平壤柳京饭店基岩变形特性现场测定

平壤柳京饭店是一座正在建设中的摩天大楼,共105层,高323.55m。地基主要由细粒砂岩、粉砂岩及粉砂质粘板岩组成,其中前者占50%以上。现场试验采用一种经过改进的BJ-110钻孔弹模计,用它测定的模量就是真实值,不需要任何修正。测试成果表明细粒砂岩的弹性模量介于6—14GPa,粉砂岩约为21GPa,粉砂质粘板岩小于3GPa。大楼建设过程中曾进行了沉降观测,根据大楼自重及沉降值反算基础的平均变形模量为6GPa,与测量结果对照,两者比较接近。本文还提出了一种估算基础整体变形模量的近似方法。     

Early Archean crustal evolution of the Jack Hills Zircon source terrane inferred from Lu-Hf, Pb/Pb, and δO systematics of Jack Hills zircons

Several lines of isotopic evidence - the most direct of which is from Hadean Jack Hills zircons - suggest a very early history of crust formation on Earth that began by about 4.5 Ga. To constrain both the fate of the reservoir for this crust and the nature of crustal evolution in the sediment source region of the Jack Hills, Western Australia, during the early Archean, we report here initial ¹⁷⁶Hf/¹⁷⁷Hf ratios and δ¹⁸O systematics for <4 Ga Jack Hills zircons. In contrast to the significant number of Hadean zircons which contain highly unradiogenic ¹⁷⁶Hf/¹⁷⁷Hf requiring a near-zero Lu/Hf reservoir to have separated from the Earth’s mantle by 4.5 Ga, Jack Hills zircons younger than ca. 3.6 Ga are more radiogenic than -13ε (CHUR) at 3.4 Ga in contrast to projected values at 3.4 Ga of -20ε for the unradiogenic Hadean reservoir indicating that some later juvenile addition to the crust is required to explain the more radiogenic younger zircons. The shift in the Lu-Hf systematics together with a narrow range of mostly mantle-like δ¹⁸O values among the <3.6 Ga zircons (in contrast to the spread towards sedimentary δ¹⁸O among Hadean samples) suggests a period of transition between 3.6 and 4 Ga in which the magmatic setting of zircon formation changed and the highly unradiogenic low Lu/Hf Hadean crust ceased to be available for intracrustal reworking. Constraining the nature of this transition provides important insights into the processes of crustal reworking and recycling of the Earth’s Hadean crust as well as early Archean crustal evolution.     

Application of precise 142Nd/144Nd analysis of small samples to inclusions in diamonds (Finsch,South Africa) and Hadean Zircons (Jack Hills,Western Australia)

¹⁴⁶Sm–¹⁴²Nd and ¹⁴⁷Sm–¹⁴³Nd systematics were investigated in garnet inclusions in diamonds from Finsch (S. Africa) and Hadean zircons from Jack Hills (W. Australia) to assess the potential of these systems as recorders of early Earth evolution. The study of Finsch inclusions was conducted on a composite sample of 50 peridotitic pyropes with a Nd model age of 3.3 Ga. Analysis of the Jack Hills zircons was performed on 790 grains with ion microprobe ²⁰⁷Pb/²⁰⁶Pb spot ages from 3.95 to 4.19 Ga. Finsch pyropes yield 100 × ?¹⁴²Nd = ? 6 ± 12 ppm, ?¹⁴³Nd = ? 32.5, and ¹⁴⁷Sm/¹⁴⁴Nd = 0.1150. These results do not confirm previous claims for a 30 ppm ¹⁴²Nd excess in South African cratonic mantle. The lack of a ¹⁴²Nd anomaly in these inclusions suggests that isotopic heterogeneities created by early mantle differentiation were remixed at a very fine scale prior to isolation of the South African lithosphere. Alternatively, this result may indicate that only a fraction of the mantle experienced depletion during the first 400 Myr of its history. Analysis of the Jack Hills zircon composite yielded 100 × ?¹⁴²Nd = 8 ± 10 ppm, ?¹⁴³Nd = 45 ± 1, and ¹⁴⁷Sm/¹⁴⁴Nd = 0.5891. Back-calculation of this present-day ?¹⁴³Nd yields an unrealistic estimate for the initial ?¹⁴³Nd of ? 160 ?-units, clearly indicating post-crystallization disturbance of the ¹⁴⁷Sm–¹⁴³Nd system. Examination of ^146,147Sm–^142,143Nd data reveals that the Nd budget of the Jack Hills sample is dominated by non-radiogenic Nd, possibly contained in recrystallized zircon rims or secondary subsurface minerals. This secondary material is characterized by highly discordant U–Pb ages. Although the mass fraction of altered zircon is unlikely to exceed 5–10% of total sample, its high LREE content precludes a reliable evaluation of ¹⁴⁶Sm–¹⁴²Nd systematics in Jack Hills zircons.     

