A thermodynamic model for Ca–Na clinoamphiboles in Na2O–CaO–FeO–MgO–Al2O3–SiO2–H2O–O for petrological calculations

A calibration is presented for an activity–composition model for amphiboles in the system Na₂O–CaO–FeO–MgO–Al₂O₃–SiO₂–H₂O–O (NCFMASHO), formulated in terms of an independent set of six end‐members: tremolite, tschermakite, pargasite, glaucophane, ferroactinolite and ferritschermakite. The model uses mixing‐on‐sites for the ideal‐mixing activities, and for the activity coefficients, a macroscopic multicomponent van Laar model. This formulation involves 15 pairwise interaction energies and six asymmetry parameters. Calibration of the model is based on the geometrical constraints imposed by the size and shape of amphibole solvi inherent in a data set of 71 coexisting amphibole pairs from rocks, formed over 400–600 °C and 2–18 kbar. The model parameters are calibrated by combining these geometric constraints with qualitative consideration of parameter relationships, given that the data are insufficient to allow all the model parameters to be determined from a regression of the data. Use of coexisting amphiboles means that amphibole activity–composition relationships are calibrated independently of the thermodynamic properties of the end‐members. For practical applications, in geothermobarometry and the calculation of phase diagrams, the amphibole activity–composition relationships are placed in the context of the stability of other minerals by evaluating the properties of the end‐members in the independent set that are in internally consistent data sets. This has been performed using an extended natural data set for hornblende–garnet–plagioclase–quartz, giving the small adjustments necessary to the enthalpies of formation of tschermakite, pargasite and glaucophane for working with the Holland and Powell data set.     

Holocene reworking of drift‐mantled hillslopes in the Scottish Highlands

Episodic erosion and resedimentation of valley‐side glacigenic drift is evident at three sites in the Scottish Highlands in the form of buried in situ palaeosols intercalated with stacked sediment units. Radiocarbon dating of 10 palaeosols exposed in sections in debris cones suggests that gully erosion and redeposition of drift represents asynchronous debris flow and slopewash activity within the past 6⋅5 cal.kyr. Palynological and charcoal analyses confirm that reworking was unrelated to burning of vegetation, and post‐dated the main phase of anthropogenic woodland clearance at two sites, although the possibility that recent debris flow activity in Glen Docherty may have been associated with removal of woodland cover cannot be dismissed. However, the collective evidence points to discrete, extreme storm‐generated events of random occurrence as the most likely cause of episodes of enhanced slope reworking at the sites investigated. Evidence for periodic climatic deterioration is more equivocal. By implication, the accumulation of substantial debris cones in upland Britain may reflect primarily the reworking of sediment during extremely rare, intense rainstorms, essentially independent of progressive climate changes. Consequently, caution is necessary in using debris flow stratigraphies alone as a means of reconstructing former long‐term climatic changes. Copyright © 2000 John Wiley & Sons, Ltd.     

西藏终碛湖溃决形式研究

西藏终碛湖众多,一旦发生溃决,将造成巨大损失。冰湖溃决机制的研究对冰湖溃决预测和溃后灾害评估是十分必要的。将冰湖终碛堤视为天然堆石坝,用水力学和土力学理论研究冰湖溃决的力学机制。重点研究溢流型溃决形式和管涌型溃决形式,根据野外观测数据和前人的研究,发现溢流型溃决的溃口多呈梯形或圆弧状形,对比真实数据发现溃口顶宽与坝高的关系,并且所有冰川终碛堤都表现为局部溃决。通过实地考察、取样分析,判断光谢措终碛堤的可能渗透破坏形式。     

北京郊区农田土壤中滴滴涕和六六六地球化学特征研究

北京是中国政治、经济和文化中心,人口密集。近年来,随着社会经济快速发展,环境问题,特别是持     

Alpine metamorphism in the south-east Tauern Window, Austria: 1. P–T variations in space and time

