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The radioactive decay of lutetium-176 to hafnium-176 has been used to study Earth’s crust−mantle differentiation that is the primary agent of the chemical and thermal evolution of the silicate Earth. Yet the data interpretation requires a well-defined hafnium isotope growth curve of the bulk Earth, which is notoriously difficult to rec...
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... Lu − Hf Isotopes. Eight zircon grains were extracted from five thin sections of the eucrite Agoult. All eight zircon grains displayed no zoning structure with back-scattered electron and cathodoluminescence imaging (28). The grains were cleaned with 2 N HNO 3 and decomposed by concentrated HF + HNO 3 at 220 °C. Subsequently, the decomposed samples were evaporated and dissolved in 6 N HCl at 180 °C, followed by further evaporation and redissolution in 2.5 N HCl. Then, each dissolved grain was divided into two aliquots for determinations of Hf isotope ratios ( ca . 90%) and 176 Lu/ 177 Hf ( ca . 10%), respectively. The sample aliquots for Hf isotope ratio measurements were processed for chemical separation with a two-step ion exchange procedure ( Table S4). The first separation step, designed for U − Pb dating, used 0.05 mL of Eichrom anion exchange resin AG1-X8 with 200 – 400 mesh, in which matrix elements including Hf were eluted in 2.5 N HCl followed by elution of Pb and U in 0.5 N HNO . Hafnium and Zr were purified in the second step using 0.1 mL of Eichrom Ln-spec resin (100 – 150 μ m), where Zr was eluted with 6 N HCl + 0.06 N HF followed by Hf elution in 2 N HF (39). The purified Hf fractions were evaporated and redissolved in 0.3 – 0.5 mL of 0.5 N HNO 3 containing a trace amount of HF for isotope analysis. The sample aliquots for 176 Lu/ 177 Hf determination were not processed for chemical separation to avoid any artificial Lu/Hf fractionation. The Hf isotope analyses were performed on a Neptune Plus multicollector inductively coupled plasma mass spectrometer (Thermo Fisher Scientific) attached to an Aridus II desolvating nebulizer (Cetac Technologies) at The University of Tokyo. The instrumental sensitivity was enhanced by installing a high-efficiency vacuum interface rotary pump (TRIVAC D 65B, Oerlikon Leybold Vacuum) and by using high-transmission Jet sample and X-skimmer cones. The achieved sensitivity was 3,500 – 4,000 V/ppm for Hf at a sample uptake rate of ∼ 150 μ L/min. For isotope ratio measurements of purified Hf fractions, isotopes of 174 Hf, 176 Hf, 177 Hf, 178 Hf, 179 Hf, and 180 Hf as well as 172 Yb, 175 Lu, and 182 W were monitored with static mode on nine Faraday cups. We found that the interferences of Yb, Lu, and W on Hf isotopes are negligible due to efficient separation of Hf in the ion exchange chemistry. Data were acquired using an integration time of 1.0 s for periods of 75 – 150 s. The total Hf signal intensities obtained during the sample analyses range from 4 V to 21 V. The ion beams of five procedural blanks were measured using the same procedure as the samples, and the Hf signal intensities of 3 – 7 mV with an average of 4 mV were obtained, indicating that the procedural Hf blanks were less than 1 pg. The blank contribution was corrected by subtracting the average signal intensity of the five blank measurements, even though this blank correction would cause only a ∼ 10 ppm change in the resulting mean 176 Hf/ 177 Hf value. The mass bias factor was calculated by normalizing the measured 179 Hf/ 177 Hf to 0.7325 (1) with an exponential law. Hafnium isotope ratios corrected for mass bias were further normalized to reference values of 180 Hf/ 177 Hf = 1.886666, 178 Hf/ 177 Hf = 1.467168, and 176 Hf/ 177 Hf = 0.282160 for Johnson Matthey Company (JMC)-Hf 475 (40) to allow accurate comparison with literature values. Analytical uncertainties on sample Hf isotope ratios (Table S1) combined the internal precisions (2 SE) and the reproducibility of the JMC-Hf 475 standard analyses (2 SD), added in quadrature. The internal precisions are variable, depending on the Hf amounts available for analyses. The 176 Lu/ 177 Hf ratios in the sample aliquots without chemical separation were calculated from measured 175 Lu/ 177 Hf ratios and the 176 Lu/ 175 Lu value of 0.026549 (41). The 175 Lu/ 177 Hf measurements were carried out on the Neptune Plus under wet plasma conditions using a Scott-type spray cham- ber. Data were acquired with dynamic mode on the secondary electron multiplier over 10 cycles using the integration time of 8.4 s for 175 Lu and 4.2 s for 177 Hf. The instrumental 175 Lu/ 177 Hf fractionation was corrected by reference to multiple measurements of Lu − Hf solution (0.5 N HNO 3 with a trace amount of HF) prepared by mixing ultrapure Hf and Lu from 1,000-ppm standard solutions from SPEX. Analytical uncertainties on 175 Lu/ 177 Hf combine the internal precisions of the sample analyses (2 SE) and the reproducibility of the Lu − Hf solution (2 SD). The precision and accuracy of our Lu − Hf isotope analyses were evaluated by analyzing the TEMORA standard zircon as an unknown sample during the course of this study. We obtained mean 176 Lu/ 177 Hf and initial 176 Hf/ 177 Hf values of 0.0011 ± 0.0004 and 0.282668 ± 0.000016 (2 SD, n = 6) (Table S1), in agreement with the previously reported values (42, 43). Whole-Rock Lu Isotopes. Five whole-rock fractions of the eucrite Agoult and three fractions of two individual terrestrial basalts (JB-1b and JB-2) were analyzed for 176 Lu/ 175 Lu. The fractions were digested in a mixture of concentrated HF + HNO 3 on a hot plate at 130 °C and converted to a soluble form by repeated evaporation with concentrated HNO 3 , followed by disso- lution in 6 N HCl. For accurate and precise Lu isotope ratio measurements, efficient separation of Lu from Yb and Hf is required. The separation of Lu was performed using three types of resins following the procedures of ref. 44 (Table S5): ( i ) removal of Fe and U from bulk sample using Bio-Rad AG1- X8 with 200 – 400 mesh; ( ii ) separation of heavy rare earth elements (REE) from most other elements including Hf using Eichrom Ln-spec resin with particle sizes of 100 – 150 μ m; and ( iii ) separation of Lu from Yb as well as Hf using Eichrom Ln-spec resin with particle sizes of 20 – 50 μ m in 120-mm-long col- umn. The last step was repeated for further purification of Lu from Yb. These separation protocols reduce the Yb/Lu ratio by ∼ 10 5 for basaltic samples, with total Lu yields higher than 90%. The Lu isotope ratio measurements were made on the Neptune Plus multicollector inductively coupled plasma mass spectrometer attached to the Aridus II desolvating nebulizer at The University of Tokyo. We used a standard “ H ” sample cone instead of the high-transmission Jet sample cone for Lu isotope analyses, because use of the Jet sample cone could cause mass dis- crimination that significantly diverges from the exponential law for heavy REE (45). Data were acquired using an integration time of 8.4 s over 60 cycles. Nine Faraday cups were used to simultaneously monitor 172 Yb, 173 Yb, 175 Lu, 176 (Lu + Yb + Hf), 177 Hf, 179 Hf, 182 W, 184 W, and 186 W. Following ref. 44, all Lu standards and samples were doped with National Institute of Standards and Technology (NIST) SRM 3163 W standard to correct for mass bias. The mass bias factor was calculated in each analysis by normalizing 186 W/ 184 W to 0.92767 (46) with an exponential law. To account for the difference in mass bias factors for Lu and W, 176 Lu/ 175 Lu ratios corrected for mass bias were further normalized to the 176 Lu/ 175 Lu value of 0.026549 (41) for the SPEX Lu standard solution using the mean value obtained for this standard on any given analytical session. The contribution of isobaric interferences by 176 Yb and 176 Hf on 176 Lu was evaluated by monitoring 173 