Glauconite at Different Stages of Lithogenesis in Lower Cambrian Rocks of Western Lithuania

It is shown that glauconite was mainly formed under diagenetic conditions in terrigenous–clayey rocks (Rausven Unit) of the Lower Cambrian Virbalis Formation in western Lithuania. This was preceded by bioturbation at some levels of geological column and local short-term reworking at other levels. Different forms of glauconite and its interrelation with ambient minerals in diagenesis and epigenesis are considered. A two-phase micaceous (glauconite–illite) composition of globules has been revealed and crystallochemical characteristics of each phase is presented.     

Isotopic and Geochemical Characteristics of Western Arctic Ice-Rafted Sediments

Doklady Earth Sciences - The isotope-geochemical characteristics (LaN/YbN, Sm/Nd, εNd(t), 207Pb/206Pb, and 87Sr/86Sr) of ice-rafted sediments in several areas of the Western Arctic (Fram...     

数值拟合法在修正K-Ar全岩年龄值方面的应用

K Ar法是地质工作中常用的测年方法 ,根据测试对象的不同 ,可分为全岩以及单矿物K Ar法。通常情况下 ,前者的结果要比后者的结果偏低。本文在对华南及华北地区部分K Ar同位素年龄值进行详细分析的基础上 ,以黑云母年龄为基准值 ,采用数值拟合法 ,对该样品的全岩年龄值的修正问题进行了初步探讨     

K-Ar Radiometric Age Determinations of White Micas from the Piemont Zone,French-Italian Western Alps

The olivine-clinopyroxene (Fe-Mg partition) geothermometer of Powell and Powell (1974) was derived on the basis of clinopyroxene mixing parameters which imply a large miscibility gap in CaFeSi₂O₆-CaMgSi₂O₆-CaAl₂SiO₆ clinopyroxenes at 950° C. Application of the Powell and Powell thermometer in an empirical way (ignoring likely errors in mixing parameters) is limited by the fact that almost all natural clinopyroxene-olivine pairs are constrained by the form of the equation to have 1-bar temperatures within the narrow (915–1,060° C) limits of their calibration points.Temperatures obtained from the Powell and Powell thermometer have been compared with those obtained from clinopyroxene-orthopyroxene (miscibility gap) thermometers; agreement with the latter is poor. There are discrepancies between calculated and observed (experimental) temperatures for iron-rich clinopyroxene-olivine pairs. It is concluded that application of the thermometer in its present form is unlikely to produce reliable results.     

辽西凌源地区义县组下部层位的U—Pb测年及意义

辽西凌源地区义县组的下部层位为大王杖子层，通过对该层位及相关层位样品中锆石的LA—ICP—MS的U—Pb测年，获得大王杖子层的形成年代为125～122Ma。经过综合分析，得出以下初步结论：①辽西凌源地区与北票-义县地区的义县组底界是不等时的；凌源地区义县组下部层位在时代上相当于北票-义县地区的义县组尖山沟层（砖城子层）；②凌源地区的张家口组与义县组之间有约5～6Ma的时间间隔。这不仅验证了凌源地区张家口组与义县组之间为角度不整合接触的可靠性，也暗示该5～6Ma的间隔期为冀北-辽西地区中生代构造格架转换的关键时期；该时期也是我国东北地区中生代岩浆作用的鼎盛时期；同时在冀北-辽西地区，该间隔期之后发生了热河动物群的大爆发，说明该间隔期也是一个重要的生物界限。     

内蒙古阿尔山地区下寒武统苏中组混合沉积特征及形成环境研究

以内蒙古阿尔山地区下寒武统苏中组为研究对象,综合区域地层、岩石结构、剖面特征、粒度分布特征,对苏中组碳酸盐岩夹碎屑岩的沉积环境进行了深入分析.从粒度分布特征来看,苏中组砂岩粒度分布表现出双峰和多峰不对称,偏度以正偏为主,峰度数值多且比较低,分选性差,以粗粒物质为主等特征;运用萨胡图解投点、判别函数计算确定内蒙古阿尔山地...     

