K‐ and Si‐rich glasses in harzburgite from Damaping,north China

A study of potassium‐ and silica‐rich glass (SiO₂ = 65.3–67.4%, K₂O = 7.1–9.8%, Na₂O = 4.4–6.5%) in spongy clinopyroxene rims from anhydrous spinel harzburgite, collected from Damaping (Hannuoba, north China), is reported here. The corroded surface of clinopyroxene along with clear chemical zonation (homogeneous core and partially melted rim) suggests that incongruent melting of primary clinopyroxene is responsible for generating the Si‐rich glass in clinopyroxene rims. The degree of clinopyroxene melting is estimated to be higher than 15%. In order to generate glass with K₂O contents of 7.0 to 9.8% by clinopyroxene melting at a degree of 15% in a closed system, K₂O contents in the primary clinopyroxene should be greater than 1.0 wt%, suggesting a very deep origin for the Damaping harzburgite.     

Calibration of a hysteretic model for glass fiber reinforced gypsum wall panels

Glass fi ber reinforced gypsum(GFRG) wall panels are prefabricated panels with hollow cores, originally developed in Australia and subsequently adopted by India and China for use in buildings. This paper discusses identifi cation and calibration of a suitable hysteretic model for GFRG wall panels fi lled with reinforced concrete. As considerable pinching was observed in the experimental results, a suitable hysteretic model with pinched hysteretic rule is used to conduct a series of quasi-static as inelastic hysteretic response analyses of GFRG panels with two different widths. The calibration of the pinching model parameters was carried out to approximately match the simulated and experimental responses up to 80% of the peak load in the post peak region. Interestingly, the same values of various parameters(energy dissipation and pinching related parameters) were obtained for all fi ve test specimens.     

显微CT技术在古代料珠研究中的应用——以河南淅川县马川墓地出土料珠为例

本文首次运用显微CT技术对中国早期料珠进行研究。X-射线衍射(XRD)及CT切片分析结果表明,河南淅川县马川墓地出土的料珠为玻璃珠,与西周时期的釉砂珠在结构上存在显著区别。显微CT技术为料珠材质的鉴定提供了一种新方法。结合玻璃珠的三维模型表明,战国时期玻璃珠内的气泡以球形为主,内部存在许多细小不规则的空隙,应是采用模压法工艺制造;这是在研究中首次发现战国时期采用模压法工艺制造玻璃珠。西汉时期玻璃珠内的气泡是纺锤状,应是采用拉制法工艺制造。显微CT技术能清晰无损地揭示古代玻璃珠内部结构特点,显示了该技术在古代玻璃珠制造工艺研究中有着广阔的运用前景。     

Determination of Reference Values for NIST SRM 610–617 Glasses Following ISO Guidelines

We present new reference values for the NIST SRM 610–617 glasses following ISO guidelines and the International Association of Geoanalysts’ protocol. Uncertainties at the 95% confidence level (CL) have been determined for bulk‐ and micro‐analytical purposes. In contrast to former compilation procedures, this approach delivers data that consider present‐day requirements of data quality. New analytical data and the nearly complete data set of the GeoReM database were used for this study. Data quality was checked by the application of the Horwitz function and by a careful investigation of analytical procedures. We have determined quantitatively possible element inhomogeneities using different test portion masses of 1, 0.1 and 0.02 μg. Although avoiding the rim region of the glass wafers, we found moderate inhomogeneities of several chalcophile/siderophile elements and gross inhomogeneities of Ni, Se, Pd and Pt at small test portion masses. The extent of inhomogeneity was included in the determination of uncertainties. While the new reference values agree with the NIST certified values with the one exception of Mn in SRM 610, they typically differ by as much as 10% from the Pearce et al. (1997) values in current use. In a few cases (P, S, Cl, Ta, Re) the discrepancies are even higher.     

A Raman spectroscopic study of shock-wave densification of vitreous silica

The densification processes in SiO₂ glass induced by shock-wave compression up to 43.4 GPa are investigated by Raman spectroscopy. At first, densification increases with increasing shock pressure. A maximum densification of 11% is obtained for a shock pressure of 26.3 GPa. This densification is attributed to the reduction of the average Si−O−Si angle, which occurs first by the collapse of the largest ring cavities, then by further reduction of the average ring size. For higher shock pressures, a different structural modification is observed, resulting in decreasing densification with increasing shock pressure. Indeed, the recovered densification becomes very small, with values of 1.8 and 0.5% at 32 and 43.4 GPa, respectively. This is attributed to partial annealing of the samples due to high after shock residual temperatures. The study of the annealing process of the most densified glass by in situ high temperature Raman spectroscopy confirms that relaxation of the Si−O−Si angle starts at a lower temperature (about 800 K) than that of the siloxane rings (about 1000 K), thus explaining the high intensity of the siloxane defect bands in the samples schocked at compressions of 32 and 43.4 GPa. The large intensity of the siloxane bands in the nearly undensified samples shocked by compressions above 30 GPa may be explained by the relaxation during decompression of five- and six-fold coordinated silicon species formed at high pressure and high temperature during the shock event. Received: March 30, 1998 / Revised, accepted: August 21, 1998     

The granite-upper mantle connection in terrestrial planetary bodies: an anomaly to the current granite paradigm?

