湖北宜昌王家湾五峰组顶部Chondrites的发现及其环境意义

本文报道了湖北宜昌王家湾剖面五峰组笔石页岩段观音桥层发现的遗迹化石Chondrites的分布及其生态特点。结合生物相和同期上扬子海盆相对海平面的变化,分析了盆地水体底域在缺氧一富氧转折时期的古氧相变化特征：指出五峰组笔石页岩段上部地层沉积底域为典型的缺氧环境,在其与上覆观音桥段之间的沉积转换面附近发生了从无氧到有氧的转变,观音桥段中Hirnantia动物群繁盛于富氧的海底环境。     

太阳星云凝聚过程的岩石学模型：（1）球粒陨石的凝聚成因

建立类地行星区太阳星云凝聚过程的岩石学模型，对于合理解释陨石、地球和类地行星的成因关系，探讨地球起源和估算地球的整体成分都有着重要意义。本文中根据天体化学和太阳系演化学说关于太阳星云物理化学条件的基本分析，以及实验凝聚岩石学的研究结果，推断在太阳星云盘的类地行星区中可能有星云的气－固和气－液－固两种凝聚作用发生。通过对球粒陨石中球粒和基质矿物成分及结构构造特征的对比，论证了绝大多数球粒的气－液－固凝聚成因和基质的气－固凝聚成因，并讨论了球粒陨石各化学群的凝聚成因模式。     

Earth and Mars – Distinct inner solar system products

Composition of terrestrial planets records planetary accretion, core–mantle and crust–mantle differentiation, and surface processes. Here we compare the compositional models of Earth and Mars to reveal their characteristics and formation processes. Earth and Mars are equally enriched in refractory elements (1.9 × CI), although Earth is more volatile-depleted and less oxidized than Mars. Their chemical compositions were established by nebular fractionation, with negligible contributions from post-accretionary losses of moderately volatile elements. The degree of planetary volatile element depletion might correlate with the abundances of chondrules in the accreted materials, planetary size, and their accretion timescale, which provides insights into composition and origin of Mercury, Venus, the Moon-forming giant impactor, and the proto-Earth. During its formation before and after the nebular disk's lifetime, the Earth likely accreted more chondrules and less matrix-like materials than Mars and chondritic asteroids, establishing its marked volatile depletion. A giant impact of an oxidized, differentiated Mars-like (i.e., composition and mass) body into a volatile-depleted, reduced proto-Earth produced a Moon-forming debris ring with mostly a proto-Earth's mantle composition. Chalcophile and some siderophile elements in the silicate Earth added by the Mars-like impactor were extracted into the core by a sulfide melt (∼0.5% of the mass of the Earth's mantle). In contrast, the composition of Mars indicates its rapid accretion of lesser amounts of chondrules under nearly uniform oxidizing conditions. Mars’ rapid cooling and early loss of its dynamo likely led to the absence of plate tectonics and surface water, and the present-day low surface heat flux. These similarities and differences between the Earth and Mars made the former habitable and the other inhospitable to uninhabitable.     

华南泥盆纪Chondrites的特征及其对古氧相的示踪

系统描述了发育于广西六景、贵州独山、贵阳乌当泥盆纪3个浅海沉积区Cruziana遗迹相Chondrites的产出特征,结合华南泥盆纪其他5个浅海沉积区Cruziana遗迹相的Chondrites资料,对Chondtites的寄主岩系颜色分级、遗迹组构、潜穴直径、遗迹属种的综合研究表明,只有寄主岩系为深灰色-黑色,岩性为灰岩、泥灰岩,潜穴直径小于1 mm,无其他遗迹化石共生时,Chondrites才是贫氧环境标志性遗迹化石的新认识,而个体粗大的Chondrites常发育在常氧环境中.     

