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1.
The Mambéré Formation constitutes a horizontal unit located in the western and southwestern part of the Central African Republic. Stratigraphical and sedimentological study provides strong argument to attribute these deposits a glacial origin. A palaeogeographical reconstruction has been outlined in order to precise the age of the formation. Two main categories of glacial deposits have been recognized: glaciogenic deposits made of basal tills (with facetted pebbles) and flow tills (with flattened blunt pebbles); reworked glacial deposits formed of sandstones and conglomeratic sandstones, in continuous beds, lenses or isolated blocks, together with siltstones and bedded sandstones. The southerly provenance of the detrital material is demonstrated by quartz grain surface analysis and heavy-mineral study. This material results essentially from the dismantling of the Precambrian Schistoquartzitic Complex and secondarily from the Granitogneissic Complex. According to the palaeomagnetic polar paths and the migration of the glacial centers over the African continent during the Palaeozoic, the Mambéré Formation may be attributed a Lower Silurian age by reference to similar formations observed in Cameroon or a Lower Carboniferous age by comparison with the glacial formations reported from Niger and Egypt. 相似文献
2.
Gert Hoschek 《Contributions to Mineralogy and Petrology》1974,47(4):245-254
P, T, \(X_{{\text{CO}}_{\text{2}} }\) relations of gehlenite, anorthite, grossularite, wollastonite, corundum and calcite have been determined experimentally at P f =1 and 4 kb. Using synthetic starting minerals the following reactions have been demonstrated reversibly
- 2 anorthite+3 calcite=gehlenite+grossularite+3 CO2.
- anorthite+corundum+3 calcite=2 gehlenite+3 CO2.
- 3anorthite+3 calcite=2 grossularite+corundum+3CO2.
- grossularite+2 corundum+3 calcite=3 gehlenite+3 CO2.
- anorthite+2 calcite=gehlenite+wollastonite+2CO2.
- anorthite+wollastonite+calcite=grossularite+CO2.
- grossularite+calcite=gehlenite+2 wollastonite+CO2.
3.
Dr. Christoph Hoffmann 《International Journal of Earth Sciences》1976,65(1):939-966
In the central area of the early paleozoic Damara belt migmatites and some types of granites (sensu lato) crop out. Conventional petrographic data were collected and melting experiments were carried out with 63 samples of such rocks. Based on these data, migmatite genesis can be classified as follows:
- Formation by partial melting and separation of more liquid and more crystalline fractions, the melting behaviour of these fractions has to be principally similar then.
- Formation by injection of “geologically liquid” crystal-melt mixes into rocks of (incidentally) similar or (more frequently) dissimilar melting behaviour.
- Formation by partial melting of metasediments of originally different composition. The method is applied and demonstrated for outcrops with complicated interrelations and it is shown that temperature estimates are possible thereby (670° to 710° at 4–5 kb H2O pressure in the central Damara belt).
4.
Laihunite Research Group 《中国地球化学学报》1982,1(1):105-114
Laihuite reported in the present paper is a new iron silicate mineral found in China with the following characteristics:
- This mineral occurs in a metamorphic iron deposit, associated with fayalite, hypersthene, quartz, magnetitc, etc.
- The mineral is opaque, black in colour, thickly tabular in shape with luster metallic to sub-metallic, two perfect cleavages and specific gravity of 3.92.
- Its main chemical components are Fe and Si with Fe3+>Fe2+. The analysis gave the formula of Fe Fe 1.00 3+ ·Fe 0.58 2+ ·Mg 0.03 2+ ·Si0.96O4.
- Its DTA curve shows an exothermic peak at 713°C.
- The mineral has its own infrared spectrum distinctive from that of other minerals.
- This mineral is of orthorhombic system; space group:C 2h /5 ?P21/c; unit cell:α=5.813ű0.005,b=4.812ű0.005,c=10.211ű0.005,β=90.87°.
- The Mössbauer spectrum of this mineral is given, too.
5.
Dr. Christoph Hoffmann 《Contributions to Mineralogy and Petrology》1970,27(4):283-320
In the southern Apennin (= northern part of the region dealt with) and the Coasta Chain (= southern part) there are metabasalts wich are classified in the northern part as:
- Glaucophane rocks of the albite-lawsonite-glaucophane-subfacies with the assemblage glaucophane + pumpellyite + lawsonite ±albite ±aragonite ±muscovite (7 rock analyses, 8 mineral analyses). These rocks are conceived as relics of an older burial metamorphism.