High abundance of early Archaean grains and the age distribution of detrital zircons in a sillimanite-bearing quartzite from Mt Narryer, Western Australia

SHRIMP U–Pb analyses are reported for a detrital zircon population from a sample of sillimanite-bearing quartzite from the Narryer sedimentary succession in the Narryer Terrane of the northwestern Yilgarn Craton. The detrital zircons define two distinctive age groups, an older group from 4000 Ga to 4280 Ma and a younger group from 3750 to 3250 Ma. The abundance of older group zircons of about 12% far exceeds the abundance of about 2% reported in the first discovery of ancient zircons in a quartzite from the Narryer metasediments, and is equivalent to the abundance of >3900 Ma zircons in metaconglomerate sample W74 from the Jack Hills, confirmed by new measurements reported in this paper. Most analyses of the Narryer and the Jack Hills detrital zircon populations are discordant. The Jack Hills zircon analyses are dominated by strong recent Pb loss whereas the Narryer zircon analyses have had a more complex history and have experienced at least one Pb loss event, possibly associated with the high-grade metamorphism at ca. 2700 Ma, and a further disturbance of the U–Pb systems during relatively recent times. Although the number of analyses is limited and many of the zircon analyses are discordant, the age distributions of the older (>3900 Ma) zircons from the Narryer and Jack Hills samples are different, suggesting a complex provenance for the ancient zircons. The distribution of ages in the younger population of Mt Narryer zircons is similar to that reported for zircons from the surrounding Meeberrie gneiss, supporting previous suggestions that zircons from the gneisses or their precursors were a major contributor to the detrital zircon suite. The younger zircon population from Jack Hills sample (W74), lacks the strong age peak from 3600 to 3750 Ma present in the Narryer zircon population, and conversely the strong zircon age group at ca. 3350–3500 Ma in the Jack Hills population is only weakly represented in the Narryer zircon population. The age distributions for the Narryer and the Jack Hills zircon populations are taken as benchmarks for comparing zircon populations from quartzite occurrences elsewhere in the Yilgarn Craton.     

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

We report δ⁷Li, Li abundance ([Li]), and other trace elements measured by ion probe in igneous zircons from TTG (tonalite, trondhjemite, and granodiorite) and sanukitoid plutons from the Superior Province (Canada) in order to characterize Li in zircons from typical Archean continental crust. These data are compared with detrital zircons from the Jack Hills (Western Australia) with U–Pb ages greater than 3.9 Ga for which parent rock type is not known. Most of the TTG and sanukitoid zircon domains preserve typical igneous REE patterns and CL zoning. [Li] ranges from 0.5 to 79 ppm, typical of [Li] in continental zircons. Atomic ratios of (Y + REE)/(Li + P) average 1.0 ± 0.7 (2SD) for zircons with magmatic composition preserved, supporting the hypothesis that Li is interstitial and charge compensates substitution of trivalent cations. This substitution results in a relatively slow rate of Li diffusion. The δ⁷Li and trace element data constrain the genesis of TTGs and sanukitoids. [Li] in zircons from granitoids is significantly higher than from zircons in primitive magmas in oceanic crust. TTG zircons have δ⁷Li (3 ± 8‰) and δ¹⁸O in the range of primitive mantle-derived magmas. Sanukitoid zircons have average δ⁷Li (7 ± 8‰) and δ¹⁸O higher than those of TTGs supporting genesis by melting of fluid-metasomatized mantle wedge. The Li systematics in sanukitoid and TTG zircons indicate that high [Li] in pre-3.9-Ga Jack Hills detrital zircons is a primary igneous composition and suggests the growth in proto-continental crust in magmas similar to Archean granitoids.     