Transport of solids in protoplanetary disks: Comparing meteorites and astrophysical models

We review models of chondrite component transport in the gaseous protoplanetary disk. Refractory inclusions were likely transported by turbulent diffusion and possible early disk expansion, and required low turbulence for their subsequent preservation in the disk, possibly in a dead zone. Chondrules were produced locally but did not necessarily accrete shortly after formation. Water may have been enhanced in the inner disk because of inward drift of solids from further out, but likely not by more than a factor of a few. Incomplete condensation in chondrites may be due to slow reaction kinetics during temperature decrease. While carbonaceous chondrite compositions might be reproduced in a “two-component” picture (Anders, 1964), such components would not correspond to simple petrographic constituents, although part of the refractory element fractionations in chondrites may be due to the inward drift of refractory inclusions. Overall, considerations of chondrite component transport alone favor an earlier formation for carbonaceous chondrites relative to their non-carbonaceous counterparts, but independent objections have yet to be resolved.     

Oxygen isotopic compositions of chondrules: Implications for evolution of oxygen isotopic reservoirs in the inner solar nebula

We review the oxygen isotopic compositions of minerals in chondrules and compound objects composed of a chondrule and a refractory inclusion, and bulk oxygen isotopic compositions of chondrules in unequilibrated ordinary, carbonaceous, enstatite, and Kakangari-like chondrites, focusing on data acquired using secondary ion mass-spectrometry and laser fluorination coupled with mass-spectrometry over the last decade. Most ferromagnesian chondrules from primitive (unmetamorphosed) chondrites are isotopically uniform (within 3–4‰ in Δ¹⁷O) and depleted in ¹⁶O (Δ¹⁷O>−7‰) relative to amoeboid olivine aggregates (AOAs) and most calcium–aluminum-rich inclusions (CAIs) (Δ¹⁷O<−20‰), suggesting that these classes of objects formed in isotopically distinct gaseous reservoirs, ¹⁶O-poor and ¹⁶O-rich, respectively. Chondrules uniformly enriched in ¹⁶O (Δ¹⁷O<−15‰) are exceptionally rare and have been reported only in CH chondrites. Oxygen isotopic heterogeneity in chondrules is mainly due to the presence of relict grains. These appear to consist of chondrules of earlier generations and rare refractory inclusions; with rare exceptions, the relict grains are ¹⁶O-enriched relative to chondrule phenocrysts and mesostasis. Within a chondrite group, the magnesium-rich (Type I) chondrules tend to be ¹⁶O-enriched relative to the ferrous (Type II) chondrules. Aluminum-rich chondrules in ordinary, enstatite, CR, and CV chondrites are generally ¹⁶O-enriched relative to ferromagnesian chondrules. No systematic differences in oxygen isotopic compositions have been found among these chondrule types in CB chondrites. Aluminum-rich chondrules in carbonaceous chondrites often contain relict refractory inclusions. Aluminum-rich chondrules with relict CAIs have heterogeneous oxygen isotopic compositions (Δ¹⁷O ranges from −20‰ to 0‰). Aluminum-rich chondrules without relict CAIs are isotopically uniform and have oxygen isotopic compositions similar to, or approaching, those of ferromagnesian chondrules. Phenocrysts and mesostases of the CAI-bearing chondrules show no clear evidence for ¹⁶O-enrichment compared to the CAI-free chondrules. Spinel, hibonite, and forsterite of the relict refractory inclusions largely retained their original oxygen isotopic compositions. In contrast, plagioclase and melilite of the relict CAIs experienced melting and ¹⁶O-depletion to various degrees, probably due to isotopic exchange with an ¹⁶O-poor nebular gas. Several igneous CAIs experienced isotopic exchange with an ¹⁶O-poor nebular gas during late-stage remelting in the chondrule-forming region. On a three-isotope diagram, bulk oxygen isotopic compositions of most chondrules in ordinary, enstatite, and carbonaceous chondrites plot above, along, and below the terrestrial fractionation line, respectively. Bulk oxygen isotopic compositions of chondrules in altered and/or metamorphosed chondrites show evidence for mass-dependent fractionation, reflecting either interaction with a gaseous/fluid reservoir on parent asteroids or open-system thermal metamorphism. Bulk oxygen isotopic compositions of chondrules and oxygen isotopic compositions of individual minerals in chondrules and refractory inclusions from primitive chondrites plot along a common line of slope of 1, suggesting that only two major reservoirs (gas and solids) are needed to explain the observed variations. However, there is no requirement that each had a permanently fixed isotopic composition. The absolute (²⁰⁷Pb–²⁰⁶Pb) and relative (²⁷Al–²⁶Mg) chronologies of CAIs and chondrules and the differences in oxygen isotopic compositions of most chondrules (¹⁶O-poor) and most refractory inclusions (¹⁶O-rich) can be interpreted in terms of isotopic self-shielding during UV photolysis of CO in the initially ¹⁶O-rich (Δ¹⁷O−25‰) parent molecular cloud or protoplanetary disk. According to these models, the UV photolysis preferentially dissociates C¹⁷O and C¹⁸O in the parent molecular cloud and in the peripheral zones of the protoplanetary disk. If this process occurs in the stability field of water ice, the released atomic ¹⁷O and ¹⁸O are incorporated into water ice, while the residual CO gas becomes enriched in ¹⁶O. During the earliest stages of evolution of the protoplanetary disk, the inner solar nebula had a solar H₂O/CO ratio and was ¹⁶O-rich. During this time, AOAs and the ¹⁶O-rich CAIs and chondrules formed. Subsequently, the inner solar nebula became H₂O- and ¹⁶O-depleted, because ice-rich dust particles, which were depleted in ¹⁶O, agglomerated outside the snowline (5 AU), drifted rapidly towards the Sun and evaporated. During this time, which may have lasted for 3 Myr, most chondrules and the ¹⁶O-depleted igneous CAIs formed. We infer that most chondrules formed from isotopically heterogeneous, but ¹⁶O-depleted precursors, and experienced isotopic exchange with an ¹⁶O-poor nebular gas during melting. Although the relative roles of the chondrule precursor materials and gas–melt isotopic exchange in establishing oxygen isotopic compositions of chondrules have not been quantified yet, mineralogical, chemical, and isotopic evidence indicate that Type I chondrules may have formed in chemical and isotopic equilibrium with nebular gas of variable isotopic composition. Whether these variations were spatial or temporal are not known yet.     

