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Osmium isotopes, whole rock and mineral geochemical data from peridotite xenoliths from two Miocene McMurdo Volcanic Group cinder cones in the Transantarctic Mountains (TAM) in Southern Victoria Land, Antarctica, reveal that the underlying mantle preserves evidence for major mid-Proterozoic lithosphere formation despite the crust being dominated by late Neoproterozoic-Ordovician (~0.65–0.47 Ga) rocks. The Hooper Crags xenolith suite is dominated by harzburgites with highly refractory olivine Mg# (up to 92.3) and depleted bulk rock major and platinum group element + Re abundances, with 187Os/188Os ratios indicating depletion in the mid-Proterozoic. Pipecleaner Glacier xenoliths, 18 km distant, are lherzolites with olivine Mg# ( 250 km) East Antarctic Craton lithosphere shielding the immediately adjacent circum-cratonic mantle from being affected by convective asthenosphere-driven erosion. This contrasts with mantle lithosphere accreted distally to the East Antarctic Craton (represented by the now-detached Zealandia continent), which did not attain extreme thickness and has therefore been more susceptible to tectonic reworking and lateral translation.

The ultramafic mantle sections of the Yarlung-Zangbo ophiolites (YZO) along the suture of India and Asia in Tibet preserve the mantle history of the formerly intervening oceanic lithosphere. Fifty-two ophiolitic peridotites from three localities (Purang, Baigang and Zedang) reveal that these rocks comprise Mesozoic depleted mantle (peak mode 187Os/188Os = 0.126), mixed with more ancient mantle domains (187Os/188Os: 0.113–0.121, with model ages up to 2.2 Ga), probably through subduction or delamination of older lithosphere prior to its re-encapsulation into Mesozoic oceanic lithosphere. Whole-rock major and trace elements indicate that this composite mantle lithosphere experienced moderate to high degrees (∼10–30%) of partial melting in the Permian-Triassic, possibly due to the rifting of the back-arc basin in the northern margin of East Gondwana and the opening of Neo-Tethys. However, the generally flat primitive upper mantle-normalized highly siderophile element patterns do not match the depleted lithophile element characteristics. Sub-vertical (Pd/Ir)N-Al2O3 variations, coupled with the occurrence of variable amounts of interstitial base metal sulfides (BMS) and correlations with (Pd/Ir)N and Cu contents, indicate the addition of S-saturated (or BMS-rich) melts or fluids into this oceanic lithosphere. This may have occurred at ∼130–120 Ma during a new episode of Neo-Tethyan subduction, during which S-saturated forearc basaltic magmas were produced and subsequently overprinted the overlying peridotitic lithospheric mantle. The Tibetan YZO illustrate the complex life cycle of ophiolitic peridotites related to multi-stage regional tectonic events, and provide insights into understanding geodynamic mechanisms that have operated in the Earth’s upper mantle.

The North China Craton (NCC) is an atypical ancient landmass that suffered lithospheric destruction. Previous studies suggest that the eastern part of the lithospheric mantle of the NCC has been thinned and modified in the Mesozoic. However, the initiation time and mechanism of the destruction remain controversial. Mafic magmatism could provide a unique window into deciphering the lithospheric mantle composition and its evolution. Here we present geochemical and geochronological data of the diamond-bearing alkaline basalts from Lan'gan, located in the southeastern margin of the NCC. Zircon U-Pb dating yielded an average age of 174 ± 14 Ma, representing the first reported Jurassic basalts in the eastern NCC. The Lan'gan basalts are enriched in light rare earth elements (LREE) and large ion lithosphile elements (LILE). Sr-Nd-Pb-Hf isotopic compositions (87Sr/86Sr(t) = 0.70646–0.70925, eNd(t) = −2.1 to −4.9, 206Pb/204Pb(t) = 17.14–18.12, 207Pb/204Pb(t) = 15.28–15.61, 208Pb/204Pb(t) = 37.82–38.67, and zircon eHf(t) = −17 to −21) are enriched compared to depleted mantle. The presence of primary amphibole indicates that the magma source of the basalts was water enriched. These observations suggest that, the lithospheric mantle of the eastern NCC were significantly refertilized, likely by slab derived fluids/melts from the Paleo-Pacific subduction. Owing to the Paleo-Pacific subduction, the lithospheric mantle of the eastern NCC were reduced in viscosity and intensity, and finally promoted partial melting in a limited scale to generate the investigated alkaline basalts. Hence, the discovery of diamond in the Lan'gan basalts demonstrates that the lithosphere of the NCC remained thick, and that large-scale destruction had not initiated in the early Jurassic beneath this region.