节理非线性问题的约束函数法

接触非线性主要表现在其接触状态的突变而导致的非光滑性,这种非光滑性可以通过约束函数进行光滑逼近,进而可以用Newton法得到近似解,此方法称之为约束函数法。岩土工程中常用的Goodman单元就是一种类型的接触模型,但其参数的确定及计算的收敛性都存在着一定的困难。然而把约束函数应用到常规的Goodman单元中则可以解决上述困难,在详细地给出了其有限元法后,给出了处理刚体位移的一种简便方法。作为算例,给出了叠梁和三峡3# 坝段坝基稳定性的计算结果。     

Sub-micron scale distributions of trace elements in zircon

Sub-micron scale zoning of Ti concentrations and correlations between concentrations of Ti and other trace elements (P, Ce, and Y) and cathodoluminescent (CL) banding is observed in natural zircons. Ion images were made using the Caltech Microanalysis Center’s CAMECA NanoSIMS 50L with an O⁻ primary beam focused to ~300 nm on the sample surface. The high spatial resolution of this technique allows for interrogation of chemical variations at or below the scale of CL banding in natural zircons. Images produced in this manner display two types of correlations among Ti, P, Ce, and Y (which appears to be a proxy for CL intensity): strong (correlation coefficients >0.8) and subtle (correlation coefficients ~0.15–0.4). Strongly correlated images, which display Ti variations of ca. a factor of 3 between adjacent CL bands and overall elevated trace element concentrations in CL-dark bands, were found within an oscillatory-zoned, trace element enriched sector of a CL sector-zoned zircon. Three possible causes for such correlations include: temperature-dependent equilibrium partitioning, trace element partitioning limited by diffusion in the host melt and surface-controlled, non-equilibrium growth. Comparison of our data with the expected results of these processes suggests that: (1) Ti partitioning in zircon is dependent upon non-equilibrium effects in addition to temperature and/or (2) the incorporation of elements that co-vary with Ti in zircon (e.g., Y, P and Ce) is also temperature-dependent. Sub-micron scale, high-Ti regions are also found within Proterozoic Adirondack and >4 Ga Jack Hills zircons as well as trace element enrichments (including Ti) along cracks within Jack Hills zircons.     

Coupled THM processes in EDZ of crystalline rocks using an elasto-plastic cellular automaton

This paper aims at a numerical study of coupled thermal, hydrological and mechanical processes in the excavation disturbed zones (EDZ) around nuclear waste emplacement drifts in fractured crystalline rocks. The study was conducted for two model domains close to an emplacement tunnel; (1) a near-field domain and (2) a smaller wall-block domain. Goodman element and weak element were used to represent the fractures in the rock mass and the rock matrix was represented as elasto-visco-plastic material. Mohr–Coulomb criterion and a non-associated plastic flow rule were adopted to consider the viscoplastic deformation in the EDZ. A relation between volumetric strain and permeability was established. Using a self-developed EPCA^2D code, the elastic, elasto-plastic and creep analyses to study the evolution of stress and deformations, as well as failure and permeability evolution in the EDZ were conducted. Results indicate a strong impact of fractures, plastic deformation and time effects on the behavior of EDZ especially the evolution of permeability around the drift.     

A novel interface element with asymmetric nodes and its application on concrete-faced rockfill dam

Based on the Goodman element, the Guyan reduction method is introduced to develop the interface element with asymmetric nodes, which accomplishes the coarse-fine mesh transition between soil and structure in finite element models by providing a different number of nodes on the two sliding surfaces. The number of Gauss points is greater than that of the traditional Goodman element, which ensures its accuracy. The developed interface element is employed in the dynamic elasto-plastic analysis of CFRDs. The results indicate that the use of the constructed interface element can significantly decrease the number of elements with little influence on the accuracy.     