南极格罗夫山陨石的磁化率

我国在南极格罗夫山发现并收集到大量南极陨石,需要一种无损、快速简单的分类方法。陨石磁化率(χ)的主要贡献是其中的铁镍金属,因而有可能成为一种简便有效的分类参数。同时,磁化率是陨石的一个重要物理参数。我们在国内首次开展陨石磁化率的研究,通过对模拟陨石磁化率样品的测量,证明可以通过不同取向的测量平均,将样品的大小和形状等几何因素的影响减小在仪器的测量精度范围之内。完成了首批613块南格格罗夫山陨石的磁化率测量,除普通球粒陨石外,还包括火星陨石、灶神星陨石、碳质球粒陨石、中铁陨石、橄榄陨铁、橄辉无球粒陨石等特殊类型。根据质量磁化率,可以划分大部分H、L、LL群陨石。特别重要的是,磁化率对于划分非平衡的普通球粒陨石化学群提供了更为可靠的参数。格罗夫山H群陨石的磁化率分布与南极其他地区的陨石十分相似,二者相对降落型陨石均向低质量磁化率方向平移0.2（logχ, 10^-9m³/kg）,反映了风化作用对南极陨石磁化率的平均影响程度;格罗夫山L群陨石的质量磁化率分布同样较降落型陨石偏低0.2左右,但南极其他地区的陨石与沙漠陨石的磁化率分布相似,二者均更为离散和偏低,可能反映了不同的风化程度。     

On the origin of the “kleine Kügelchen” called Chondrules

In this paper we investigate two major issues: (1) What are chondrules, and (2) why do they exist? We review the literature pertaining to each question and explore answers. We discuss the diversity of chondrules, especially with regard to their igneous textures and compositions. We review the constraints that have been placed experimentally on the thermal histories of chondrules and list those fundamental properties that all chondrule formation models must explain quantitatively in order to be considered predictive, quantitative models. We provide background on the three major classes of chondrule formation models currently being discussed, and scrutinize each with respect to how well they adhere to the experimental constraints placed on chondrule formation. Finally, we list several unresolved issues that are now or will soon be at the forefront of chondrule research.     