We present major- and trace-element concentrations, Sr–Nd–Hf isotopic compositions, Re Os isotopes, and highly siderophile element (HSE) abundances of 17 xenolithic mantle peridotites from the Nuomin volcanic field to constrain the assembly and evolution of the Xing'an–Mongolia Orogenic Belt (XMOB), Northeast China. The Nuomin peridotites are divided into five groups (harzburgite groups Haz-1, Haz-2, and Haz-3, and lherzolite groups Lhz-1 and Lhz-2). The Haz-1 peridotites are characterized by refractory chemical compositions (Al2O3 contents of 1.03–2.30 wt% and olivine forsterite (Fo) numbers of 90.7–92.5) that are best interpreted as residues after high degrees of mantle partial melting. The Haz-2 and Haz-3 peridotites exhibit slightly more fertile compositions (Al2O3 of 1.72–1.80 wt% and Fo of 89.0–89.9 for the Haz-2, and Al2O3 of 2.86 wt% and Fo of 91.2 for the Haz-3), resulting from refertilization by silicate melts. The Lhz-1 samples are more fertile (Al2O3 of 2.90–3.64 wt% and Fo of 89.1–90.3) than the Lhz-2 samples (Al2O3 of 1.64–2.16 wt% and Fo of 90.9–91.3). The combination of trace-element data (Ti/Eu ratio) and Sr–Nd–Hf isotopic compositions indicates the presence of at least three peridotite end-members (Haz-1, Haz-2, and Lhz-1–Lhz-2) beneath the Nuomin area, which can be explained by the infiltration of two distinct metasomatic agents (MA1: composition similar to potassic basaltic rocks in the Wudalianchi–Erkeshan–Keluo area, and MA2: Fe–Ti-enriched melt). HSE abundances and Os isotopic data show that the Os isotopic compositions of the Haz-1, Lhz-1, and Lhz-2 peridotites were not significantly affected by lithophile-element-dominated metasomatism and can be used to constrain the melt extraction ages of these peridotites. The lower 187Os/188Os ratios of Haz-1 peridotites define a prominent rhenium depletion age (TRD) of ~1.6 Ga and represent fragments of the Paleo–Mesoproterozoic lithospheric mantle rather than reflecting the heterogeneous characteristics of the asthenosphere or extraneous emplacement. In contrast, the Lhz-1 and Lhz-2 lherzolite groups together have a narrow range of 187Os/188Os ratios that give younger TRD ages (~0.5 to 1.0 Ga). Our data demonstrate that both the Paleo–Mesoproterozoic and Neoproterozoic subcontinental lithospheric mantle coexist beneath the XMOB and that they correspond respectively to the bimodal age peaks of crustal growth of ~1.6 Ga and ~0.8 Ga defined by the XMOB granitoids. The XMOB was assembled primarily during the Phanerozoic by multiple blocks that had formed from the Paleoproterozoic to Neoproterozoic. The similar chemical and Sr–Nd–Hf isotopic signatures of both young and old lithospheric mantle indicate that the large-scale metasomatism event involving potassic melts most likely occurred during the evolution of the Paleo–Asian Ocean. The crustal materials carried to the mantle by multiple subduction events could be an effective source of potassium for the origin of potassic basaltic rocks.

Mantle xenoliths exhumed from beneath the South Island of New Zealand offer an opportunity to investigate the role of lithospheric mantle water in influencing deep lithosphere deformation and formation of the narrow Southern Alps mountain range during orogeny along the Australia–Pacific plate boundary. Fourier transform infrared spectrometry (FTIR) water measurements on clinopyroxene (cpx), orthopyroxene (opx) and olivine of peridotite xenoliths from seven localities across the Zealandia continent reveal a lateral variation of H2O within the Oligocene–Miocene lithospheric mantle. There is a “wet” domain beneath what is now the Southern Alps mountain range with average measured H2O concentrations of 610 ppm for cpx and 298 ppm for opx. In contrast, dominantly “dry” domains with average H2O concentrations of 110 ppm for cpx and 49 ppm for opx reside beneath East Otago, Chatham Island and Auckland Islands. Contrasting H2O concentrations within olivine (calculated to be 60 to 100 ppm for the wet domain versus

While the mantle roots directly beneath Archean cratons have been relatively well studied because of their economic importance, much less is known about the genesis, age, composition and thickness of the mantle lithosphere beneath the regions that surround the cratons. Despite this knowledge gap, it is fundamentally important to establish the nature of relationships between this circum-cratonic mantle and that beneath the cratons, including the diamond potential of circum-cratonic regions. Here we present mineral and bulk elemental and isotopic compositions for kimberlite-borne mantle xenoliths from the Parry Peninsula and Central Victoria Island, Arctic Canada. These xenoliths provide key windows into the lithospheric mantle underpinning regions to the North and Northwest of the Archean Slave craton, where the presence of cratonic material has been proposed. The mantle xenolith data are supplemented by mineral concentrate data obtained during diamond exploration. The mineral and whole rock chemistry of peridotites from both localities is indistinguishable from that of typical cratonic mantle lithosphere. The cool mantle paleogeotherms defined by mineral thermobarometry reveal that the lithospheric mantle beneath the Parry Peninsula and Central Victoria Island terranes extended well into the diamond stability field at the time of kimberlite eruption, and this is consistent with the recovery of diamonds from both kimberlite fields. Bulk xenolith Se and Te contents, and highly siderophile element (including Os, Ir, Pt, Pd and Re) abundance systematics, plus corresponding depletion ages derived from Re-Os isotope data suggest that the mantle beneath these parts of Arctic Canada formed in the Paleoproterozoic Era, at ∼2 Ga, rather than in the Archean. The presence of a diamondiferous Paleoproterozoic mantle root is part of the growing body of global evidence for diamond generation in mantle roots that stabilized well after the Archean. In the context of regional tectonics, we interpret the highly depleted mantle compositions beneath both studied regions as formed by mantle melting associated with hydrous metasomatism in the major Paleoproterozoic Wopmay-Great Bear-Hottah arc systems. These ∼2 Ga arc systems were subsequently accreted along the margin of the Slave craton to form a craton-like thick lithosphere with diamond potential thereby demonstrating the importance of subduction accretion in building up Earth’s long-lived continental terranes.

The timing and mechanisms of continental crust formation represent major outstanding questions in the Earth sciences. Extinct-nuclide radioactive systems offer the potential to evaluate the temporal relations of a variety of differentiation processes on the early Earth, including crust formation. Here, we investigate the whole-rock 182W/184W and 142Nd/144Nd ratios and zircon Δ 17 O values of a suite of well-studied and lithologically-homogeneous meta-igneous rocks from the Acasta Gneiss Complex, Northwest Territories, Canada, including the oldest-known zircon-bearing rocks on Earth. In the context of previously published geochemical data and petrogenetic models, the new 142Nd/144Nd data indicate that formation of the Hadean–Eoarchean Acasta crust was ultimately derived from variable sources, both in age and composition. Although 4.02 Ga crust was extracted from a nearly bulk-Earth source, heterogeneous μ 142Nd signatures indicate that Eoarchean rocks of the Acasta Gneiss Complex were formed by partial melting of hydrated, Hadean-age mafic crust at depths shallower than the garnet stability field. By ∼3.6 Ga, granodioritic–granitic rocks were formed by partial melting of Archean hydrated mafic crust that was melted at greater depth, well into the garnet stability field. Our 182W results indicate that the sources to the Acasta Gneiss Complex had homogeneous, high-μ182W on the order of +10 ppm—a signature ubiquitous in other Eoarchean terranes. No significant deviation from the terrestrial mass fractionation line was found in the triple oxygen isotope (16O–17O–18O) compositions of Acasta zircons, confirming homogeneous oxygen isotope compositions in Earth's mantle by 4.02 Ga.

