Mineralogy and petrography of Riphean rocks in the Moscow graben

Based on the study of Upper Precambrian rocks penetrated by the Pavlovskii Posad parametric borehole in the 1770–4780 m interval, the Riphean succession is underlain by quartzose sandstones. The aulacogen within the Moscow Syneclise was covered by sediments accumulated during the intense chemical weathering of a peneplain. Above the 3550 m level, Upper Precambrian rocks comprise arkoses with abundant garnet. The immature (in terms of lithology and mineralogy) arkosic sequence was probably accumulated in grabenshaped structures (aulacogens).     

Revision of the stratigraphy of Permian and supposed Permian rocks of Southern Scotland

The formal stratigraphy of the Permian basins of southern Scotland is described for the first time. These rocks consist of piedmont breccias and lavas, overlain by wadi-fan and dune complexes, and alluvial fan and floodplain sediments. The sequences are inferred to be Stephanian to Lower Permian in age and correlatable with similar continental sediments in England and with the Lower Rotliegendes of Germany and the North Sea.

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Zusammenfassung Erstmals wird hier eine stratigraphische Gliederung der permischen Beckensedimente im südlichen Schottland gegeben. Diese Gesteine bestehen aus Piedmont-Brekzien und Laven, die von Fanglomeraten und Dünenkomplexen überlagert werden. Alluviale Fächer und Schwemmflächen-Sedimente gehören hierzu. Diese Serien sollen ein Alter von Stephan bis Unter-Perm aufweisen und vergleichbar mit ähnlichen kontinentalen Sedimentfolgen in England und im Unter-Rotliegenden von Mitteleuropa sein.

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Résumé La stratigraphie des formations des bassins permiens du Sud de l'Ecosse est ici décrite pour la première fois. Ces roches sont des brèches de piedmont et des laves, surmontées par un complexe de dépôts d'épandage et de dunes, et par des cones et des dépôts alluviaux. Les couches seraient à rapporter au Stéphanien et au Permien inférieur, et à correler avec des sédiments continentaux semblables en Angleterre et avec le Rothliegend inférieur d'Allemagne et de la Mer du Nord.

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The geochemistry of the potassium-rich Permian volcanic rocks of Devonshire,England

This paper re-defines the Permian volcanics of Devonshire as belonging to the high-potassium shoshonitic suite of rocks commonly associated with a late or post-orogenic tectonic setting. Factor analysis is used to classify the rocks into four well defined groups based upon major and extensive trace element data. They are interpreted on an Andean-type plate collision model as being derived from a subduction zone at a depth of some 300 km beneath Hercynian Europe.     

The Roadian Stage of the Permian and problems of its global correlation

Ammonoids, conodonts, and fusulinids from the type sections of the Roadian and contiguous stages in western Texas and adjacent areas are analyzed and partially revised. Four successive Roadian ammonoid assemblages are distinguished and correlated with conodont zones; data on their distribution are presented. Based on the results obtained, the Roadian Stage is identified in the Boreal and Tethyan regions. Boundaries of the Roadian Stage defined accurately in the type sections of Texas are hardly recognizable elsewhere. Recognition of the upper boundary is especially difficult. Occurrence of Roadian fossils means that deposits of this age are present in a sequence, but they cannot be differentiated from underlying and overlying beds. Like in the type area, the stage lower boundary based on conodonts is above the level of significant changes in marine biota within the Boreal and Tethyan realms as well. The upper boundary is not marked by noticeable biotic events either. Correlation of the Roadian deposits is imprecise because their boundaries are formally established using distribution of relatively rare conodonts.     

塔里木盆地二叠纪火成岩的同位素年代学

在分区概述了塔里木盆地二叠纪火山一沉积地层的划分和对比的基础上,本文报道了2件玄武岩样品、2件辉长岩样品、1件辉绿岩样品、1件正长岩样品、1件英安斑岩样品和1件花岗闪长岩样品的锆石U-Pb法定年,表明强烈的火成活动发生在早二叠世（玄武岩定年294 Ma,287 Ma）,可延续到中二叠世（辉长岩定年265 Ma）.空间上,火山活动的中心位于巴楚一柯坪地区.玄武岩喷发可分为2个旋回,分别称南闸组和阿恰群中（火山岩）段;前者伴有英安斑岩（285 Ma）喷发和辉长岩（283.1 Ma）、辉绿岩（283 Ma）侵入,正长岩（281.7 Ma）则代表了区域上岩浆分异的晚期阶段.巴楚及邻近地区辉绿岩规律的北西走向指示了区域拉张应力场方向为北东一南西向.Ar-Ar法测年未获得理想的坪年龄值,仍支持了二叠纪早期发生过热事件的认识.     