柴达木盆地南缘石炭系Chondrites遗迹化石的发现及其地质意义

在柴达木盆地南缘野外地质调查过程中,在祁曼塔格山前石拐子剖面下石炭统石拐子组和乌图美仁庆华铁矿附近剖面的上石炭统缔敖苏组中发现了大量Chondrites遗迹化石。经鉴定,研究区的Chondrites遗迹化石主要包括Chondrites fenxiangensis Yang,1984（分乡丛藻迹）;Chondrites filifalx Volk,1964（细枝丛藻迹）和Chondrites maqianensis Yang,1988（玛沁丛藻迹）3个遗迹种。根据研究区的Chondrites遗迹化石特征,结合岩性特征和其他实体化石资料,认为石拐子地区早石炭世为台洼沉积环境,乌图美仁庆华铁矿地区晚石炭世为局限碳酸盐岩台地沉积环境。另外,探讨了生物扰动对两个地区储集层的改造作用。该研究对恢复柴达木盆地南缘的沉积环境和古生态以及评价研究区的储集层物性具有重要的借鉴意义。     

富钙长石-橄榄石包体与其他部分典型包体W-L边的成因

球粒陨石中的富Ca、Al包体(简称CAI)形成于星云演化的最初始阶段,保存了大量星云形成和演化的各种信息。研究认为,包体的成因主要包括星云直接凝聚和熔融结晶,少部分甚至经历过高温蒸发过程。部分CAI最外层具有由一种或几种矿物组成的Warking-Lovering边(简称为W-L边),CAI和其W-L边对于认识早期星云环境和界定CAI的形成时间等均具有重要意义。目前,对于W-L边的形成过程研究并不深入,且一直存在争议。本文主要介绍了三个典型包体:C#1(富钙长石-橄榄石包体)、GRV 022459-2RI5(A型包体)和GRV 021579-3RI5(富尖晶石球粒状包体)及其W-L边的矿物岩石学和氧同位素组成特征。C#1包体明显经历过熔融结晶过程,W-L边氧同位素组成具有与包体内部矿物相似的富~(16)O同位素特征,表明W-L边的成因与包体的形成过程密切相关,形成于同一富~(16)O同位素组成区域,且W-L边属于包体熔融结晶过程后期的产物。矿物岩石学特征表明,GRV 022459-2RI5属于星云直接凝聚形成,其W-L边为包体形成过程最晚期星云凝聚产物。GRV021579-3RI5经历过熔融结晶过程,其W-L边为包体结晶最后阶段的产物。     

The nature,origin and modification of insoluble organic matter in chondrites,the major source of Earth’s C and N

All chondrites accreted ∼3.5 wt.% C in their matrices, the bulk of which was in a macromolecular solvent and acid insoluble organic material (IOM). Similar material to IOM is found in interplanetary dust particles (IDPs) and comets. The IOM accounts for almost all of the C and N in chondrites, and a significant fraction of the H. Chondrites and, to a lesser extent, comets were probably the major sources of volatiles for the Earth and the other terrestrial planets. Hence, IOM was both the major source of Earth’s volatiles and a potential source of complex prebiotic molecules.Large enrichments in D and ¹⁵N, relative to the bulk solar isotopic compositions, suggest that IOM or its precursors formed in very cold, radiation-rich environments. Whether these environments were in the interstellar medium (ISM) or the outer Solar System is unresolved. Nevertheless, the elemental and isotopic compositions and functional group chemistry of IOM provide important clues to the origin(s) of organic matter in protoplanetary disks. IOM is modified relatively easily by thermal and aqueous processes, so that it can also be used to constrain the conditions in the solar nebula prior to chondrite accretion and the conditions in the chondrite parent bodies after accretion.Here we review what is known about the abundances, compositions and physical nature of IOM in the most primitive chondrites. We also discuss how the IOM has been modified by thermal metamorphism and aqueous alteration in the chondrite parent bodies, and how these changes may be used both as petrologic indicators of the intensity of parent body processing and as tools for classification. Finally, we critically assess the various proposed mechanisms for the formation of IOM in the ISM or Solar System.     

