Metasomatic effects in the Faraday Metagabbro,Bancroft, Ontario,Canada

Summary The Middle Proterozoic Faraday Metagabbro in the Bancroft area of eastern Ontario has been subjected to syn-orogenic textural and mineralogical modifications resulting in the formation of scapolite-bearing metagabbro and gabbroic blastomylonite assemblages. The elemental flux during cryptic and overt scapolitization has been calculated usingGresens general metasomatic equation which applies corrections for density and volume changes during alteration. Metasomatic variation diagrams using analyses from two primary gabbros and six altered rocks indicate that Na, K, Cl, Li, Rb, and Ba are the principal introduced elements and that Cu and S were removed. These changes are very similar to those involved in the formation of metasomatic nepheline-bearing rocks elsewhere in the district and, furthermore, nephelinization and scapolitization were broadly coincident in time and space. It is concluded that the nephelin- and scapolite-bearing rocks and their cryptic facies are different manifestations of the same metasomatic agent and that the source of the fluids was a possible horizon of evaporitic sediments within the country rocks in which the gabbro was emplaced.

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Metasomatose im Faraday-Metagabbro, Bancroft, Ontario, Kanada

Zusammenfassung Der Mittel-proterozoische Faraday-Gabbro in der Umgebung von Bancroft (Ost-Ontario) erfuhr synorogene Veränderungen in Textur und Mineralogie, die zur Bildung skapolit-haltiger Metagabbros und gabbroider Blastomylonite führten. Die während kryptischer und offener Skapolitisierung stattfindende Elementtransport wurde mit Hilfe der vonGresens entwickelten generellen metasomatischen Gleichung errechnet; Korrekturen für Varänderungen in spezifischer Dichte und Volumen wurden angebracht. Metasomatische Variationsdiagramme basierend auf Analysen an zwei primären Gabbros und sechs modifizierten Gesteinen zeigen, daß Na, K, Cl, Li, Rb und Ba die hauptsächlich zugeführten Elemente darstellen, und daß Cu-und S-Konzentrationen abgebaut wurden. Diese Veränderungen sind vergleichbar mit solchen, wie sie bei der Bildung metasomatischer, Nephelin-haltiger Gesteine erkannt wurden. Außerdem fallen Nephelinisierung und Skapolitisierung zeitlich und räumlich in etwa zusammen. Daraus kann geschlossen werden, daß Nephelin- und Skapolit-haltige Gesteine und deren kryptische Phasen durch den gleichen metasomatischen Prozeß entstanden sind, und daß die Herkunft der umwandelnden Lösungen möglicherweise in evaporitischen Sedimenten zu suchen ist, in die der Gabbro intrudierte.

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With 3 Figures     

Marble mylonites in the Bancroft shear zone, Ontario, Canada: microstructures and deformation mechanisms

Mylonitization of medium-grade marbles in the Bancroft shear zone, Ontario, Canada, is characterized by decreasing grain-size of both calcite and graphite, and a variety of textures. Calcite grain-sizes vary from several millimeters in the protolith, to 50–200 μm in mylonite, to <30 μm in ultramylonite. Corresponding calcite grain shapes are equant in the protolith, elongate in protomylonite (first-developed dimensional preferred orientation), equant in coarse mylonite, elongate in fine mylonite (second-developed dimensional preferred orientation) and generally equant in ultramylonite, which suggests that external energy (applied stress) that tends to elongate grains competed with internal energy sources (e.g. distortional strain) that favor equant shapes. Graphite grain-size changes from several millimeters to centimeters in the protolith to submicroscopic in ultramylonite. In the mylonitic stages, graphite is present as dark bands, while in the ultramylonitic stage it is preserved as a fine coating on calcite grains.Based on textural evidence, twinning (exponential creep; regime I), dynamic recrystallization (power law creep; regime II) and possibly grain boundary sliding superplasticity (regime III) are considered the dominant deformation mechanisms with increasing intensity of mylonitization; their activity is largely controlled by calcite grain-size. Calcite grain-size reduction occurred predominantly by the process of rotation recrystallization during the early stages of mylonitization, as indicated by the occurrence of core and mantle or mortar structures, and by the grain-size of subgrains and recrystallized grains. Grain elongation in S-C structures indicates the activity of migration recrystallization; these structures are not the result of flattening of originally equant grains. Differential stress estimates in coarse mylonites and ultramylonites, based on recrystallized grain-size, are 2–5 and 14–38 MPa, respectively. Initial grain-size reduction of graphite occurred by progressive separation along basal planes, analogous to mica fish formation in quartzo-feldspathic mylonites.Calcite-graphite thermometry on mylonitic and ultramylonitic samples shows that the metamorphic conditions during mylonitization were 475 ± 50°C, which, combined with a differential stress value of 26 MPa, gives a strain rate of 1.2 x 10⁻¹⁰s⁻¹ based on constitutive equations; corresponding displacement rates are <38 mmyr⁻¹.     

