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The Yellowstone hotspot track in the northwestern US has a 17-myr history that began with eruption of the voluminous Columbia River basalts (CRB), and produced an eastward track with the bimodal rhyolite and basaltic eruptive centers of the Snake River Plain (SRP) as the North American Plate drifted westwards. We have generated the first Hf isotopic data on basalts in this large igneous province along with bulk-rock trace-element abundance patterns and Sr-Nd isotopic ratios to assess the hypothesized kinship with co-located rhyolites throughout the hotspot track. The isotopic compositions for all three elements span much of the compositional range observed in mantle-derived basalts worldwide. Varying between a high of +11.3 in parts of the CRB and a low of −8.3 in some of the late SRP basalts, the new ε Hf values are geographically controlled, similar to the shift first documented with Sr and Nd isotopes across the "0.706 Sr line," which marks the boundary between thin- accreted young ocean lithosphere and arc terranes in the west to thick, old cratonized crust in the east. This observation shows that there is significant lithospheric control on the isotopic compositions of both basalts and rhyolites associated with the Yellowstone hotspot track. Modeling of assimilation and fractional crystallization (AFC) processes in seven basaltic lava flows filling the 2-Ma Big Bend Ridge Caldera at Mesa Falls, Idaho, near the eastern end of the hotspot track suggests that the crustal contribution to the Nd and Hf concentration budgets increases systematically with time and was significant. A comparison of new and previously published bulk-rock major-oxide concentrations (e.g., the alkalis Na 2 O and K 2 O) with our previously published data for H 2 O, Cl, F and S in olivine-hosted melt inclusions suggests that the volatiles are sub-crustal, possibly from the lithospheric mantle, and degas extensively during magma ascent and crystallization. • New trace element and Nd-, Hf- and Sr-isotope data for Yellowstone hotspot and Columbia River basalts. • First Hf isotopic ratios on basalts in region agree with new and previous Nd and Sr isotopic results that crustal thickness influences composition. • Seven basaltic lava flows in Big Bend Ridge Caldera show crustal contamination grew in significance through time. • Isotopic data compared with olivine-hosted melt inclusion volatile compositions indicate a sub-crustal source for H 2 O. [ABSTRACT FROM AUTHOR]

A comprehensive, internally consistent U-Pb and Lu-Hf isotope data set for 93 mantle-derived zircons from the Yakutian kimberlite province confirms and further refines the four major episodes of kimberlite magmatism on the Siberian craton: 421–409 Ma (Late Silurian-Early Devonian), 358–353 Ma (Late Devonian-Early Carboniferous), 226–218 Ma (Late Triassic), and 161–144 Ma (Middle-Late Jurassic). The relatively narrow, constant range of εHf values between +2 and +10 for both the Paleozoic and Mesozoic mantle-derived zircons (and by inference kimberlites) suggests that the volatile-rich magmas were repeatedly sourced from the convecting upper mantle beneath the Siberian craton. This finding is in keeping with the narrow and constant range of εNd values for groundmass perovskites from the Yakutian kimberlite province between +1.8 and +5.5 between 420 and 150 Ma. Our preferred model implies that the convecting upper mantle beneath the Yakutian kimberlite province ‘recovered’ rapidly back to ambient conditions shortly after the giant plume-related flood volcanic event that produced the Siberian Traps at 250 Ma. Although close spatial relationships exist between kimberlites and flood basalts on the Siberian craton during both the Paleozoic and Mesozoic, exact timing of the igneous events and the isotopic compositions of the diverse deep-sourced melting products rule out any direct genetic links. Besides the highly economic kimberlite-hosted diamond deposits of Late Devonian age (e.g., Mir and Udachnaya), the Siberian craton also contains significant Mesozoic placer diamond deposits (e.g., along the Anabar river), for which lamproite sources have been suggested recently. Our study shows that mantle-derived zircon megacryst fragments from the Ebelyakh placer deposit have Late Triassic ages of ca. 224 Ma. Their long-term depleted Hf isotopic compositions (+8.5 εHf) suggest that the alluvial diamonds were sourced from asthenosphere-derived Triassic kimberlites rather than from lithospheric mantle derived isotopically enriched lamproites. [ABSTRACT FROM AUTHOR]

The timing for the onset of plate tectonics, along with the secular changes in the tectonic settings of continental crust formation, continue to be debated. Recent interpretations based on the increase in zircon 176Hf/177Hf ratios at the time of crystallisation (expressed as εHf (t) with respect to chondritic evolution) have been used to ascertain changes in geodynamic settings in the early Earth, specifically in the 3.8–3.6 Ga interval. This increase is widely interpreted as a change in magma generation, from source(s) dominated by ancient crust to source(s) dominated by juvenile inputs from the mantle. At issue, Hf isotope variations remain limited in the early Earth due to the long decay of the Lu Hf system. This feature, along with the scarcity of rocks and minerals of Eo/Mesoarchaean and Hadean ages, generate large uncertainties over the nature and the timing of the interactions between mantle and crustal reservoirs. The distinction between mantle and crustal sources becomes much clearer in the Palaeoproterozoic, and the study of ancient terranes with several billion years of protracted crustal evolution may hold the key to unlock complex mantle–crust interactions. Here we investigate high-grade metamorphic rocks from the Anabar shield, which contain zircons that crystallised between the Eoarchaean (oldest core at 3814 ± 16 Ma) and the Palaeoproterozoic (youngest core at 2251 ± 15 Ma and youngest rim at 1910 ± 21 Ma). The combination of in situ U Pb and Hf isotope analyses in zircon indicates the formation of the continental crust in the Siberian Craton in the Eoarchaean, and a conspicuous metamorphic event at 2.0–1.9 Ga. We demonstrate that 2.0–1.9 Ga zircon ages reflect recrystallisation processes under subsolidus conditions, involving the breakdown of high-Lu/Hf minerals (i.e. garnet and pyroxene). The εHf (t) shift at 2.0–1.9 Ga towards more radiogenic values may not be related to a change in magmatic style and sources, but rather to resetting of the Lu Hf system in response to heating and metamorphic reactions on a mineral scale. Our findings challenge the widely-evoked mechanism of changes in tectonic style and magma sources to account for vertical arrays in the εHf (t) versus crystallisation age space. This calls for considering alternative options, including those based on petrographic data, when interpreting Hf isotope variations in the Hadean/Archaean detrital zircon record. [Display omitted] • Evidence for the oldest crust formation in the Siberian Craton at ∼3.8 Ga. • Hf isotope data show two main evolution stages of the Anabar shield: i) decreasing εHf (t) (0 to −15) from 3.5 to 2.0 Ga; and ii) a large εHf (t) variation (−25 to 10) at ∼1.9 Ga. • The breakdown of high-Lu/Hf minerals during high-grade metamorphism releases radiogenic Hf, which is incorporated into new or recrystalised zircon to produce a large εHf (t) range. • Metamorphic breakdown reactions are a complementary mechanism for 'vertical shifts' in εHf (t) , typically attributed to mixing of ancient crust and mantle-derived magmas. • Changes in geodynamic settings in the early Earth are not necessarily a direct cause of abrupt shifts in εHf (t) in detrital zircon datasets. [ABSTRACT FROM AUTHOR]