Melting and differentiation of early-formed asteroids: The perspective from high precision oxygen isotope studies

A number of distinct methodologies are available for determining the oxygen isotope composition of minerals and rocks, these include laser-assisted fluorination, secondary ion mass spectrometry (SIMS) and UV laser ablation. In this review we focus on laser-assisted fluorination, which currently achieves the highest levels of precision available for oxygen isotope analysis. In particular, we examine how results using this method have furthered our understanding of early-formed differentiated meteorites. Due to its rapid reaction times and low blank levels, laser-assisted fluorination has now largely superseded the conventional externally-heated Ni “bomb” technique for bulk analysis. Unlike UV laser ablation and SIMS analysis, laser-assisted fluorination is not capable of focused spot analysis. While laser fluorination is now a mature technology, further analytical improvements are possible via refinements to the construction of sample chambers, clean-up lines and the use of ultra-high resolution mass spectrometers.High-precision oxygen isotope analysis has proved to be a particularly powerful technique for investigating the formation and evolution of early-formed differentiated asteroids and has provided unique insights into the interrelationships between various groups of achondrites. A clear example of this is seen in samples that lie close to the terrestrial fractionation line (TFL). Based on the data from conventional oxygen isotope analysis, it was suggested that the main-group pallasites, the howardite eucrite diogenite suite (HEDs) and mesosiderites could all be derived from a single common parent body. However, high precision analysis demonstrates that main-group pallasites have a Δ¹⁷O composition that is fully resolvable from that of the HEDs and mesosiderites, indicating the involvement of at least two parent bodies. The range of Δ¹⁷O values exhibited by an achondrite group provides a useful means of assessing the extent to which their parent body underwent melting and isotopic homogenization. Oxygen isotope analysis can also highlight relationships between ungrouped achondrites and the more well-populated groups. A clear example of this is the proposed link between the evolved GRA 06128/9 meteorites and the brachinites.The evidence from oxygen isotopes, in conjunction with that from other techniques, indicates that we have samples from approximately 110 asteroidal parent bodies (∼60 irons, ∼35 achondrites and stony-iron, and ∼15 chondrites) in our global meteorite collection. However, compared to the likely size of the original protoplanetary asteroid population, this is an extremely low value. In addition, almost all of the differentiated samples (achondrites, stony-iron and irons) are derived from parent bodies that were highly disrupted early in their evolution.High-precision oxygen isotope analysis of achondrites provides some important insights into the origin of mass-independent variation in the early Solar System. In particular, the evidence from various primitive achondrite groups indicates that both the slope 1 (Y&R) and CCAM lines are of primordial significance. Δ¹⁷O differences between water ice and silicate-rich solids were probably the initial source of the slope 1 anomaly. These phases most likely acquired their isotopic composition as a result of UV photo-dissociation of CO that took place either in the early solar nebula or precursor giant molecular cloud. Such small-scale isotopic heterogeneities were propagated into larger-sized bodies, such as asteroids and planets, as a result of early Solar System processes, including dehydration, aqueous alteration, melting and collisional interactions.There is increasing evidence that chondritic parent bodies accreted relatively late compared to achondritic asteroids. This may account for the fact that apart from a few notable exceptions’ such as the aubrite-enstatite chondrite association, known chondrite groups could not have been the parents to the main achondrite groups.     

Classification of five new ordinary chondrites from North West Africa

We classified five new ordinary chondrites from North West Africa. NWA 3010 is an L6(S5), NWA 3011 is an L5(S5), NWA 3012 is an LL4(S5), NWA 3013 is an L5(S5), and NWA 3014 is an H4(S1). The meteorites experienced a range of terrestrial alteration, with NWA 3010 equal to weathering grade W2, NWA 3011 equal to W3, NWA 3012 equal to W3, NWA 3013 equal to W2, and NWA 3014 equal to W4.     