High-precision measurements of W isotopic ratios have enabled increased exploration of early Earth processes. However, when applying W isotopic data to understand the geological processes, it is critical to recognize the potential mobility of W and hence evaluate whether measured W contents and isotopic compositions reflect the primary petrogenetic processes or instead are influenced by the effects of secondary inputs/mobility. Furthermore, if we are to better understand how W is partitioned between different minerals during melting and metasomatic processes it is important to document the likely sinks for W during these processes. In addition, an understanding of the main hosts for W in the crust and mantle is critically important to constrain how W is cycled and stored in the crust-mantle geochemical cycle. As a first step to investigate these issues, we have carried out in situ concentration measurements of W and other HFSEs in mineral phases within a broad spectrum of crustal and mantle rocks, along with whole-rock concentration measurements. Mass balance shows that for tonalitic gneiss and amphibolite, the major rock-forming minerals can adequately account for the bulk W budget, and for the pristine ultramafic rocks, olivine and orthopyroxene are the major controlling phases for W whereas for metasomatized ultramafic rocks, significant W is hosted in Ti-bearing trace phases (e.g., rutile, lindsleyite) along grain boundaries or is inferred to reside in cryptic W-bearing trace phases. Formation or decomposition of these phases during secondary processes could cause fractionation of W from other HFSEs, and also dramatically modify bulk W concentrations in rocks. For rocks that experienced subsequent W enrichment/alteration, their W isotopic compositions may not necessarily represent their mantle sources, but could reflect later inputs. The relatively small suite of rocks analyzed here serves as a reconnaissance study but allows some preliminary speculations on their significance for crust-mantle HFSE and siderophile element budgets – to be tested in future studies. The significant concentration of W, as well as Nb and Ta hosted in rutile and titanite has interesting implications for the budget of W during crust-mantle recycling. Crust-mantle recycling models invoking the recycling of rutile-bearing eclogites to satisfy the mantle Nb/Ta ratio carry the penalty that the very high W/U and W/Th ratios of these rocks results in a concomitant large deviation from the primitive mantle-like ratios estimated for bulk continental crust. Similarly, data from the single amphibolite sample investigated in this study are inconsistent with models implicating the partial melting of amphibolite-bearing subducted slabs as a major process for formation of continental crust in the Earth’s early history. Either the current widely accepted estimates for bulk continental crust W/U and W/Th ratios are in error, or partial melting or other processes lowers the W/U or W/Th of melt residues during their return to the mantle. The present small dataset cannot properly evaluate this, requiring further investigation. Finally, the lithospheric mantle has the potential to store substantial amounts of W, for example via infiltration by W-rich melts/fluids, and thus may act as a source for W mineralization in the crust.

This contribution presents a new method for Re–Os isotope dating organic-rich sedimentary (ORS) rocks by thermal ionization mass spectrometry using an H 2 O 2 –HNO 3 solution as the digestion medium, rather than CrO 3 –H 2 SO 4 or inverse aqua regia . The main underlying principle of this method is that H 2 O 2 –HNO 3 digestion would preferentially liberate hydrogenous Re and Os, and minimize the dissolution of non-hydrogenous detrital Re and Os, thereby providing more accurate and precise ages. A series of tests were performed, and the experimental data demonstrate the fundamental controls on spike–sample equilibrium and that the amount of detrital Re and Os incorporated into the system are subjected to the volumetric ratio of H 2 O 2 to HNO 3 . The optimum method is a H 2 O 2 :HNO 3 ratio of 5 to complete spike–sample equilibration, and to minimize the amount of detrital Re and Os in the system. A comparison of our new method with inverse aqua regia and CrO 3 –H 2 SO 4 showed that the three techniques yield indistinguishable Re–Os results, suggesting complete spike–sample equilibrium was achieved by all of the digestion techniques. Moreover, the data show that our new technique leaches out the least amount of detrital Re and Os isotopes relative to conventional methods Thus, we propose the H 2 O 2 –HNO 3 method may increase the precision and accuracy of Re–Os depositional ages of organic-rich sedimentary systems.

The zinc (Zn) stable isotope system has great potential for tracing planetary formation and differentiation processes due to its chalcophile, lithophile and moderately volatile character. As an initial approach, the terrestrial mantle, and by inference, the bulk silicate Earth (BSE), have previously been suggested to have an average δ 66 Zn value of ∼+0.28‰ (relative to JMC 3-0749L) primarily based on oceanic basalts. Nevertheless, data for mantle peridotites are relatively scarce and it remains unclear whether Zn isotopes are fractionated during mantle melting. To address this issue, we report high-precision (±0.04‰; 2SD) Zn isotope data for well-characterized peridotites ( n = 47) from cratonic and orogenic settings, as well as their mineral separates. Basalts including mid-ocean ridge basalts (MORB) and ocean island basalts (OIB) were also measured to avoid inter-laboratory bias. The MORB analyzed have homogeneous δ 66 Zn values of +0.28 ± 0.03‰ (here and throughout the text, errors are given as 2SD), similar to those of OIB obtained in this study and in the literature (+0.31 ± 0.09‰). Excluding the metasomatized peridotites that exhibit a wide δ 66 Zn range of −0.44‰ to +0.42‰, the non-metasomatized peridotites have relatively uniform δ 66 Zn value of +0.18 ± 0.06‰, which is lighter than both MORB and OIB. This difference suggests a small but detectable Zn isotope fractionation (∼0.1‰) during mantle partial melting. The magnitude of inter-mineral fractionation between olivine and pyroxene is, on average, close to zero, but spinels are always isotopically heavier than coexisting olivines (Δ 66 Zn Spl-Ol = +0.12 ± 0.07‰) due to the stiffer Zn-O bonds in spinel than silicate minerals (Ol, Opx and Cpx). Zinc concentrations in spinels are 11–88 times higher than those in silicate minerals, and our modelling suggests that spinel consumption during mantle melting plays a key role in generating high Zn concentrations and heavy Zn isotopic compositions of MORB. Therefore, preferential melting of spinel in the peridotites may account for the Zn isotopic difference between spinel peridotites and basalts. By contrast, the absence of Zn isotope fractionation between silicate minerals suggests that Zn isotopes are not significantly fractionated during partial melting of spinel-free garnet-facies mantle. If the studied non-metasomatized peridotites represent the refractory upper mantle, mass balance calculation shows that the depleted MORB mantle (DMM) has a δ 66 Zn value of +0.20 ± 0.05‰ (2SD), which is lighter than the primitive upper mantle (PUM) estimated in previous studies (+0.28 ± 0.05‰, 2SD, Chen et al., 2013b; +0.30 ± 0.07‰, 2SD, Doucet et al., 2016). This indicates that the Earth’s upper mantle has a heterogeneous Zn isotopic composition vertically, which is probably due to shallow mantle melting processes.