Proterozoic volcanism in the Jack Hills Belt,Western Australia: Some implications and consequences for the World's oldest zircon population

Rare felsic volcanic rocks of dacitic to rhyolitic composition occur in the central part of the Jack Hills metasedimentary belt in the Narryer Terrane of Western Australia, interleaved with clastic sedimentary rocks and amphibolite. Representative samples of the four identified felsic volcanic units reveal a similar complex pattern of zircon age distribution, with all samples containing zircon populations at ∼3.3–3.4, ∼3.0–3.1, ∼2.6 and ∼1.8–1.9 Ga. The ∼3.3–3.4 Ga zircons show well-developed oscillatory zoning in cathodoluminescence (CL) images and are interpreted as inherited igneous zircon derived from granitic precursors, similar to the ∼3.3 Ga trondhjemitic granitoids currently exposed along the northern and southern margins of the belt. The ∼3.0–3.1 Ga zircons also reveal well-developed oscillatory zoning in CL and are most likely derived from granitoid and/or volcanic rocks of this age, as recorded in the Murchison domain to the south and possibly also present in the Narryer Terrane. The ∼2.6 Ga population matches the age of nearby late Archean granitoids intruding the Jack Hills belt and their oscillatory zoning and U–Th chemistry is consistent with their origin from such a source. The youngest discrete group of zircon grains, with ages ranging from ∼1970 to ∼1775 Ma, show strong oscillatory zoning and average Th/U ratios of 0.76, features consistent with an igneous origin. These younger zircons are therefore interpreted as defining the age of crystallisation of the volcanic rocks. These results establish that the Jack Hills metasedimentary belt contains significant post-Archean components. Taken together with similar results obtained from zircon occurring as detrital grains in clastic sedimentary rocks at Jack Hills, these results overturn the generally-accepted view that the belt is entirely Archean in age and that sedimentation was completed around 3.0 Ga ago. Instead, there is a distinct possibility that much of the material currently exposed in the Jack Hills belt formed in the Proterozoic. A further implication of this study is that the metamorphism affecting these rocks also occurred in the Proterozoic and consequently the rocks should not be considered as forming an Archean greenstone or metasedimentary belt. The paucity of zircons >4 Ga in the known Proterozoic sedimentary rocks and their total absence in the felsic volcanic rocks suggests that such ancient source rocks were no longer present in the area.     

Correlated microanalysis of zircon: Trace element, δO, and U-Th-Pb isotopic constraints on the igneous origin of complex >3900 Ma detrital grains

The origins of >3900 Ma detrital zircons from Western Australia are controversial, in part due to their complexity and long geologic histories. Conflicting interpretations for the genesis of these zircons propose magmatic, hydrothermal, or metamorphic origins. To test the hypothesis that these zircons preserve magmatic compositions, trace elements [rare earth elements (REE), Y, P, Th, U] were analyzed by ion microprobe from a suite of >3900 Ma zircons from Jack Hills, Western Australia, and include some of the oldest detrital zircons known (4400-4300 Ma). The same ∼20 μm domains previously characterized for U/Pb age, oxygen isotope composition (δ¹⁸O), and cathodoluminescence (CL) zoning were specifically targeted for analysis. The zircons are classified into two types based on the light-REE (LREE) composition of the domain analyzed. Zircons with Type 1 domains form the largest group (37 of 42), consisting of grains that preserve evolved REE compositions typical of igneous zircon from crustal rocks. Grains with Type 1 domains display a wide range of CL zoning patterns, yield nearly concordant U/Pb ages from 4400 to 3900 Ma, and preserve a narrow range of δ¹⁸O values from 4.7‰ to 7.3‰ that overlap or are slightly elevated relative to mantle oxygen isotope composition. Type 1 domains are interpreted to preserve magmatic compositions. Type 2 domains occur in six zircons that contain spots with enriched light-REE (LREE) compositions, here defined as having chondrite normalized values of La_N > 1 and Pr_N > 10. A subset of analyses in Type 2 domains appear to result from incorporation of sub-surface mineral inclusions in the analysis volume, as evidenced by positively correlated secondary ion beam intensities for LREE, P, and Y, which are anti-correlated to Si, although not all Type 2 analyses show these features. The LREE enrichment also occurs in areas with discordant U/Pb ages and/or high Th/U ratios, and is apparently associated with past or present radiation damage. The enrichment is not attributed to hydrothermal alteration, however, as oxygen isotope ratios in Type 2 domains overlap with magmatic values of Type 1 domains, and do not appear re-set as might be expected from dissolution or ion-exchange processes operating at variable temperatures. Thus, REE compositions in Type 2 domains where mineral inclusions are not suspected are best interpreted to result from localized enrichment of LREE in areas with past or present radiation damage, and with a very low fluid/rock ratio. Correlated in situ analyses allow magmatic compositions in these complex zircons to be distinguished from the effects of secondary processes. These results are additional evidence for preservation of magmatic compositions in Jack Hills zircons, and demonstrate the benefits of detailed imaging in studies of complicated detrital zircons of unknown origin. The data reported here support previous interpretations that the majority of >3900 Ma zircons from the Jack Hills have an origin in evolved granitic melts, and are evidence for the existence of continental crust very early in Earth’s history.     

