High-T phase transition of synthetic ANaB(LiMg)CMg5Si8O22(OH)2 amphibole: an X-ray synchrotron powder diffraction and FTIR spectroscopic study

The synthetic amphibole Na_0.95(Li_0.95Mg_1.05)Mg₅Si₈O₂₂(OH)₂ was studied in situ at high-T, using IR OH-stretching spectroscopy and synchrotron X-ray powder diffraction. At room-T the sample has P2₁ /m symmetry, as shown by the FTIR spectrum. It shows in the OH region two well-defined and intense absorptions at 3,748 and 3,712 cm⁻¹, respectively, and two minor bands at 3,667 and 3,687 cm⁻¹. The main bands are assigned to the two independent O–H groups in the primitive structure. The two minor bands evidencing the presence of small amount of vacant A-site (^A□_0.05). With increasing T, these bands shift continuously and merge into a unique absorption at high temperature. A change as a function of increasing T is revealed by the evolution of the refined unit-cell parameters, whose trend shows a transition to C2/m at about 320–330°C. The spontaneous scalar strain, fitted with a tricritical 2–6 Landau potential, gives a T _c of 325(10)°C (β parameter = 0.27). Comparison with the second-order P2₁ /m ⇔ C2/m phase transition at 255°C for synthetic amphibole ^ANa_0.8^B(Na_0.8Mg_1.2)^CMg₅Si₈O₂₂(OH)₂ indicates that the substitution of Na with Li at the B-sites strongly affects the thermodynamic character and the T _c of the phase transition. The comparison of LNMSH amphiboles with cummingtonitic ones shows that the high-T thermodynamic behaviour is affected by A-site occupancy.     

GM（1,1）模型在铁路路基冻胀监测中的应用

通过对季节性冻土区铁路路基冻胀量与地层温度的监测,可以了解监测段的冻胀变化过程,但无法对未来的发展趋势作出有效预测。本文采用GM（1,1）模型对监测段落路基的冻胀变形及冻结深度的变化情况进行预测。结果表明,此预测方法可以在现有监测数据的基础上有效预测短期内路基冻胀的发展趋势。根据模型预测结果,可以提前采取有效整治措施,便于决策者对轨道检验周期、维修周期、限速周期等作出合理调整。     

Negative Ce Anomaly in the Indian Banded Iron Formations: Evidence for the Emergence of Oxygenated Deep-Sea at 2.9-2.7 Ga

Abstract: Major and rare earth element contents are reported for Late Archean banded iron formations (BIFs) in the Bababudan Group of the Dharwar Craton, South India. The BIFs are mostly composed of SiO₂ (average1ρ = 54.88.1 wt%) and Fe₂O₃* (44.38.2 wt%). The Al₂O₃ and TiO₂ contents are remarkably low, suggesting that detrital components were starved during the BIF deposition. The BIFs have a LREE-enriched pattern with a relatively high (La/Yb)_N (6.644.07). Total REE concentrations (RE) vary from 5.2 to 65.3 ppm. The REE patterns are characterized by the presence of a very large negative Ce anomaly (Ce/Ce*: 0.13-0.83) and a positive Eu anomaly (Eu/Eu*: 0.96-2.45). The Eu/Eu* decreases and (La/Yb)_N increases with a increase of RE. These correlations of REE indices are similar to those of modern hydrothermal iron-rich sediments near a mid-ocean ridge (MOR). Greenstones associated with the BIFs have MORB-like geochemical features. These geochemical and geological lines of evidence indicate that the depositional site of the BIFs was remote from a continent and/or island arc and that the BIFs were in situ hydrothermal sediments near a MOR. A striking negative Ce anomaly in the BIFs indicates that oxygenated deep-sea environments emerged at 2.9-2.7 Ga. The existence of contemporaneous Mn deposits in the Dharwar Craton supports this assertion. Our scenario of oxygen in the Earth's surface of the Late Archean is different from long-held notion that the atmosphere and ocean were persistently anoxic throughout the Archean.     

