxygen isotopes and of O and Hf isotopes in zircons from these rhyolites reveals significant diversity in inferred δ18Omelt values, ranging from +1.9 to +10.5‰ ( SMOW), and in zircon Hf isotope compositions, which range from εHf = −39 to +9. This newly identified isotopic diversity shows that the syn- CRB rhyolites were derived from high-percentage melting of the crust. Low-δ18O rhyolites, which fingerprint the melting of hydrothermally altered crust, are concentrated at the edge of the North American craton. This suggests that the conditions of crustal heating, faulting, and hydrothermal alteration required for the production of these rhyolites were concentrated there by the contrasts in crustal thickness and rheology associated with the boundary between the North American craton and younger accreted terranes. [ABSTRACT FROM AUTHOR]

Highlights: [•] Oldest zircons of Africa are from the Limpopo Belt in South Africa. [•] They have crystallization ages up to 3.95Ga, and Hf model ages up to 4.51Ga. [•] Most zircons formed after 3.7Ga, and reveal Hf model ages <4.01Ga. [•] Our datasets support the model of a long-lived Hadean mafic protocrust reworked completely at <4.0Ga. [•] The Early Earth was covered by a partially open stagnant lid. [Copyright &y& Elsevier]

An igneous zircon reference material (OG1) was characterised for U-Pb isotopes by ID-TIMS, and utilised to evaluate SIMS (SHRIMP) instrumental mass fractionation (IMF) of radiogenic Pb isotopes (207Pb*/206Pb*). The TIMS 207Pb*/206Pb* reference value for OG1 was 0.29907 ± 0.00011 (95% confidence limit), 3465.4 ± 0.6 Ma. The high 207Pb* (∼ 30 μg g−1), negligible common Pb, and isotopic homogeneity permitted precise (± 1–2‰) 207Pb*/206Pb* measurements within the analytical sessions. External reproducibility of mean 207Pb*/206Pb* ratios between sessions was demonstrated for one instrument, yielding a mean IMF of +0.87 ± 0.49‰. The mean 207Pb*/206Pb* ratios between instruments were dispersed beyond uncertainties, with session IMF values from +3.6 ± 1.7‰ to −2.4 ± 1.3‰, and a grand mean IMF value (twenty-six sessions) of +0.70 ± 0.52‰, indicating a tendency towards elevated 207Pb*/206Pb*. The specific causes of variability in IMF are unclear, but generally reflect subtle differences in analytical conditions. The common practice in SIMS of assuming that IMF for Pb+ is insignificant could result in systematic age biases and underestimated uncertainties, of critical importance for precise correlation of Precambrian events. Nevertheless, a zircon RM such as OG1 can be readily incorporated into routine dating to improve 207Pb*/206Pb* accuracy and external reproducibility. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The O''okiep Copper District is underlain by voluminous 1035–1210 Ma granite gneiss and granite with remnants of metamorphosed supracrustal rocks. This assemblage was intruded by the 1030 Ma copper-bearing Koperberg Suite that includes jotunite, anorthosite, biotite diorite and hypersthene-bearing rocks ranging from leuconorite to hypersthenite. New sensitive high-resolution ion microprobe age data demonstrate the presence of 1700–2000 Ma zircon as xenocrysts in all of the intrusive rocks, and as detrital zircon in the metasediments of the Khurisberg Subgroup. These data are consistent with published Sm–Nd model ages of c. 1700 Ma (TCHUR) and c. 2000 Ma (TDM) of many of the intrusives that support a major crust-forming event in Eburnian (Hudsonian) times. In addition, U–Th–Pb analyses of zircons from all major rock units define two tectono-magmatic episodes of the Namaquan Orogeny: (1) the O''okiepian Episode (1180–1210 Ma), represented by regional granite plutonism, notably the Nababeep and Modderfontein Granite Gneisses and the Concordia and Kweekfontein Granites that accompanied and outlasted (e.g. Kweekfontein Granite) regional tectonism [F2(D2)] and granulite-facies metamorphism (M2); (2) the Klondikean Episode (1020–1040 Ma), which includes the intrusion of the porphyritic Rietberg Granite and of the Koperberg Suite that are devoid of regional planar or linear fabrics. Klondikean tectonism (D3) is reflected by major east–west-trending open folds [F3(D3a)], and by localized east–west-trending near-vertical ductile folds [‘steep structures’; F4(D3b)] whose formation was broadly coeval with the intrusion of the Koperberg Suite. A regional, largely thermal, amphibolite- to granulite-facies metamorphism (M3) accompanied D3. This study demonstrates, inter alia, that the complete spectrum of rock-types of the Koperberg Suite, together with the Rietberg Granite, was intruded in a short time-interval (<10 Myr) at c. 1030 Ma, and that there were lengthy periods of about 150 Myr of tectonic quiescence within the Namaquan Orogeny: (1) between the O''okiepian and Klondikean Episodes; (2) from the end of the latter to the formal end of Namaquan Orogenesis 800–850 Ma ago. [ABSTRACT FROM AUTHOR]