Yb and 177 Hf, respectively. While the contribution of 176 Hf was negligible, 176 Yb interference correction was necessary for all samples. For the correction, the mass bias factor for Yb was assumed to be identical to that for W, and the literature 176 Yb/ 173 Yb value of 0.79640 (47) was used. The interference correction produces accurate results for Yb-doped Lu standard solutions with 173 Yb/ 175 Lu up to 1.5 × 10 − 4 , indicating that the correction method is robust for the sample analyses which yielded 173 Yb/ 175 Lu of ≤ 3.4 × 10 − 5 (Fig. S2). Analytical uncertainties of each 176 Lu/ 175 Lu analysis (Table S2) combine the internal precisions (2 SE) and the reproducibility of the SPEX Lu standard solution analyses (2 SD), added in quadrature. To allow accurate comparison with literature values (44), we also reported the 176 Lu/ 175 Lu obtained for a NIST SRM 3130a Lu standard solution during the course of this study (Table 2 and Table S2). ACKNOWLEDGMENTS. We thank T. Ohno and O. Nebel for helpful discussion about analytical methods, and S. Nakai and Q.-Z. Yin for supplying precious standards. Constructive comments by two anonymous reviewers were helpful in improving the manuscript. This work was supported by the Australian Research Council and the Japan Society for the Promotion of ...Similar publications
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... Iizuka et al. 25 measured 176 Hf/ 177 Hf ratios in zircon grains extracted from the Agoult eucrite meteorite. Eucrites are basaltic meteorites that are thought to have formed in the crust of asteroid Vesta soon after the formation of the solar system. ...
... Eucrites are basaltic meteorites that are thought to have formed in the crust of asteroid Vesta soon after the formation of the solar system. Iizuka et al. 25 used these measurements to constrain the solar system initial 176 Hf/ 177 Hf ratio (0.279781 ± 0.000018). The typical size of zircon grains in eucrites is ∼20 μm, but those extracted from Agoult were ∼80 μm. ...
... Zirconium and Hafnium Separation. A two-stage procedure modified from Zhang 50 and Iizuka et al. 25 was developed for separating Zr and Hf from Yb, Lu and other interfering elements (Table 1; Figure 1). In a first step, DGA (N,N,N′,N′-tetra-n-octyldiglycolamide) resin from Eichrom (previously TODGA; now DGA normal 51,52 ) is used to collect a Zr−Hf cut, as described by Zhang et al. 53 in their protocol for Ti separation. ...
Zircons are found in extraterrestrial rocks from the Moon, Mars, and some differentiated meteorite parent-bodies. These zircons are rare, often of small size, and have been affected by neutron capture induced by cosmic ray exposure. The application of the ¹⁷⁶Lu–¹⁷⁶Hf decay system to zircons from planetary bodies such as the Moon can help establish the chronology of large-scale differentiation processes such as the crystallization of the lunar magma ocean. Here, we present methods to measure the isotopic composition of Hf of extraterrestrial zircons dated using ID-TIMS U–Pb after chemical abrasion. We introduce a 2-stage elution scheme to separate Hf from Zr while preserving the unused Zr fraction for future isotopic analysis. The effect of neutron capture is also re-examined using the latest thermal neutron capture cross sections and epithermal resonance integrals. Our tests show that the precision of Hf isotopic analyses is close to what is theoretically attainable. We have tested this method to a limited set of zircon grains from lunar rocks returned by the Apollo missions (lunar soil 14163, fragmental polymict breccia 72275, and clast-rich breccia 14321). The model ages align with previously reported values, but further work is needed to assess the chronology of lunar magma ocean crystallization as only a handful of small zircons (5 zircons from 3 samples) were analyzed, and the precision of the analyses can be improved by measuring more and larger lunar zircon grains.