The terrestrial fauna of the Late Triassic Pant-y-ffynnon Quarry fissures,South Wales,UK and a new species of Clevosaurus (Lepidosauria: Rhynchocephalia)

Pant-y-ffynnon Quarry in South Wales yielded a rich cache of fossils in the early 1950s, including articulated specimens of new species (the small sauropodomorph dinosaur Pantydraco caducus and the crocodylomorph Terrestrisuchus gracilis), but no substantial study of the wider fauna of the Pant-y-ffynnon fissure systems has been published. Here, our overview of existing specimens, a few described but mostly undescribed, as well as freshly processed material, provides a comprehensive picture of the Pant-y-ffynnon palaeo-island of the Late Triassic. This was an island with a relatively impoverished fauna dominated by small clevosaurs (rhynchocephalians), including a new species, Clevosaurus cambrica, described here from a partially articulated specimen and isolated bones. The new species has a dental morphology that is intermediate between the Late Triassic Clevosaurus hudsoni, from Cromhall Quarry to the east, and the younger C. convallis from Pant Quarry to the west, suggesting adaptive radiation of clevosaurs in the palaeo-archipelago. The larger reptiles on the palaeo-island do not exceed 1.5?m in length, including a small carnivorous crocodylomorph, Terrestrisuchus, and a possible example of insular dwarfism in the basal dinosaur Pantydraco.     

The effect of water on accessory phase solubility in subaluminous and peralkaline granitic melts

The solubilities of columbite, tantalite, wolframite, rutile, zircon and hafnon were determined as a function of the water contents in peralkaline and subaluminous granite melts. All experiments were conducted at 1035 °C and 2 kbar and the water contents of the melts ranged from nominally dry to approximately 6 wt.% H₂O. Accessory phase solubilities are not affected by the water content of the peralkaline melt. By contrast, solubilities are affected by the water content of the subaluminous melt, where the solubilities of all the accessory phases examined increase with the water content of the melt, up to 2 wt.% H₂O. At higher water contents, solubilities are nearly constant. It can be concluded that water is not an important control of accessory phase solubility, although the water content will affect diffusivities of components in the melt, thus whether or not accessory phases will be present as restite material. The solubility behaviour in the subaluminous and peralkaline melts supports previous spectroscopic studies, which have observed differences in the coordination of high field strength elements in dry vs. wet subaluminous granitic glasses, but not for peralkaline granitic glasses. Lastly, the fact that wolframite solubility increases with increasing water content in the subaluminous melt suggests that tungsten dissolved as a hexavalent species.     

Quaternary stresses revealed by calcite twinning inversion: insights from observations in the Savonnières underground quarry (eastern France)

Calcite samples were extracted both from the rock matrix and the superficial coating of a karstified fault plane of an underground quarry, located in the eastern border of the Paris basin. The karstification is dated as Quaternary. Analysis of mechanical calcite twinning reveals that only the calcite matrix has also undergone a compression trending WNW that can be attributed to the Mio-Pliocene alpine collision. Both coating and matrix have undergone a strike-slip regime with σ₁ roughly trending north–south, that could correspond to the regional present-day state of stress, a strike-slip compression rather trending NNW, modified by local phenomena. To cite this article: M. Rocher et al., C. R. Geoscience 335 (2003).     

HYDROGEOLOGY

正20141756 Chen Ruige(Mathematical College,China University of Geosciences,Beijing100083,China);Zhou Xun Numerical Simulation of Groundwater Level Fluctuation in a Coastal Confined Aquifer with Sloping Initial Groundwater Level Induced by the Tide(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,32(7),2013,p.1099-1104,6 illus.,16 refs.) Key words:confined water,groundwater level     

METAMORPHIC PETROLOGY

正20141408 Cai Jia(Institute of Geology,Chinese Academy of Geological Sciences,Beijing100037,China);Liu Fulai Petrogenesis and Metamorphic P-T Conditions of Garnet-Spinel-Biotitebearing Paragneiss in Danangou Area,Daqingshan-Wulashan Metamorphic Complex Belt(Acta Petrologica Sinica,ISSN1000-0569,CN11-1922/P,29(7),     

SERIALS

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