A suite of 18 zircon gemstones from placers in the Highland/Southwestern Complex, Sri Lanka, were subjected to a comprehensive study of their radiation damages and ages. The investigation included X-ray diffraction, Raman and PL spectroscopy, electron microprobe, PIXE and HRTEM analysis, as well as (U-Th)/He and SHRIMP U-Th-Pb age determinations. Zircon samples described in this study are virtually homogeneous. They cover the range from slightly metamict to nearly amorphous. Generally concordant U-Th-Pb ages averaging 555 ± 11 Ma were obtained. Late Ordovician zircon (U-Th)/He ages scattering around 443 ± 9 Ma correspond reasonably well with previously determined biotite Rb-Sr ages for rocks from the HSWC. Slightly to moderately metamict zircon has retained the radiogenic He whereas only strongly radiation-damaged zircon (calculated total fluences exceeding ∼3.5 x 10[sup18] α-events/g) has experienced significant He loss. When compared to unannealed zircon from other localities, Sri Lanka zircon is about half as metamict as would correspond to complete damage accumulation over a ∼555 m.y. lasting self-irradiation period, suggesting significant annealing of the structural radiation damage. Insufficient consideration of this has often resulted in significant underestimation of radiation effects in zircon. We suggest to estimate "effective α-doses" for Sri Lanka zircon by multiplying total α-fluences, which were calculated using the zircon U-Th-Pb age, by a correction factor of 0.55. This conversion may be applied to literature data as well, because all gem-zircon samples from Sri Lanka (this work and previous studies) seem to reveal the same general trends of property changes depending on the radiation damage. The use of "effective α-doses" for Sri Lanka zircon contributes to more reliable quantitative estimates of radiation effects and makes possible direct comparison between natural and synthetic ratiation-damaged... [ABSTRACT FROM AUTHOR]