Abstract The Pennine rocks exposed in the south-east Tauern Window, Austria, contain mineral assemblages which crystallized in the mid-Tertiary ‘late Alpine’regional metamorphism. The pressure and temperature conditions at the thermal peak of this event have been estimated for rocks at four different structural levels using a variety of published and thermochemically derived geobarometers and geothermometers. The results are: (a) In the garnet+chlorite zone, 2–5 km structurally above the staurolite+biotite isograd: T= 490.50°C, P= 7° 1 kbar; (b) Within 0.5 km of the staurolite+biotite isograd: T= 560±300C, P=7.1 kbar; (c) In the staurolite+biotite zone, c. 2.5 km structurally below the staurolite+biotite isograd: T= 610±30°C, P=7.6±1.2 kbar; (d) In the staurolite+biotite zone, 3–4 km structurally below the staurolite+biotite isograd: T= 630±40°C, P= 6.6±1.2 kbar. The pressure estimates imply that the total thickness of overburden above the basement-cover interface in the mid-Tertiary was c. 26.4 km. This overburden can only be accounted for by the Austro-Alpine units currently exposed in the vicinity of the Tauern Window, if the Altkristallin (the ‘Middle Austro-Alpine’nappe) was itself buried beneath an ‘Upper Austro-Alpine’nappe or nappe-pile which was 7.4 km thick at that time. The occurrence of epidote + margarite + quartz pseudomorphs after lawsonite in garnet, indicates that part of the Mesozoic Pennine cover sequence in the south-east Tauern experienced blueschist-facies conditions (T<450°C, P<12 kbar) in early Alpine times. Evidence from the central Tauern is used to argue that the blueschist-facies imprint post-dated the main phase of tectonic thickening (D¹_A) and was thus a direct consequence of continental collision. Combined oxygen-isotope and fluid-inclusion studies on late-stage veins, thought to have been at lithostatic pressure and in thermal equilibrium with their host rocks during formation, suggest that they crystallized from aqueous fluids at 1.1±0.4 kbar and 420.20°C. Early Alpine, late Alpine and vein-formation P–T constraints have been used to construct a P–T path for the base of the Mesozoic cover sequence in the south-east Tauern Window. The prograde part of the P–T path, between early and late Alpine metamorphic imprints, is unlikely to have been a smooth curve and may well have had a low dP/dT overall; the decompression (presumably due to erosion) which occurred immediately before the thermal peak and possibly also earlier in the Tertiary, was probably partly or completely cancelled by the effects of early- to mid-Tertiary (D²_A) tectonic thickening. The thermal peak of metamorphism was followed by a phase of almost isothermal decompression, which implies a period of rapid uplift in the middle Tertiary. The peak metamorphic P–T estimates are compared with the solutions of England's (1978) one-dimensional conductive thermal model of the Eastern Alps, and are shown to be consistent with the idea that the late Alpine metamorphism was caused by tectonic burial of the Pennine Zone beneath the Austro-Alpine nappes in the absence of extraneous heat sources, such as large intrusions, at depth.     

大青山逆冲推覆构造形成演化过程的流体证据

大青山逆冲断层带内热液脉体十分发育,按其产状可划分为充填脉和边缘脉。根据形成时间主要划分为3期:早期石英脉、中期石英脉和晚期方解石脉。早期石英脉中流体包裹体类型较为复杂,见有气液两相、含CO2三相、纯CO2及少量单液相等4种类型原生包裹体,分析表明流体主要来源于地壳深部或上地幔。中期石英脉中主要发育气液两相包裹体和少量单液相包裹体,流体主要来源于大气降水,并且有少量岩浆热液混入。晚期方解石脉内仅含有气液两相包裹体及少量的单液相包体,流体主要来源于层间建造水。根据逆冲变形事件期次、时间,结合热液脉体形成深度数据,确定了大青山逆冲推覆体系变形演化历史:印支期逆冲推覆事件发生在地壳7～8 km深度,燕山中期逆冲推覆事件发生在3～6 km范围内,而燕山晚期逆冲推覆事件发生近地表2 km范围内。     

空间信息支持下的沉积相分析方法及其应用

依据各沉积相的平面分布形态,将沉积相划分为扇形沉积相带、席状沉积相带和条带状沉积相带,并分别对不同类型的沉积相带采取不同的缓冲方法,再依据瓦尔特相律,对空间上已知沉积相类型的井进行分析,最终做到利用计算机辅助或代替人工的工作,根据已知单井沉积相的类型而自动进行平面沉积相的研究。将这种方法应用于大港油田孔南地区孔二段时期的沉积相研究中,证明了此方法的可行性。     