Calcite–graphite isotope thermometry in amphibolite facies marble, Bancroft, Ontario

This study presents calcite–graphite carbon isotope fractionations for 32 samples from marble in the northern Elzevir terrane of the Central Metasedimentary Belt, Grenville Province, southern Ontario, Canada. These results are compared with temperatures calculated by calcite–dolomite thermometry (15 samples), garnet–biotite thermometry (four samples) and garnet–hornblende thermometry (three samples). Δ_cal‐gr values vary regularly across the area from >6.5‰ in the south to 4.0‰ in the north, which corresponds to temperatures of 525 °C in the south to 650 °C in the north. Previous empirical calibration of the calcite–graphite thermometer agrees very well with calcite–dolomite, garnet–biotite and garnet–hornblende thermometry, whereas, theoretical calibrations compare less well with the independent thermometry. Isograds in marble based on the reactions rutile + calcite + quartz =titanite and tremolite + calcite + quartz = diopside, span temperatures of 525–600 °C and are consistent with calculated temperature–X(CO₂) relations. Results of this study compare favourably with large‐scale regional isotherms, however, local variation is greater than that revealed by large‐scale sampling strategies. It remains unclear whether the temperature–Δ_cal‐gr relationship observed in natural materials below 650 °C represents equilibrium fractionations or not, but the regularity and consistency apparent in this study demonstrate its utility for thermometry in amphibolite facies marble.     

The internal structure of glacial landforms: an example from the Halton till plain, Scarborough Bluffs, Ontario

Current views on the internal structure of many glacial landforms need further definition. For example, drumlinized Halton till plain near the Scarborough Bluffs, Ontario would traditionally be. viewed as a lodgement till sheet, but it was found to consist of complex sedimentary assemblages including sediment flows, melt-out, deformation and lodgement tills. These facies vary spatially depending on whether deposition occurred beneath grounded ice or within subglacial cavities. Proglacial sediments bury portions of the till plain. Surface Rutings and drumlins clearly indicate the action of subglacial processes on the surface of Halton drift. Sedimentary structures at the contact between stratified sediments and diamictons within the Late Wisconsinan Halton drift are similar to those in older beds exposed at Scarborough Bluffs. The demonstration of the role of grounded ice in Halton drift and the similarity of sedimentary structures to those of the underlying Thorncliffe and Sunnybrook sediments suggests that the action of grounded ice cannot be ruled out in the case of the lower beds, as has been done by Eyles & Eyles ( Geology 11 , 146–152, 1983). Thus, surface Halton drift may be a model for recognition of similar environments of deposition in older beds beneath Halton. This analysis indicates flaws in a recent re-evaluation of Scarborough Bluffs sediment interpreted as solely lacustrine and not directly affected by glaciers.     