中国西部元古代蓝片岩带——世界上保存最好的前寒武纪蓝片岩

阿克苏附近所发现的元古界阿克苏群为一完整的蓝片岩-绿片岩系列,我们通过野外调查肯定了这一认识,并认为它是高压-温相的变质块体,长40km,宽约2.5km.该变质岩由强烈片理化的绿泥石-黑硬绿泥石石墨片岩、黑硬绿泥石-多硅白云母片岩、绿片岩、蓝片岩及少量石英岩、变铁质岩组成.原岩包活泥质岩、砂岩、基性玻屑凝灰岩、块状熔岩、枕状熔岩及少量深海沉积物.蓝片岩的矿物组合:青铝闪石-绿帘石-绿泥石-钠长石-石英-阳起石.阿克苏群为世界上真正的前震旦纪蓝片岩之一,其变质年龄至少有800Ma.     

中国区域年代地层研究取得重要进展

近10余年来,特别是2000年召开第三届地层会议后,中国年代地层研究得到很快发展。首先,在全国地层委员会主持下,经各断代工作组专家们的共同努力,编制完成了《中国区域年代地层（地质年代）表》,系统建立了从震旦系至第四系中共102个阶（其中包括52个陆相地层区的阶）和新建3个系级单位。从2001年开始,在中国地质调查局的大力支持下,由全国地层委员会主持,组织全国知名地质科研院所、高校和部分地质调查院的专家,围绕中国区域年代地层表,开展了系统的建阶研究。5年来,共涉及45个阶,9个界线层型和2个新建系及2个统级单位的研究,取得重要进展。先后已有4个全球界线层型（GSSPs）被国际地质科学联合会批准建立在中国,还有3～4个全球界线层型正待国际地质学科学联合会批准建立在中国,另有3～4个界线层型剖面有望争取成为全球的界线层型。其他研究所涉及到的阶、系、统等单位,也有明显进展,成熟度明显提高,为《中国区域年代地层（地质年代）表》的广泛应用奠定了重要基础。     

西藏甲玛-卡军果推-滑覆构造系特征

通过矿区填图和路线调查,结合室内研究,指出:①甲玛-卡军果推-滑覆构造系由印度-欧亚板块碰撞引发,具有递进变形、自盆地中心向边部推覆、新盖老等特点,强变形于50Ma±。②推覆体下盘为叶巴组构造岩系;推覆体由上侏罗统和下白垩统碳酸盐-碎屑沉积岩系构成,主体为轴面北倾的复式褶皱,自南而北分为前部带、中部带和后部带。滑覆构造系推覆形成的复背斜轴部高位岩块失稳向北滑覆形成,自南而北分为后部带、中部带和前部带。③导致矿区蚀变的主要岩浆活动发生于推覆强变形后的松弛期,上侵受近南北向基底断裂和推覆断裂联合控制,就位受控于前部带推-滑覆褶断系,其后发生多次构造-岩浆-成矿液叠加,造就甲玛铜多金属矿床。     

Li_2O-(Mg、Zn、Ni)O-V_2O_5三元体系的相平衡

对Li_2O-(Mg、Zn、Ni)O-V_2O_5三元体系在500—800℃相图的研究表明,在每个系统内部都出现了一个依端员组分摩尔比为1:2:1的化合物。即橄榄石型的LiMgVO_4,硅铍石型的LiZnVO_4和尖晶石型的LiNiVO_4。不同的是,Li_2O-MgO-V_2O_5中发现了第二个三元相和一个固溶体。LiO_2-NiO-V_2O_6中得出一个固溶体,而LiZnNO_4中未得固溶体。     

The Removal of Dissolved Metals by Hydroxysulphate Precipitates during Oxidation and Neutralization of Acid Mine Waters, Iberian Pyrite Belt