... Even under such circumstance, the Lu-Hf chronometer has been used for the study of crust-mantle evolution of various planetary bodies such as Earth 10 , Moon 12 , Mars 13 , and Vesta 15 and orogenic movements of the Earth 16 . However, instead of the half-life values measured by the nuclear experiments and the two evaluated values 42,43 , the decay constant of 1.867 × 10 −11 yr −1 measured by the isochron method for terrestrial rocks 32 has been used for their analyses 10,12,13,15,16 . ...
... With both chronometers the more precise ages for samples could be obtained, and even if the U-Pb chronometer cannot be used, the Lu-Hf system could be used for dating a sample consistent with the U-Pb method. Although the value reported by the isochron for terrestrial rocks 32 has been used for analysis in cosmochemistry and geochemistry at present 10,12,13,15,16 , the present result shows that there is no need to change drastically the results using this value. The Lu chronometer is a powerful tool to study the ages of astrophysical events, evolution of planetary bodies in the solar system, and orogenic movements of the Earth. ...
... If decay acceleration occurs, the abundance of 176 Lu relative to 175 Lu should decrease. However, no evidence of the 176 Lu deficient has been found in meteorites 10,51 . ...
The ¹⁷⁶Lu-¹⁷⁶Hf nuclear decay is a powerful tool to measure the age of astrophysical and geological events and has been used as a “cosmochronometer”. However, the half-life values of ¹⁷⁶Lu measured with various experiments differ significantly. Furthermore, the half-life values evaluated from Lu-Hf isochrons in meteorites and terrestrial rocks with known ages show two different values. Here we report half-life measurements using a method that is almost independent of various uncertainties. To the best of our knowledge this is the most accurate value of ¹⁷⁶Lu half-life. We measure the total energy released from ¹⁷⁶Lu decay using a windowless 4π solid angle detector based upon bismuth germanate (BGO) scintillation crystals, where a natural Lu sample is located inside of the detector. The measured half-life of (3.719 ± 0.007) × 10¹⁰ yr corresponding to a decay constant of (1.864 ± 0.003) × 10⁻¹¹ yr⁻¹ is consistent with that obtained from the analysis of terrestrial rocks within the uncertainty.
... The average δ 18 O is 7.7‰ ± 0.8‰ (2 standard deviations [SD], n = 51) and higher than the mantle-like value of 5.3‰ ± 0.3‰ (Valley et al., 1998). The zircon ε Hf (t) value using the CHUR (chondritic uniform reservoir) composition (Iizuka et al., 2015) is 10.3‰ ± 1.7‰ (2SD, n = 13), which is identical to the range of ε Hf values for mid-ocean ridge basalt (MORB) and primitive island arc rocks (Chauvel et al., 2008;Iizuka et al., 2017). ...
Zircon geochronology has contributed to our understanding of the longevity of transcrustal magmatic systems; however, most studies focus on zircon records from felsic rocks due to the restricted occurrence of zircon in mafic-ultramafic rocks. We present U−Pb age, geochemical, and Hf−O isotope data for zircons from a hornblendite peridotite in the Hida Belt, Japan, that offers a unique opportunity to investigate the lifetime of a long-lived mafic plumbing system in an arc setting. We found two zircon U−Pb age clusters: an incompatible element-rich cluster at 196 Ma and an incompatible element-poor cluster at 186 Ma. Their homogeneous isotopic signatures (δ18O = 7.7‰ ± 0.8‰, εHf = 10.3‰ ± 1.7‰) indicate the same magma source despite the 10 m.y. age gap. These two clusters are explained by different zircon formation mechanisms that differ depending on whether or not zircon saturation requires differentiated melt with high SiO2. The enriched older zircons formed by local zircon saturation at the mafic melt-olivine interface, whereas the younger depleted zircons precipitated from the last drop of interstitial felsic melt co-existing with hornblendes. Our finding substantiates the longevity of mafic systems at lower crusts, which sustain transcrustal magma systems and crustal evolution.