薄互层地震波形特征研究——以博兴洼陷沙四段滩坝砂为例

陆相断陷湖盆中薄互层非常普遍,如滩坝砂岩,具有横向变化快、单层厚度薄等特点,加之受地震资料分辨率低等因素的影响,致使其地震预测难度极大。文中在分析博兴洼陷沙四段滩坝砂岩发育区各种岩性地球物理特征的基础上,从正演模型入手,结合实际验证,分析了不同岩性及其组合的地震反射特征,找出了研究区砂体组合反射在地震波形结构、极大值两侧面积比等地震属性上的表现形式,总结了薄互层及其组合模式与地震反射各属性的对应关系,以此进行地震属性预测,取得良好效果,在东营凹陷西部沙四段滩坝砂岩储层的勘探中较准确地预测出储层的发育带。     

西藏高原与喜马拉雅的隆升历史和研究方法:回顾与进展

西藏高原和喜马拉雅的隆升历史是新生代以来众多地质事件的边界条件。因此,它对于我们理解新生代全球气候变冷以及亚洲环境变化等许多地质过程都具有深远的意义。尽管各种替代指标已经被广泛应用于研究高原隆升历史,然而,不同方法所得出的高原隆升历史并不一致。这主要归咎于一些替代指标本身存在多解性和不确定性,从而严重阻碍了获取正确的高原隆升历史。在对这些替代指标进行详细的阐述之后,对其指示的高原隆升历史进行重新评估,并结合在高原腹地开展的工作,提出了原西藏高原的隆升模式,即拉萨地体和羌塘地体在始新世就已经达到现在的海拔高度,而此时青藏高原北部还是低地,南部和西部可能还处在海洋环境。在中新世时,高原向北、向东和向南生长并在第四纪时形成现在的高原特征。     

松辽盆地徐家围子断陷边界断裂生长过程的定量 分析

徐家围子断陷位于松辽盆地中部,受徐西和宋西两条边界断裂控制。基于地震反射剖面地质解译成果,应用断层沿走向位移 长度曲线形态分析方法和沿倾向生长速率分析方法,对两条断裂的生长演化过程进行了初步的研究。结果表明,沙河子期(136~144 Ma)为最主要的生长期,徐西断层的平均生长速率为35 m/Ma, 宋西断层的平均生长速率为71 m/Ma,断陷边界断裂总体平均生长速率大于60 m/Ma,两条断层主要呈现独立生长状态,只在重叠的部位发生微弱的软连接;营城期(126~136 Ma)也是主要的生长期,徐西断层的平均生长速率为18 m/Ma,宋西断层的平均生长速率为85 m/Ma,二者发生硬连接,并基本结束了硬连接过程,以重叠处宋西断层的强烈活动为特征,断陷盆地的规模逐渐扩大,沉积厚度随之增加;营城期后断层只在局部连接地点发生微弱活动。断层生长过程中伴生构造的位置基本与油气田的分布相吻合,对它的深入研究将有助于油气勘探。     

太行山中生代岩浆作用过程中的壳幔岩浆混合作用:岩石学和地球化学证据

太行山中生代岩浆岩的主体———石英二长岩中常见闪长质包体。无论包体还是寄主岩石中均可见斜长石具有成分和结构的不平衡现象,即斜长石具有富钙的核(An=57~65)和富钠的幔部(An=20~35),而且两者变化截然。这是壳幔岩浆发生混合作用的记录:核部代表基性岩浆中早期结晶的斜长石(或代表花岗岩中斜长石由于高温基性岩浆的注入而发生部分熔融形成的残留核?),而幔部代表从混浆中结晶的斜长石。与此类似,角闪石也发育成分环带,其核部为相对富Al和Ti的黄褐色的韭闪石,而边部为贫Al和Ti的绿色调的浅闪石。韭闪石形成于较高的温度,浅闪石形成于较低的温度,也反映了壳幔岩浆混合的过程。壳幔岩浆混合模式同样得到地球化学数据的支持,太行山中生代岩浆岩的高K2O和MgO、高分异稀土模式(和Eu异常不明显)、高Sr-Ba和富集的Sr-Nd同位素特征等均与来自富集地幔的基性岩浆的混合有关。     