A suite of peridotite xenoliths from the Chidliak kimberlite province provides an ideal opportunity to assess the age of the mantle lithosphere beneath the eastern Hall Peninsula Block (EHPB) in southern Baffin Island, Nunavut and to provide constraints on the lithospheric architecture of this region. The new dataset comprises highly siderophile element (HSE) abundances and Re Os isotopic compositions for 32 peridotite xenoliths sampled from four Late Jurassic-Early Cretaceous kimberlite pipes (CH-1, -6, -7, and -44). These peridotites represent strongly depleted mantle residues, with bulk-rock and olivine chemistry denoting melt extraction extents of up to 40%. The vast majority of samples show PPGE (Pt and Pd) depletion relative to IPGE (Os, Ir, and Ru) ((Pt/Ir)N: 0.10–0.96, median = 0.57; (Pd/Ir)N: 0.03–0.79, median = 0.24), coupled with mostly unradiogenic Os isotopic compositions (187Os/188Os = 0.1084–0.1170). These peridotites display strong correlations between 187Os/188Os and melt depletion indicators (such as olivine Mg number and bulk-rock Al2O3, (Pd/Ir)N), suggesting that an ancient (~2.8 Ga) melt depletion event governed the formation of the Chidliak lithosphere. The prominent mode of TRDerupt model ages at ca. 2.8 Ga matches the main crust-building ages of the EHPB, demonstrating temporal crust-mantle coupled in the Meso-Neoarchean. These ancient melt-depletion ages are present throughout the depth of the ~200 km thick lithospheric mantle column beneath Chidliak. The Meso-Neoarchean formation age of the EHPB mantle broadly coincides with the timing of stabilization of the lithospheric mantle beneath the Greenlandic portion of the North Atlantic Craton (NAC). This, along with the similarity in modal mineralogy, chemical composition and evolutionary history, indicates that the EHPB, southern Baffin Island was once contiguous with the Greenlandic NAC. The mantle lithosphere beneath both the EHPB and the NAC show a similar metasomatic history, modified by multiple pulses of metasomatism. These multiple metasomatic events combined to weaken and thin the lithospheric mantle, culminating in the formation of the Labrador Sea and Davis Strait separating the EHPB from the Greenlandic NAC in the Paleocene.

Although trace element concentrations in clinopyroxene serve as a useful tool for assessing the depletion and enrichment history of mantle peridotites, this is not applicable for peridotites in which the clinopyroxene component has been consumed (~ 25% partial melting). Orthopyroxene persists in mantle residues until ~ 40% melting and it is therefore this mineral that offers petrological insights into the evolution of refractory peridotites. Major and trace element concentrations in orthopyroxene ± clinopyroxene from two spinel facies harzburgitic xenolith suites from New Zealand are examined. Samples from Cape L'Evique (CLEV) on Chatham Island contain traces of clinopyroxene ( 45) and low orthopyroxene Al2O3 (generally

Well-resolved W-182 isotope anomalies, relative to the present mantle, in Hadean-Archean terrestrial rocks have been interpreted to reflect the effects of variable late accretion and early mantle differentiation processes. To further explore these early Earth processes, we have carried out W concentration and isotopic measurements of Eoarchean ultramafic rocks, including lithospheric mantle rocks, metakomatiites, a layered ultramafic body and associated crustal gneisses and amphibolites from the Uivak gneiss terrane of the Saglek Block, northern Labrador, Canada. These analyses are augmented by in situ W concentration measurements of individual phases in order to examine the major hosts of W in these rocks. Although the W budget in some rocks can be largely explained by a combination of their major phases, W in other rocks is hosted mainly in secondary grain-boundary assemblages, as well as in cryptic, unidentified W-bearing `nugget' minerals. Whole rock W concentrations in the ultramafic rocks show unexpected enrichments relative, to elements with similar incompatibilities. By contrast, W concentrations are low in the Uivak gneisses. These data, along with the in situ W concentration data, suggest metamorphic transport/re-distribution of W from the regional felsic rocks, the Uivak gneiss precursors, to the spatially associated ultramafic rocks. All but one sample from the lithologically varied Eoarchean Saglek suite is characterized by generally uniform similar to+11 ppm enrichments in W-182 relative to Earth's modern mantle. Modeling shows that the W isotopic enrichments in the ultramafic rocks were primarily inherited from the surrounding W-182-rich felsic precursor rocks, and that the W isotopic composition of the original ultramafic rocks cannot be determined. The observed W isotopic composition of mafic to ultramafic rocks in intimate contact with ancient crust should be viewed with caution in order to plate constraints on the early Hf-W isotopic evolution of the Earth's mantle with regard to late accretionary processes. Although W-182 anomalies can be erased via mixing in the convective mantle, recycling of W-182-rich crustal rocks into the mantle can produce new mantle sources with anomalous W isotopic compositions that can be tapped at much later times and, hence, this process should be considered as a mechanism for the generation of W-182-rich rocks at any subsequent time in Earth history. (C) 2016 Elsevier B.V. All rights reserved.

