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1.
M. Boucarut M. Clin P. Pouchan Cl. Thibault 《International Journal of Earth Sciences》1985,74(1):123-137
The volcanic and sedimentary successive paleogeographic reconstructions, as well the volcanic emissions as the fluvial, lacustrine and marine deposits, are compared to the tectonic mechanisms, and show that the geologic history is controlled:
- During Pliocene and lower Pleistocene times, by a collapse tectonics in the Red Sea - Aden Gulf area with a correlative uplift of the Tadjoura - Ali Sabîh hörst (a southern prolongation of the Danakil horst), and by a tectonic shear according to a NE-SW trend, which gives rise to NW-SE trending uplifts and basins (Nazaret phase of the Ethiopian rift).
- From the middle Pleistocene time, by the progressive opening, according to an EW direction, of the Gulf of Tadjoura, as a western prolongation of the Aden rift. A correlative epiglyptic arching, according to an EW direction, is located westwards. It appears as a superimposed structure with respect to the previous building.
2.
P. Soler 《Mineralium Deposita》1987,22(2):135-143
About 1,500 samples of Pb and Zn concentrates and ores from 89 ore deposits of the polymetallic province of the Andes of central Peru have been analyzed. The distributions of Cd, In, Ge, Ga, Ag, Bi, Se, Hg, and Sn in these ore deposits can be reported on the basis of the typology of ore deposits, i.e., some types of ore deposits (syndiagenetic without associated volcanism and volcano-sedimentary of Triassic-Lias, exhalative sedimentary of Upper Jurassic) show very characteristic minor and trace element patterns; the temperature of ore formation that controls the abundance of Bi and Hg, in general, and of Ag, Se, and Sn in the Tertiary hydrothermal deposits; the age and nature of the country rock, e.g., an In, Ga, and Sn positive anomaly and Cd negative anomaly appears in the deposits with Paleozoic country rock; the geographic position of ore deposits, e.g., in the northern part of the province an In, Ga, Ge, and Cd positive anomaly appears. 相似文献
3.
Dr. Harald Dill 《International Journal of Earth Sciences》1985,74(3):447-466
In the North Bavarian Basement (FR Germany) as well as in the Thuringian Forest (GDR) both of which belonging to the Saxothuringian Zone antimony mineralizations have been worked up to the early fifties. Mineralogical and geological investigations led to the following classification of antimony ore deposits and -concentrations:
- Stratabound and stratiform fahlore (Fahlerz) mineralization in Silurian and Lower Devonian black shales.
- Sulphosalt- and stibnite-bearing veins (partly associated with native gold) in wall rocks of the Late Variscan granites.
- Monometallic and monomineralic antimony lodes along anticlinal structures.
- Sulphosalt-bearing lead-zinc veins.
4.
Detailed sedimentological investigations were performed on sediments from DSDP-Site 594 (Chatham Rise, east of New Zealand) in order to reconstruct the evolution of paleoclimate and paleoceanographic conditions in the Southwest Pacific during the last 6 million years. The results can be summarized as follows:
- High accumulation rates of biogenic opal and carbonate and the dominance of smectites in the clay fraction suggest increased oceanic productivity and an equable dominantly humid climate during the late Miocene.
- During Pliocene times, decreasing contents of smectites and increasing feldspar/quartz ratios point to an aridification in the source area of the terrigenous sediments, culmunating near 2.5 Ma. At that time, accumulation rates of terrigenous components distinctly increased probably caused by increased sediment supply due to intensified atmospheric and oceanic circulation, lowered sea level, and decreased vegetation cover.
- A hiatus (1.45 to 0.73 Ma) suggests intensified intermediate-water circulation.
- Major glacial/interglacial cycles characterize the upper 0.73 Ma. During glacial times, oceanic productivity and terrigenous sediment supply was distinctly increased because of intensified atmospheric and oceanic circulations and lowered sea level, whereas during interglacials productivity and terrigenous sediment supply were reduced.
- An increased content of amphibols in the sediments of Site 594 indicates increased volcanic activities during the last 4.25 Ma.
5.
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
6.
Xueyuan Yu 《中国地球化学学报》1985,4(2):150-158
The Niutoushan basaltic cone, consisting of subalkali (quartz-tholeiite and olivine-tholeiite) and alkali basalts, is Late Tertiary in age. Its major characteristics are generalized as follows:
- Both early subalkali and late alkali bali basalts are formed under the same geological environment.
- The continuity in chemical composition from subalkali to alkali and the low FeO/MgO in alkali basalts show that they are the products of cognate magmatic differentiation.
- The change from low REE abundance and weak enrichment of LREE in subalkali to high REE abundance and strong enrichment of LREE in alkali basalts indicates obvious REE enrichment and fractionation during magmatic differentiation. Weak positive Eu anomalies in the REE patterns are indicative of their formation under low oxygen fugacity conditions.
- According to the calculated values, 70–75% of the primary olivine tholeiitic magma had been separated as subalkaline basaltic magma, the rest residual magma became alkaline basaltic magma. This result is consistent to the field observation that the outcrop area of subalkali basalts is four times as much as that of alkali basalts.