成都经济区天降水与下渗水元素地球化学特征及土壤元素输入输出通量

论文研究了成都经济区天降水和下渗水中元素含量、在农田耕层中的输入输出通量及其影响因素.研究表明,研究区雨水中含有大量SO2-4、NO-3等酸性物质,雨水中SO2-4 >NO-3>Cl-.雨水中Ca2 和NH 4含量最高,且NH 4>Ca2 >K >Na >Mg2 .雨水的pH与阴、阳离子摩尔浓度差值具有显著相关性.下渗水中以Ca2 为主要阳离子,且Ca2 >Na >Mg2 >K >NH 4;HCO-3为主要阴离子,且HCO-3>NO-3>SO2-4>Cl->F-,下渗水pH与阳、阴离子摩尔浓度差值具有显著相关性.不同地区雨水中Pb>As>Cd>Se>Hg,下渗水中Pb>As>Se>Cd>Hg,因此,Cd、Pb、Se和Hg等元素累积在耕层中,而As则被下渗水携带迁移出耕层进入地下水.由降雨输入土壤中的Cd通量均大于下渗水输出Cd的通量,局部地区As下渗通量高于雨水输入通量的5.45～13.16倍.土壤中元素的下渗比与土壤质地、pH有关.     

Metamorphism of carbonaceous material in the Tono contact aureole, Kitakami Mountains, Japan

Abstract Optical and X-ray studies of carbonaceous material in the Tono contact metamorphic aureole, Kitakami Mountains, northeast Japan, have revealed that metamorphic graphitization proceeded through two discontinuous changes: first, optically anisotropic domains develop within the coaly phytoclast, forming transitional material, and then, ordered graphite crystallizes by the decomposition of pre-existing carbonaceous materials. Coaly material disappears in the uppermost chlorite zone. Transitional material appears in the middle of the lower chlorite zone. Graphite appears in the upper chlorite zone and its modal abundance increases across the andalusite iso-grad to the cordierite isograd where all the carbonaceous materials have converted to graphite. The apparently continuous variation in the crystallographic parameters of the bulk carbonaceous material during graphitization is largely due to variation in the modal proportions of three types of carbonaceous materials. The temperature of graphitization in the present area is at least 100°C higher than the temperature in the Sanbagawa and New Caledonia high-pressure metamorphic terrains, probably due to the slow reaction rate of metamorphic graphitization and to the short duration of contact metamorphism.     

东天山准噶尔-哈萨克斯坦板块与塔里木板块缝合线的再厘定及其意义

摘要：文中以板块构造理论为指导思想,以大量地质、物探、化探、遥感资料为依据,在全面分析前人对东天山造山带板块缝合线的认识基础上,重新厘定研究区准噶尔-哈萨克斯坦板块与塔里木板块缝合带的位置。经研究确定：东天山造山带康古尔塔格和阿齐克库都克两条断裂之间所夹持的区域,为准噶尔-哈萨克斯坦板块和塔里木板块陆 陆碰撞的缝合带,即康古尔塔格-阿齐克库都克碰撞缝合带。该碰撞缝合带既有板块边界划分意义,又有实体物质组成和特定结构、构造及其演化历史的独立构造单元,也是东天山地区重要的多金属成矿带,故该带对东天山造山带Cu、Ni、Au、Ag等多金属矿产的形成和空间分布起着重要的控制作用。     

Windpolished boulders and bedrock in the Scottish Highlands: evidence and implications of Late Devensian wind activity

The present day maritime climate of Scotland is primarily characterized by strong winds which, in very exposed sites, lead to modern windpolish of rock surfaces. The widespread existence of in situ relict windpolished boulders and bedrock surfaces in Scotland has enabled a reconstruction of prevalent Late Devensian (Late Weichselian) including Loch Lomond Stadial (Younger Dryas) palaeo-wind directions. Previous reconstructions of palaeo-wind directions have been indirect and based mainly on the distribution of aeolian sediments and former glaciers. Observations of relict windpolished microforms and their distribution on boulders and bedrock outcrops on various rock types at 55 sites in different parts of the Scottish Highlands have been used to establish a palaeo-wind map for the area. The reconstruction indicates two sets of dominating wind directions, one between SE and SW and one between NW and N. The maximum age of the windpolish is 16-10 cal. ka BP, but most of it presumably developed during the Loch Lomond Stadial 13-12 cal. ka BP, inferred from the distribution of windpolish sites in relation to the deglaciation chronology and establishment of vegetation.     