Canada is host to at least six separate cratons that comprise a significant proportion of its crustal extent. Of these cratons, we possess knowledge of the cratonic lithospheric roots beneath only the Slave craton and, to a lesser extent, the Superior craton, despite the discovery of many new diamond-bearing kimberlites in Canada's North. Here we present the first age, composition and geothermal information for kimberlite-borne peridotite xenoliths from two localities within the central Rae craton: Pelly Bay and Repulse Bay. Our aim is to investigate the nature and evolution of the deep lithosphere in these regions and to examine how events recorded in the mantle may or may not correlate with the complex history of crustal evolution across the craton. Peridotite xenoliths are commonly altered by secondary processes including serpentinization, silicification and carbonation, which have variably affected the major element compositions. These secondary processes, as well as mantle metasomatism recorded in pristine silicate minerals, however, did not significantly modify the relative compositions of platinum-group elements (PGE) and Os isotope ratios in the majority of our samples from Pelly Bay and Repulse Bay, as indicated by the generally high absolute PGE concentrations and mantle-like melt-depleted PGE patterns. The observed PGE signatures are consistent with the low bulk Al2O3 contents (mostly lower than 2.5%) of the peridotites, as well as the compositions of the silicate and oxide minerals. Based on PGE patterns and Os model ages, the peridotites from both localities can be categorized into three age groups: Archean (3.0–2.6 Ga overall; 2.8–2.6 Ga for Pelly Bay and 3.0–2.7 Ga for Repulse Bay), Paleoproterozoic (2.1–1.7 Ga), and “Recent” (

The accretionary mobile belts surrounding ancient cratonic cores are an important facet of the growth and preservation of continental landmasses. Peridotites from Nuominhe in the Xing'an Mongolia Orogenic Belt (XMOB) provide an additional opportunity to examine the age, structure and evolution of mantle lithosphere separating two of the largest existing ancient continental nuclei: the North China Craton and the Siberian Craton. This suite of mantle rocks comprises fertile to refractory garnet- and spinel-facies harzburgites and lherzolites. Their lithophile element systematics show that the peridotites were metasomatized to variable extent by silicate‑carbonate melts. Despite this, the highly siderophile element and Os isotope systematics appear to have been largely undisturbed. The Nuominhe peridotites have Re-depletion Os model ages (TRD) that range from 0.5 Ga to 2.4 Ga, with three peaks/major ranges at ~2.0–2.4 Ga, ~1.4–1.5 Ga and ~ 0.8 Ga, of which the latter two are closely similar to those data from other XMOB localities reported in the literature. The only section of the mantle that appears to have ages which correlate with crust formation is the suite with Neoproterozoic (~0.8 Ga) depletion ages, while the older mantle domains document older episodes of mantle depletion. Given the lack of correlation between equilibrium temperatures and bulk composition or TRD ages, the Nuominhe peridotites were inter-mixed in the mantle column, most likely as a result of incorporation of recycled older continental mantle fragments into juvenile Neoproterozoic mantle during the orogenic processes responsible for new lithosphere formation. Geothermobarometry of the Nuominhe peridotites indicates a conductive geotherm of ~60 mWm−2 and therefore a lithosphere thickness of ~125 km, which is thicker than most Phanerozoic continental terranes, and even thicker than Proterozoic regions that comprise the larger cratonic unit of the Siberian craton. This thick Proterozoic lithosphere sandwiched between the converging North China and Siberian cratons was evidently partly constructed from recycled refractory continental mantle fragments, perhaps extant in the convecting mantle, or in-part derived from the surrounding cratons, leading to a composite nature of the mantle in this re-healed continental suture. Re-accretion of recycled refractory old continental mantle fragments plays a significant role in affecting mantle composition and controlling the thickness of circum-cratonic landmasses between cratonic blocks.

Geothermal energy is one of the keys for understanding the mechanisms driving the plate tectonics and mantle dynamics. The surface heat flux, as measured in boreholes, provides limited insights into the relative contributions of primordial versus radiogenic sources of the interior heat budget. Geoneutrino, electron antineutrino that is produced from the radioactive decay of the heat producing elements, is a unique probe to obtain direct information about the amount and distribution of heat producing elements in the crust and mantle. Cosmochemical, geochemical, and geodynamic compositional models of the Bulk Silicate Earth (BSE) individually predict different mantle neutrino fluxes, and therefore may be distinguished by the direct measurement of geoneutrinos. Due to low counting statistics, the results from geoneutrino measurements at several sites are inadequate to resolve the geoneutrino flux. However, the JUNO detector, currently under construction in South China, is expected to provide an exciting opportunity to obtain a highly reliable statistical measurement, which will produce sufficient data to address several vital questions of geological importance. However, the detector cannot separate the mantle contribution from the crust contribution. To test different compositional models of the mantle, an accurate a-priori estimation of the crust geoneutrino flux based on a three-dimensional (3-D) crustal model is important. This paper presents a 3-D crustal model over a surface area of 10° × 10° grid surrounding the JUNO detector and a depth down to the Moho discontinuity, based on the geological, geophysical and geochemical properties. This model provides a distinction of the thickness of the different crustal layers together with the corresponding Th and U abundances. We also present our predicted local contribution to the total geoneutrino flux and the corresponding radiogenic heat. Compared to previous studies where the surface layer is subdivided into a few geologic units and each of them is considered to have the same geochemical property, our method has provided an effective approach to reduce the uncertainty of geoneutrino flux prediction by constructing the composition of the surface layer through cell by cell which are independent to each other.