... Over time, melting residues (refractory mantle) develop very radiogenic (elevated) 176 Hf/ 177 Hf ratios (positive ε Hf ), and crustal lithologies (former magmas) comparatively low radiogenic ratios (negative ε Hf ) (Fig. 4g). For global interpretation, Hf isotope compositions are normalized to the Chondritic Uniform Reservoir (CHUR; Blichert-Toft and Albarède 1997; Bouvier et al. 2008;Iizuka et al. 2015) and transformed into epsilon Hf notation (ε Hf ), with CHUR approximating the bulk silicate Earth composition. For instance, Figure 4g illustrates a magma source produced by partial melting of the mantle at 2600 Ma (green spot in Fig. 4g) and that differentiates into mafic and felsic lithologies, which are both characterized by specific 176 Lu/ 177 Hf content. ...
The study of magmatic and metamorphic processes is challenged by geological complexities like geochemical variations, geochronological uncertainties, and the presence/absence of fluids and/or melts. However, by integrating petrographic and microstructural studies with geochronology, geochemistry, and phase equilibrium diagrams investigations of different key mineral phases, it is possible to reconstruct pressure-temperature-deformation-time histories. Using multiple geochronometers in a rock can provide a detailed temporal account of its evolution, as these geological clocks have different closure temperatures. Given the continuous improvement of existing and new in-situ analytical techniques, this contribution provides an overview of frequently utilised petrochronometers such as garnet, zircon, titanite, allanite, rutile, monazite/xenotime, and apatite, by describing the geological record that each mineral can retain, and explaining how to retrieve this information. These key minerals were chosen as they provide reliable age information in a variety of rock types and, when coupled with their trace element composition, form powerful tools to investigate crustal processes at different scales. This review recommends best applications for each petrochronometer, highlights limitations to be aware of, and discusses future perspectives. Finally, this contribution highlights the importance of integrating information retrieved by multi-petrochronometer studies to gain an in-depth understanding of complex thermal and deformation crustal processes.
... Grains with d 18 O values in the 4.5-6.5 ‰ range signify continental crust extraction events, considering the errors associated with measuring d 18 O values by SHRIMP or SIMS, and recognizing that incorporation of a small amount of sediments into the source region may produce minimal age smearing ). The 176 Lu decay constant of 1.867 Â 10 -11 (Söderlund et al., 2004) and the present-day chondritic parameters reported by Iizuka et al. (2015) were used to calculate the initial Hf isotopic compositions. ...
River sand detrital zircons from several rivers flowing through the Peninsular Indian cratons were analyzed for U-Pb, Lu-Hf, and O isotopes to characterize the Precambrian crustal evolution of the Indian Shield and to constrain its role in the early supercontinent cycles. Analyzed river sand zircon samples exhibit a prominent age grouping at 2.7-2.4 Ga and additional peaks at 1.8-1.7 Ga, 1.0-0.8 Ga, and 0.6-0.5 Ga. The time-related Hf and O isotope trends of the Indian zircons display a slight offset from the global trends. The age peaks and distinct Hf-O isotopic compositions of the Indian zircons also lack coherence with the global patterns associated with supercontinent cycles, implying a discrete crustal evolutionary history for the Indian Shield. Their contrasting εHf-age trajectories indicate that the Indian Shield was accreted to the Columbia/Nuna supercontinental framework through a collision event that postdated the 2.1-1.8 Ga global-scale orogeny, and was part of a long-lived subduction system along the margin of Rodinia. This implies that the Indian Shield occupied a peripheral paleo-position