Early to mid Carboniferous I-type granites distributed in a broad meridional belt west of Sydney, southeastern Australia, represent the last phase of granite magmatism in the southern Lachlan Fold Belt. Rare inherited zircon in the granites, in combination with zircon precipitated from the melt phase of the magmas, provides direct evidence of the nature and age of the source rocks from which the granites were derived, and the isotopic compositions of those rocks. Most granites from the north and central parts of the belt, represented by the Wuuluman, Home Rule, Oberon and Lett plutons (334 ± 3, 328 ± 4, 339 ± 2 and 328 ± 2 Ma, respectively), are characterized by scarce inherited zircon dominantly of Siluro-Devonian age, consistent with all being derived from a common zircon-poor source rock of mid to late Devonian age. Based on the isotopic compositions of the igneous zircon rims, that source was relatively homogeneous and immature (δ 18 O zrn 6–7‰, εHf(t) 0–+4). Two samples of the Tarana pluton (331 ± 2 Ma), near the centre of the belt, show evidence for heterogeneity in that source and the presence of a more evolved component that is also more zircon rich. Together with the Lett pluton from the same geochemical suite, their zircon rim compositions define a mixing array between more and less evolved end members (δ 18 O zrn 5.5–9.5‰, εHf(t) -4–+4). Only in the southern Chapmans Creek pluton (327 ± 3 Ma) is there clear evidence that the source of the granite also contained a minor component with a similar older protolith to the LFB early Palaeozoic sediments that host most of the LFB pre-Carboniferous granites. Presence of that component, which overwhelmingly dominates the inheritance in the pre-Carboniferous granites, is also reflected in a slightly elevated whole rock initial 87 Sr/ 86 Sr (> 0.7050) and igneous δ 18 O zrn (ca. 7.5‰), but not in the igneous zircon εHf(t) (ca. +2). The amount of restitic zircon in granite is determined by not only the proportion of restite present but also the zircon contents of the various source rock components. The process of restite unmixing does not necessarily mean that more mafic, restite-rich granites will contain more inherited zircon. [ABSTRACT FROM AUTHOR]

Drill core samples from the 3.33 Ga high-alumina-type Commondale komatiites from the southern Kaapvaal craton (South Africa) were analysed for major, trace elements and Hf- isotope compositions in order to place possible constraints on their mantle sources and the process and timing of mantle depletion. The initial εHf isotope values range from + 6.5 to + 9.1 indicating a strongly depleted mantle source. This contrasts with previously published initial εNd values on the same geologic unit that reflect only minor depleted mantle sources of + 2. Trace element modelling and modelling of the Hf-Nd isotope composition of the mantle source indicate that the strongly incompatible element-depleted trace element patterns may be explained by a mantle source that was depleted to high-degrees (ca. 40%) in the garnet stability field prior to high- degree melting of the restitic mantle in the spinel stability field. The depletion in the garnet-stability field may have been related to a plume event that produced the low-alumina Barberton-type komatiites. However, the decoupled Hf-Nd isotope compositions cannot be explained by such a mechanism. We discuss several possible scenarios that may explain the trace element distribution as well as the isotope composition of the Commondale komatiites. Based on trace and isotope modelling, we consider three different models (1) the decoupled Hf-Nd isotope compositions resulted from a depleted mantle source overprint by melt-depleted garnet-pyroxenite components that originated from older crustal differentiation events and were delaminated into the mantle; (2) the decoupling resulted from subduction fluids that overprinted a highly depleted mantle source and added Th, Nd and other light-rare-Earth elements (LREE) shortly before eruption of the komatiites and triggered the high degree of melting; (3) a possible origin from a mantle source that experienced fractionation processes in an early magma ocean, followed by at least three mantle depletion events. The trace element and Hf-Nd isotope composition of the Commondale komatiites reveal that parts of the Archean mantle must have been highly heterogeneous due to komatiite extraction and possible delamination processes of lower crustal restites. [ABSTRACT FROM AUTHOR]

It is well-established that lanthanide rare earth elements (REEs) have the potential to record the nature and source characteristics of their host magmas, in both whole-rock and their minerals. Accessory minerals that concentrate REEs are especially useful in crustal evolution studies, both for their elemental and isotopic information; the classic and unrivalled example being zircon. Approaches using a single radiogenic isotopic system, or one radiogenic and one stable isotope system (e.g., Hf and O) in one REE-bearing mineral (usually zircon) are common, but those involving multiple isotopes in several minerals remain scarce despite offering many advantages. Importantly, the latter approaches also allow comparing different techniques and provide evidence on whether isotopic systems were disturbed by secondary processes. This contribution documents several isotopic systems within the abundant accessory mineral of Caledonian high Ba-Sr granitoids from Northwest Scotland. We present a multi-isotope study of titanite, zircon and apatite from two localities (Strontian and Rogart), which were selected for their contrasting whole-rock isotopic signatures - the former deriving from a depleted mantle source, whereas the latter derived from a strongly enriched mantle source. New in-situ Sm-Nd in titanite and apatite and Hf in zircon isotope data are discussed and compared with in-situ oxygen isotope data previously published for the same samples. An internal consistency is observed for Nd isotopes in apatite and titanite. Nd isotopes values for both minerals strongly correlate with Hf isotopes in zircon. Isotopic data at the mineral scale confirm the Strontian and Rogart source characteristics previously defined from whole-rock isotope data, with the Rogart having a more enriched signature than the Strontian source along the "Caledonian Parental Magma Array"(CPMA). In contrast, a significant discrepancy exists between whole-rock and REE-mineral oxygen isotope data as the latter can be affected by post emplacement alteration and hence can be misinterpreted. Importantly, the contribution of sediments in the CPMA source(s) can be estimated from a diagram combining Sm-Nd isotopic signatures and (La/Sm) N in apatite and titanite. Overall, we demonstrate that detailed petrogenetic records are not only available in zircons but also in magmatic titanite and apatite, and we suggest that integrated multi-mineral approaches have potential to maximise constraints from in-situ mineral isotope geochemistry. [ABSTRACT FROM AUTHOR]