This study examines the removal of dissolved metals during the oxidation and neutralization of five acid mine drainage (AMD) waters from La Zarza, Lomero, Esperanza, Corta Atalaya and Poderosa mines (Iberian Pyrite Belt, Huelva, Spain). These waters were selected to cover the spectrum of pH (2.2–3.5) and chemical composition (e.g., 319–2,103 mg/L Fe; 2.85–33.3 g/L SO₄⁼) of the IPB mine waters. The experiments were conducted in the laboratory to simulate the geochemical evolution previously recognized in the field. This evolution includes two stages: (1) oxidation of dissolved Fe(II) followed by hydrolysis and precipitation of Fe(III), and (2) progressive pH increase during mixing with fresh waters. Fe(III) precipitates at pH < 3.5 (stages 1 and 2) in the form of schwertmannite, whereas Al precipitates during stage 2 at pH 5.0 in the form of several hydroxysulphates of variable composition (hydrobasaluminite, basaluminite, aluminite). During these stages, trace elements are totally or partially sorbed and/or coprecipitated at different rates depending basically on pH, as well as on the activity of the SO₄⁼ anion (which determines the speciation of metals). The general trend for the metals which are chiefly present as aqueous free cations (Pb²⁺, Zn²⁺, Cu²⁺, Cd²⁺, Mn²⁺, Co²⁺, Ni²⁺) is a progressive sorption at increasing pH. On the other hand, As and V (mainly present as anionic species) are completely scavenged during the oxidation stage at pH < 3.5. In waters with high activities (> 10⁻¹) of the SO ₄⁼ ion, some elements like Al, Zn, Cd, Pb and U can also form anionic bisulphate complexes and be significantly sorbed at pH < 5. The removal rates at pH 7.0 range from around 100% for As, V, Cu and U, and 60–80% for Pb, to less than 20% for Zn, Co, Ni and Mn. These processes of metal removal represent a significant mechanism of natural attenuation in the IPB.     

Y11B航空物探(电/磁)综合站西北找水初步成果

1997年9月23日～10月8日,在甘肃省安西—敦煌地区用Y11B航空物探(电/磁)综合站和GPS导航定位进行了地下水勘查试生产工作。用均匀大地模型,结合已知的水文地质资料,初步圈定了淡水区、过渡类型水区、咸水区和苦水区及泉水湖。所推断的水质和土壤含盐量与大的水文地质单元和1:20万水文地质普查报告都吻合得很好,且细节更为清楚。对差异较大的地方做了分析和解释。     

西藏曲水县达布斑岩铜(钼)矿床成岩成矿年代学研究

本文采用锆石LA-ICP-MS微区U-Pb测年技术,对冈底斯成矿带东段曲水县达布斑岩Cu(Mo)矿床北部达布矿区含矿斑岩体、南部显角囊含矿花岗闪长斑岩岩体进行了年代学研究,通过对3件岩体样品中单颗粒锆石的分析,达布主矿体花岗闪长斑岩样品206Pb/238U年龄加权平均值为16.5±0.05Ma(n=15,MSWD=3),达布主含矿体二长花岗斑岩样品年龄为16.1±0.13Ma(n=15,MSWD=1.03),南部显角囊矿体花岗闪长斑岩年龄为16.2±0.04Ma(n=13,MSWD=0.0064)。对达布矿床斑岩Cu(Mo)矿床主矿体中4件辉钼矿样品,显角囊矿体中6件辉钼矿样品,分别进行了Re-Os同位素测试,等时线年龄分别为14.6±0.50Ma(MSWD=0.35,主矿体)、14.8±0.23Ma(MSWD=1.3,显角囊)。结合前人研究以及本次测年结果认为:1)达布斑岩铜(钼)矿床岩体侵位的年龄应限定在16Ma左右,成矿时代为14Ma左右,成矿时间差小于0.86Ma,与区域上"成矿瞬时发生"的成矿规律是一致的;2)矿床产出于印度-亚洲大陆板块后碰撞伸展环境。