The pyrope-coesite rocks and their country rocks at Parigi,Dora Maira Massif,Western Alps: detailed petrography,mineral chemistry and PT-path

Both the coarse- and fine-grained varieties of the partly coesite-bearing pyrope-quartzites, their interlayered jadeite-kyanite rocks, and the biotite-phengite gneiss country rock common to all of them were subjected to detailed petrographic and textural studies in order to determine the sequence of crystallisation of their mineral constituents, which were also studied analytically by microprobe. Prior to pyrope and coesite growth, the Mg-rich metapelites were talc-kyanite-chlorite-rutile-ellenbergerite schists which — upon continued prograde metamorphism — developed first pyrope megacrysts in silica-deficient local environments at the expense of chlorite + talc + kyanite, and subsequently the smaller pyrope crystals with coesite inclusions from reacting talc + kyanite. Based on geobarometrically useful mineral inclusions as well as on experimentally determined phase relations, a prograde PT-path — simplified for water activity = 1 — is constructed which passes through the approximate PT-conditions 16 kbar and 560° C, 29 kbar and 720° C, and finally up to 37 kbar at about 800° C, where the Mg-rich metapelite was a pyrope-coesite rock with phengite, kyanite, and talc still present. During the retrograde path, pyrope was altered metasomatically either into phlogopite + kyanite + quartz or, at a later stage, to chlorite + muscovite + quartz. Both assemblages yield PT-constraints, the latter about 7–9 kbar, 500–600° C. The country rock gneisses have also endured high-pressures of at least 15 kbar, but they provide mostly constraints on the lowest portion of the uplift conditions within the greenschist facies (about 5 kbar, 450° C). Microprobe data are presented for the following minerals: pyrope, ellenbergerite, dumortierite (unusually MgTi-rich), jadeite, vermiculite (formed after Na-phlogopite?), paragonite, and for several generations of phengite, chlorite, talc, phlogopite, dravite, and glaucophane in the high-pressure rocks, as well as for biotite, chlorite, phengites, epidote, garnet, albite, and K-feldspar in the country rock gneisses. An outstanding open problem identified in this study is the preservation of minerals as inclusions within kyanite and pyrope beyond their PT-stability limits.     

西藏西北部晚二叠世地层新资料

<正> 藏北地区的晚二叠世地层,文世宣等(1979)报导了羌塘东部双湖热觉茶卡一带的上二叠统,命名为热觉茶卡组。梁定益等(1983)在羌塘西部多玛附近发现位于下二叠统之上和下三叠统之下的一套含Waagenophyllum和腕足类的碎屑岩和碳酸盐地层,称吉普日阿群。诺林(1946)把塔什立克湖至窝尔巴错一带的二叠系称塔什立克湖群,该群的顶     

The petrography of Southern Tibet

Summary Mineralogical investigations of rock samples from the Transhimalaya and Tibetan Himalaya allow the conclusion that during the last glaciations in this area there was long distance glacial transport. The samples from the Mt. Everest group, the highest region of the continental crust, provide an account of the petrological data collected from this area. They depict a juxtaposition of sedimentary series and granitic intrusive bodies and also extreme tectonic action deep into their cystalline structure.     

浙江舟山群岛首次发现二叠纪变质岩

浙江舟山群岛大衢岛及周边若干小岛出露少量变质岩系,包括斜长角闪岩、片麻岩、片岩、大理岩等,以往被归为陈蔡岩群。LAICP-MS锆石U-Pb测年结果表明,黑云斜长片麻岩变质新生锆石或岩浆锆石的变质边年龄在260~270Ma之间,大理岩的变质年龄为261.1±1.3Ma,侵入变质岩的未变形伟晶岩脉年龄为258.0±1.6Ma,表明该套变质岩系的变质时代约为260Ma,不能归入加里东期变质的陈蔡岩群。这是在华南东北缘地区首次发现二叠纪变质岩,为探讨华南东吴运动和全球海西运动,甚至泛大陆的重建提供了重要新信息。     