Our study of Colorado Plateau and Rio Grande rift spinel peridotite xenoliths determined bulk Lu–Hf budgets and cpx, opx, and whole rock 176 Hf/ 177 Hf to evaluate the potential age significance of Lu/Hf–Hf isotope correlations in sub-continental lithospheric mantle (SCLM) derived xenoliths. The samples have fertilities (spinel Cr# range from 0.1 to 0.5), and equilibration temperatures (950–1050 °C) that overlap with those of spinel peridotites commonly used in Lu–Hf dating studies. The Lu/Hf of clinopyroxene (cpx) and its associated whole rock (WR) are similar in fertile samples, but cpx has a lower Lu/Hf than that of the WR in refractory samples. Orthopyroxene (opx) has systematically higher Lu/Hf than cpx, but in many samples, the opx and cpx have identical 176 Hf/ 177 Hf, suggesting that the Hf isotope composition of these minerals is supported by the Lu/Hf of the WR rather than that of the individual minerals. Many opx fractions and whole rocks have less radiogenic 176 Hf/ 177 Hf than their corresponding cpx (but similar to that of the host magma), reflecting contamination. Because the 176 Hf/ 177 Hf of cpx is supported by the WR Lu/Hf, it is necessary to use the latter rather than the cpx Lu/Hf for isochron dating. However, because the actual WR Lu/Hf values are susceptible to secondary overprinting, we recommend using model WR Lu/Hf values (determined from mineral Lu and Hf concentrations and modal abundances) to construct external cpx isochrons. Model WR and measured cpx 176 Hf/ 177 Hf are correlated (r 2 = 0.98) in a suite of eastern Colorado Plateau xenoliths and yield an apparent age of 1.2 Ga (versus 1.5 Ga when – incorrectly – using cpx Lu/Hf). Despite the good correlation between Lu/Hf and 176 Hf/ 177 Hf, we do not find correlations between indicators of melt depletion and Lu/Hf or 176 Hf/ 177 Hf. This suggests that Lu/Hf– 176 Hf/ 177 Hf correlations are not the result of melt depletion. Instead, we propose that Lu/Hf– 176 Hf/ 177 Hf correlations are the result of mixing between depleted and enriched components (e.g. metasomatism of depleted lithospheric mantle). We emphasize that additional data should be utilized (e.g. whole rock Lu–Hf budget, degree of metasomatism, opx 176 Hf/ 177 Hf) when interpreting apparent Lu–Hf isochrons for age significance. [ABSTRACT FROM AUTHOR]

Zircon is the ideal tool for unraveling Earth's history because of its refractory nature, being readily datable by the U–Pb isotope system, and owing to the fact that its Hf isotope composition can be precisely determined. However, most analyzed zircons have experienced Pb-loss to various degrees, resulting in present-day measured 207 Pb/ 206 Pb ages being younger than that of the time of crystallization, if the loss is ancient. This is of particular importance for ancient zircons from the Archean and the Hadean, notably the Jack Hills zircons. A zircon Lu–Hf and U–Pb isotope evolution model has been developed and shows that Pb-loss at 3700 Ma affecting a simple zircon population that crystallized at 4350 Ma can reproduce most of the broad ε Hf versus 207 Pb/ 206 Pb age trend observed for Jack Hills Hadean zircons. In addition, the model demonstrates that crystals having experienced widely different degrees of Pb-loss (2–80%) appear only slightly discordant (0.1–2.2%), while their apparent 207 Pb/ 206 Pb ages are different from that of crystallization by up to 466 My. This is insignificant for calculating initial Hf isotope compositions but results in major shifts in initial ε Hf values by up to 11.3 units. This effect is particularly relevant to the global Hadean/Archean detrital zircon record for which several apparent ε Hf versus age trends, similar to that defined by the Jack Hills Hadean zircons, stand out and could be fully or partly artificial. To overcome, or at least significantly reduce, these issues, multiple U–Pb analyses should be undertaken for each detrital zircon. Simultaneous measurement of Hf and U–Pb isotopes by the split-stream technique is the ideal approach because it can provide information about the cause of discordance (Pb-loss or concurrent analysis of two unrelated growth zones) and thereby allow for the most robust and accurate Hf isotope data to be obtained. [ABSTRACT FROM AUTHOR]

Abstract: Zircon grains from two Precambrian carbonatites from Fennoscandia (Siilinjärvi and Tiksheozero) were studied by in-situ geochemical and isotope methods. Zircon domains which preserved primary mantle signatures were identified by a combination of microscopic investigations of thin sections of the carbonatite rocks and separated zircon grains (optical microscopy, optical microscopy combined with cathodoluminescence (OM–CL), and scanning electron microscopy). All studied samples show evidence for alteration processes caused by infiltration of late-stage carbonatite melt/s or fluid/s. This led to different changes in the geochemistry and isotope composition of altered zircon domains. For the 2.6Ga old Siilinjärvi carbonatite complex, zircon grains underwent solid state recrystallization mainly at their rims. Zircon cores often preserved primary mantle signatures and register high HREE/LREE ratios, undisturbed U–Pb ages, εHf values close to CHUR (chondritic uniform reservoir), and δ18O values typical for the mantle. The solid state recrystallization of zircon occurred mainly in contact with a late-stage carbonatite melt or fluid and led to (i) diffusion driven loss of HREE, Th, and U, (ii) partial disturbance of the U–Pb system, (iii) a small shift of the δ18O toward lower values, and (iv) higher CL intensities in such zircon domains. Contrarily, zircons from the 2.0Ga old Tiksheozero complex underwent a coupled dissolution–reprecipitation process. Dissolved–reprecipitated zircon domains typically have a distinctive patchy texture in BSE images and sometimes contained abundant micro-inclusions of calcite, phlogopite, apatite, and baddeleyite. The EDS spectra documented that these non-luminescent zircon regions have much higher concentrations of Ca (and sometimes Fe) indicating an “impure” zircon composition. In addition, many trace elements are highly enriched in such “impure” zircon. Enrichment of Th (and to a lower degree of U) resulted in high Th/U ratios (>1) and disturbance of the U/Pb ages. Hf and O isotope values varied widely even within a single zircon grain. Isotope signatures attest a complex crystallization history of carbonatites and can best be interpreted as melt mixing processes of different carbonatite melt pulses. The non-luminescent reprecipitated zircon domains in Tiksheozero are often rimmed by zircon with high CL-intensity recrystallized in a solid state as well as by new zircon overgrowths. These zircon regions consist of pure zircon without elevated concentrations of Ca and Fe. Solid state recrystallization was accompanied by annealing that caused volume loss resulting in fractures that are now frequently filled with calcite (often containing a minor proportion of apatite) and phlogopite which sampled the withdrawn elements from the recrystallized zircon. Co-crystallizing calcite may thus lead to HREE depletion in newly grown zircon. It is expected that interaction with carbonatite melts can lead to similar changes in zircon grains from other sub-continental mantle rocks. Then, the primary geochemical and isotope systems of zircon may be changed despite its chemical and physical robustness. Infiltration of late-stage carbonatite melts seems to be a common process within many carbonatitic rocks that may hamper to determine the primary geochemical and isotope signatures of carbonatitic zircons. [Copyright &y& Elsevier]