Copper isotopes have been successfully applied to many fields in geochemistry, and in particular, as a strongly chalcophile element, the isotope systematics of Cu can be potentially applied as a proxy for crust–mantle and core–mantle differentiation processes. However, to date, the Cu isotopic composition of distinct silicate reservoirs in the Earth, as well as the behaviour of Cu isotopes during igneous processes and slab dehydration are not well constrained. To address these issues, here we report high-precision (±0.05‰; 2SD) Cu isotope data for 132 terrestrial samples including 28 cratonic peridotites, 19 orogenic peridotites, 70 basalts (MORBs, OIBs, arc basalts and continental basalts) and 15 subduction-related andesites/dacites sourced worldwide. The peridotites are classified into metasomatized and non-metasomatized groups, based upon their rare earth element (REE) patterns and the presence or lack of minerals diagnostic of metasomatism (e.g., phlogopite). The metasomatized peridotites span a wide range of δ65Cu values from −0.64 to +1.82‰, in sharp contrast to the non-metasomatized peridotites that exhibit a narrow range of δ65Cu from −0.15 to +0.18‰ with an average of + 0.03 ± 0.24 ‰ (2SD). Comparison between these two groups of peridotites demonstrates that metasomatism significantly fractionates Cu isotopes with sulfide breakdown and precipitation potentially shifting Cu isotopes towards light and heavy values, respectively. MORBs and OIBs have homogeneous Cu isotopic compositions ( + 0.09 ± 0.13 ‰ ; 2SD), which are indistinguishable from those of the non-metasomatized peridotites within uncertainty. This suggests that Cu isotope fractionation during mantle partial melting is limited, even if sulfides are a residual phase. Compared with MORBs and OIBs, arc and continental basalts are more heterogeneous in Cu isotopic composition. In particular, basalts that were collected from a traverse across the Kamchatka arc over a distance of 200 to 400 km from the trench show a large range of δ65Cu from −0.19 to +0.47‰, and samples with higher Ba/Nb ratios tend to be isotopically more heterogeneous. The large Cu isotopic variations in arc and continental basalts most probably reflect the involvement of recycling crustal materials in their sources. Collectively, the dataset obtained in this study suggests that the bulk silicate Earth (BSE) has an average δ65Cu value of + 0.06 ± 0.20 ‰ (2SD).

The role played by ancient melt-depleted lithospheric mantle in preserving continental crust through time is critical in understanding how continents are built, disrupted and recycled. While it has become clear that much of the extant Archean crust is underpinned by Archean mantle roots, reports of Proterozoic melt depletion ages for peridotites erupted through Phanerozoic terranes raise the possibility that ancient buoyant lithospheric mantle acts as a “life-raft” for much of the Earth's continental crust. Here we report the largest crust–lithospheric mantle age decoupling (∼2.4 Ga) so far observed on Earth and examine the potential cause for such extreme age decoupling. The Phanerozoic (

Previous studies have shown that the eastern North China Craton (NCC) lost its ancient lithospheric mantle root during the Phanerozoic. The temporal sequence, spatial extent, and cause of the lithospheric thinning, however, continue to be debated. Here we report olivine compositions, whole-rock Re–Os isotopic systematics, and platinum-group element abundances of small ( 92) lithospheric mantle is largely absent. Osmium isotopic data suggest the Wudi peridotites experienced melt depletion primarily during the Paleoproterozoic (~ 1.8 Ga), although an Archean Os model age for one xenolith indicates incorporation of a minor component of Archean lithospheric mantle. These data suggest that a previously unrecognized Paleoproterozoic orogenic event removed and replaced the original Archean lithospheric mantle beneath the sedimentary basin at the southern edge of the Bohai Sea. By contrast, the Fuxin peridotites, entrained in Cretaceous basalts that crop out along the northern edge of the eastern NCC, document the coexistence of both ancient (≥ 2.3 Ga) and modern lithospheric mantle components. Here, the original Late Archean–Early Paleoproterozoic lithospheric mantle was, at least partially, removed and replaced prior to 100 Ma. Combined with literature data, our results show that removal of the original Archean lithosphere occurred within Proterozoic collisional orogens, and that replacement of Precambrian lithosphere during the Mesozoic may have been spatially associated with the collisional boundaries and the strike–slip Tan–Lu fault, as well as the onset of Paleo-Pacific plate subduction.

Tungsten concentration and isotopic data, coupled with highly siderophile element (HSE) concentration and Os isotopic data for = 3.66 billion year-old ultramafic, mafic, and felsic supracrustal rocks from the Nuvvuagittuq Greenstone Belt, were investigated to place additional constraints on the nature and origin of W-182 heterogeneities in the early Earth. The absolute and relative abundances of HSE in the mafic and ultramafic rocks are generally similar to those in modern rocks with comparable MgO contents. Further, most samples plot close to 3.8 to 4.4 Ga reference lines on a Re-187-Os-187 isochron diagram, indicating that HSE abundances in most Nuvvuagittuq samples remained undisturbed by post-Eoarchean metamorphic events. All Nuvvuagittuq samples analyzed show well-resolved W-182 excesses, ranging from + 6 to + 17 ppm, compared with the modern isotopic composition of W. The observed level of HSE abundances, coupled with the W-182 enrichments of these rocks is seemingly inconsistent with their derivation from mantle that was isolated from a HSE-rich and W-182-depleted late accretionary component. However, the absence of correlation between W and MgO contents, as well as variable W enrichment relative to elements with similar incompatibilities suggest that the W in the Nuvvuagittuq samples involved fluid transport of the W in either the crust or the mantle, and that it has little genetic relationship with the HSE. Given the lack of evidence for extensive redistribution of W in the crust, the HSE and W elemental and isotopic systematics of the Nuvvuagittuq rocks may be explained by a model whereby peridotitic mantle, with modern-like HSE abundances, was metasomatized by fluids derived from a W-182-rich crustal component that had been recycled into the mantle via subduction or delamination. The source of the W-182 excess carried by this crustal component remains enigmatic. It was most likely inherited from either pre-late accretionary, or early-depleted parental mantle reservoirs. (C) 2014 Elsevier B.V. All rights reserved.