Retention of strontium,cesium, lead and uranium by bacterial iron oxides from a subterranean environment

Bacteriogenic Fe oxides (BIOS) and groundwater samples were collected 195 m underground at the Stråssa Mine in central Sweden. Ferrous iron oxidizing bacteria, including stalked Gallionella ferruginea and filamenous Leptothrix sp., were prominent in the BIOS samples. The BIOS samples were found to contain only poorly ordered (amorphous) hydrous ferric oxide, as determined by X-ray diffraction. Inductively coupled plasma mass spectroscopy revealed hydroxylamine-reducible Fe and Mn oxide contents that ranged from 55 to 85% on a dry weight basis. Concentrations of Sr, Cs, Pb and U in filtered groundwater ranged from 0.002 to 1.8 μM. Solid phase concentrations of these heavy metals in the BIOS spanned the 0.04–2.23 mmol/kg range. Distribution coefficients (K_d values), calculated as the ratio between BIOS and dissolved heavy metal concentrations, revealed solid phase enrichments that, depending on the heavy metal and Fe oxide content of the sample, extended from 10^3.0 to 10^4.7. At the same time, however, a strong inverse linear relationship was found between log K_d values and the corresponding mass fraction of reducible oxide in the samples, implying that metal uptake was strongly influenced by the relative proportion of bacterial organic matter in the composite solids. Based on the metal accumulation properties of the BIOS, an important role can be inferred for intermixed Fe oxides and bacterial organic matter in the transport and fate of dissolved metals in groundwater systems.     

高分异花岗岩浆可能是华南花岗岩型铀矿床主要铀源——来自诸广山南体花岗岩锆石铀含量的证据

锆石的U-Pb测年、Hf和O同位素及稀土、微量元素的研究与应用已获得诸多进展,但锆石中铀含量所蕴藏的地质意义却较少被关注。华南花岗岩型铀矿床的铀源一直存在争议,不同观点认为其分别来自早期已固结地质体、分异岩浆、地幔柱或热点以及U、Th、K富集圈。为尝试利用锆石中的铀含量来追索铀源,本文通过搜集诸广山南体花岗岩锆石U-Pb同位素测年文献,掌握了该花岗岩中14个岩体、37件样品、3种岩性,共467个锆石定年数据。通过数据分析发现印支期(253Ma、244Ma)和燕山期(139Ma、124Ma)具高分异特征的4件酸性岩脉(小岩体)样品中锆石的铀含量明显高于同期岩体。依据铀矿床中高分异酸性岩脉(小岩体)侵位期、基性岩脉侵位期、铀成矿早期(140~90Ma)三者的良好对应关系,结合这一锆石铀含量指示,初步认为华南花岗岩型铀矿床中铀可能主要来自高分异花岗岩浆;推测花岗岩型铀成矿可能属壳幔混合作用结果,即铀源来自地壳分异岩浆,成矿流体和矿化剂主要来自地幔,而成矿空间受断裂系统控制。岩体锆石铀含量或可在铀源丰度、矿床品位判别等方面发挥积极作用。     

基于克里格法刻画砂岩型铀矿U、Ra和U-Ra平衡系数垂向分布规律——以二连盆地芒来铀矿床为例

砂岩型铀矿是绿色经济可采的重要能源矿种,目前是世界上重要的铀矿勘探类型之一。二连盆地芒来铀矿床、鄂尔多斯盆地纳岭沟铀矿床铀矿体多呈板状产出,板状铀矿体成因备受关注。为研究砂岩型铀矿内部U、Ra和铀镭平衡系数（Kp）分布的垂向分布规律,本文以二连盆地芒来铀矿床为例,采用具有网格精度高优点的克里格插值法研究U、Ra和Kp垂向分布规律,分别利用放射性样品分析数据和定量伽马测井五点式反褶积法反演U含量数据,通过克里格法精细刻画砂岩型矿体中U、Ra和Kp分布的垂向分布规律。研究发现,该矿床板状矿体内部具有卷状的特征,Kp分布形态可以用来判断含氧含铀水的运移方向以及氧化强弱。该方法对研究铀矿体形态、铀矿成矿规律和后续地浸开采具有重要意义。     