- Rocks with pumpellyite and chlorite or also chlorite alone, that are interpreted as reaction rims between the metastable glaucophane rocks and the country rock (phyllites, quartzites). The assemblages pumpellyite + chlorite and chlorite alone are to be found (2 rock analyses and 2 mineral analyses).
- Rocks with lawsonite and/or epidote belong to the same mineral facies as the country rock: a facies similar to the greenschist facies (called “lawsonite-albite-chlorite-subfacies”) which is characterized by the assemblages lawsonite + albite + chlorite ±calcite and also epidote ±lawsonite + albite + chlorite ± muscovite. These types are attributed to a younger dynamo-metamorphism (2 rock analyses).
6.
T. J. Munson S. W. Denyszyn J. M. Simmons M. Kunzmann 《Australian Journal of Earth Sciences》2020,67(3):321-330
AbstractAn interpreted CA–IDTIMS age of 1642.2?±?3.9?Ma for a volcanogenic tuffaceous siltstone from the previously undated Fraynes Formation of the Birrindudu Basin in the northwestern Northern Territory enables a rigorous chronostratigraphic correlation to be made with the economically important Barney Creek Formation of the southern McArthur Basin. This result supports previous interpretations that these geographically widely separated formations are probably linked in the subsurface. It also establishes the stratigraphic interval encompassing the Fraynes and Barney Creek formations as a potential target for greenfields base metals and petroleum exploration programs across the greater McArthur Basin.
- KEY POINTS
A new interpreted CA–IDTIMS age provides a chronostratigraphic link between the Fraynes Formation of the Birrindudu Basin and the economically important Barney Creek Formation of the southern McArthur Basin.
The Fraynes and Barney Creek formations are probably linked in the subsurface.
This stratigraphic level is a potential target for greenfields base metals and petroleum exploration across the greater McArthur Basin.
7.
Geological and geochemical characteristics of REE iron formation (REEIF), a term proposed by Prof. Tu Kuang-chih to specify a special type of Precambrian iron formations rich in REE, are discussed in this paper with special reference to its REE contents, REE distribution patterns, the formation mechanism, the relationship between its development and the multi-stage evolution of the continental crust in China, and the implications of REE as an indicator of oxidation state for ancient atmosphere. Major conclusions are outlined as follows:
- REEIFs are characterized by high REE concentrations against the very low REE levels in normal Precambrian iron formations.
- REEIFs are formed by marine sedimentary-diagenetic processes in miogeosynclines or transition zones during Proterozoic times To some extent, volcanic activity may play an important role in the deposition of ore-forming materials. In a broader sense, REEIFs belong to Fe-bearing dolomite formations. Most REEIFs in China may be superimposed by late geological processes such as hydrothermal-metasomatism, migmatization and metamorphism. Generally, REEIFs have much in common with stratabound ore deposits in respect to their characteristic features.
- Similar to Precambrian iron formations, REE are enriched in LREE. But, the degree of LREE enrichment is noticed to increase of total REE content. Most REEIFs are characterized by high ratios of σ Ce/σY, (Mg+Fe)/Ca, Na/K, Nb/Ta, Zr/Hf, Th/U, Ba/Sr, etc.
- The extensive occurrence of REEIFs indicates higher REE abundance in the continental crust of China, thus lending further support to the multi-stage theory regarding the evolution of chemical elements and the differentiation in the continental crust of China.
- Preliminary data seem to support the time-dependence of REE distribution patterns and relative Eu contents of REEIFs in China.
8.
Massive sulfide deposits located on Hercynian islets of northwestern Morocco exhibit four main characteristics: They are strata-bound massive pyrrhotite deposits mined for sulfur and/or base metals occasionally occurring as sulfides of workable grade. Volcanic rocks with which these massive sulfide orebodies are associated are scarce, although always present as acid flows of submarine emissions of either rhyolitic or more often quartz-keratophyric nature. Later on, basic plutonics intruded the pelitic country rocks. Stockworks underlying the massive sulfide orebodies are common, but not systematic. When present, they occur in siltite ± phyllite ± carbonate rocks at the wall of massive sulfide lenses. They consist of fissural disseminations transformed by epimetamorphic recrystallization and by one schistosity generally concordant with s0. Associated alterites and exhalites belong to three types, i.e., sericitite (or biotite-rich rock), chloritite, and/or chert (jasper). Generally well located in a back-arc basin environment characterized by a two-phase geological history, i.e., “extension and volcanism, compression and metamorphism”, these volcano-sedimentary deposits exhibit distal features with regard to the volcanism coeval with their sedimentation. They are mostly linked with strongly reducing environmental properties entailing pyrrhotite and/or magnetite syngenetic deposition, whatever the iron activity. 相似文献
9.