Ophiolitic trondhjemites: a possible analogue for Hadean felsic 'crust'

It has been argued that >4.0 Ga detrital zircons preserved in sediments of the Jack Hills, western Australia, preserve evidence for a well‐developed continental crust on the Earth at 4.4–4.5 Ga ago. Here, it is shown that there are geochemical similarities between the Jack Hills zircons and the zircons found in trondhjemites in ophiolite sequences, suggesting that the Earth's first felsic crust may have formed in a manner analogous to modern ophiolitic trondhjemites. The trondhjemites of the Oman ophiolite were formed by the hydrous partial melting of the upper (hornblende) gabbros in the roof‐zone of an axial magma chamber. A similar hydrous melting of a mafic protolith may have operated during the Hadean, to create small volumes of felsic rocks within a dominantly mafic crust, obviating the need to postulate a felsic continental crust at 4.4–4.5 Ga.     

测定岩体变形特性的BEM-1-D76型钻孔弹模仪

本文对本所研制的BEM-1-D76型钻孔弹模仪的基本原理和各项技术指标、测试方法及现场使用情况作了介绍,并且与国外同类仪器进行了比较,从而表明该仪器是现场测定岩体变形特性的有效新设备。     

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

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

数值流形方法在P型自适应分析中的初探

将数值流形方法应用于P型自适应分析，推导单元不同阶次的位移函数及其单元刚度矩阵表达式，引入了对应情况下的节理单元及其刚度矩阵，编制了计算程序，数值算例表明该算法可行。     

深基坑开挖的有限元模拟与实验研究

本文根据Ｇｏｏｄｍａｎ接触面单元和Ｄｕｎｃａｎ－Ｃｈａｎｇ模型编制了二维有限元程序ＳＪＫ。考虑了工程实际中分步开挖、支撑等一系列施工过程,利用模型试验对该程序进行了验证,实测结果与理论计算两者较为接近,为工程设计和施工提供参考。     

接触面单元计算方法探讨

针对接触面单元的构造特性,提出了一种接触面单元计算方法。该方法有效地克服了Goodman接触面单元有可能存在的两侧单元相互嵌入的缺陷,解决了单元应力误差难以控制的问题。详细介绍了该方法的数值实现过程,使其在数值计算中易于使用,并通过数值模型验证了该方法的合理性与有效性。     

淋溪河水电站大野坪滑坡体渗流应力耦合分析

软弱夹层的渗流、应力耦合作用是影响滑坡体稳定性的主要因素。为正确评价含软弱夹层的大野坪滑坡体的整体稳定性,基于Biot固结微分方程,采用虚位移原理,按照Goodman单元的形成格式,引入Desai单元控制嵌入的思想,构造了二维4节点耦合薄层单元,给出了能够模拟滑坡体蠕变特性的弹黏塑性本构模型,编制了相应的有限元程序,并用孔压实测数据检验了程序的正确性。同时,对大野坪滑坡体处于正常蓄水位和水位骤降两种工况的渗流场、应力场进行了非线性有限元耦合分析。结果表明：正常蓄水位,滑坡体处于稳定状态;而水位骤降工况,使滑坡体中前部孔隙水压力、位移、剪应力水平等均有大幅度地提高,塑性区沿着软弱夹层向上也有较大发展,致使滑坡体有可能沿着软弱夹层在中前部发生局部折线滑动,对滑坡体的稳定性极为不利。最后,采用刚体极限平衡法,对耦合分析的结果进行校核,两者结论一致。该研究成果为全面评价淋溪河水电站建设的可行性提供了重要的理论依据,建立耦合单元研究软弱夹层耦合特性的方法,为其他含软弱夹层的滑坡体的稳定性评价提供了有益的借鉴。     