浙西下寒武统大陈岭组沉积异常及其海啸成因初探

前人对浙西下寒武统大陈岭组沉积相分析一直存在半深水相和浅水相两种观点。大陈岭组化石极少,仅中上部产营漂浮或游泳生活的节头虫类Arthicocephalus, Arthricocephalites和Changaspis,不见底栖类化石。对大陈岭组碳酸盐岩碳氧同位素分析显示,对应于产半深水相生物化石的层位存在碳同位素正漂移,表明此处水体较深;但该组大量发育碳酸盐岩台坪相的沉积标志-鸟眼构造,与较深水相生物和碳同位素正漂移的解释结果相悖。作者在对浙西开化、常山、江山寒武系野外调查时发现大陈岭组存在一套地震-海啸沉积岩系,且海啸岩的产出层位与江山较深水相化石、碳同位素正漂移层位相当。研究认为,海啸作用可以使不同环境的沉积物相互混合,造成沉积异常,浙西下寒武统大陈岭期沉积异常是海啸事件的反映,海啸作用把较深水生物和沉积物带到浅水区沉积下来,并造成碳氧同位素短暂、急剧的正漂移。     

浙西下寒武统大陈岭组地震液化脉微量元素特征研究

地震液化脉是地震作用引起的软沉积变形的重要构造之一,前人对脉体形态学和动力学做了大量的研究工作,但对其成因的微观地球化学行为研究较少。笔者采取开化裴岭脚剖面2期地震事件沉积的3套地震液化脉层样品21块,分别对其脉体和含脉体围岩做了微量元素分析。结果显示,液化脉中Cs、Ba、Th、Zr、Hf、Cr、Rb、Nb等反映陆源性质元素明显高于含脉体围岩,而Sr、Y、Ni反映海相沉积特征元素则表现为含脉体围岩高于脉体。通过对V、Mo富集度和微量元素特征参数Sr/Ba、Th/U等的综合研究,发现液化脉体表现为氧化环境,含脉体围岩为还原环境,且脉体和围岩均具有淡水作用特点。研究认为,早寒武世大陈岭期白云质灰岩沉积过程中有蚀源区陆源碎屑物的补入;在地震突发振动力作用下,富含水的软沉积层液化泄水,因化学沉积物和碎屑沉积物性质的差异,塑性碳酸盐沉积物随水部分流失,使得单位体积内碳酸盐沉积含量低于围岩,导致脉体中更富陆源物质;地震事件沉积层属潮上带,特别是地震液化泄水后期至成岩期,含地震液化脉沉积层曾暴露地表,受后期陆源物的再补给及大气降水淋滤蚀变作用影响,表现为古气候和古盐度异常,为浙西大陈岭组浅水沉积提供了地球化学的证据。     

Characteristics and Dolomitization of Upper Cambrian to Lower Ordovician Dolomite from Outcrop in Keping Uplift, Western Tarim Basin, Northwest China

Late Cambrian to Early Ordovician sedimentary rocks in the western Tarim Basin, Northwest China, are composed of shallow-marine platform carbonates. The Keping Uplift is located in the northwest region of this basin. On the basis of petrographic and geochemical features, four matrix replacement dolomites and one type of cement dolomite are identified. Matrix replacement dolomites include (1) micritic dolomites (MD1); (2) fine–coarse euhedral floating dolomites (MD2); (3) fine–coarse euhedral dolomites (MD3); and (4) medium–very coarse anhedral mosaic dolomites (MD4). Dolomite cement occurs in minor amounts as coarse saddle dolomite cement (CD1) that mostly fills vugs and fractures in the matrix dolomites. These matrix dolomites have δ18O values of ?9.7‰ to ?3.0‰ VPDB (Vienna Pee Dee Belemnite); δ13C values of ?0.8‰ to 3.5‰ VPDB; 87Sr/86Sr ratios of 0.708516 to 0.709643; Sr concentrations of 50 to 257 ppm; Fe contents of 425 to 16878 ppm; and Mn contents of 28 to 144 ppm. Petrographic and geochemical data suggest that the matrix replacement dolomites were likely formed by normal and evaporative seawater in early stages prior to chemical compaction at shallow burial depths. Compared with matrix dolomites, dolomite cement yields lower δ18O values (?12.9‰ to ?9.1‰ VPDB); slightly lower δ13C values (?1.6‰–0.6‰ VPDB); higher 87Sr/86Sr ratios (0.709165–0.709764); and high homogenization temperature (Th) values (98°C–225°C) and salinities (6 wt%–24 wt% NaCl equivalent). Limited data from dolomite cement shows a low Sr concentration (58.6 ppm) and high Fe and Mn contents (1233 and 1250 ppm, respectively). These data imply that the dolomite cement precipitated from higher temperature hydrothermal salinity fluids. These fluids could be related to widespread igneous activities in the Tarim Basin occurring during Permian time when the host dolostones were deeply buried. Faults likely acted as important conduits that channeled dolomitizing fluids from the underlying strata into the basal carbonates, leading to intense dolomitization. Therefore, dolomitization, in the Keping Uplift area is likely related to evaporated seawater via seepage reflux in addition to burial processes and hydrothermal fluids.     