- The basaltic rocks of Niutoushan show an S-type distribution straddling the thermal barrier on Ol′-Ne′-Qu′ diagram and an evolution tendency for Ne to increase with increasing FeO/MgO. This is in agreement with the melting experimental data on olivine basalts at 10–20 kb.
- Mantle-derived inclusions (spinel lherzolite) in this area occur in both alkali olivine basalts and olivine tholeiites. The latter is of extremely rare occurrence. The formation temperature and pressure of the inclusions in alkalibasalts and olivine tholeiites have been calculated. The results show that the alkaline basaltic magma was separated from the subalkaline basaltic magma at about 20 kb.
7.
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.
8.
Prof. Jean -Claude Vicente 《International Journal of Earth Sciences》1975,64(1):343-394
Hercynian absolute ages obtained from many plutonites and metamorphites of the Sierras Pampeanas compel to consider this polymetamorphic domain rather as an intermediate hinterland and axis of divergent symmetry between the two elementary geosyncline ranges (Cuyanides and Bolivianides) of the south america hercynian orogen. Attempt of Cuyanides paleogeographic organization indice to define during the geosyncline period (Cambrian to Devonian): the Pampean zone which consist of:
- an internal sub-zone (eastern) or pampean s. st. with hinterland significance
- a more external sub-zone (western) or transpampean or Umango sub-zone with intermediate features between eugeanticlinal ridge and eugeosynclinal furrow;
- the Calingasta zone as a typical eugeosynclinal furrow with pelagic-terrigenous ordovician sedimentation and ophiolitic magmatism followed by early silurian than devonian Flyschs;
- the Zonda zone as an external ridge with neritic cambro-ordovician facies and devonian flyschs.
9.
According to their material sources, China’s pegmatities can be divided into two broad types: (1) the crust-source pegmatites derived mainly from the upper continental crust, which can be subdivided into metamorphic differentiated, mixed metasomatic and anatectic magmadifferentiated pegmatites, and (2) the mantle-source pegmatites generated from the mantle, including those related to late differentiates and carbonatites. In space, carbonatites are usually accompanied with alkaii syenite. The criteria of discriminating the two-source pegmatites of China are listed as follows:
- Rock-forming minerals (micas and feldspars);
- REE distribution patterns;
- Zr/Hf ratios in zircons; and
- Species of apatite and REE contents.
10.
Based on research on the “Xinyu-type” Sinian iron deposits in Jiangxi Province and metamorphosed iron deposits in Jiangkou and Qidong of Hunan, Sanjiang and Yingyangguan of Guangxi, Longchuan of Guangdong and some other areas in Fujian, the authors have come to the following conclusions:
- The metamorphosed late Precambrian iron ores widespread in south China may be roughly assigned to two ore belts, namely the Yiyang-Xinyu (Jiangxi)-Jiangkou(Hunan)-Sanjiang (Guangxi) ore belt or simply the north ore belt, and the Songzheng(Fujian)-Shicheng (Jiangxi)-Bailing (Longchuan of Guangdong)-Yingyangguan (Guangxi) ore belt or the south ore belt. Tectonically, the former lies along the southern margin of the “Jangnan Old Land”, while the latter along the northwestern border of the “Cathaysian Old Land”.
- Iron deposits of this type occur exclusively in the same interglacial horizon of the Sinian Glaciation in south China. Above and below the ore bed there lie the glacial till-bearing volcanic-sedimentary layers.
- Based on sedimentary features, the iron formations can be divided into four types: silica-iron-basalt formation, silica-iron-clastic rock formation, silica-iron-tuff formation and silica-iron-carbonate rock formation, which progressively grade into each other.
- Iron ores were formed at the late stage of late Proterozoic rifting in neritic environments, with their distribution governed by the rift valleys on the margins of the “Jiangnan Old Land” and “Cathaysian Old Land”. Consequently, intense mafic volcanism as well as weathering and denudation of palaeocontinent during rifting provided material sources for the formation of iron deposits. Meanwhile, warm and humid stationary neritic environment during the south China great glacial period constitutes favorable palaeoclimatologic and palaeogeographic conditions for the deposition of iron ores.
- The iron formations have undergone regional metamorphism of greenschist-amphibolite facies.
11.
Dr. Elmar Sabelberg 《GeoJournal》1986,13(1):59-66
The “South-Italian city” is characterized at four different levels as an independent cultural-genetic city-type:
- The characteristics arrangement of the functional areas and the residential areas of different social groups is represented in a model.
- From the model, developments and changes in the arrangement of the functional areas can be identified which clearly deviate from those which are derived from the universal city model.
- Some of the structural individuality can be directly explained by the peculiar features of the respective social and economic history.
- Some of the special features must, however, be traced back to a wider historico-cultural background. Through this run processes which flow through the universal city development in similar forms, to the deviating structure of the “South-Italian city”.
12.
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
13.
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.
14.
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.
15.