Abstract: The Earth''s upper mantle is commonly depicted as a “marble cake” assemblage of a refractory component mingled with varying amounts of geochemically diverse enriched components. This depleted component controls the major element composition of Mid-Oceanic Ridge Basalts (MORBs). It has long been considered a fairly uniform reservoir, depleted by early melting and well homogenized by subsequent convective stirring. We present new Hf, Nd, Pb and Sr isotopes and trace element data for basalts from the center of the Lucky Strike segment of the Mid-Atlantic Ridge (MAR). Despite the limited size of our sampling area (1.6km along-axis by 5km across), these data show a large range of isotopic compositions (similar to that of the whole MAR). It has recently been shown that part of the reason for not observing more segments with correlated Hf–Nd isotope systematics may be the lack of fine-scale sampling. Our data confirm this idea and show strong correlations between all isotope ratios. The systematics of Hf–Nd isotopes in Lucky Strike basalts define an atypical correlation, distinct from the global mantle array, with an anomalously high εHf for a given εNd. We illustrate that this atypical trend is the signature of an ancient refractory mantle rather than the product of kinetic processes during the melting event. The existence of this mantle component at Lucky Strike allows us to discuss the structure of the upper mantle around the Azores. [Copyright &y& Elsevier]

Abstract: Detrital zircon grains of the Cenozoic Lower Rhine Basin were dated by the U–Pb method and simultaneously analyzed for initial Hf signatures to (1) identify distinct geodynamic events recorded in the W-European basement and cover rocks and (2) estimate the addition of juvenile crust in relation to these. Approximately 350 zircon grains extracted from 4 Miocene to Quaternary sand samples were investigated by back-scattered electron (BSE) and cathodoluminescence (CL) imaging. One third of these zircons were found to be sufficiently homogeneous for laser ablation U–Pb dating, which was performed by two individual and spatially well separated laser-spot analyses on the same grain, substantiating zircons have identical ages for the two intra-grain analyses. Approximately 40 zircons showed different ages. Our U–Pb dating results document distinct periods of primary magmatic zircon growth between 2.7 and 0.03Ga. These ages correspond to worldwide known subduction–collision cycles. The oldest terrains exposed today along the Rhine River and the Alps belong to the Variscan cycle. Therefore, all zircon grains older than ca. 0.4Ga must have been extracted from Paleozoic or Mesozoic–Cenozoic cover rocks containing detrital grains inherited from pre-Variscan basement; only the Cenozoic zircons require direct transport to the basin. From the dated homogeneous zircons 34 grains were selected for Hf isotope analysis, showing large variations in initial Hf isotope ratios (εHfi) between −10.9 and +15.2. Twelve of the 13 Precambrian grains yield positive or zero εHfi values, with a single 1025-Ma old grain having a negative value of −10.9. For the 21 zircon grains younger than 0.6Ga, a series of 9 grains yield positive or zero εHfi, whereas the remaining 12 zircons have negative values as low as −5.8. Approximately 60% of the zircon crystals reflect addition of juvenile crust having positive or zero εHfi being extracted from the mantle around the time indicated by their U–Pb ages. For some cases, juvenile crust addition may be somewhat older than indicated by the U–Pb ages because zircon growth may occur during later differentiation of rocks originally devoid of zircon. For such cases, εHfi values are necessarily less positive than that of the juvenile magma, depending on the Lu/Hf and crustal residence times of the zircon-free rock. A few εHfi values between +11.4 and +15.2 corroborate the existence of highly fractionated, Lu-enriched and Hf-depleted asthenospheric mantle in Mid-Proterozoic times. In agreement with earlier detrital zircon studies, our new data demonstrate that crustal recycling during continent collision events significantly increased in Phanerozoic times, being relatively rare during Precambrian times where intra-plate plume activity and oceanic arc attachment were dominant. [Copyright &y& Elsevier]

Abstract: There is hot debate on whether there is a Paleo-Tethyan suture within Qiangtang and on how the suture extends in central Tibet. In situ Hf and U–Pb isotopes, and rare earth element (REE) analyses of zircons, together with bulk chemistry, have helped us identify a significant, and previously unknown stage of subduction-related magmatism along the southern part of the eastern Qiangtang block, north of the Shuanghu suture, central Tibet. SHRIMP and LA-ICP-MS zircon U–Pb data demonstrate that the magmatism started as early as 275Ma, lasted until 248Ma, and took place at the same time as blueschist and eclogite were forming in the central Qiangtang high- to ultrahigh-pressure metamorphic belt (QMB). The positive εHf(t) values of the magmatic zircons range from 9.71 to 16.73, and indicate derivation of magma from a relatively uncontaminated, depleted mantle. Variations in εHf(t) values and the REE patterns of magmatic zircons, combined with substantial heterogeneities in the whole-rock chemistry, suggest that the arc-related magmatism occurred in pulses, and was long-lived. The present data can be interpreted in terms of a history of progressive subduction during the Early Permian and Early Triassic, during which time continental fragments of EQ affinity were tectonically eroded and subducted into the mantle, along with the subducted oceanic slab. The temporal and spatial correlations between the arc-like volcanic belt and the high-pressure metamorphic belt suggest a Late Paleozoic ocean (Paleo-Tethys) existed between the western and eastern Qiangtang blocks, and that the ocean was closed by northwards subduction. [Copyright &y& Elsevier]

Abstract: In situ analyses of hafnium isotopes in zircon combined with U–Pb zircon ages, and trace element data, provide new information on the characterization and evolution of magnetite–apatite (“Kiruna-type”) deposits and the tectonic environments in which they occur. The Lyon Mountain granite in the Adirondack Mountains of New York is the host to numerous zircon-bearing magnetite–apatite deposits. Hafnium isotopic compositions and rare earth element contents in individual zircon crystals were measured in situ in both the host granites and the ore bodies by laser ablation inductively coupled plasma-mass spectrometry. Hafnium isotopic compositions in the ore zircon can be divided into two groups: those that have initial εHf (t) values that are indistinguishable from those of the host granites (e.g., εHf (t) less than +7) and are typical of relatively juvenile Proterozoic crust, and those that have extremely radiogenic εHf (t) values (as high +40). Two models are proposed to explain the observed εHf (t) values in the zircon crystals: 1) early-formed ore bodies containing magnetite, apatite, and clinopyroxene were remobilized by secondary fluid alteration, releasing Zr and Hf for the crystallization of new zircon; or alternatively, 2) fluids responsible for ore formation have interacted with garnet-bearing rocks during retrograde metamorphism, scavenging rare earth elements and radiogenic Hf. Previous work done to determine the U–Pb ages from the same zircon crystals, which were analyzed for the Hf isotopic composition in this study, revealed that ore bodies record a mineralizing event that is 20 to 60m.y. younger than the age of granite emplacement. This age discrepancy, plus the highly radiogenic εHf (t) values in the ore zircon crystals, suggests that the fluids responsible for this younger event could not have been derived from the granite hosts. These data argue that magnetite–apatite deposits in the LMG have multiple mineralizing events superimposed upon one another and that early-formed deposits may be reworked, modified and redeposited by fluids subsequent to magma crystallization. [Copyright &y& Elsevier]