Geochemistry and petrography of impact breccias and target rocks from the 145 Ma Morokweng impact structure, South Africa

Morokweng is a large, 145 Ma impact structure in the Northwest Province of South Africa. The impact origin of this structure and its melt rock has been confirmed by ample evidence of shock metamorphism in clasts within the melt rock and samples from granitoid basement below the melt body. The age of this structure is indistinguishable from the biostratigraphic age of the Jurassic-Cretaceous (J-K) boundary. The size of Morokweng, for which diameters ranging from 70 to 165 kilometers have been quoted before, and which has important implications regarding its relation to the J-K boundary, remains an open question.Here we present new results of a detailed petrographic and chemical investigation of impact melt rock and country rock samples. The granophyric melt rock is mostly unaltered and contains a large number of gabbroic and felsic clasts. The occurrence of baddeleyite, formed from high-temperature dissociation of primary zircon, indicates a high-temperature origin. The impact melt rock body, which in the cores investigated here has a thickness of at least 120 m, shows no statistically significant variation or trend in chemical composition with depth or geographic location. Chemical data for impact melt rock, breccia dike/vein breccia samples, granite, quartzite, and basic to mafic clasts were used in harmonic least squares mixing calculations to determine the source rock types and their proportions involved in the formation of the impact melt rock. Granite is the dominant target rock component (50 to 63% by weight; depending on target composition input to the mixing models), with significant (35 to 50%) mafic contributions, and a (possible) minor contribution of quartzite. New platinum group element (Ru, Rh, Pd, Os, Ir, and Pt), Re, and Au data, as well as data for other siderophile elements (Cr, Co, Ni, and Ir), confirm the presence of up to ∼ 5% of a chondritic component in the melt rock. The indigenous contribution of the PGEs from the target rocks is negligible. Normalized PGE abundance patterns and interelement ratios of Morokweng impact melt rock indicate that the projectile was likely of ordinary chondritic (possibly L chondrite) composition, but the choice of the meteoritic compositional data influences this interpretation.     

The structure and mechanisms of the formation of coastal terrigenous rocks in Permian epicontinental basins of northern Russia

Structure and mechanisms of the formation of coastal paragenetic associations are widespread in the Permian terrigenous sequences of northern Russia. They are examined using the Kungurian-Ufimian rocks of northeastern Pai-Khoi as an example. Analysis of bed successions in the 620-m-thick section interval made it possible to distinguish 37 cyclothems, each being the result of execution of one transgression-regression sedimentation cycle. Based on the results obtained, the structural-genetic characteristics of bed successions of two types are given. The first type is represented by the Liur-Yaga ideal cyclothem related to landscapes of open coasts, which exist in both transgression and regression phases of sedimentation. The second type is represented by the Tab-Yu ideal cyclothem related to the formation of lagoon-bar systems in the regression phase of the sedimentation cycle and their destruction during transgressions. In the Pechora and Taimyr basins, bed successions of the two types were revealed in similar (with respect to composition and structure) Permian formations of different ages. It is likely that the proposed models are universal enough to be applicable for studying the terrigenous epicontinental rocks of humid zones irrespective of their age.     

Differentiation and correlation of the Riphean rocks of Eastern Siberia

The Riphean (upper) portion of the Proterozoic interval is treated as an era divided into four systems on the basis of stromatolith morphology. The evolution of the stromatoliths is traced into the Lower Cambrian in order to demonstrate that divisions of system rank can be identified by the stages of stromatolith morphogenesis, from columnar through tabular and, in the Lower Cambrian, "nodular" and laminar. The Riphean stromatoliths, in the main, represent Baicalia and Conophyton, even through other major taxons are present. The authors, at the present stage in the the development of Riphean stratigraphy, seem to assign the rank of genera to Baicalia and Conophyton. --Mark E. Burgunker.     