湘西—黔东北地区下寒武统铅锌矿矿床地质特征及成因探讨

湘西—黔东北地区下寒武统铅锌矿严格赋存于台地边缘礁滩相产出的藻礁灰岩中,其实质属断裂构造控矿,具有MVT型矿床的典型特征。成矿时代可能为晚志留世至早石炭世。(中)低温度、中高盐度流体从上地壳岩石地层中浸出铅锌,顺断裂通道运移至碳酸盐岩围岩中,围岩受水岩反应和交换作用释放的海水硫酸盐经热化学还原作用转化为还原硫,还原硫与铅锌金属络合物相结合而成矿。该类成矿过程中受区域挤压应力影响的断裂构造始终起到至关重要的作用。     

Carbonate Platform Margin Slope Characteristics of Cambrian Chefu Age in Baojing-Fenghuang and Adjacent Areas, Western Hunan, China

The Cambrian paleogeography in south China can be divided into Yangtze platform, plat-form margin slope (including upper slope and lower slope) and basin. The carbonate gravity deposits are well developed there, particularly in the Yangtze platform adjacent areas. This paper mainly deals with declivity fan characters of the Chefu age in Fenghuang acUacent areas, western Hunan Province. Accord-ing to their distribution and thickness, three main declivity fans have been divided in the study areas,namely, Dama ( ∈ c-dsf), Machong ( ∈ c-msf) and Huangheymm ( ∈ c-hsf) declivity fans. Each fan‘s characters are described in detail in this paper. Based on their distribution range, scale and fossiliferous layers, two peak periods (fair developmental period) are distinguished: (1) Linguagnostus reconditus Zone (time), and (2) Glyptagnostus reticulatus Zone (time). They were characterized by huge thickl imestone breccia layers (single layer 3--4 in thick) and dosely spaced spread. Besides, there are also two develolmaental periods: (1) Lej op yge laevigata- Proagnostus bulbus Zone (time), and (2) Agnos-ms inexpeetans-Proceratopyge protracta Zone (time) to Erixanium Zone (time) to Corynexochus plumula-Sinoproceratopyge cf. kiangshanensis Zone (time), while Glyptagnostus stolidotus Zone (time) was an interstitial period (without or rare limestone breccias). All these features may verify the relative movement of the earth crust and paleodimate variety of the Chefu age in the study areas.     

冀北甲山正长岩的矿物学、地球化学及Sr-Nd同位素特征

甲山岩体形成于早白垩世晚期,可划分为3个单元。电子探针分析结果表明,碱性长石主要为Na-正长石和歪长石,少量为正长石;角闪石主要为钙角闪石中的铁浅闪石,少数为铁角闪石和铁阳起石;单斜辉石属钙铁辉石和普通辉石。化学成分上,该岩体富S i、全碱、全Fe、REE、Th、Ga、Nb、Zr、H f,贫Mg、Ba、Sr、Ti,Cr、Co、N i、V等过渡元素亏损,富轻稀土,中等铕负异常,具有A型花岗岩的特点。甲山正长岩的N(87Sr)/N(86Sr)初始比值ISr=0.701 41~0.707 41,εNd(t)值为-2.27~-5.58,表明岩浆为富集的大陆岩石圈地幔部分熔融形成。岩石圈的拆沉和减薄作用是引发岩石圈地幔部分熔融的原因之一,岩石圈地幔的富集作用可能发生在中元古代晚期。     