Concentrations of the highly siderophile elements (HSE) Re, Os, Ir, Ru, Pt, and Pd and 187 Os/ 188 Os isotopic compositions are reported for seven Apollo 17 impact melt rocks. These data are used to examine the dominant chemical signature of the impactor that formed the melts. Six of the samples (72355, 72435, 72535, 76035, 76055, and 76135) have poikilitic textures; one sample (73235) has an aphanitic texture. Data for the samples define linear correlations when Ir is plotted versus other HSE concentrations, with y -intercepts indistinguishable from zero for most HSE in most rocks. Scatter about some of the trends, and occasional trends with positive y -intercepts, indicate either mixing of additional components that are heterogeneously distributed within several rocks, or modest fractionation of some HSE by volatilization, crystal fractionation, or other processes, during formation and evolution of the melt sheet. There is no statistical difference between the aphanitic and poikilitic samples in terms of HSE ratios after visible granulitic clasts were removed from aphanite 73235. Hence, earlier speculations that the two types of impact melt rocks at this site may have been generated by different impactors are not supported by our data. Most Apollo 17 samples examined here and in prior studies are characterized by very similar HSE signatures, consistent with a common impactor. These samples are characterized by elevated Ru/Ir, Pd/Ir, and Re/Os, relative to most chondrites. Collectively, the data indicate that the impactor was characterized by the following HSE ratios (2 σ ): Re/Ir 0.093 ± 0.020, Os/Ir 1.03 ± 0.28, Ru/Ir 1.87 ± 0.30, Pt/Ir 2.36 ± 0.31, Pd/Ir 1.85 ± 0.41, and present-day 187 Os/ 188 Os of 0.1322 ± 0.0013. The results most likely mean that the impactor was a body with a bulk composition that was just outside the range of meteoritic compositions currently sampled on Earth.

We present a new approach to obtain rapid and precise (0.1 % or better) Os isotopic compositions for small (nanogram to sub-nanogram) amounts of Os extracted from geological samples using static collection with Faraday cups and amplifiers equipped with 1012 Ω resistors, by negative thermal ionization mass spectrometry (N-TIMS/Triton Plus). The results show that the measurement repeatability of Os isotopic ratios (190Os/188Os, 187Os/188Os and 186Os/188Os) changes as a function of signal intensity that varied from 0.005 to 0.05 V for 192OsO3− (here and throughout the text, given intensities are equivalent signals that would be obtained using a 1011 Ω standard amplifier; 0.001 V (1 mV) is equivalent to ~ 62500 cps). At 192OsO3− ion beams greater than 0.02 V with 50 ratios measured over a 10 min acquisition time, the repeatability on 187Os/188Os, as well as 186Os/188Os and 190Os/188Os, is better than that obtained by the conventional peak-hopping electron multiplier (SEM) at 192OsO3− = ~ 200,000 cps with 500–100 ratios measured over a 30–60 min acquisition time. At 192OsO3− ion beams of ~ 0.04 V or above, the 187Os/188Os and 186Os/188Os data for loads of 1 and 0.1 ng Os reference materials can be measured with a repeatability of

Accurately dating the formation and modification of Earth’s sub-cratonic mantle still faces many challenges, primarily due to the long and complex history of depletion and subsequent metasomatism of this reservoir. In an attempt to improve this, we carried out the first study on peridotites from the Kaapvaal craton (Finsch Mine) that integrates results from Re-Os, Lu-Hf, Sm-Nd and Sr-isotope systems together with analyses of major-, trace- and platinum-group elements. The Finsch peridotites are well-suited for such a study because certain compositional features reflect they were highly depleted residues of shallow melting (1.5 GPa) at ambient Archean mantle temperatures. Yet, many of them have overabundant orthopyroxene, garnet and clinopyroxene compared to expected modal amounts for residues from partial melting. Finsch peridotites exhibit a wide range of rhenium depletion ages (TRD) from present day to 2.7 Ga, with a prominent mode at 2.5 Ga. This age overlaps well with a Lu-Hf isochron of 2.64 Ga (eHf (t) = +26) which records silico-carbonatitic metasomatism of the refractory residues. This late Archean metasomatism is manifested by positive correlations of Pt/Ir and Pd/Ir with 187Os/188Os ratios and good correlations of modal amounts of silicates, especially garnet, with Os isotope ratios. These correlations suggest that the Highly Siderophile Elements (HSE) and incompatible element reenrichment and modal metasomatism result from one single major metasomatic event at late Archean. Our detailed study of Finsch peridotites highlights the importance of using multiple isotopic systems, to constrain the ages of events defining the evolution of lithospheric mantle. The Re-Os isotope system is very effective in documenting the presence of Archean lithosphere, but only the oldest TRD ages may accurately date or closely approach the age of the last major partial melting event. For a meaningful interpretation of the Re-Os isotope systematics the data must be combined with HSE patterns, trace-element compositions and ideally other isotopic systems, e.g. Lu-Hf. This is highlighted by the widespread evidence in Finsch peridotites of Pt, Pd and Re enrichment through significant Base Metal Sulfide (BMS) addition (mainly in the range of 0.002–0.08 wt%) that systematically shifts the mode of TRD model ages to younger ages.