Analytical errors calculated for individual spot 206Pb/238U measurements of zircon analyzed using high mass resolution secondary ion mass spectrometry (HR-SIMS, e.g., SHRIMP II) were assessed using natural zircon (z6266) and synthetic glass standards (NIST SRM 610). Evidence for U/Pb homogeneity of these materials includes new thermal ionization mass spectrometry (TIMS) U–Pb analyses of 22 fragments of z6266 zircon from two laboratories, which are identical within error and yield a weighted mean 206Pb/238U age of 559.0±0.2 Ma. TIMS U–Pb analyses of the SRM 610 yielded homogeneous 206Pb/238U=0.2566.Errors in HR-SIMS 206Pb/238U measurements are distinguished in increasing hierarchy as within-spot, within-session (internal), and external. Replicate SHRIMP measurements of 208Pb+/206Pb+ and 248[ThO]+/254[UO]+ in SRM 610 demonstrate that within-spot analytical errors are sufficient (i.e., MSWD''s∼1) to account for the dispersion of data. In contrast, it was not possible with SRM 610 to reproduce the 206Pb+/238U[Ox=0,1,2]+ ratios from spot-to-spot within the limits of the within-spot errors, after correcting the data for obvious systematic variations in the discrimination of the Pb and U isotopes. Identical findings were made following replicate 206Pb+/238U[Ox]+ analyses of z6266 zircon. That is, for both glass and zircon standards, there remained on average about ±1% (1σ) unaccounted variation per 206Pb+/238U[Ox]+ analysis (i.e., MSWDs≫1). Thus, unlike for 248[ThO]+/254[UO]+, the within-session errors in 206Pb+/238U[Ox]+ were necessarily higher than the within-spot errors.In contrast to 208Pb+/206Pb+ and 248[ThO]+/254[UO]+, the 206Pb+/238U[Ox]+ ratios in glass and zircon are significantly fractionated relative to accepted values, and it seems probable that this difference underlies the larger within-session errors for 206Pb+/238U[Ox]+. The usual methods (e.g., using 254[UO]+/238U+) to correct for the inherent discrimination are imperfect and sensitive to small differences in analytical conditions between spots. Matrix variations are ruled out, leaving the precise cause(s) of the additional variation in 206Pb+/238U[Ox]+ currently undetermined, and a hindrance to decreasing the uncertainties in spot 206Pb/238U measurements. The minimum within-session error for an individual 206Pb/238U measurement is the standard deviation (dispersion) of the discrimination-corrected 206Pb+/238U[Ox]+ values for a homogeneous reference material (e.g., SRM 610). The external error in 206Pb/238U additionally incorporates the standard deviation of the mean of the discrimination-corrected 206Pb+/238U[Ox]+ for a natural zircon standard. The analysis of 206Pb+/270[UO2]+ offers an improvement over measuring 206Pb+/238U+ because variable discrimination is reduced or eliminated with respect to 254[UO]+/238U+ and counting statistics are superior. [Copyright &y& Elsevier]

A geochronological investigation of metasedimentary rocks from southern Baffin Island using the Geological Survey of Canada SHRIMP II (sensitive high-resolution ion microprobe) has characterized the ages of detrital zircon populations to determine their provenance, bracket timing of deposition, and distinguish potentially distinct sequences of rocks. Four lithologically and structurally distinct metasedimentary packages have been identified; each appears to have been derived from a different source region. In the structurally lowest package, all analysed zircons are Archean, and > 90% have ages between 2.83 and 2.63 Ga; these rocks are interpreted as the northernmost exposures of the Paleoproterozoic Povungnituk Group of the Cape Smith Belt, northern Quebec, with detritus derived from the Superior craton. Occupying the intermediate structural levels, the most abundant supracrustal rocks on southern Baffin Island are siliciclastic and carbonate units of the Lake Harbour Group, and the Tasiuyak paragneiss. Five samples show a dominantly Paleoproterozoic signature (2.2–1.9 Ga), with only rare Archean zircons; the provenance of this detritus is uncertain. In the distinct package of feldspathic quartzite and pelite that stratigraphically overlies the Lake Harbour Group, all of the analysed detrital grains are Archean, ~80% are > 2.83 Ga, with a small proportion of the grains in excess of 3.0 Ga; all of this material is thought to be derived from the Archean craton exposed on the Hall Peninsula east of the study area. Finally, at the highest structural level, a sample associated with the Hall Peninsula orthogneisses contains zircons with prominent modes at 2.92, 2.82, and 2.77 Ga, consistent with derivation from the surrounding orthogneisses.Une étude géochronologique de roches métasédimentaires de l'île de Baffin méridionale, au moyen de la microsonde à ions SHRIMP II de la Commission géologique du Canada, a caractérisé les âges de populations de zircons détritiques afin de déterminer leur provenance, d'encadrer la séquence de déposition et d'identifier des séquences de roches potentiellement différentes. Quatre ensembles métasédimentaires, distincts par leur lithologie et leur structure, ont été identifiés; chaque ensemble semble provenir d'une région-source différente. Dans l'ensemble inférieur, selon la structure, tous les zircons analysés sont de l'Archéen et >90 % ont des âges entre 2,83 et 2,63 Ga; ces roches sont interprétées comme les affleurements les plus nordiques du Groupe de Povungnituk (Paléoprotérozoïque) de la Ceinture de Cape Smith, dans le Québec septentrional, avec des détritus provenant du craton du Supérieur. Au niveau structural intermédiaire, les roches supracrustales les plus abondantes sur le sud de l'île de Baffin sont des unités siliclastiques et à carbonates du Groupe de Lake Harbour et le paragneiss de Tasiuyak. Cinq échantillons montrent une signature à dominance paléoprotérozoïque (2,2–1,9 Ga) avec seulement de rares zircons archéens; la source de ce détritus est incertaine. Dans l'ensemble distinct de quartzite feldspathique et de pélite qui recouvre stratigraphiquement le Groupe de Lake Harbour, tous les grains détritiques analysés datent de l'Archéen, ~80 % sont plus âgés que 2,83 Ga et une petite proportion des grains a plus de 3,0 Ga; on croit que tout ce matériel provient du craton archéen affleurant sur la péninsule de Hall, à l'est de la région sous étude. Finalement, au niveau structural supérieur, un échantillon associé aux orthogneiss de la péninsule de Hall contient des zircons avec des modes dominants de 2,92, 2,82 et 2,77 Ga, ce qui concorde avec une provenance des orthogneiss avoisinants.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