Abstract: The bulk of sedimentary provenance studies use similarities in the detrital zircon age patterns or “barcodes” in sedimentary systems and potential source regions to make interpretations about palaeogeographic settings. While this “age-only” approach is generally considered to be effective, it is limiting because the timing of zircon growth events may not be unique to specific terrains and important rock forming events may be associated with little zircon growth. To a significant extent these limitations can be overcome by employing additional isotopic data sets such as Sm–Nd and Lu–Hf that provide information on the crustal evolution of the source region, and allow comparisons with sedimentary packages. As an example, the age spectra of detrital zircons in Palaeoproterozoic metasedimentary rocks in the eastern Gawler Craton in southern Australia are virtually identical to the dominant zircon growth timelines in adjacent older domains of the Gawler Craton, presenting a prima facie case that it was the source region. However, whole rock Nd isotopic data indicate that the pre-existing proto Gawler Craton was isotopically too crustally evolved (ε Nd (1850 Ma ) −10) to have supplied the bulk of the sediment to the relatively more juvenile metasedimentary units (ε Nd (1850 Ma) −1 to −5). In addition, zircon Hf isotopic compositions from ca 2000 Ma detrital zircons in the metasedimentary rocks (ε Hf (2000 Ma) +2 to +5) are significantly more juvenile than 2000 Ma rocks in the adjacent Gawler Craton (ε Hf (2000 Ma) −2 to −5). The combination of bulk rock Nd and Hf zircon data suggest that the Gawler Craton is not a viable source region for the metasedimentary packages, despite the striking similarity between detrital zircon ages and zircon crystallisation events within the craton. [Copyright &y& Elsevier]

Abstract: The present paper reports trace element concentrations of 15 elements (V, Cr, Fe, Zr, Nb, Mo, Sn, Sb, Hf, Ta, W, Lu, Pb, Th and U) as well as Pb and Hf isotope data for four relatively homogeneous and large (centimeter size) rutile grains. Methods employed are SIMS, EMP, LA-ICP-MS, ID-MC-ICP-MS and TIMS. For most elements homogeneity is usually within ±10% and occasionally variations are even narrower (±5%), particularly in the core of two of the studied grains. The trace element concentrations of the grains span a broad compositional range (e.g., Zr concentrations are ca. 4, 100, 300 and 800 ppm). Provisional concentration values, calculated based on the homogeneity of the element and agreement between techniques, are presented for Zr, Nb, Sn, Sb, Hf, Ta, W and U. The present work represents a significant step forward in finding a suitable mineral standard for rutile microanalysis and encourages not only further search for mineral standards but also applications of rutile in the field of geochemistry and geochronology. In this sense, the rutiles presented here are useful as mineral standard in general in-situ rutile measurements, particularly for Zr-in-rutile thermometry, quantitative provenance studies (Nb and Cr concentrations as index of source rock type) and U–Pb dating. One of the studied grains has a relatively high U concentration (ca. 30 ppm) and rather constant U–Pb ages (1085.1 to 1096.2 Ma, 207Pb/235U ages and 1086.3 to 1096.6 Ma, 206Pb/238U ages), favoring its application as an age standard for U–Pb rutile dating. Since Lu concentrations in rutile are very low and Hf concentrations can be relatively high (tens of ppm), detrital rutiles may be suitable for obtaining initial Hf isotope composition of source rocks, therefore the rutiles presented here can be used as calibration material for in-situ rutile Hf isotope studies. [Copyright &y& Elsevier]

Abstract: In this study we demonstrate that the combination of U–Pb and Lu–Hf isotope data obtained by laser ablation-inductive coupled plasma-mass spectrometry provides a powerful tool for distinguishing zircon domains grown during several metamorphic or magmatic events from altered domains affected by complete single or multiple Pb-loss. This discrimination is possible because the U–Pb and Lu–Hf isotope systems are decoupled during zircon alteration. Initial 176Hf/177Hf once “incorporated” into the zircon lattice remains nearly unaffected during later alteration processes which cause Pb-loss. Zircon overgrowths always have higher initial 176Hf/177Hf than previously grown domains, due to the incorporation of additional radiogenic 176Hf formed by 176Lu decay in the rock''s matrix between successive zircon growth events. Incorporation of such 176Hf into zircon domains affected by post-growth alteration is negligible. By applying the U–Pb and Lu–Hf systems, in combination with cathodoluminescence imaging, we show that zircon in the Sand River orthogneiss of the Limpopo Belt grew during magma crystallization at 3.28 Ga and anatectic events at 2.64 Ga and 2.02 Ga. Our data demonstrate that abundant zircon domains underwent multiple Pb-loss, and that many of the 2.02 Ga domains result from complete Pb-loss from zircon overgrowth domains already formed at 2.64 Ga. In contrast, all domains of complex zoned zircon grains from the Zanzibar granodiorite gneiss were formed during a single magmatic event at 2.61 Ga, as indicated by their uniform Hf isotope composition, but most subsequently suffered multiple Pb-loss. [Copyright &y& Elsevier]

Abstract: We report the results of a comprehensive isotopic investigation of zircons from metamorphosed tonalites and amphibolites from Lushan in the far south of the Trans-North China Orogen of the North China Craton that reveal the oldest rocks yet dated from the orogen. A detailed investigation of the internal structures of zircons, combined with targeted SIMS U–Pb and oxygen isotope analyses and ICP-MS Hf zircon analyses, has resulted in the discovery of previously unknown geological events in the North China Craton. Magmatic zircon from the tonalite and amphibolite was found to be essentially coeval with a small spread of ages from 2829±18 Ma to 2832±11 Ma in the tonalites and from 2838±35 Ma to 2845±23 Ma in amphibolite. Hafnium isotope data suggest derivation of both tonalite and amphibolite from a depleted mantle source with minor crustal contamination. Oxygen isotope ratios in zircons range from 5.1 to 7.3‰ VSMOW, with high δ18O results recorded only from metamorphic domains. The earliest stage of metamorphic zircon growth, present in all four samples analyzed in this study, occurred between 2772±17/22 in the tonalites and 2776±20 and 2792±12 Ma in the amphibolites. A younger metamorphic event at 2638±61 in the tonalite and between 2671±13 and 2651±13 Ma in the amphibolites is recognized in zircons from three of the four samples investigated. This is the first time that metamorphic events at either of these times have been recorded in the North China Craton. Importantly, there is no evidence for the 1.8 Ga high-grade metamorphic event that is manifest in the northern and central parts of the Trans-North China Orogen. [Copyright &y& Elsevier]