W. E. G. Taylor 《International Journal of Earth Sciences》1968,58(2):564-587
The paper presents novel information on the Caledonian orogeny in Ireland. A series of Dalradian (Upper Precambrian-Lower Cambrian) metasedimentary rocks occur as an envelope to a granitic igneous complex at Slieve Gamph, Western Ireland. These metasedimentary rocks have been deformed at several distinct times and evidence is shown for the following sequence of events:
- formation of major nappe structures and a tectonic slide. The axial-plane traces of the folds probably trended N. E.-S. W.
- formation of upright, gently plunging folds with axial-plane traces of the folds trending N. E.-S. W. Emplacement of the components of the Slieve Gamph igneous complex.
- formation of a conjugate set of folds:
- Open folds with N. N. E.-S. S. W. trending axial-planes which dip to the east,
- Open folds with E.W. trending axial-planes which dip to the north.
- formation of kink-bands, open and conjugate folds with an axialplane trace trending N. W.-S. E.
10.
Dr. Bernd Lammerer 《International Journal of Earth Sciences》1976,65(1):525-535
- Multispectral scanning imageries, revealed from ERTS-1 satellite, show a young lineament pattern in the region of the Northern Calcareous Alps. The statistical distribution of the lineament directions accords well with that of mapped faults. On the other hand, many of these lineaments are not mapped as faults. A more complex type of fracture is supposed for them, composed of many joints and minor faults. With increasing length of the fracture, the acute angle of the shear system increases from about 40° at joints to 70° at faults and 80° at lineaments.
- The satellite imagery shows a relationship between the structures of the folded molasse and the alpine nappes. The mimer and depth of folds, the width of the folded zone, and the lateral limitation of the synclines are related to the amount of thrusting of parts of the nappe system. A model for the genesis of the folded molasse is given.
11.
江西冷水坑矿区构造-岩浆活动的年代学约束 总被引：6，自引：3，他引：3
江西省冷水坑矿区火成岩-构造演化一直缺少系统的年代学制约.作者运用LA-ICP-MS锆石U-Pb和40Ar/39Ar测年技术,对冷水坑矿区两套火山岩地层(打鼓顶组和鹅湖岭组)、含矿花岗斑岩和主推覆断层F2进行了年代学测试,结果表明,打鼓顶组流纹质含角砾熔结凝灰岩形成于160.8±1.9Ma,鹅湖岭组合角砾熔结凝灰岩则具有间歇性和多期喷发特点,其最初活动时间为159Ma,而主体形成于146.6±2.2Ma;矿区含矿花岗斑岩与打鼓顶组、鹅湖岭组几乎同期形成,年龄介于163.6 ±2.1Ma～154.3±3.0Ma之间;研究区构造活动起始时间不晚于加里东期,推覆断层F2中保留有40Ar/39Ar年龄为398.5±2.6Ma的构造活动痕迹,中生代重新复活,导致震旦系叠覆于鹅湖岭组之上,年龄晚于146.6Ma,可能对含矿斑岩体起破坏作用. 相似文献
12.
K-Ar dating on a suite of volcanic rocks from the island of Principe gives the following chronology.
- Basal palagonite breccia (30.6 ± 2.1 Ma).
- Older Lava Series (OLS) basalt (23.6±0.7 Ma) and hawaiite (19.1±0.5 Ma).
- Younger Lava Series (YLS) nephelinite (5.60±0.32 Ma) and basanite (3.51 ±0.15).
- Intrusive phonolite (5.32±0.17 Ma, 5.48±0.19 Ma), tristanite (4.89±0.15 Ma) and trachyphonolite (6.93±0.68 Ma) plugs.
13.