Dr. Barbara Theilen-Willige 《International Journal of Earth Sciences》1982,71(1):318-327
The following facts have supported the origin of the Araguainha circular structure in Central Brazil by a meteoritic impact:
- the almost circular contour
- the impact-morphologic sequence including a central uplift, ring walls and a basin rim of escarpments
- outcrops of suevites and mixed breccias
- the evidence of shock metamorphism
- the presence of shatter cones, and
- negative anomalies of the total intensity of the magnetic field at the center of the ring structure.
16.
A. Gandin M. Tongiorgi A. Rau C. Virgili 《International Journal of Earth Sciences》1982,71(3):881-894
In Southwestern Mediterranean Europe (NE Spain, Sardinia and NW Apennines e. g. Monti Pisani and Punta Bianca) the Middle-Triassic transgression on a margin of an intracratonic basin appears to be controlled by the different morphology and tectonic activity of the margin itself. The analysis of some sequences leads to recognize three different kinds of margins:
- margin with a narrow shelf sloping toward a very shallow restricted basin (Central and Southwestern Sardinia);
- margin with a broad shelf gently sloping toward a shallow basin (NE Spain, Monti Pisani, NW Sardinia);
- margin with a narrow shelf and steep slope marked by tectonic and volcanic activity (Punta Bianca).
17.
In Sconser quarry, Isle of Skye, a thin Tertiary basic sill is cut by vertical veins which formed fluid conduits in a major meteoric-hydrothermal system. In order to study the relative mobility of different elements during hydrothermal metamorphism, sill material adjacent to a large (6 mm wide) vein was cut into slices and subjected to geochemical and isotopic analysis. Isotopic evidence indicates that the basic magma which formed the sill was contaminated by Lewisian (Archaean) gneisses at depth, while material from Torridonian (Proterozoic) sandstone country rocks was introduced by hydrothermal fluids after crystallisation. The behaviour of the different elements during hydrothermal metamorphism divides them into 4 groups.
- Large-ion low-charge elements Ba, K, Rb and Cs were strongly leached from the wall rock in the vicinity of the vein.
- Other elements including Sr and Pb were depleted near the vein, but isotopic evidence indicates addition of some material from the fluids. This two-way nuclide transport forms an exchange process.
- Many high-field-strength elements including the REE are slightly enriched near the vein, but Nd isotope evidence reveals no addition of material from fluids. These elements must have been relatively enriched by the removal of other elements (mainly Si and Al).
- Ca and Na were added to the wall rock from fluid. The variable mobility of these elements is explained by the differing ease with which they could be incorporated into a new albite-calcite-chlorite-epidote mineralogy. The constitution of this hydrothermal mineralogy was largely determined by the primary igneous mineralogy, though the composition of hydrothermal fluids had a subordinate influence.
18.
Prof. Dr.-Ing. Hansgeorg Förster 《International Journal of Earth Sciences》1987,76(2):373-388
The term fault-block mountains refers to an orogen, formed in an ensialic back arc by extension. The voluminous magmatism due to underplating of hot oceanic lithosphere, extrem thinning of the continental lithosphere and partial melting as well as mantle diapirs will be examplified by three ore provinces:
- Southwestern North America (Middle Tertiary peralkaline ignimbrites and resurgent cauldrons)
- Central Iran (Infracambrian ignimbrites and riebeckitegranite)
- Arabian Shield (Infracambrian alkaligranites and rhyolites, 625-570 m.y.).
19.
Prof. C. A. Kogbe 《International Journal of Earth Sciences》1978,67(2):662-674
The ferruginous deposits of north-western Nigeria occur extensively capping sediments which outcrop over thousands of square kilometers. These deposits could be subdivided into 3 major groups:
- Ferruginous oolites;
- Crusty/Concretionary laterites;
- Ferruginous sandstones.
20.
《Comptes Rendus Geoscience》2019,351(5):355-365
Located in northern Niger, the NW–SE Téfidet trough is the western branch of the Ténéré rift megasystem.Here we present a tectono-sedimentary analysis of the Téfidet trough, based on the combined use of satellite imagery, field observations and measures, and available literature. We use these data to analyse the sedimentary facies and the tectonic deformations (faults, folds, basins) in the Téfidet trough, and derive their relative chronology. Doing so, we characterize synrift and postrift deformations and their interactions with sedimentation.Altogether our analyses suggest that the Téfidet trough was affected from the Cretaceous to the Paleogene by three major tectonic periods.
- •The first period was a rifting stage with extension and transtension during the Albian–Aptian times. The mean extension was ∼N60° and dominantly produced NW–SE-trending normal faults, a few strike-slip faults locally associated with small folds with sigmoidal axis and small reverse faults, and progressive unconformities.
- •the second period was also a rifting time, which prevailed during the Upper Cretaceous. The regime was marked by transtensional to extensional tectonics, under a ∼N130° shortening and a ∼N60° trending stretching. The end of this period saw the closure of the Téfidet trough.
- •the third period was a postrift stage. It was characterized by a ∼N70° extensional to transtensional regime during the Oligocene–Pliocene. It mainly produced post-sedimentary extensional faults and fractures and alkaline volcanism. We eventually discuss these deformation phases in relation with the Cretaceous Gondwana breakup and its related rifting events in West and North Africa, and with the subsequent Africa–Europe collision.