黑云母和锆石化学组分对岩浆结晶条件的约束:以滇西北衙超大型金矿床为例

中酸性岩浆含矿性差异一直是矿床学的研究热点。滇西北衙超大型金多金属矿床(探明金资源量超过370t)内发育成矿二长花岗斑岩体和非成矿黑云母二长花岗斑岩体、煌斑岩体,是研究岩体含矿性差异、富碱岩浆结晶时物理化学条件及其成矿效应的良好选区。本文在详细的岩相学观察基础上,对成矿的二长花岗斑岩、未成矿的黑云母二长花岗斑岩和煌斑岩中黑云母和锆石开展矿物化学分析,厘定了北衙富碱岩浆的结晶条件。北衙成矿二长花岗斑岩体的锆石结晶温度(843℃)稍高于黑云母二长花岗斑岩体的锆石结晶温度(807℃),鉴于金在熔体中溶解度随温度升高而增大,表明在岩浆演化初期二长花岗斑岩体具有更高的金溶解度。同时,利用锆石微量元素组分估算的二长花岗斑岩体的lg(f_(O_2))(-10. 67)高于黑云母二长花岗斑岩体(-15. 00),表明二长花岗斑岩体具有更高的氧逸度。在岩浆演化过程中高氧逸度会抑制金以硫化物形式沉淀,从而增强了二长花岗斑岩体的成矿潜力。除此之外,二长花岗斑岩具有最低的黑云母结晶温度(二长花岗斑岩、黑云母二长花岗斑岩、煌斑岩依次对应644℃、723℃、766℃)和最浅的侵位深度(1. 46～1. 74km、4. 03～5. 02km、2. 53～2. 72km)。高压条件下母岩浆中出溶的流体几乎没有能量形成裂隙,而且也很难发生对金属富集有重要影响的流体不混溶作用。二长花岗斑岩体侵位深度与矽卡岩中石榴石发育的含石盐子晶的三相包裹体的捕获深度(～2km)近似,进一步暗示二长花岗斑岩体侵位后发生流体沸腾作用。因此,岩浆氧逸度和侵位深度的差异可能是黑云母二长花岗斑岩体和煌斑岩体未成矿的原因。     

U-Pb age and genetic significance of heterogeneous zircon populations in rocks from the Favourable Lake area,Northwestern Ontario

The study evaluates the relationships between measured U-Pb ages and zircon characteristics of five morphologically, texturally, and isotopically complex zircon populations and compares the zircon development stages to the orogenic evolution of the Favourable Lake area. Two distinct zircon types from a hornblendite xenolith in a granitoid batholith of the Sachigo subprovince of the Superior Province yield U-Pb ages of 2729.0±6.8 Ma and 2714.8 _–6.4 ^+7.4 Ma, which date specific metamorphic phases coinciding with major plutonic pulses in the batholith. Zircons from a metamorphosed felsic dike, crosscutting the hornblendite, consist of an old zircon component with a minimum age of 2788 Ma possibly reflecting igneous crystallization 2950 Ma ago, and a younger component with an inferred age of 2725±15 Ma, probably reflecting metamorphism during batholith emplacement.In the Berens River subprovince to the south, granodiorite forms both a late tectonic phase in a large batholith and a post-tectonic pluton intruded into the batholith, yet zircons from these granodiorites have identical ages of 2697.3±1.7 Ma and 2696.2±1.2 Ma, respectively. The late tectonic granodiorite also contains inherited zircons with a minimum age of 2767 Ma which are indirect evidence for the presence of old sialic crust in this subprovince. Zircons from a sheared monzonite near the boundary fault between the two subprovinces yield an upper intercept age of 2769 _–26 ⁺⁶³ Ma, which we interpret as the intrusion age of the monzonite. This rock is older than most dated units in the surrounding batholiths and suggests that the boundary is a long-lived Archean structure.A lower intercept age of about 1750 Ma for zircons of the hornblendite is the result of chemical alteration of the zircons. This, and a similar lower intercept age shown by the sheared monzonite zircons, are thought to reflect increased fluid activity and possibly shearing during the Early Proterozoic Hudsonian orogeny which occurred in the Churchill Province to the northwest. A later Pb-loss mainly from near-surface domains of the zircons is indicated by lower intercept ages of about 500–100 Ma.Publication approved by the Director, Ontario Geological Survey     