We report the discovery of one of the largest ancient (>3.0 Ga) crustal terranes on Earth. Granitoids with crystallization ages >3.0 Ga and/or Sm-Nd depleted mantle model ages ≥3.2 Ga define a -1000 x 100 km belt on the western margin of the Rae craton, Canada, referred to herein as the Perry River terrane (PRT). Zircon U-Pb-Hf-O isotope and whole-rock geochemical data from granitoids show that the PRT is a predominantly juvenile 3.3--3.2 Ga terrane that was partially reworked by more evolved ca. 3.1 Ga magmatism. These findings call for a reassessment of the timing and extent of ancient continental growth on Earth. A global compilation of zircon Hf isotope data from 3.6 to 3.0 Ga igneous rocks reveals clusters of relatively juvenile (initial εHf -2 to +3) rocks at ca. 3.31 and ca. 3.23 Ga, which include samples from the PRT and 13 other terranes worldwide. Other global zircon data sets also document age peaks between 3.3 and 3.2 Ga, and a cluster of broadly chondritic initial εHf values around 3.2 Ga. The 3.3--3.2 Ga period may therefore have been a time of enhanced net continental growth on Earth, and the PRT is one of the largest terranes preserved from that time. Furthermore, zircon Hf isotope data from 3.3--3.1 Ga PRT granitoids and 3.5--3.0 Ga igneous rocks worldwide yield little evidence for parent magmas that interacted with or derived from pre--3.6 Ga continental material. Contrary to some continental-growth models, this latter observation suggests that the volume of continental crust established by 3.6 Ga was relatively small. [ABSTRACT FROM AUTHOR]

The Assean Lake Crustal Complex (ALCC) located at the northwest periphery of the Superior Province in northern Manitoba, Canada, hosts an ancient assembly of rocks that record a complex and prolonged crustal history spanning more than two billion years from ∼3.9 to 1.8 Ga. A supracrustal assemblage consisting of amphibolite-grade greywacke, quartz arenite, arkose, mafic to intermediate volcanics, and to a lesser extent iron formation dominates the ALCC and likely formed in a shallow marine arc/back-arc setting. The supracrustal rocks are intruded by amphibolite-grade, calc-alkaline tonalite to granite orthogneiss. Nd model ages for felsic para- and orthogneisses range from ∼3.5 to 4.2 Ga and suggest that Paleoarchean basement may be preserved at Assean Lake. SHRIMP U–Pb zircon ages and ID-TIMS conventional U–Pb zircon and monazite ages show that felsic magmatism occurred at ∼3.1–3.2 Ga whereas a record extending back to at least 3.9 Ga is preserved in detritus in paragneiss that may have a depositional age of ∼3.2 Ga. Orthogneiss was metamorphosed at ∼2.68 Ga whereas local migmatisation of paragneiss occurred at ∼2.61 Ga. Monazite growth events at ∼2.6, 2.45, and 1.8 Ga might represent episodes of accretion of Archean crustal segments including the ALCC and possibly the Sask craton (Trans-Hudson basement) along the northwest Superior Province margin. At present, matching segments of the exotic ALCC are unknown but remnants may exist in parts of the Sask craton. [Copyright &y& Elsevier]