Concentrations of trace elements in orthopyroxenes and clinopyroxenes, and the Sr, Nd, Hf and Pb isotopic compositions of clinopyroxenes from 11 well-characterized spinel peridotite xenoliths carried in the ~ 30 Ma Yangyuan alkali basalts, North China Craton, reveal a complex history of chemical modification of the lithospheric mantle. The clinopyroxenes were separated from a suite of peridotites for which whole-rock Re–Os isotopic systematics have previously suggested a melt depletion event at ~ 1.8 Ga, and were chosen to span a range of rare earth element (REE) patterns with (La/Yb) N = 0.13 to 8.2. Present-day isotopic compositions are highly variable: 87 Sr/ 86 Sr = 0.70229 to 0.70443, e Nd = − 0.6 to + 24, 206 Pb/ 204 Pb = 15.74 to 19.08, and e Hf = + 13.5 to + 167. Partial melting models indicate that the Yangyuan clinopyroxenes have light REE (LREE) abundances that are too high to be pristine residues of fractional melting, reflecting subsequent enrichment of the LREE, e.g., via melt addition. Ancient melt addition accounts for the decoupling observed between Nd and Hf isotopic data for most samples, although a few samples may also have been modified by recent melt addition, shortly before the entrainment of the xenoliths into the host basalt. Strontium, Nd and Pb isotopic systems provide no useful age constraints for this suite, although some samples have Paleoproterozoic model ages. By contrast, Yangyuan clinopyroxenes yield a Lu–Hf correlation trend corresponding to an apparent age of 1.66 ± 0.10 Ga (2 σ ) that is within uncertainty of their whole-rock Os model age (1.8 ± 0.2 Ga). Given that the crust in this area originally formed during the Archean, these results suggest mantle lithosphere removal and replacement during the Paleoproterozoic. Our data demonstrate that, in some instances, the Lu–Hf isotope system may be used as a complement to the whole‐rock Re–Os isotope system in dating melt depletion of peridotites.

The petrology, mineral compositions, whole rock major/trace element concentrations, including highly siderophile elements, and Re–Os isotopes of 99 peridotite xenoliths from the central North China Craton were determined in order to constrain the structure and evolution of the deep lithosphere. Samples from seven Early Cretaceous–Tertiary volcanic centers display distinct geochemical characteristics from north to south. Peridotites from the northern section are generally more fertile (e.g., Al2O3 = 0.9–4.0%) than those from the south (e.g., Al2O3 = 0.2–2.2%), and have maximum whole-rock Re-depletion Os model ages (TRD) of ∼1.8 Ga suggesting their coeval formation in the latest Paleoproterozoic. By contrast, peridotites from the south have maximum TRD model ages that span the Archean–Proterozoic boundary (2.1–2.5 Ga). Peridotites with model ages from both groups are found at Fansi, the southernmost locality in the northern group, which likely marks a lithospheric boundary. The Neoarchean age of the lithospheric mantle in the southern section matches that of the overlying crust and likely reflects the time of amalgamation of the North China Craton via collision between the Eastern and Western blocks. The Late Paleoproterozoic (∼1.8 Ga) lithospheric mantle beneath the northern section is significantly younger than the overlying Archean crust, indicating that the original lithospheric mantle was replaced in this region, either during a major north–south continent–continent collision that occurred during assembly of the Columbia supercontinent at ∼1.8–1.9 Ga, or from extrusion of ∼1.9 Ga lithosphere from the Khondalite Belt beneath the northern Trans-North China Orogen, during the ∼1.85 Ga continental collision between Eastern and Western blocks. Post-Cretaceous heating of the southern section is indicated by high temperatures (>1000 °C) recorded in peridotites from the 4 Ma Hebi suite, which are significantly higher than the temperatures recorded in peridotites from the nearby Early Cretaceous Fushan suite (

Xenolithic peridotites having a similar range of major element compositions from two nearby localities in the Trans-North China Orogen, North China Craton, provide a rare opportunity to explore effects resulting from both primary partial melting and secondary processes on Os isotopes and highly siderophile element (HSE) abundances. HSE patterns of peridotites from Hannuoba are similar to those of orogenic peridotite massifs worldwide, but are rare for xenolithic peridotites. These patterns can be explained by relatively low degrees of melt depletion, coupled with long-term preservation of sulfides. By contrast, peridotites from Yangyuan have major element compositions similar to or slightly more depleted than Hannuoba xenoliths, but are characterized by distinct, highly fractionated HSE patterns with lower total HSE abundances and Os, Pd and Re depletions relative to Ir. Some of the latter HSE characteristics must reflect secondary processes. The low S and Se contents of Yangyuan peridotites, coupled with scarcity of observable sulfides, suggest that they experienced sulfide breakdown, possibly as a result of interaction with a S-undersaturated melt/fluid. This may have occurred under oxidizing conditions, as suggested by the somewhat higher ƒO 2 recorded in the Yangyuan peridotites compared to the Hannuoba peridotites, as well as the metal-deficient composition of rare, mono-sulfide-solid solution (mss) sulfides within the Yangyuan peridotites. We speculate that under such conditions, Os, Pd, and possibly Re, more strongly partition into a sulfide liquid, or the oxidizing medium (melt or fluid), than Ir and Pt and, thus, become depleted. These effects would have been imposed on original patterns that were similar to those in the Hannuoba suite. The good correlation between 187 Os/ 188 Os and major element indices of melt depletion in the Yangyuan rocks, coupled with the poor correlation between 187 Os/ 188 Os and 187 Re/ 188 Os, suggests that the S, Os, Pd and Re removal was recent. Hence, the long-term Re–Os isotopic systematics of these rocks would not have been affected, and Re depletion model ages, based on Os isotopes, remain viable to constrain the timing of melt deletion in these peridotites. The similarity of model age distributions between Yangyuan and Hannuoba peridotites (T RD = 0 to 1.7 and 0 to 1.5 Ga, respectively) is consistent with this, and further indicates that these peridotites formed in the Paleoproterozoic.

Automatic greenhouse production is quite new in China. For the development of our modern agriculture it is a significant issue to accurately formulate the simulation growth models of greenhouse plants in different environments. The objective of our study was to develop an approach to calibrate the growth model of greenhouse crop. In this paper, an adaptive genetic algorithm (GA) is proposed and evaluated for this issue. This new algorithm is composed of two GAs. The primary one is utilized to parameterize the growth model and the secondary is to determine the algorithmic parameters of the primary GA. The superior performance of this new procedure is demonstrated through its applications to three test functions and the greenhouse optimization problems compared with other two GAs. This presented technique may be a fine framework for the development of similar application for complex biological models that require parameterization when a new set of environmental conditions arises or there is a need to account for differences among subspecies or varieties.