during the assembly of the two Precambrian supercontinents. The ca. 2.6-2.4 Ga Indian river sand zircons have remarkably low δ¹⁸O values that are distinct from the global zircon O isotopic record. This period coincides with the fragmentation of the Archean supercraton and the flaring-up of a subaerial Large Igneous Province that facilitated the generation of ¹⁸O-depleted magmas. Depending on whether the 2.6-2.4 Ga zircons with low δ¹⁸O values (<4.7‰) are considered or not, approximately 2.77‰ or 1.78‰ rise in the zircon δ¹⁸O values occurred between ca. 2.4 Ga and ca. 1.87 Ga (decoupled from zircon Lu-Hf isotopes), further suggesting that the fine-grained sediments were enriched in ¹⁸O after the Great Oxidation Event. These high δ¹⁸O sediments were subsequently incorporated into the magmatic systems resulting in elevated δ¹⁸O in the zircons crystallizing from such melts. Nevertheless, a ca. 0.9 Ga peak of >10‰ in δ¹⁸O system was followed by a pronounced δ¹⁸O drop at ca. 0.759 Ga, suggesting that δ¹⁸O of recycled sedimentary reservoirs was not the only controlling factor for zircon δ¹⁸O characteristics. Variations in the O-Hf data for Indian and global zircons could be attributed to the initiation of the supercontinent cycle at ca. 2.0 Ga. A significant volume of the juvenile crust was added during the 3.0 - 2.7 Ga mafic magmatism in the Indian Shield, as underlined by the Hf model ages of all the zircon grains and those with mantle-like δ¹⁸O signatures. A gradual addition of continental crust during ca. 3.6 Ga to 3.1 Ga can also be deduced, with the oldest crust being derived from the mantle at ca. 4.4 Ga.
... The errors of zircon Hf isotope data are set at 2SE. The 176 Lu decay constant (1.867 × 10 − 11 year − 1 ), 176 Hf/ 177 Hf and 176 Lu/ 177 Hf ratios (0.282793 and 0.0338, respectively) of the chondrite were used in our calculations (Iizuka et al., 2015;Söderlund et al., 2004). ...
This paper focuses on the UPb ages and LuHf isotopes in zircons in a long-lived anatectic terrane, to understand both the nature of melting events and controls on Hf-isotope ratios in the zircon record. We focus on rocks from the Wuyi-Yunkai orogeny, South China, that mainly comprises Proterozoic basement rocks that generated numerous granitoids during Early Paleozoic granulite facies metamorphism. We investigate zircons from three anatectic granites and one migmatite. Zircon UPb dates for individual samples vary between ~465 and ~ 410 Ma, covering the duration of the orogeny. UPb dates for two samples define three normal distributions with populations spaced by ~15–20 Myr, indicating protracted and pulsed melting events. The inherited pre-orogenic zircon cores yield a wide spread of εHf(435) values (−39.0 to −2.8), whilst all Early Paleozoic, magmatic syn-orogenic cores and rims have a narrower range shifted to higher values ranging between −14.3 and + 5.5 and no systematic variation with the date of the analytical spot. The data suggest that the magmatic syn-orogenic zircons grew from isotopically heterogeneous melts with ~9 to 16 ε units variation for individual samples. The narrower ranges compared to the inherited cores suggest that some magma homogenization must have occurred, and the upward shift of the εHf(435) values is likely due to the influence of non-zircon Hf rather than due to mixing with an external less-evolved magma. Thus, the samples record a ~ 55 Myr, multi-pulsed melting event, during which heterogeneous crustal magmas had their Hf isotopic composition controlled by inherited zircon dissolution modified by contributions from non-zircon phases.
... -11 yr -1 from Scherer et al. (2001) and Sö derlund et al. (2004) to calculate initial Hf isotopic compositions. Uncertainties associated with the radiogenic-ingrowth correction were propagated using the algorithms of Ickert (2013) and e Hf values were calculated using CHUR values provided in Iizuka et al. (2015). Results can be found in Table S6. ...