Abstract: The Zhimafang peridotite body recovered by a pre-pilot borehole (PP1) of the Chinese Continental Scientific Drilling Project occurs in gneiss from the southern Sulu ultrahigh-P (UHP) terrane, east-central China. Detailed petrographic observation of the freshest lherzolites reveals the existence of pre-peak mantle relics, rare enstatite inclusions (Opx1) in garnet, and coarse-grained diopside (Cpx1) in the peridotites. Matrix phases Ol+Grt+Opx+Cpx±Phl represent the assemblage of the peak-stage. At least >1.5 GPa pressure increase is recognized from the mantle setting to the peak-stage of subduction-zone UHP metamorphism at ~800 °C and 6.8 GPa for the peridotites. All peridotitic minerals have high Mg# (Ol, 91–93, Cpx, 93–94 and Opx, 92–94). Garnets are depleted in LREE, and have increased abundances from Pr through the MREE to a plateau of heavy REE (HREE) at about 10 times chondrite. In contrast, clinopyroxenes display humped REE patterns with high (La/Yb)N values of 27–68. Phlogopite is a major carrier of Ba (5205 ppm) and Th (5.5 ppm). Partition coefficients (D Cpx/Grt) for REE between clinopyroxene and garnet decrease from LREE (~100) to HREE (<1 but >0.1), suggesting that clinopyroxene and garnet equilibrated at low-T (<1100 °C). Zircons from three phlogopite and/or magnesite-bearing peridotites show very low 176Lu/177Hf values (between 10−3 and 10−6), and a wide range in 176Hf/177Hf ratios (0.28221–0.28250). The zircons with low 176Hf/177Hf and relatively high 176Lu/177Hf document that metasomatism affected the peridotite protolith. The model ages (T DM) of zircons mostly cluster around 1.3–1.4 Ga, which probably reflects the metasomatic source. These chemical data combined with previous published bulk-rock major and trace element data indicate that the Zhimafang peridotites probably represent depleted and metasomatized subcontinental lithospheric mantle (SCLM) beneath the Sino-Korean craton. Investigation of the Sulu UHP metamorphic garnet peridotites provides additional insights into the Earth''s geochemical and tectonic evolution, and enlarges our understanding of the exhumation of orogenic peridotites. [Copyright &y& Elsevier]

Abstract: Ten new single zircon fragments, analyzed by solution chemistry and MC-ICP-MS, of the 91500 zircon standard show no evidence to support a recent claim based on in situ data that this reference material is heterogeneous in terms of its radiogenic Hf isotope composition and as a consequence should be abandoned as a reliable interlaboratory standard. Rather, the larger spread in 176Hf/177Hf among in situ data compared with solution chemistry data may reflect the uncertainties resulting from prominent isobaric interference corrections inherent to the in situ analytical protocol. The unweighted mean values of 176Hf/177Hf and 176Lu/177Hf measured for the ten zircon fragments of this study are 0.282313±0.000008 (2σ) and 0.000311±0.000136 (2σ), respectively. Pooling the mean 176Hf/177Hf of this work with those of published solution chemistry studies results in a value of 0.282308±0.000006 (2σ; relative to 176Hf/177Hf=0.282163 for JMC-475), which is recommended here as the currently best estimate of the Hf isotopic composition of this standard. All published studies agree on a value of ~0.0003 for the corresponding 176Lu/177Hf ratio. [Copyright &y& Elsevier]

Abstract: Matrix-matched calibration by natural zircon standards and analysis of natural materials as a reference are the principle methods for achieving accurate results in microbeam U–Pb dating and Hf isotopic analysis. We describe a new potential zircon reference material for laser ablation ICP-MS that was extracted from a potassic granulite facies rock collected in the southern part of the Bohemian Massif (Plešovice, Czech Republic). Data from different techniques (ID-TIMS, SIMS and LA ICP-MS) and several laboratories suggest that this zircon has a concordant U–Pb age with a weighted mean 206Pb/238U date of 337.13±0.37 Ma (ID-TIMS, 95% confidence limits, including tracer calibration uncertainty) and U–Pb age homogeneity on the scale used in LA ICP-MS dating. Inhomogeneities in trace element composition due to primary growth zoning prevent its use as a calibration standard for trace element analysis. The content of U varies from 465 ppm in pristine parts of the grains to ~3000 ppm in actinide-rich sectors that correspond to pyramidal faces with a high degree of metamictization (present in ca. 30% of the grains). These domains are easily recognized from high intensities on BSE images and should be avoided during the analysis. Hf isotopic composition of the Plešovice zircon (>0.9 wt.% Hf) is homogenous within and between the grains with a mean 176Hf/177Hf value of 0.282482±0.000013 (2SD). The age and Hf isotopic homogeneity of the Plešovice zircon together with its relatively high U and Pb contents make it an ideal calibration and reference material for laser ablation ICP-MS measurements, especially when using low laser energies and/or small diameters of laser beam required for improved spatial resolution. [Copyright &y& Elsevier]

Abstract: We describe an in situ method for simultaneous measurement of U–Pb–Hf isotopes and trace element compositions of zircons using a quadrupole and multiple-collector inductively-coupled-plasma mass spectrometer (Q-ICP-MS and MC-ICP-MS, respectively) connected to a single excimer laser-ablation system. A laser-generated zircon aerosol was split behind the ablation cell into two transport tubes via a Y-shaped connector and simultaneously introduced into the two mass spectrometers. Hafnium isotopes were measured on the MC-ICP-MS instrument, while U–Pb ages and trace element compositions were determined using the Q-ICP-MS. The precision and accuracy of this method was evaluated using six well-known and widely used zircon standards (91500, Temora-2, GJ-1, Mud Tank, BR266 and Monastery). Analyses were carried out using spot sizes of 32, 44 and 60 μm. For the 44 and 60 μm spot, the resulting U–Pb ages, Hf isotopic and rare earth element (REE) compositions of these six zircons agree with recommended/reported values within 2σ error. The difference in relative standard deviations (RSD) of 206Pb/238U ages between split-flow measurements and those obtained separately on the Q-ICP-MS is within ∼20% for 91500, Temora-2 and GJ-1, and ∼60% for Mud Tank (due to its lower U and Pb concentrations). Our method provides a precise approach for determining the U–Pb age and the Hf isotopic and trace element compositions of zircon within a single ablation event. This is in particular important for analysis of zircons that are small or contain complicated zoning patterns. Finally, the REE composition of zircon BR266 is more homogeneous than other zircons and could be a suitable standard by which to benchmark new standards for microprobe analyses of zircons. [Copyright &y& Elsevier]