The most ancient rocks in the geological record provide insights into the processes that shaped the evolution and composition of the first continental masses. To better constrain these processes, we made a detailed study of a ca. 3.86 Ga felsic meta-igneous rock from the Eoarchean Saglek Block (North Atlantic Craton) that experienced high-grade metamorphism at ca. 3.5 Ga. Our robust zircon-isotope plus trace-element analyses reveal metamorphic zircon domains with δ18O values up to +9‰ at ca. 3.5 Ga, which are the highest values so far measured in any pre-3.0 Ga zircons, metamorphic or igneous, extracted from unambiguous (meta)igneous host rocks. Such elevated zircon δ18O signatures clearly document the involvement of mature supracrustal precursors (mafic volcanics ± clastic/chemical sediments) during the reworking of 3.86 Ga crust at ca. 3.5 Ga. This study provides unequivocal evidence for hydrosphere-crust interactions and reworking processes resulting in metamorphic zircon growth at ca. 3.5 Ga, namely 1 Ga before the Archean-Proterozoic transition. [ABSTRACT FROM AUTHOR]

The Dom Feliciano Belt Ediacaran post-collisional magmatism is widespread in southern Brazil and Uruguay and is represented by the Florianópolis Batholith in its northern sector. The Zimbros Suite (Area 1) comprises the Zimbros Granite, emplaced within the Major Gercino Shear Zone (MGSZ) at the waning stages of its activity, and the Morro dos Macacos Granite, emplaced nearby but outside the high-strain zones. Conversely, the Cambirela Plutono-volcanic Suite (Area 2) occurs far from the MGSZ deformation sites and encompasses the Ilha, Vila da Penha, and Serra do Tabuleiro granites and the Cambirela Silicic Volcanic Sequence (rhyolites + ignimbrites). The plutonic units from both areas are coeval (ca. 590 Ma) and characterised by high-SiO 2 (74–79 wt%, except for the Zimbros Granite <74 wt%) , metaluminous to slightly peraluminous, mildly alkaline, high-K, reduced (Fe# > 0.84) A 2 -type granites that compose two distinct shallow-level plutono-volcanic systems installed in a post-collisional setting at the final stages of the Dom Feliciano Belt. The units emplaced far from the MGSZ (Area 2) are derived mostly from crustal sources with minor mantle contribution. They were likely produced by dehydration melting of quartz-feldspathic (+hornblende) subalkaline rocks of low water contents and reduced character. Field relations, the metaluminous to slightly peraluminous A-type character, the weakly negative ƐNd t , high Fe#, Ce/Nb and Y/Nb ratios and the low to intermediate δ18O values (+3.4 to +7.3 ‰) are compatible with such conditions. In contrast, the dataset for the Zimbros Suite (Area 1), coupled with the previous interpretations that attest to the mantle origin of this unit, points to rocks derived from fractional crystallisation of tholeiitic melts with large crustal assimilation of rocks with similar composition to the source rocks of Area 2 (i.e. subalkaline, hornblende-bearing quartz-feldspathic rocks), hybridized at shallow-level conditions and accompanied by recurrent mantle contribution favoured by the MGSZ. The Cambirela Plutono-volcanic Suite volcanic units share all the characteristics presented for the granitic rocks and are composed of earlier, crystal-poor rhyolites (586 ± 5.0 Ma) and later ignimbrites with sharp faciological variation (580 ± 4.8 Ma) indicating different maturity stages of long-lived magma chambers. The variable U-Th contents and the bimodal δ18O signatures (+3.4 ± 0.2‰ and + 6.9 ± 0.2‰) of the volcanic units further indicate open-system magmatic processes and the co-eruption of melts from distinct magma chambers of the Cambirela plutono-volcanic system. • A-type magmatism (ca. 590 Ma) comprises two coeval shallow-level magmatic systems. • Mantle and crustal sources give rise to granitic magmas mainly through AFC processes. • Late-stage post-collisional magmatism marks the Dom Feliciano Orogen collapse. • Shear zones play a key role in the ultimate magma sources and evolutionary processes. [ABSTRACT FROM AUTHOR]