Sr、He同位素指示河西走廊中西部地震活动性

河西走廊地处青藏活动地块东北部边缘,为祁连山地震构造带和南北地震构造带的交汇部位,历史上曾发生过多次中强以上的破坏性地震。2008年5月12日汶川80级特大地震发生后,河西地震带是否会发生中强震是一个较受关注的问题。文中分析了河西走廊张掖、武威、酒泉盆地地下水中的Sr、He同位素特征。结果显示,这3个地区的地下水经历了3种不同的循环路径,不是源自黑河、石羊河、疏勒河的地表径流,而是祁连山降水在出山前下渗深大断裂后的补给。这表明河西走廊盆地内的断裂带现今活动性仍然很强,玉门、高台、民乐、永昌等位于断裂带交汇处或附近的区域未来发生中、强震的可能性较大,应加强对这些地区地下水的实时监测。     

Carbon isotope thermometry in marbles of the Adirondack Mountains, New York

Abstract Carbon isotope thermometry has been applied to coexisting calcite and graphite in marbles from throughout the Adirondack Mountains, New York. Eighty-nine calcite-graphite pairs from the amphibolite grade NW Adirondacks change systematically in temperature north-westwards from 680 to 640 to 670° C over a 30-km distance, reflecting transitions from amphibolite facies towards granulite facies to the north-west and to the south-east. Temperature contours based on calcite-graphite thermometry in the NW Adirondacks parallel mineral isograds, with the orthopyroxene isograd falling above 675° C, and indicate that regional metamorphic temperatures were up to 75° C higher than temperatures inferred from isotherms based on cation and solvus thermometry (Bohlen et al. 1985). Fifty-five calcite-graphite pairs from granulite grade marbles of the Central Adirondacks give regional metamorphic temperatures of 670–780° C, in general agreement with cation and solvus thermometry. Data for amphibolite and granulite grade marbles show a 12%oo range in δ¹³C_cal and δ¹³C_gr. A strong correlation between carbon isotopic composition and the abundance of graphite (C_gr/C_rock) indicates that the large spread in isotopic compositions results largely from exchange between calcite and graphite during closed system metamorphism. The trends seen in δ¹³C _vs. C_gr/C_rock and δ¹³C_cal vs. δ¹³C_gr could not have been preserved if significant amounts of CO₂-rich fluid had pervasively infiltrated the Adirondacks at any time. The close fit between natural data and calculated trends of δ¹³C vs. C_gr/C_rock indicates a biogenic origin for Adirondack graphites, even though low δ¹³C values are not preserved in marble. Delamination of 17 graphite flakes perpendicular to the c-axis reveals isotopic zonation, with higher δ¹³C cores. These isotopic gradients are consistent with new graphite growth or recrystallization during a period of decreasing temperature, and could not have been produced by exchange with calcite on cooling due to the sluggish rate of diffusion in graphite. Samples located >2km from anorthosite show a decrease of 0.5-0.8%oo in the outer 100 μ of the grains, while samples at distances over 8 km show smaller core-to-rim decreases of c.0.2%oo. Correlation between the degree of zonation and distance to anorthosite suggests that the isotopic profiles reflect partial overprinting of higher temperature contact metamorphism by later granulite facies metamorphism. Core graphite compositions indicate contact metamorphic temperatures were 860–890° C within 1 km of the Marcy anorthosite massif. If samples with a significant contact metamorphic effect (Δ(_cal-gr) <3.2%oo) are not included, then the remaining 38 granulite facies samples define the relation Δ¹³C(_cal-gr) = 3.56 ± 10⁶T^-2 (K).