安徽南陵—无为地区二叠系烃源岩有机地球化学特征

通过系统的野外剖面测量和样品采集,运用岩石热解、有机碳测试、有机显微组分镜检、气相色谱-质谱等对采集的样品进行分析测试,综合评价南陵—无为地区二叠系碳酸盐岩、煤和泥岩露头样品的有机质丰度、类型和成熟度,并分析有机质的来源及沉积环境。研究结果表明:栖霞组、孤峰组、龙潭组为有利烃源岩发育层段。其中栖霞组有机质类型为Ⅲ型,孤峰组为Ⅱ2型,有机质演化程度均处于高成熟阶段;龙潭组有机质类型为Ⅱ1型,处于成熟阶段。栖霞组烃源岩形成于受陆源影响的碳酸盐台地环境;孤峰组烃源岩形成于较深水的低能陆棚环境;龙潭组烃源岩形成于有陆源输入的滨岸环境。     

Polymetallic sulfide ores hosted in Late Permian carbonate at the Alanish locality,northern Iraq: petrography and mineral chemistry

Polymetallic sulfide ores (Zn, Pb, Fe, Cu, Ag, and Cd) found in the Alanish locality of northern Iraq are hosted by dolostone in the Late Permian Chia Zairi Formation. The Alanish locality is one of several Zn–Pb deposits that are widespread in northern Iraq, situated along the northern passive margin of the Arabian plate. This paper describes the ore deposit classification, mineral chemistry, and paragenetic sequence of the area and proposes an ore formation model. We report the presence of acanthite and greenockite for the first time in Iraq. A brine solution derived from the sedimentary basin formed the primary sulfide ore minerals (sphalerite, galena, acanthite, pyrite, chalcopyrite, greenockite, and marcasite). The pre-tectonic mineralization is characterized by replacement textures including (1) high-Fe, low-Zn, dark-colored, coarse-grained sphalerite; (2) deformed anisotropic coarse-grained galena; and, (3) idiomorphic cubes of crushed pyrite. Conversely, the post-tectonic mineralization is characterized by open-space filling textures, including (1) low-Fe, high-Zn, light-colored, fine aggregated sphalerite; (2) fine-grained galena; and, (3) the existence of acanthite and marcasite. Although galena is an Ag carrier, both mineralization phases contained non-argentiferous galena. Non-sulfides (smithsonite, cerussite, and goethite) have replaced older sulfides in many areas due to supergene process. Gangue minerals present are dolomite, calcite, barite, and siderite. Open spaces and cavity filling of small paleo-karsts, replacement, veins, and veinlets are common features of the ore body. Metals were sourced from brines generated in the sedimentary basin, whereas sulfur was derived from nearby evaporates. Sediment compaction and tectonic activity, probably during Late Cretaceous, were the driving forces that squeezed and moved ore-bearing fluids derived from the sedimentary basin. Multiple stages of ore-bearing fluids were epigenetically intruded into the Late Paleozoic dolostone, forming an epigenetic strata-bound Mississippi Valley-type deposit precipitated under a temperature of 120 °C, as indicated by the cadmium fractionation in sphalerite and galena. Dolomitization and tectonic activity provided the necessary permeability for accumulating ores. The main ore body is directly connected to a fault plane and to adjacent dolostone that is frequently fractured and brecciated.     

四川宣汉地区二叠系硅岩地球化学特征及成因研究

四川宣汉地区二叠系茅口组和吴家坪组的硅岩,主要以结核状、条带状和团块状产出。根据硅岩的岩石学及地球化学特征,对其成因进行了系统研究。野外观察硅岩形态多样,与围岩呈缝合线状接触,在剖面上受一定层位控制,团块状硅岩中含石灰岩斑块等。显微镜下观察,硅岩中见方解石残余结构及白云石菱形假晶等。野外观察和显微镜下观察表明这些硅岩应为交代作用形成。常量元素分析表明硅岩以SiO₂为主（69.61％～99.21％）,其他化学成分含量较低（0.01％～16.07％）,Fe/Ti、（Fe+Mn）/Ti及Al/（Al+Fe+Mn）值反映了硅岩的形成与热水活动有关,样品点在Al-Fe-Mn三角图中的投影位于富铁端;微量元素Co/Ni、V、Ti/V、Th/U和Rb/Sr值都较低,样品点在（Cu+Co+Ni）-Fe-Mn三角图中的投影也位于富铁端;硅岩中稀土元素总量低（低于10×10^-6）,Ce明显负异常,Eu弱负异常,LREE/HREE值低,Eu/Eu^*值相对较高。上述特征表明研究区硅岩在形成过程中有热水物质参与沉积,在成岩过程中通过SiO₂交代作用形成。