Zircon is often used to study granites (sensu lato) and continental crust because it is very resistant and can be analyzed for various isotope systems that provide time and source information about their parental melts. Granites with different petrological histories have distinct bulk-rock silicon isotope compositions but it is unclear if these differences are also detectable in zircon because of superimposed fractionation effects (e.g., related to temperature, silica content, magmatic processes). The present study explores the Si isotope signatures of zircon from various granite types to constrain their isotope fractionation behavior and uses them as igneous petrogenetic tools, and possibly as granite source discriminators when zircon is found in detrital sediments. Our results show that although Si isotope compositions in zircon can be modified by secondary (post-crystallization) processes such as alteration/weathering and metamorphism, they are primarily controlled by zircon-melt isotope fractionation, which depends on both zircon crystallization temperature and magma silica content. Once these fractionation effects are understood and filtered out, a pattern emerges between Si isotope signatures of zircons from different granite types that is consistent with theoretical and experimental results as well as with known Si isotope differences at the bulk-rock scale. Silicon isotope ratios in zircon can track magma evolution (e.g., temperature and SiO2 changes) and, hence, reveal complex processes that involved magma mingling, fractional crystallization, and/or multiple sources. This study, therefore, illustrates that Si isotopes in zircon can be used to investigate magma evolution and represents a useful complement to existing techniques in granite studies involving zircon (e.g., U-Th-Pb, Lu-Hf and O isotopes) provided that it is not used as a stand-alone technique.
... KDE (black lines) and histograms (grey bars) showing the U-Pb and Hf (red dots) results in the 0-3600 Ma and 440-870 Ma (in the blue boxes) intervals. (A-B) Khenifra area (Nappe Zone, WMM); (C) εHf versus age plot in the Khenifra area [CHUR: Chondritic Uniform Reservoir(Iizuka et al., 2015); DM: depleted mantle(Chauvel et al., 2008)]; Ordvician (D) and Devonian (E) samples from Azrou area (Nappe Zone, WMM); (F) Zekkara area (EMM). Color bars indicate the most common detrital zircon populations recognized in all the samples. ...
The systematic acquisition of U–Pb geochronological data from detrital zircon grains has become an essential tool in tectonic studies focused on reconstructing the pre–Variscan geography of the northern Gondwanan passive margin. New detrital zircon ages for 16 samples from the Cambrian–Lower Devonian succession of the Moroccan Mesetas (northern Morocco) are reported here. The results, combined with previously published data, reassert the strong West African Craton affinity of the Paleozoic sedimentary rocks, characterized by dominant Cadomian/Pan–African (c. 850–540 Ma) and Eburnean (c. 2.2–1.9 Ga) detrital zircon populations and a minor Leonian/Liberian (c. 2.5 Ga) population. Primary sources of these zircon grains are well established as the West African Craton located just to the south, but also in the Precambrian basement that locally crops out in the Moroccan Mesetas themselves. During the Cambrian–Early Ordovician, erosion preferentially dismantled Cadomian (c. 590–540 Ma) arc–derived rocks of the Gondwanan continental margin, while later, the slightly older Pan–African (c. 650–600 Ma) basement became the main sediment source. In the studied samples, irregularly present minor detrital zircon populations suggest additional sediment provenance from secondary sources such as: (i) remote northeastern African cratons (e.g., Saharan Metacraton and/or Arabian–Nubian Shield) that likely could have provided the c. 1.1–0.9 Ga and, possibly, the c. 1.9–1.7 Ga zircon grains, and (ii) rift–related Cambrian–Early Ordovician volcanic centers in the Moroccan Mesetas that supplied heterogeneously distributed – although locally dominant in small areas – sedimentary detritus before rift abortion and burial underneath the overlying passive margin sedimentary succession. [Supplementary material in Mendely Data, doi: 10.17632/vw94rkbx75.6]
... In the 1980s, the ability of the Lu-Hf system as a potential geochronometer and tracer was demonstrated. Since then, a combination of U-Pb and Hf isotopes has been carried out on magmatic, metamorphic and detrital as well as extra-terrestrial zircons (Kemp et al. 2007;Iizuka et al. 2015;Sreenivas et al. 2019). The technological developments facilitated the measurement of oxygen isotopes in zircons by laser heating/gassource mass spectrometry and ion microprobe/secondary ion mass spectrometer (Valley et al. 1994;Peck et al. 2001;Whitehouse and Nemchin 2009). ...