Earthquake data analysis: An example from Sweden

Methods and results of earthquake data analysis are illustrated by the seismicity of Sweden in the period 1951–1976, summarizing a comprehensive research project for the past five years. Starting from the regional structural properties, methods are given for the evaluation of instrumental and macroseismic observations, including error analysis and source identification. The resulting earthquake distribution is investigated in relation to space (various types of seismicity mapping), time (periodicities) and magnitude (frequency-magnitude and energy-magnitude relations). The tectonophysical explanations of the earthquake origin are still subject to considerable uncertainty and can be treated only by way of discussions. The engineering applications, stimulated recently by the nuclear power industry, can be placed on much more reliable ground. They include calculations of seismic risk and fracture risk as well as investigations of certain phenomena of practical consequences, especially rockbursts.This review is primarily addressed to those who have use for seismological data in their work, especially geologists, tectonophysicists and engineers. It is important for them to realize how the seismological data are obtained, their reliability and their range of application. Sweden is here mainly used as an example, but the developed methods have a general applicability to any earthquake region, with proper modifications.In short, our purpose is two-fold: (1) to summarize recent research on the seismicity of Sweden: (2) to introduce all users of seismological data into methods and results.     

铀的地球化学性质与成矿——以华南铀成矿省为例

铀是强不相容元素,随着岩浆演化而不断富集,在岩浆演化末期受结构氧增加影响进入独居石、磷钇矿等副矿物中。岩浆演化通常无法直接形成达到工业品位的铀矿床。铀是对氧逸度敏感的变价元素。在表生风化过程中岩体(层)中的铀被氧化为UO_2~(2+)而极易溶解进入水体中,并可在还原环境沉淀而富集成矿,氧化还原界面是找矿的理想选区。大气水可通过断裂构造系统进入一定深度,并受热源作用形成高氧逸度的热液而萃取出岩体(层)中的铀在还原位置沉淀富集形成矿床。新元古代氧化事件以及Marinoan冰期结束使得表生风化过程中更多的U进入水体;而寒武纪生命大爆发,易在沉积盆地底部形成还原环境,有利于U的沉淀富集。受上述三方面因素控制,在华南形成了广泛分布的富铀黑色页岩层,并被之后的沉积物覆盖,成为华南各型铀矿床的铀源层。印支期构造运动使部分富铀黑色页岩层发生部分熔融形成了富铀的S型花岗岩,该类岩石亦是之后铀成矿作用的铀源岩。燕山运动后期华南发生伸展构造背景下的岩浆热事件为以大气水为主的高氧逸度热液的形成并作用于铀源岩(层)提供了有利条件,促使华南各类型铀矿床开始在白垩纪集中形成。     

内蒙古赤峰南窝铺铀矿床英安岩的SHRIMP锆石U-Pb年龄、地球化学特征及地质意义

南窝铺铀矿床位于西拉木伦缝合带以南、康宝—围场—赤峰断裂带(华北北缘断裂带的一部分)以北的白乃庙加里东期岛弧带和华北古板块北缘海西期俯冲—碰撞带,属沽源—红山子铀成矿带北东段红山子—广兴铀成矿亚带的一个铀矿床,铀矿体赋存在额里图组安山岩—英安岩—流纹岩组合中.该组合中的英安岩SHRIMP锆石n(206Pb)/n(238...     

基准面旋回在砂岩型铀矿勘查中的应用--以东胜铀矿床为例

近年来以基准面旋回为参照面的高分辨率层序地层学迅速发展,其最大的优势在于能够适用于受多重因素控制的陆相沉积盆地,并有效提高层序地层分析的准确度和分辨率。基准面旋回原理也同样适用于砂岩型铀矿的勘探开发研究和实践,它控制了砂岩、泥岩的空间分布和岩石孔渗、封闭性能,决定了地层结构的叠加样式。文章以东胜铀矿床为例,分析了基准面旋回在砂岩型铀矿勘探开发中的应用。认为:基准面升降旋回中形成的砂、泥岩地层结构配置良好;长期基准面上升早期形成的辫状河河道砂岩具连通性好、粒度粗、碎屑含量高、杂基含量低及孔渗条件好等特点,是重要的含矿层。     

Distinguishing tsunami and storm deposits: An example from Martinhal, SW Portugal

Geological identification of past tsunamis is important for risk assessment studies, especially in areas where the historical record is limited or absent. The main problem when using the geological evidence is to distinguish between tsunami and storm deposits. Both are high-energy events that may leave marine traces in coastal stratigraphic sequences. At Martinhal, SW Portugal both storm surge and tsunami deposits are present at the same site within a single stratigraphic sequence, which makes it suitable to study the differences between them, excluding variations caused by local factors.