Analysis of underground openings with a distinct shear zone

SummaryAnalysis of Underground Openings with a Distinct Shear Zone A procedure for the analysis of deformations and stresses in the surrounding of an underground opening is demonstrated. For duplication of rock discontinuities in the finite element analysis the joint element of Goodman, Taylor and Brekke is used. A special technique was developed in order to consider the limited tensile strength, the reduction of shearing strength after reaching the peak strength and the limited closure of the joint. A Coulomb failure criterion is used for determining shear fracture. Results of two examples of tunnels with one distinct joint are shown.

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ZusammenfassungBerechnung von Felshohlräumen mit einer ausgeprägten Scherzone Ein Verfahren zur Berechnung der Verformungen und Spannungen in dem einen Hohlraum umschließenden Gebirge wird erläutert. Zur Nachbildung von Diskontinuitäten wird das von Goodman, Taylor und Brekke entwickelte Kluftelement verwendet. Für dieses linienförmige Element wurde eine spezielle Rechentechnik entwickelt, die die begrenzte Zugfestigkeit der Kluft, den Abfall der Scherfestigkeit nach Erreichen der Spitzenfestigkeit auf die Restscherfestigkeit und die begrenzte Zusammendrückbarkeit erfaßt. Zur Bestimmung des Schubbruches wird das Coulombsche Bruchkriterium benutzt. Berechnungsergebnisse von zwei Beispielen aus dem Tunnelbau mit einer diskret nachgebildeten Großkluft werden gezeigt.

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RésuméAnalyse numérique des excavations en roche parcourue par un joint On montre une méthode pour calculer les déformations et les contraintes autour d'un tunnel. Dans la méthode des Eléments Finis on prend un élément développé par Goodman, Taylor et Brekke pour copier des joints. Une méthode de calcul a été développée pour tenir compte de la résistance de traction limitée, la réduction de l'effort de cisaillement après avoir exhausté la résistance de pointe et la fermeture limitée des joints. Pour déterminer la rupture de cisaillement le critère de Coulomb est utilisé. A deux exemples montrés la roche est parcourue par un grand joint.

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Abstract of a short report delivered at the International Symposium on Numerical Methods in Soil Mechanics and Rock Mechanics, Karlsruhe, 1975.

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With 8 Figures     

CO<Subscript>2</Subscript> fluid inclusions in Jack Hills zircons

The discovery of Hadean to Paleoarchean zircons in a metaconglomerate from Jack Hills, Western Australia, has catalyzed intensive study of these zircons and their mineral inclusions, as they represent unique geochemical archives that can be used to unravel the geological evolution of early Earth. Here, we report the occurrence and physical properties of previously undetected CO₂ inclusions that were identified in 3.36–3.47 Ga and 3.80–4.13 Ga zircon grains by confocal micro-Raman spectroscopy. Minimum P–T conditions of zircon formation were determined from the highest density of the inclusions, determined from the density-dependence of the Fermi diad splitting in the Raman spectrum and Ti-in-zircon thermometry. For both age periods, the CO₂ densities and Ti-in-zircon temperatures correspond to high-grade metamorphic conditions (≥5 to ≥7 kbar/~670 to 770 °C) that are typical of mid-crustal regional metamorphism throughout Earth’s history. In addition, fully enclosed, highly disordered graphitic carbon inclusions were identified in two zircon grains from the older population that also contained CO₂ inclusions. Transmission electron microscopy on one of these inclusions revealed that carbon forms a thin amorphous film on the inclusion wall, whereas the rest of the volume was probably occupied by CO₂ prior to analysis. This indicates a close relationship between CO₂ and the reduced carbon inclusions and, in particular that the carbon precipitated from a CO₂-rich fluid, which is inconsistent with the recently proposed biogenic origin of carbon inclusions found in Hadean zircons from Jack Hills.