Over the past three decades, the advent of sophisticated imaging, in-situ measurements as well as data deconvolution techniques led to remarkable progress in the field of heavy mineral research. The prevalence of zircon in a wide range of igneous, sedimentary and metamorphic rocks has been used frequently in estimating provenance, depositional age, tectonic settings, drainage evolution, and crustal evolution studies. However, the biased age spectra (induced by hydrodynamic fractionation, sampling and measurement protocol and inheritance) yielded by detrital zircons reinvigorated the need to utilise other heavy mineral phases (monazite, apatite, titanite and rutile) to address a range of geological processes. Different heavy minerals are moderate to highly durable and provide variable responses to magmatic and metamorphic events thereby providing clues that may be missed by single detrital grain analysis. Thus, emphasising the multi-mineral detrital approach as an indispensable method to investigate several geological processes. The present review highlights the role of detrital zircon and the associated limitations in using a single heavy mineral approach in geological studies. This review further emphasizes the advantages of using multi-mineral/proxy studies and discussed the scope of heavy mineral research.
... The reported uncertainty on the initial 176 Hf/ 177 Hf ratios and ε Hf values includes propagation of the 2σ uncertainty on the measured 176 Lu/ 177 Hf ratios and the 207 Pb/ 206 Pb dates calculated in quadrature. The 176 Lu decay constant of 1.867 ± 8 × 10 − 11 and CHUR values of 176 Lu/ 177 Hf = 0.0338 and 176 Hf/ 177 Hf = 0.282793 were used (Iizuka et al., 2015). The resultant initial 176 Hf/ 177 Hf ratios and ε Hf values are plotted against the isotope evolution curves for the DM and CHUR. ...
Lu-Hf laser ablation-multi-collector-inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) analysis was conducted on ~1800 detrital zircon grains from successor basins of the Archean Abitibi and Pontiac subprovinces of Ontario and Quebec, Canada, and paired with previous U-Pb LA-MC-ICP-MS analyses of the same grains. Results are used to constrain the isotopic character of magmatic source domains of the zircon grains to establish the sedimentary provenance of the ~2690-2670 Ma successor basins, to provide constraints on terrane configurations and amalgamations at the time of basin formation, and to assess their significance for the record of crust-mantle growth in the region. The majority of results (95%) yield ε Hf values of + 1 to + 10 for ~2850-2675 Ma zircon, and clusters along compositions of the Archean depleted mantle (DM), which is based on projections of modern MORB compositions. Subordinate results, comprising ~2% of the data set, yielded values (ε Hf > +10) corresponding to extremely depleted mantle compositions, reflecting anomalously depleted sources in the ~2950-2670 Ma age range. The remaining 3% correspond to chondritic uniform reservoir (CHUR)-like to negative ε Hf values that reflect primitive sources and/or evolved magmas in zircon that crystallized in the ~3250-3050 Ma and ~2950-2670 Ma age ranges. While Neoarchean grains dominate the data set (~88%), approximately 12% are Mesoarchean. The Lu-Hf data collected on these zircon grains, when compared with published isotopic results, preserve signatures indicative of derivation from exotic crustal domains juxtaposed during ~2690-2670 Ma amalgamation of the southern Superior Province. Since depleted compositions are characteristic of Neoarchean and Mesoarchean zircon groups in the southern Superior Province, and sources include local and distal domains that were likely separated by many 100s of kilometers prior to amalgamation, it is inferred that a depleted upper mantle reservoir was not only well-established, but prevalent in the mantle below each of these areas during their construction. Based on the predominant Hf isotope signatures in the detrital zircon results and predicted isotopic trends produced by probable geodynamic mechanisms, crustal growth by direct differentiation from a depleted mantle reservoir is likely to have been moderated by subduction-accretion processes.