Alexander A. Godovikov George C. Kennedy 《Contributions to Mineralogy and Petrology》1968,19(2):169-176
Prior experimental work has shown that in the laboratory the mineralogy of eclogites is sensitive to the ratio of CaO ∶ MgO ∶ FeO and that the reaction pyroxene + kyanite?garnet + quartz proceeds to the right at high pressures in rocks rich in magnesium and to the left in rocks rich in calcium and iron. Typical basalts crystallized at high pressure never contain kyanite. The chemistry and mineralogy of a large number of naturally occurring eclogites show they belong to three classes.
- Kyanite-free magmatic eclogites, rich in magnesium, from:
- kimberlites
- dunites and serpentinites.
- Kyanite-bearing eclogites and grosspydites rich in CaO and low in FeO with intermediate MgO from:
- kimberlites
- gneisses.
- Kyanite-free eclogites of metamorphic origin rich in iron with low magnesium and intermediate amounts of calcium from:
- glaucophane schists
- gneisses.
14.
R. Catalano B. d'Argenio C. B. Gregor A. E. M. Nairn G. Nardi P. Renda 《International Journal of Earth Sciences》1984,73(2):577-598
The Mesozoic lavas and minor intrusions in the thrust sheets of western Sicily have the following characteristics:
- The lavas in the Triassic Mufara Formation in the north were broken into fragments which rotated independently within the incompetent strata that enclose them. This behavior is characteristic of igneous rocks found within the more internal (northerly) thrust units.
- The Jurassic lavas in the more external (southerly) units have consistent directions which agree with those of the Ammonitico Rosso limestones in the same zone and lie about 30° clockwise from those of coeval autochthonous formations in Tunisia.Schult's presumed Cretaceous directions from Custonaci on the north coast (similar to those found in the Cretaceous Scaglia Rossa at Terrasini to the east byChannel et al., 1980) are rotated still more (140°) with respect to those of the autochthonous Iblean platform of SE Sicily. These differences are believed to reflect rotation of the thrust sheets during tectonic transport in Cenozoic times, the internal units being the most strongly rotated.
- All the igneous rocks are highly altered: generally the original mineralogy cannot be completely determined. Relative abundances of some of the less mobile elements (Ti, Sr, Y) suggest that they are intraplate basalts.
15.
Dr. Holger Kulke 《International Journal of Earth Sciences》1974,63(3):970-998
Caliches: Large areas of the northern Sahara and the Algerian High Planes are covered by mostly 1–5 m thick caliches. Their age (Pliocene in the Sahara) decreases to the north and their precipitation is generally independent of groundwater. Their profile is composed (from top to base) as follows: Upper soil, loose and mostly of eolian origin. Upper part of caliche, with very characteristic, dense, partly layered-knobby texture, formed slowly by solutional and reprecipitational processes of ± freely outcropping caliches under addition of eolian material. Under part of caliche, highly porous, somewhat chalky and greyish-white; precipitated mainly by capillar rise of solutions in permeable and calcareous rocks. Substratum, preferentially calcareous sandstones, alluvial deposits and marls. The mineralogy of the caliches (whose main components are represented in fig. 4 A-C) is rather monotonous: in addition to relicts of the substratum (partly dissolved or pushed aside by precipitation of calcite), there are only newly formed low-Mg-calcite and some quarzine (length-slow quartz). Sr-contents of calcite rise clearly from substratum to upper part of caliche. Gypsiferous Crusts (or Cementations): They are found mainly in the surroundings of Chotts (flat, ± saline lakes) and in oases of the NE-Algerian Sahara. Their formation began — mostly caused climatically — after the period of caliche formation and is still continuing in some places. Most of these gypsum-crusts are formed by evaporation of near-surface groundwaters in sandy soils. Water saturated in gypsum precipitates large crystals of gypsum (relatively low in Sr), partly filled by sand, at groundwater-surface. Fine crystalline crusts (relatively high in Sr) are formed by ascendent waters with lower gypsum content ± directly under the landsurface. 相似文献
16.
B. Lammerer I. Fruth D. D. Klemm E. Prosser K. Weber-Diefenbach 《International Journal of Earth Sciences》1976,65(1):436-459
Geologic, petrological and geochemical investigations have been carried out in the western part of the “Zillertaler Alpen”. Important results are:
- The premetamorphic material of the Greiner series consists of conglomerates, breccias, arcosic-sandstones or greywackes, bituminous shales, volcanic lavas and tuffs.