徐州大北望寒武系徐庄组海绿石成因探讨

徐州大北望寒武系徐庄组发育不同类型海绿石，为探讨不同类型海绿石的成因，基于海绿石的矿物学、地球化学及沉积环境分析，利用偏光显微镜、X 射线衍射及电子探针等方法对各含海绿石岩层及不同类型海绿石进行系统对比研究查明海绿石的指相意义。结果表明，徐庄组发育颗粒状、碎屑假象状和胶团状三种类型海绿石，其中颗粒状海绿石具有中—高含量钾、高含量铁、砂岩中—高含量铝、石灰岩中低含量铝等特征；碎屑假象状海绿石具有变化大的钾、铁、铝，且保持着其母质形态特征；胶团状海绿石具有高钾、高铁、低铝特点。颗粒状海绿石成因符合颗粒绿化理论，砂岩中海绿石易受环境影响；碎屑假象状海绿石成因符合层状晶格理论及假象替代理论，受到交代和溶蚀作用，因受较强的水动力条件影响成分变化较大；胶团状海绿石是凝胶状海绿石通过胶结作用沉淀，形成于稳定环境中。     

豫西寒武纪叠层石微生物化石及其钙化特征

微生物的钙化机理是当今微生物碳酸盐岩研究的热点。微观条件下,在豫西寒武纪碳酸盐岩叠层石中发现了大量微生物化石,形态特征明显,为典型蓝细菌属的丝状葛万菌(Girvanella)和球状肾形菌(Renalcis)。根据豫西寒武纪叠层石明暗纹层中微生物化石的赋存状态及相关化石证据,可以判断叠层石的钙化分为微生物的物理和化学2种作用方式,其中物理钙化有2种钙化途径,而化学钙化又有化学诱导和化学控制2种钙化模式和多种钙化途径。在扫描电镜下能够清晰地看到各种钙化方式的结果和微生物主动营造作用所留下的证据,即磨圆度较低的颗粒物和深色灰泥等。结果表明叠层石的有机成因和水动力条件对其钙化方式具有重要影响。     

滇西地区下地壳铅同位素的组成及其意义

滇西地区新生代碱性侵入岩中广泛分布的麻粒岩包体可以代表该地区的下地壳岩石,为了确定滇西下地壳岩石的铅同位素组成,我们系统采集了该区碱性岩中的麻粒岩包体,挑选出其中的长石、石榴子石等造岩矿物,测定了其铅同位素组成,在Zartman等的铅构造演化模式图上,剔除个别异常的铅同位素组成,圈出投影于下地壳铅同位素演化趋势线上及附近的铅同位素分布范围,由此确定了该区下地壳的铅同位素组成的区域,并进一步结合作者先前确定的该区上地壳及上地幔铅同位素组成,构建了该区三维岩石圈铅同位素组成,并将这一结果用于滇西金顶超大型铅锌矿床的成矿物质来源的研究中,发现颇受争议的金顶铅锌矿床中的铅并非来自上地幔,而相当于下地壳来源的铅与兰坪盆地沉积岩铅二者的混合铅。     

黔南坳陷下寒武统烃源岩地球化学特征及成因

为明确黔南坳陷下寒武统烃源岩地球化学特征及成因,采用岩石热解、GC、GC-MS等方法对3个典型剖面样品进行了系统分析。结果表明:黔南坳陷下寒武统黑色岩系为一套区域性海相优质烃源岩,厚约50~150 m;烃源岩TOC值为0.13%～15.40%,平均3.31%(n=169);烃源岩干酪根δ13C值为-35.79‰～-29.88‰,平均-32.85‰(n=35),显微组分主要为腐泥组;烃源岩干酪根海相镜质体反射率值为1.95%～3.96%,其等效镜质体反射率值为2.02%～3.47%;烃源岩饱和烃正构烷烃分布多为单峰形,主峰碳多为C22,C30藿烷和C27规则甾烷含量高,规则甾烷多为C27>C29>C28,Pr/Ph值为0.27～0.62,具较高的伽马蜡烷和硫芴含量,OEP值为0.82~1.11,C31升藿烷22S/(22S+22R)值为0.56~0.63,平均0.59;烃源岩总体具有富集轻稀土元素,Ba、Mo、V、U等元素含量高,具较强Ce负异常、Eu正异常和较高U/Th值等特征。总之,黔南坳陷下寒武统海相烃源岩分布广,厚度较大,有机质丰度高,类型好,热演化程度高,是高古生产力和缺氧环境共同作用的产物,可为黔南坳陷油气生成提供雄厚的成烃物质。     