The tsunami associated with the Lisbon earthquake of November 1st 1755 AD, had a major impact on the geomorphology and sedimentology of Martinhal. It breached the barrier and laid down an extensive sheet of sand, as described in eyewitness reports. Besides the tsunami deposit the stratigraphy of Martinhal also displays evidence for storm surges that have breached and overtopped the barrier, flooding the lowland and leaving sand layers. Both marine-derived flood deposits show similar grain size characteristics and distinctive marine foraminifera. The most important differences are the rip-up clasts and boulders exclusively found in the tsunami deposit and the landward extent of the tsunami deposit that everywhere exceeds that of the storm deposits. Identification of both depositional units was only possible using a collection of different data and extensive stratigraphical information from cores as well as trenches.     

Luminescence dating of Holocene spit deposits: An example from Skagen Odde, Denmark

Clemmensen, L. B. & Murray, A. S. 2009: Luminescence dating of Holocene spit deposits: An example from Skagen Odde, Denmark. Boreas , 10.1111/j.1502-3885.2009.00110.x. ISSN 0300-9483.
Skagen Odde is a large, active spit system in northern Denmark that started to form about 7200 years ago. Models for spit growth have usually relied on radiocarbon-dating of swale peat (Martørv). In this study, we date the spit deposits at three sites directly using Optically Stimulated Luminescence (OSL) to obtain supplementary age control on spit development. The spit deposits consist of a lowermost succession of shoreface, beach and backshore aeolian deposits topped by a swale peat and followed by an uppermost succession of aeolian sand sheet and dune deposits. The ages of the shallow marine, beach and backshore aeolian deposits at the main study site are indistinguishable, implying good resetting of the shallow marine deposits; the average age of 4640±250 years compares well with earlier model predictions based on radiocarbon-dating of swale peat. Aeolian sand extracted from the uppermost part of the swale peat at this site provides OSL ages of between 1600 and 2500 years, in good agreement with a calibrated AMS age from the same level of 2330–2200 years. The uppermost aeolian succession consists of two units separated by a thin palaeosol, and the aeolian units have OSL ages of about 1500 years and younger than 130 years. Lowermost spit deposits at the two additional sites have average ages of 5010±240 and 3730±190, respectively, supporting the existing chronology for spit growth based on radiocarbon-dating.     

Geologic urban hindplanning: An example from a hellenistic-byzantine city,stobi, Yugoslavian macedonia

Stobi flourished between about 400b.c. anda.d. 600, and, like modern cities, was afflicted by several environmental-geologic difficulties. A large Christian church was built upon poorly compacted artificial fill, resulting in severe foundation problems. An earthquake did extensive damage to the Roman theatre between two stages of its construction. A catastrophic mudflow destroyed structures lying below a cliff of flysch sandstone and shale. After the third or fourth centurya.d. severe desiccation of the climate set in, leading to devegetation, flooding, and dust storms. Structures on the flood plain were buried in several meters of fine sediment. Stobi finally was abandoned, and the structures eventually were buried by wind-blown dust accumulating at the rate of about 1 meter per millenium.     