The Paleoproterozoic Wopmay orogen is modeled as a simple arc-continent collision involving the Archean Slave craton and an enigmatic continental arc terrane termed the Hottah terrane. Hottah is a composite terrane that includes a juvenile 2.6-2.1 Ga basement and a younger 1.93-1.90 Ga continental arc. The extent and crustal age structure of the terrane is poorly known which limits interpretations as to its origin, and eventual role in the development of the orogen. Multi-isotopic (U-Pb, Hf, O) analyses of detrital zircon from rocks of the Hottah terrane and its cover sequence are used to indirectly evaluate its age and crustal characteristics. The data confirm that ca 2.6-2.1 Ga crust is an important component of the terrane but Hf isotopic data indicate mostly non-juvenile compositions consistent with recycled Neoarchean crust sources. Ages of detrital zircon are distinct from those expected of the Slave craton but are similar to adjacent 2.0-1.90 Ga Paleoproterozoic terranes of northwestern Laurentia. The similarity to terranes such as the Ksituan/Buffalo Head and Taltson-Thelon magmatic zones, south and east of the Wopmay Orogen indicate that Hottah could represent a terrane that initially evolved adjacent to the earliest assembled parts of the Nuna continent between 2.0 and 1.9 Ga, and was rifted prior to the collision with the Slave margin that produced the Calderian orogeny. [ABSTRACT FROM AUTHOR]

Abstract: The western Churchill Province of the Canadian Shield experienced a prolonged and complex formation history (ca. 4.04 to 1.70Ga), with evidence for multiple episodes of orogenesis and regional magmatic activity. Here we report on the oxygen isotopic compositions of garnet and zircon recovered from lower crustal xenoliths, which have U–Pb ages between ca. 3.5 and 1.7Ga. Overall, zircon from four metabasite xenoliths from the Rankin Inlet sample suite have δ 18O values ranging from +5.5 to +8.6‰. Zircon from three metatonalite/anorthosite xenoliths and five metabasite xenoliths from the Repulse Bay sample suite have δ 18O values of +5.6 to +8.3‰. High δ 18O values (>+6.0‰) for the oldest igneous zircon cores (ca. 3.5Ga and 3.0–2.6Ga) indicate that their metatonalite/anorthosite protolith magmas were generated from, or had assimilated, supracrustal rocks that interacted previously with surface-derived fluids. Igneous zircon cores (ca. 2.9–2.6Ga) from one metabasite xenolith have δ 18O values of +5.6 to +6.4‰, which suggests a formation from a mantle-derived basaltic/gabbroic magma. Metamorphic zircon cores (ca. 2.0–1.9Ga) from one metabasite xenolith commonly have δ 18O values between +6.0 and +6.3‰, which is indicative of a basalt/gabbro protolith and localized reworking of the lower crust caused by regional-scale plate convergence. The wide range of δ 18O values (+5.5 to +8.3‰) for ca. 1.75–1.70Ga metamorphic zircon rims (identified in all xenoliths) indicates regional transient heating and reworking of mantle- and supracrustal-derived crust, induced by magmatic underplating along the crust–mantle boundary. [Copyright &y& Elsevier]