Granite formed in the terrestrial planets very soon after their accretion. The oldest granite-forming minerals (4.4 Ga zircon) and granite (4.0 Ga granodiorite) indicate conditions resembling the present-day ones, with the presence of oceans and external processes related to liquid water. As a result, the current granite paradigm states that granite is not issued directly from the melting of the mantle. However, a granite-upper mantle connection is well established from several pieces of evidence. Tiny micrometre- to millimetre-sized enclaves of granite-like glassy and crystalline materials in Earth's mantle rocks are known in oceanic and continental areas. Earth's mantle-forming minerals, such as olivine, pyroxene, and chromite, can contain silicic materials, either as glass inclusions or as crystallised products (quartz or tridymite, sanidine, K-feldspar, and/or plagioclase close to albite end-member). Importantly, the same evidence is amply found in some types of meteorites, whether they are primitive, such as ordinary chondrites, or differentiated, such as IIE irons, howardite–eucrite–diogenite (HED), and Martian shergottite–nakhlite–chassignite (SNC) achondrites. Although constituting apparently an anomaly, the granite-upper mantle connection can be reconciled with the current granite paradigm by recognising that the conditions prevailing in the formation of granite are not only necessarily crustal but can occur also at depths in mantle rocks. Unresolved problems to be explored further include whether tiny amounts of granitic material within terrestrial mantles may be hints of greater abundances and more direct mantle involvement, and what role can be played by granite trapped within the upper mantle in lithosphere buoyancy.     

Highly alkaline,high-temperature hydrothermal fluids in the early Archean ocean

Based on the petrology of hydrothermally altered Archean basaltic greenstones, thermodynamic calculations of phase equilibria were conducted to estimate the composition of a high-temperature (∼350 °C) hydrothermal fluid in an Archean subseafloor basalt-hosted hydrothermal system. The results indicate that the hydrothermal fluid was highly alkaline attributed to the presence of calcite in the alteration minerals under a high-CO₂ condition, and predict a generation of SiO₂-rich, Fe-poor hydrothermal fluids in the Archean subseafloor hydrothermal system. The chemically reactive mixing zones between alkaline hydrothermal fluids and slightly acidic-neutral seawater are characterized by inverse pH and chemical polarity to modern hydrothermal systems, leading to extensive precipitation of silica and iron oxyhydroxides on/under the seafloor. Such processes can be responsible for the abiotic formation of voluminous chert and subseafloor silica dike, the mechanism of silicification, and the pH-controlled generation of banded iron formation that has been arising mainly from the redox chemistry in the Archean ocean. Such high-temperature alkaline fluids could have had a significant role not only in the early ocean geochemical processes but also in the early evolution of life.     

海南岛屯昌玄武质科马提岩Sm-Nd同位素年龄及其地质意义

海南岛屯昌玄武质科马提岩成岩时代一直未获解决。作者利用Sm-Nd同位素法测试了5件样品,获得岩石Sm-Nd同位素等时线年龄1687±10Ma,及与其相近的Nd模式年龄1637-1756Ma。同时获得了钕同位素初始比值INd=0.510796±0.000006(2σ),εNd(T)=+6.64。表明玄武质科马提岩结晶年龄为古元古代(1687Ma),反映了海南岛在古元古时期的壳-幔分异与地壳增生的重要过程。     

Surface alteration of basalt due to cation-migration

Basaltic lava from Kilauea, Hawaii may have a red-brown surface, indicative of Fe-(hydr)oxides. This surface is not found where exposed to weathering, but at the interface between lava lobes, or in the interior of lava channels. We use several analytical techniques to determine how these Fe-(hydr)oxide surfaces may have developed. WDS-elemental distribution line profiles from the lava surface towards the lava′s interior detect an Fe-rich film of less than 5 μm thickness. Heat treatment of quenched, fresh lava samples of the same chemical composition between 600–1,090°C helps to replicate temperatures under which such an Fe-rich film might have formed. These experiments suggest that Fe-enrichment occurs above 1,020°C, whereas at lower temperatures Ca is enriched relative to Fe. One sample was treated below the glass transition temperature, at 600°C for 164 h. A depth profile with secondary neutral mass spectrometry shows an enrichment of Mg at the outer 50 nm of the glass surface. The formation of films requires cation migration, which is driven by an oxygen chemical potential between air and the reduced basalt (Fe²⁺/Fe³⁺ ratio of 13.3). The change of surface alteration from Mg to Ca film at lower temperatures, to predominantly Fe at high temperatures, is determined by a change of cation availability, largely controlled by crystallization that already occurs below 850°C, and volume crystallization that occurs above 925°C.     

Basaltic dykes of the Eastern Belt of Peninsular Malaysia: The effects of the difference in crustal thickness of Sibumasu and Indochina

Basaltic dykes of Peninsular Malaysia are confined to the Eastern Belt (Indochina/East Malaya block) as compared with the Western Belt (Sibumasu Block). The dyke intruded through a crustal fracture formed by stress developed from the evolution of two offshore basins (Malay and Penyu basins) east of Peninsular Malaysia. The Ar–Ar dating from the present study combined with the previous geochronological data indicate that the ages of dykes range from 79 ± 2 Ma to 179 ± 2 Ma. Thus it is difficult to correlate the dykes with the closure of Tethys during Permo-Triassic time because of the younger age of the dykes. The majority of the dykes exposed in the Eastern Belt may have been attributed to the difference of crustal thickness between the Eastern and Western belt of Peninsular Malaysia. A thicker Western Belt crust (13 km more than both Eastern and Central belts) is difficult to rupture with normal plate tectonic stress and therefore serves to contain the rise of a mantle derived melt. The chemistry indicates the basalts are olivine to quartz normative and are of the continental within-plate category.