钍铀比值在判别铀成矿环境中的应用研究 ——以粤北书楼丘矿床为例

钍铀比值是反映铀成矿信息的重要参数,地面伽玛能谱钍铀比值（Th/U）、分量钍铀比值（FTh/U）可分别指示花岗岩地区构造蚀变带型铀矿浅部及深部的矿化信息,多角度、多尺度呈现铀富集环境。本文重点探讨利用Th/U、FTh/U分别提取浅部和深部铀成矿信息的可能性,并在粤北书楼丘铀矿床已知勘探剖面进行方法有效性试验。试验结果表明：Th/U、FTh/U能分别指示浅表和深部铀成矿环境;Th/U、FTh/U与浅表、深部铀富集程度呈负相关,且建立了钍铀比值与铀富集程度间的判别关系;FTh/U除与深部铀富集程度相关外还与铀矿体中心埋深有关,FTh/U幅值越大,矿体埋深越深,并进一步建立FTh/U幅值与矿体中心埋深间的半定量关系式。综上,利用钍铀比值法在书楼丘外围开展铀成矿有利地段预测,并取得较好应用效果,成功预测4片浅部、5片深部铀成矿有利地段,其中FTh/U-2号深部异常已被钻探工程揭露证实。本次研究对书楼丘地区下一步找矿工作的部署与开展具有重要借鉴意义。     

Lacustrine sedimentation in a semiarid alpine setting: An example from Ladakh, northwestern Himalaya

The Lamayuru lacustrine strata in Ladakh typify many of the carbonate-rich Pleistocene alpine lakes found in the semiarid environment of the northern Himalaya. Created by a 200-m-thick landslide, the lake was in existence by at least 35,000 yr ago, and may have persisted until 500–1000 yr ago. Represented in the center by thin turbidites and laminated muds, the lacustrine sedimentation along the lake margins and low-relief deltas characteristically displays a marked contrast between (1) clastic lenses representing rapid, sporadic, matrix-poor debris flows and periglacial inputs from the alpine slopes and (2) abundant, diverse, shallow-water, biologically dominated carbonate strata, among which organism-rich, chalky beds and oncolithic and encrusted stem-rich strata predominate. Resemblances of the Lamayuru lacustrine strata and their setting to those of former lakes throughout areas north of the Greater Himalayan crest suggest that the alpine, semi-arid environment would favor diversified, spacially restricted carbonate sedimentation punctuated by occasional clastic influxes. Such a depositional regime contrasts strongly with that found immediately south of the Himalayan crest where more humid conditions promote a more continuous clastic influx into intramontane lakes.     

交代蚀变岩组分迁移量的合理计算--以内蒙古470铀矿床钠长石化粗面岩为例

文章在全面论证已有组分迁移量计算法合理性的基础上,进一步完善了笔者2000年提出的真恒量组分恒定计算法,即:利用岩石的两种实测密度计算交代蚀变岩的实有真迁移质量及其原子数。     

Ice-marginal sedimentary, glacitectonic, and morphologic features of Pleistocene drift: An example from Newfoundland

A Pleistocene drift sequence in hummocky terrain along part of the southern Avalon Peninsula of Newfoundland is interpreted to comprise complexly interrelated lodgement till, melt-out till, flow till, supraglacial and proglacial outwash, and supraglacial rhythmites. The gray and tan melt-out tills are stacked in imbricate fashion, giving rise to exceptionally thick stratigraphic sections. Contacts between melt-out tills are interpreted as remnants of shear planes because they are sharp, they dip in the up-ice direction, and they converge toward valley margins. Overlying flow tills interdigitate with supraglacial outwash. The drift sequence was deposited during a single episode of glaciation, rather than by repeated glacier advance, as previously proposed. It is the product of thrusting of englacial debris along ice-marginal shear planes, subsequent melting-out of englacial debris, and formation of supraglacial flow till and outwash. Preservation of this sequence probably is due to high content of englacial debris within the Wisconsinan ice. The sedimentary, glacitectonic, and morphologic features of this sequence are similar to those found at the margins of certain Arctic glaciers of subpolar thermal regime which have recently been the subject of Pleistocene glacial sedimentation models for west-central Canada and Great Britain. Recognition of these distinct elements indicates wisconsinan glacier lobes were of the cold Arctic type in southeastern Newfoundland. Alternative explanations for this sequence, such as deposition by glaciers of temperate thermal regime or by surging glaciers, are discounted. Because the features described here are complex and difficult to recognize, they may be more widespread in Pleistocene drift than has previously been interpreted.