Abstract: The Litchfield Province, located on the western margin of the Palaeoproterozoic Pine Creek Orogen, northern Australia, comprises variably metamorphosed pelitic and psammitic sediments, extensively intruded by voluminous granitoids and mafic rocks. SHRIMP U–Pb in situ monazite geochronology of undeformed granulite-facies migmatitic Hermit Creek Metamorphics (ca. 730°C, ca. 5kb) and mid-amphibolite-facies Fog Bay Metamorphics (ca. 600°C, ca. 4kb) indicates mid- to high-grade metamorphism affected these rocks at ca. 1855Ma. SHRIMP U–Pb analysis on low Th/U metamorphic zircon rims from the Fog Bay Metamorphics also indicate metamorphism at ca. 1855Ma. The undeformed nature of the Hermit Creek and Fog Bay Metamorphics suggest that metamorphism was not accompanied by significant penetrative strain. These observations suggest that the elevated geotherm at this time may have been due to conductive and advective thermal input within a thinned lithosphere during intra-crustal extension and rifting. Metamorphism at ca. 1855Ma in the Litchfield Province is similar in age to that reported from the Hooper Orogen and the Western and Central Zones of the Halls Creek Orogen, but not with the Eastern Zone. Furthermore, there appears no evidence for the ca. 1845–1835Ma Halls Creek Orogeny in the Litchfield Province, suggesting that the inferred suture in the Halls Creek Orogen between the Kimberley Craton and the proto North Australian Craton, may not extend into the Litchfield Province and that the Litchfield Province may have been contiguous with, or forms part of, the Kimberley Craton. The upper-amphibolite-facies Welltree Metamorphics (ca. 700°C, ca. 4kb), in contrast, preserve monazite grains that are aligned with a penetrative biotite fabric and are dated at 1813±3Ma, thus recording a previously unrecognised tectono-thermal event in the Pine Creek Orogen. [Copyright &y& Elsevier]

• SJC experienced multiple magmatism of ~2.78, ~2.69 and ~2.55 Ga. • Neoarchean magma derived from episodic juvenile crust growth and crustal reworking. • Recycling of sediments was not intense or extensive in SJC during Neoarchean. • A bottom-up tectonic regime related to plume activity is favored for NCC in Neoarchean. Recent advances in high-precision in-situ analysis of zircon U-Pb-Hf-O isotopes have significantly improved our approach to studying the origin and evolution of Archean crust. This study presents high-precision in-situ zircon U-Pb-Hf-O isotopes for the Southern Jilin Complex (SJC) on the northeastern margin of the North China Craton (NCC) and explores the potential of such an integrated approach in understanding the Archean crust evolution and its tectonic implications. The SJC consists mainly of Archean granitoid gneisses hosting minor supracrustal rock xenoliths. Zircon U-Pb data from representative lithologies reveal three episodes of magmatism at ~2.78, ~2.69 and ~2.55 Ga, respectively. The former two granitoid magmatic events are recognized for the first time in NE NCC, while the latest one is widespread over the NCC. All metamorphic zircon domains document similar metamorphic ages of 2.51–2.48 Ga, consistent with the widespread metamorphism of ~2.50 Ga in the NCC. Most concordant magmatic zircons preserve "mantle-like" O isotopic signatures, indicating the magma sources were not contaminated by large amounts of high δ18O supracrustal sediments. Hf depleted mantle model ages of magmatic zircons display one predominant peak at 2.9–2.8 Ga and two subordinate peaks at 3.3–3.2 Ga and 2.7–2.6 Ga, indicating possible episodic crust-mantle differentiation in Southern Jilin. Integrated zircon U-Pb-O-Hf data from the SJC suggest that magma sources were mainly derived from multiple episodes of reworking of juvenile or ancient crust with mantle component addition, while recycling of sediments was trivial during the Neoarchean in this region. The spatial–temporal relations of magmatism, lack of supracrustal addition to magma sources, and other geological evidence from the NCC are in favor of a bottom-up geodynamic regime possibly related to plume activities, arguing against a widespread top-down mechanism involving modern-style subduction in the NCC during the Neoarchean. [ABSTRACT FROM AUTHOR]