- The southern part of the “Zentralgneis” shows a differentiation trend from alkaline granite to quarzdiorite with predomination of granodiorite.
- Chemical relationships of granodiorite to its restitic inclusions allow the supposition of a palingenetic origin of the granitic rocks.
- At least two stages of metamorphism can be differentiated.
- Parts of the Greiner series, covered by triassic metasediments, are supposed to be of Permian age. A lower age boundary can not yet be given.
- Some vertical, northeast striking faults with throws of more than 1 or 2 kilometers produced southward verging drag folds.
- Geodynamic aspects, revealed from regional metamorphism and tectonics, are discussed.
17.
Dr. W. -A. Flügel 《GeoJournal》1983,7(4):341-351
During the “Heidelberg-Ellesmere-Island-Expedition” to Oobloyah Valley, N-Ellesmere Island, NWT, Canada in 1978 the summerly water balance of this high arctic catchment area with continuous permafrost was investigated. The following results will be presented:
- Three hydrogeological areas with different physical parameters, thawing depths and drainage are distinguished and studied on slope I, II and slope III.
- The climatic situation of summer 1978 was mainly influenced by the change of radiating and cloudy periods. Due to air temperatures (2 m above ground), which never went below 0°C, these periods regulated the thawing of the glaciers and the respective run-off.
- Most of the winterly snow cover melted before July, thereafter soil thawing and its drainage began. In none of the sediments the latter reached field capacity.
- Considering the course of daily discharge and soil water balance the three studied streams were characterized by the “Dry-Weather-Discharge-Line”, DWL, of Peri-Creek the “Radiation-Weather-Discharge-Line”, RWL, and the “Cloudy-Weather-Discharge-Line”, CWL, of Nukapingwa River and Heidelberg River.
- The periglacial streams never had a measurable sediment load not even during snow melt, whereas the glacial and mixed glacial-periglacial streams as Nukapingwa River and Heidelberg River showed a sediment drift depending on their run-off. Only in Peri-Creek the ion concentrations were correlated to discharge.
- Precipitation (snow plus rain) add up to 51% of the summerly water balance. The glaciers contributed up to 48%, and the actual evapotranspiration is only 1%.
18.
Principe is one of the volcanic centres comprising the Cameroun line in West Africa. The volcanic rocks can be divided into two stratigraphic units:
- Younger lava series — basanite and nephelinite overlying.
- Older lava series — transitional to mildly alkaline basalt and hawaiite.
- Phonolites which evolved by low pressure crystal fractionation of the younger lava series basanitic magma, and
- Tristanite — trachyte — trachyphonolite suite which may have evolved by high pressure crystal fractionation of the older lava series magma.
19.
H. Kenneweg 《GeoJournal》1994,32(1):47-53
The development of inventory activities in the field of forest damage assessment and monitoring during the last decade in Germany and the present state are recorded as far as remote sensing has been involved. Any forest inventory is influenced by external factors, and the resulting difficulties for an introduction of new technologies are described. The following tasks and/or methods are discussed: -global approaches to deforestation monitoring -working experience from local and regional case studies -vegetation and vegetation-damage monitoring in ”urban forestry” -sampling approaches for large areas -the contribution of spectral signatures and satellite remote sensing to damage assessment 相似文献
20.
K. Viswanathan 《Contributions to Mineralogy and Petrology》1972,37(4):277-290
A series of K-plagioclases have been produced metastably by ion-exchanging the plagioclases in KCl-melt. Chemical analyses and re-exchange experiments (with NaCl-melt) have proved that the K-plagioclases are truly isomorphous with plagioclases. Because of their isomorphous nature it was possible to mix them in different proportions and homogenise them, thereby producing ternary feldspars of different compositions in the system Or-Ab-An. A comparative study of the lattice constants of plagioclases, their K-equivalents and the different ternary feldspars calculated using powder data leads to the following conclusions:
- It is possible to dertermine by X-ray methods the anorthite content of a plagioclase to an accuracy of ±1% An.
- The influence of the ionic size of the bigger cations Na, Ca, and K and that of order/disorder are different on different lattice constants and it is possible to distinguish these two effects.
- The b-parameter indicates a definite structural change in plagioclases at about 25–30% An.
- It is possible to predict the average Al/Si-distributions in the four different positions T1(o), T1(m), T2(o) and T(m) of all plagioclases of all stable structural states, using the c-parameter of their K-equivalents.