Abstract: We evaluate the validity of age information obtained from two-stage Hf model ages in zircon. Multiple isotope investigations of minerals from the Kiana Granite of the Archean Sleafordian Complex from the southern Gawler Craton, Australia, reveal a complex geologic evolution of the suite. Rubidium–Sr mineral ages define a tectono-thermal event at 1673.4±4.2 Ma, associated with the Kimban orogeny. ID-TIMS U–Pb ages from single zircons yield an upper concordia intercept at 2348±21 Ma, which marks the time of magmatic emplacement. Whole-rock Nd model ages yield crustal residence ages of ∼2.8 Ga. For each single zircon grain, the Lu–Hf isotope systematic was determined by solution MC-ICPMS. Two-stage Hf model ages for the magmatic zircons vary by as much as 500 Myrs, depending on the choice of Lu/Hf for the source of the host rock, putting further emphasis on the need to constrain the source Lu/Hf of a rock used for model age calculations. An average Lu/Hf for mafic crust was assumed for the source reservoir of the rocks to calculate its Hf isotope evolution through time, which yields zircon model ages of ∼3.5 Ga that coincide with the initial growth episode postulated for the Gondwana supercontinent. It is demonstrated that two-stage zircon model ages deduced from initial Hf isotopes can provide important age information for the source of igneous rocks, and consequently on important crustal formation events, even when conventional geochronologic investigations fail, e.g., due to thermo-tectonic overprints or mixing. [Copyright &y& Elsevier]

Abstract: Zircon and baddeleyite U–Pb geochronological dating is widely used in solid Earth sciences and the advent of rapid in-situ methods of analysis, such SIMS and ICP-MS, has re-emphasized the importance of having uniform standards. Recently, it has been shown that Hf isotopic data can provide important information on these minerals since they contain high concentrations of Hf, but have low Lu/Hf ratios, which results in negligible age correction. However, the complex internal structures that result from multiple thermal events, such as inherited cores and metamorphic overgrowths, require that the Hf isotopic data be measured with high spatial resolution. However, the isobaric interferences of 176Yb and 176Lu on 176Hf hamper the precise determination of the 176Hf/177Hf ratio during in-situ laser ablation MC-ICPMS analysis. It is shown here that mass biases of Yb (β Yb) and Hf (β Hf) change with time during analyses and behave differently for solutions and solid material. Therefore, it is suggested that the mean β Yb value of the individual spot be used to obtain the precise isotopic composition for in-situ zircon and baddeleyite Hf isotopic analyses. For low Yb/Hf (176Yb/177Hf<0.001) zircon and baddeleyite, the different methods used to obtain the β Yb value have little effect on the accuracy of the Hf isotopic composition. However, the appropriate Yb isotopic abundance is necessary for high Yb/Hf (176Yb/177Hf>0.001) zircons and baddeleyites, since the interference of 176Yb on 176Hf is significant. Using the mean β Yb value of the individual spot and newly published Yb isotopic abundance data, six standard zircons and two standard baddeleyites, have been investigated using a Neptune MC-ICPMS, with 193 nm laser. For zircons, the obtained 176Hf/177Hf ratios are 0.282307±31 (2SD) for 91500, 0.282680±31 (2SD) for TEMORA, 0.281729±21 (2SD) for CZ3, 282177±17 (2SD) for CN92-1, 0.282983±17 (2SD) for FM0411, and 281234±11 (2SD) for Phalaborwa. The baddeleyites from Phalaborwa and SK10-2 have 176Hf/177Hf ratios of 0.281238±12 and 0.282738±13 (2SD). These results agree well with the values obtained by the solution method and indicate that these standards have different Hf isotopic compositions, in which the extremely low 176Lu/177Hf and 176Yb/177Hf values of CZ3 zircon and Phalaborwa baddeleyite make them excellent standards for machine calibration during in-situ zircon Hf isotopic measurement, with the other standards being more suitable for the development of the correction method. [Copyright &y& Elsevier]

Abstract: A database of >600 analyses of the zircon “standard” Harvard 91500 shows considerable heterogeneity in 176Hf/177Hf; the distribution is essentially bimodal with major peaks at 0.282284±22 and 0.282330±29 (2σ). Although the zircon shows a wide range of 176Yb/177Hf and 176Lu/177Hf, there is no correlation of 176Hf/177Hf with either parameter. This isotopic heterogeneity limits the degree to which 91500 can be used to evaluate the precision or accuracy of different treatments of mass bias and overlap corrections for in situ analysis of Hf-isotope compositions in zircons, or differences between solution and in situ data. [Copyright &y& Elsevier]

Abstract: A two-stage method is presented to separate Lu and Hf from silicate rock and mineral samples digested by either flux melting or HF–HNO3 dissolution using TODGA resin from Eichrom Industries. A first-stage chemistry employs a 2-ml cation exchange column that separates the high-field-strength elements (HFSE) and rare-earth elements (REE) from the matrix. Hf–Zr and Yb–Lu are subsequently separated from the HFSE-REE concentrates on a second-stage 0.2-ml TODGA column. This method returns sufficiently pure cuts to overcome all atomic and molecular interferences as well as the detrimental effects of Ti on Hf fractionation associated with MC-ICP-MS. Boric acid serves two roles in this method: (1) it effectively breaks down fluorides formed in the dry-down step after HF–HNO3 digestions, thereby avoiding use of perchloric acid and/or multiple dry-down and re-dissolution steps, and (2) it is added to the loading solution of the second-stage chemistry to prevent formation of Hf-fluorides that would not be retained by TODGA resin. Using these methods, international rock standards BHVO-1 (processed by both flux melting and HF–HNO3 dissolution) and BCR-2 (processed by HF–HNO3 dissolution) yield 176Hf/177Hf and 176Lu/177Hf ratios that overlap with published values. Permutations of the basic method are presented for samples with significantly elevated LREE contents and for the separation of Lu and Hf from zircon. [Copyright &y& Elsevier]

Rifting between eastern India and western Australia in the Early Cretaceous (∼140–133 Ma) resulted in the formation of the eastern Indian Ocean. Tholeiitic flood basalts erupted on the southwestern margin of Australia (Bunbury basalts at ∼132 and ∼123 Ma) and the eastern margin of India (Rajmahal Traps at ∼118 Ma) shortly after this time, while the Kerguelen Plateau began to form in the nascent ocean basin (∼119 Ma). We studied the Hf and Os isotopic systematics of the continental basalts in order to better understand the relationship between these volcanic events and the Kerguelen plume. The objective of this work was to determine the mantle sources of the continental tholeiites and the nature and quantity of continental contamination. Both the Hf and Os isotopic compositions of these basalts vary with indicators of continental contamination (SiO2, (Th/Ta)PM, (La/Nb)PM). There is no obvious correlation of γOs(T) with Sr or Nd isotopic ratios, but rough correlations are present between Os and Hf isotopes and 208Pb/204Pb; in contrast, #x03B5;Hf(T) shows strong correlations with all isotopic systems and indicators of continental crust assimilation. We demonstrate that the mantle sources of these continental tholeiites cannot originate purely from the depleted asthenosphere. An enriched mantle source is required for both of these basalt suites and the geochemical characteristics of this source are broadly consistent with those inferred to be present in the Kerguelen plume during Early Cretaceous time. The Os isotopic results suggest that at least some continental contamination is present in all samples from both the Bunbury basalts and the Rajmahal Traps. In the Rajmahal Traps, this contaminant appears to be derived from the continental crust and there is little to no evidence for involvement of subcontinental lithospheric mantle (SCLM). The Bunbury basalts have consistently unradiogenic Os isotopic compositions and high #x03B5;Hf(T) for a given #x03B5;Nd(T), characteristics ascribed to the SCLM. Previous investigations of these basalt suites have concentrated on major and trace elements and Sr, Nd and Pb isotopes; none of these results suggested the involvement of SCLM in the Bunbury basalts. Here, we emphasize that the study of Hf and Os isotopes provide additional, useful tools for deciphering mantle sources and continental contaminants involved in the petrogenesis of continental tholeiites. [Copyright &y& Elsevier]