Diagenesis of Carbonate and Siderite Deposits of the Lower Riphean Bakal Formation,the Southern Urals: Sr Isotopic Characteristics and Pb-Pb Age

The Rb-Sr and U-Pb systematics were studied for carbonate rocks of the Lower Riphean Bakal Formation of the southern Urals and related siderite ores of the Bakal iron deposit. The least-altered limestones taken at a significant distance from the Bakal ore field satisfy the strict geochemical criteria of retentivity: Mn/Sr < 0.2, Fe/Sr < 0.5, and ⁸⁷Sr/⁸⁶Sr (difference between the measured ⁸⁷Sr/⁸⁶Sr values in secondary and primary carbonate phases) < 0.001. The least-altered carbonate phases were extracted by the stepwise dissolution in 0.5 N HBr. The Pb-Pb date of limestones (1430 ± 30 Ma) defines the age of early diagenesis of carbonate sediments of the Bakal Formation. The ⁸⁷Sr/⁸⁶Sr ratio in the sedimentary environment of the Bakal carbonates (0.70457–0.70481) yields isotopic signature for the Early Riphean seawater. The Pb-Pb age of metasomatic siderites (1010 ± 100 Ma), which formed at the end of the main ore formation stage and did not undergo late epigenesis, corresponds to the final phases of the Grenville tectonogenesis. Siderites of the main ore formation stage are confined to central parts of the thickest carbonate units and have high ratios of ⁸⁷Sr/⁸⁶Sr (0.73482–0.73876) and ²⁰⁸Pb/²⁰⁴Pb (41.4–42.9). Iron-bearing solutions formed during the diagenesis of mainly Lower Riphean clayey rocks and migrated along low-density zones and faults. The solutions discharged at the interformational unconformity between the Bakal and Zigalga formations. At the contact with shales, carbonate rocks and siderites experienced the later epigenetic dolomitization (partial desideritization) caused by the circulation of solutions enriched in radiogenic ⁸⁷Sr and low-radiogenic ²⁰⁶Pb. This dolomitization occurred simultaneously with the Cadomian tectonothermal activation of the region.__________Translated from Litologiya i Poleznye Iskopaemye, No. 3, 2005, pp. 227–249.Original Russian Text Copyright © 2005 by Kuznetsov, Krupenin, Ovchinnikova, Gorokhov, Maslov, Kaurova, Ellmies.     

太平洋CC区西部沉积物地球化学特征及其成因

对太平洋CC区西部7根沉积物短柱样的常微量元素进行浓度测试,以了解沉积物元素时空分布特征及其来源和控制因素.与上地壳元素平均值(UCC)相比,研究区沉积物中MnO、P2O5、Co、Ni、Cu、Mo、Ba明显富集,Al2O3、K2O、Fe2O3、CaO、Sr等亏损.聚类和因子分析表明研究区沉积物元素有4种来源,其中Al2...     

华南下寒武统黑色岩系铂多金属矿中黄铁矿流体包裹体的He-Ar同位素体系

利用惰性气体同位素质谱仪测定了华南下寒武统具代表性的黑色岩系铂多金属矿中黄铁矿流体包裹体的He-Ar同位素组成,发现其~3He/~4He均较低,为0.43×10~(-8)～26.39×10~(-8),R/R_α为0.003～0.189,而~(40)Ar/~(36)Ar为258～287,接近大气饱和水。同位素地球化学示踪研究显示,该矿成矿流体主要由建造水(盆地热卤水)和大气饱和水(海水)组成,基本不含地幔流体或深源岩浆水。黑色岩系铂多金属矿的成矿可能与华南克拉通南缘加里东冒地槽的演化有关。在早寒武世,接受了巨厚沉积的加里东盆地中的建造水由于上覆沉积物的压力,顺层侧向迁移,并沿断裂上升与海水混合而成矿。