We report U–Pb/Hf/O isotopic measurements of zircon extracted from meta-igneous rocks exposed in the Assean Lake crustal complex, northwestern Superior craton (Canada). With crystallization ages of ca. 3.22 Ga, zircon from the Assean Lake crustal complex are among the oldest reported in the Superior craton. The Hf and O isotope compositions of zircon indicate that these meta-igneous rocks derive from a mantle component with a relatively primitive Hf isotope composition, similar to chondrites, that was uncontaminated by elevated δ18O material (ε Hf,initial ~ 0 and δ18O VSMOW ~ 5.5‰). These features are shared by the large majority of the zircon extracted from the oldest (meta)-igneous rocks exposed in Archean terranes. Positive ε Hf deviations in Archean zircons are typically observed in magmas that post-date the oldest magmatic activity in a given terrain. This temporal variability in magma source regions may reflect a sequence of events comprising: (i) felsic magmatism derived from undepleted mantle components followed by, (ii) re-melting of the same mantle component producing the depleted Hf signatures in zircon and then, (iii) accretion of the proto-craton and reworking of the whole-system enabling stabilization. • Investigation of the older TTG component of the Superior craton (Canada). • New in-situ zircon U–Pb/Hf/O isotope data. • Chondritic Hf composition for the oldest (ca. 3.22 Gyr) zircon domains. • Zircon δ18O VMOW values within mantle range. • Petrogenesis of Archean felsic granitoids. [ABSTRACT FROM AUTHOR]

We present new geochemical, U Pb age, Hf O isotope compositions for more than 400 detrital zircons collected from modern sands located throughout western Fuerteventura, Canary Islands as a proxy for the timing and origin of its plutonic history. This approach provides a new perspective and more complete time-integrated record of the islands geologic evolution. Fuerteventura U Pb detrital zircon age spectra document that magmatism was initiated at ~35 Ma, was most prolific during the main shield-building stage (30–15 Ma), youngs southward, corroborates the existence of a low magma fluxing period (15–6 Ma), and provides new evidence for the existence that Pliocene and younger (at least as young as 0.24 ± 0.02 Ma) plutons with a variety of magma compositions accompanied post-shield volcanism until recent times. Most Fuerteventura detrital zircons have sub-mantle SIMS oxygen isotope compositions (δ18O < 5.0‰), and overlap compositions reported previously for gabbro/basalt xenoliths entrained in nearby Gran Canaria lavas, interpreted to be fragments of high-temperature seawater-altered Layer 3 oceanic crust. The detrital zircon Hf isotope compositions (ε Hfi : +15.0 to −0.2) display a much larger variation than recorded in previous studies of volcanic rocks from the Canary or Cape Verde islands. This extreme isotopic variation demonstrates that Fuerteventura detrital zircons provide a more sensitive record of the involvement of multiple sources in magma genesis. The high-ε Hf (>+12) zircons document the involvement of a depleted reservoir that is isotopically most similar to Middle Atlas SCLM. The low-ε Hf zircons, specifically those <+1, document the involvement of a reservoir that is more enriched than HIMU and overlaps the composition of NW African lower crust. These extreme ε Hf compositions indicate the presence of NW African lithosphere beneath Fuerteventura during the shield-building stage of island growth. The absence of a highly depleted Hf isotopic signature in young detrital zircons is interpreted to document the removal of SCLM during a magmatic shutdown initiated at ~15 Ma. Lithosphere erosion could be linked to a pulsed edge-driven convection cell responsible for SCLM delamination along a NE-trending corridor in NW Africa. The detrital zircon Hf and O isotope compositions indicate that both oceanic and continental lithosphere have existed beneath the island. This lithosphere is heterogeneous, consisting of high-T seawater altered oceanic crust, continental lower crust, and subcontinental mantle lithosphere; consistent with formation above a complex lithospheric transition zone created during Triassic-Jurassic rifting and opening of the Central Atlantic Ocean. Importantly, this detrital zircon study demonstrates that a more complete time-integrated record of a long-lived ocean island's geological history is preserved in modern sand samples, in part because a significant portion of Fuerteventura has been removed by erosion. • Fuerteventura magmatism derives from oceanic and continental lithosphere sources (81). • Fuerteventura alkaline plutonism is unusually long-lived (~35 m.y.) (67). • A low magma fluxing period on Fuerteventura is confirmed between 15 and 6 Ma (73). • A period of continental lithosphere loss occurred at about 15 Ma (65). [ABSTRACT FROM AUTHOR]