Komatiites from a single lava flow, Carl''s Flow, in the Schapenburg Greenstone Remnant, near Barberton in South Africa, yielded very different Hf isotope compositions, depending on the manner in which the samples were treated analytically. Data from samples dissolved in Savillex beakers define a statistically significant (MSWD=0.77) isochron with an age of 3.4±0.2 Ga, which is identical within error to the probable eruption age, and an initial #x03B5;Hf of -1.3. Analyses of samples dissolved in bombs, on the other hand, plot on a linear array which, if interpreted as an isochron, gives an age of 2.9 Ga. Their initial 176Hf/177Hf, calculated using the probable eruption age of 3.45 Ga, are positive and variable, ranging from #x03B5;Hf of +1.3 to +6.3. Hf contents are much lower and Lu/Hf ratios systematically higher in the Savillex beaker-dissolved batch of komatiites, indicating that a Hf-rich phase (zircon or baddeleyite?) remained undissolved in these samples. The negative #x03B5;Hf of the Savillex beaker-dissolved samples is attributed to interaction with crust-derived fluids that affected the komatiite soon after its eruption. The anomalously low isochron age of the bomb-dissolved samples is due to the presence of a single olivine cumulate sample that appears to have lost Hf during post-emplacement alteration. Without this sample, initial #x03B5;Hf values cover a much narrower range between +4.3 and +6.3, which is believed to be that of the mantle source of the komatiites. The combination of highly positive #x03B5;Hf and lower-than-chondritic Lu/Hf indicates that the mantle source of the Carl''s Flow was garnet-enriched for a substantial period of time prior to komatiite formation and that garnet was retained in the source during the melting event that eventually produced the komatiite magma. [Copyright &y& Elsevier]

The Hf and Lu isotopic ratios of the zircon standard 91500 have been redefined by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The chemical protocol consists of a high-pressure and high-temperature acid dissolution of zircon followed by optimized two-step ion-exchange chromatography with an overall recovery better than 94%. Instrumental calibration involved an extensive characterization of standard solutions for Hf [JMC-475 250 ppb: 176Hf/177Hf=0.282161±16 (2 S.D.)] and Lu [JMC standard 50 ppb: 175Lu/176Lu=37.72±2 (2 S.D.)]. A total of 59 Hf isotopic measurements on the zircon standard 91500, including four independent dissolutions and purifications, were carried out on two Nu Plasma MC-ICP-MS instruments. The average 176Hf/177Hf is 0.282302±8 (2 S.D.) and the two MC-ICP-MS instruments give overlapping results within error. These high precision data [external error: 27 ppm (2 S.D.) for 59 measurements and 10 ppm for a single day; internal error: 10 ppm (2 S.D.)] are reproducible between duplicates and underscore the stability of the analytical protocol. The Lu isotopic composition of the zircon standard 91500 has also been redefined: 175Lu/176Lu=37.74±8 (2 S.D.). With the growing use of in situ measurement techniques using MC-ICP-MS technology, such precise reference values will be important for the calibration of laser ablation analyses in the future. [Copyright &y& Elsevier]

Ocean island basalts (OIB) exhibit significant variations in their 87Sr/86Sr, 143Nd/144Nd, 176Hf/177Hf, 186,187Os/188Os, and 206,207,208Pb/204Pb compositions that indicate contributions from multiple mantle sources. To further constrain the relationships between diverse long-lived isotopic systems in OIB, new double-spike Pb and Hf isotope data, as well as isotope dilution highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundances are reported for nineteen Icelandic picrites and basalts for which 3He/4He, 87Sr/86Sr, 143Nd/144Nd, and 186,187Os/188Os data have been reported previously (Brandon et al., 2007. GCA). Hafnium-Nd-He isotope systematics for the sample set reveal the presence of an ancient refractory source with low-3He/4He, while He-Pb isotope correlations indicate that recycled oceanic crustal components with high-3He/4He added from a less degassed mantle source are present in the Iceland plume. The highly depleted, low-3He/4He signature is sampled in the Northern and Western Volcanic Zones, likely due to higher degrees of partial melting at those localities enabling sampling of this refractory endmember. The 187Os/188Os ratios show correlations with Pb, Hf, and Nd isotope ratios indicating binary mixing between depleted and enriched sources, with no evidence for decoupling due to sulfide metasomatism. The spread of 187Os/188Os- 206,207,208Pb/204Pb data can be explained by addition of 1–11% young recycled oceanic crust to a depleted mantle source distinct from the source of Atlantic MORB. Abundances of the HSE in Northern and Western Volcanic Zone lavas overlap with those from other OIB with similar MgO contents, showing fractionated patterns that are enriched in the more incompatible Re, Pd, and Pt over the compatible Ru, Ir, and Os. Calculated parental melt HSE abundances of those lavas also overlap with those of other OIB. Eastern Volcanic Zone lavas are highly depleted in Pt and Pd relative to other Icelandic lavas. Abundances of Pt and Pd correlate with isotopic parameters, such as 206Pb/204Pb, in Icelandic lavas, indicating that the isotopically enriched endmember sampled in the Eastern Volcanic Zone is depleted in the HSE, consistent with it being mafic in nature. The abundances of MgO in the lavas also roughly correlate with isotopic parameters, supporting the identity of the depleted endmember as ultramafic and the enriched endmember as mafic. New and previously published double-spike Pb isotope data show chiefly binary mixing with an additional component present in the vicinity of the volcano Öræfajökull. Icelandic 207Pb/204Pb and 208Pb/204Pb data plot below and above the majority of Mid-Atlantic Ridge basalt data, respectively, indicating that both depleted and enriched end-members in the plume have a lower U depletion age and a higher Th/U than ambient mantle. This is consistent with the enriched and depleted end-members within the Iceland plume being <2 Ga recycled oceanic crust and lithospheric mantle, respectively. [ABSTRACT FROM AUTHOR]