Fluid inclusion studies of the Felbertal scheelite deposit

Fluid inclusion measurements on quartz, scheelite, beryl, fluorite and calcite in the metamorphosed Felbertal scheelite deposit display two main types of fluid inclusions:

1. H₂O-CO₂ fluid inclusions are characterized by variable amounts of CO₂ up to 18 wt.%. They show two or three phases at room temperature. The bulk homogenization temperatures for the inclusions range between +269 °C and +357 °C. The calculated salinities are between 2.2 and 7.8 wt.% NaCl equivalent. For the late CO₂-bearing fluid inclusions a methane component is evident from microthermometrical data (T_mclath >10.0 °C combined with T_mCO₂
2. Aqueous, two-phase fluid inclusions with salinities in the range between 0 and 11 wt.% NaCl equivalent. Their homogenization temperatures are scattered between 100 °C and 360 °C.

Both types of fluid inclusions are of Alpine origin. They do not record the conditions of the original tungsten ore formation in pre-Alpine (Upper Proterozoic) time. However, it was possible to deduce a path for the fluid evolution and the combined ore redeposition during the retrograde Alpine metamorphism and tectonism from microthermometrical and petrographical studies.     

Les granites du Massif Central Français: étude comparée des leucogranites et granodiorites

Chemical and mineralogical compositions of granitic rocks of the French Massif Central enable us to classify them into two distinct groups: (i) leucogranites, (ii) granodiorites or quartz-monzonites, separated by a natural gap. The differences between these two groups are not only chemical and mineralogical, but are also reflected by:

conditions of crystallization as deduced from compositions and from thermal metamorphism of xenoliths.

nature of inclusions and, especially, the occurrence of basic fine-grained igneous xenoliths restricted to the granodiorite — quartz-monzonite group

relations between intrusive and autochtonous migmatitic masses;

levels of formation and of intrusion; the granodioritic and quartz-monzonitic magmas have originated at deeper horizons of the earth's crust than the leucogranitic one, but have risen higher.

In our opinion these differences are linked, and the specific characteristics of the granodiorites and quartz-monzonites are related to the presence of basic igneous inclusions. These inclusions are relics of deep basic intrusions in the earth's crust, which have overheated the surrounding acid rocks beyond the minimum temperature of melting. Thus granodioritic or quartz-monzonitic melts were produced and were able to rise to superficial levels. These inclusions are missing in leucogranites. The compositions of the latter and their poor mobility suggest a wet anatectic origin in minimal PT conditions.     

Geologische und geochemische Untersuchungen im Zentralgneis und in der Greiner Schiefer Serie (Zillertaler Alpen,Tirol)

Geologic, petrological and geochemical investigations have been carried out in the western part of the “Zillertaler Alpen”. Important results are:

1. The premetamorphic material of the Greiner series consists of conglomerates, breccias, arcosic-sandstones or greywackes, bituminous shales, volcanic lavas and tuffs.
2. The southern part of the “Zentralgneis” shows a differentiation trend from alkaline granite to quarzdiorite with predomination of granodiorite.
3. Chemical relationships of granodiorite to its restitic inclusions allow the supposition of a palingenetic origin of the granitic rocks.
4. At least two stages of metamorphism can be differentiated.
5. 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.
6. Some vertical, northeast striking faults with throws of more than 1 or 2 kilometers produced southward verging drag folds.
7. Geodynamic aspects, revealed from regional metamorphism and tectonics, are discussed.

     

High-pressure relics in meta-sediments intercalated with the Weissenstein eclogite,Münchberg gneiss complex,Bavaria

The mineral assemblages in the eclogites and meta-sediments of the Münchberg gneiss complex suggest minimum pressures of about 15 kbar, and temperatures of 600±30° C for the eclogite-facies metamorphism. Both rock types underwent a subsequent amphibolite-facies metamorphism at almost the same temperature range. In the Weissenstein borehole the eclogites and meta-sediments show an intimate interlayering on a centimetre scale. Contacts between the two rock types are often sharp and untectonized suggesting in-situ metamorphism of the eclogites. The following features indicate that the gneisses were subjected to eclogite-facies metamorphism:

1. Phengite relics and phengite inclusions in garnet contain up to 3.45 Si per formula unit while amphibolite facies phengites have considerably lower Si-contents (3.0–3.25 p.f.u.).
2. Omphacite relics occur in the form of Na-augite (6–9 mol% jadeite)-oligoclase symplectites.
3. Garnets with up to 40 mol% of the pyrope component occur.

The geological and mineral-chemical data indicate that large volumes of crustal material have been buried to depths possibly exceeding 70 km. The preservation of primary eclogitic textures as well as symplectitic textures in the presence of a fluid phase, are indicative of a rapid decompression. This would suggest a tectonic uplift (e.g. underthrusting) as is also indicated by the virtually constant temperature range during the uplift.     

The structural geology of the Dalradian rocks of Slieve Gamph,Cos. Mayo and Sligo,Western Ireland

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:

1. formation of major nappe structures and a tectonic slide. The axial-plane traces of the folds probably trended N. E.-S. W.
2. 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.
3. formation of a conjugate set of folds:
   1. Open folds with N. N. E.-S. S. W. trending axial-planes which dip to the east,
   2. Open folds with E.W. trending axial-planes which dip to the north.
4. formation of kink-bands, open and conjugate folds with an axialplane trace trending N. W.-S. E.

Late phase of faulting. No isotopic dates are available for these structural events.     

Relative elemental mobility during hydrothermal alteration of a basic sill,Isle of Skye,N.W. Scotland

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.

1. Large-ion low-charge elements Ba, K, Rb and Cs were strongly leached from the wall rock in the vicinity of the vein.
2. 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.
3. 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).
4. 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.

     

Das Relief des Mars' Versuch einer zusammenfassenden Übersicht

The analysis of the martian relief leads to the conclusion that some of the most important relief elements are either concentrically or radially arranged with respect to a central structure and hence form aureoles. In this paper four different types of aureoles are identified and described:

1. impact aureoles (as result of extradynamics),
2. volcanic aureoeles (as result of lava flow through vents),
3. tectonic aureoles (as result of isostatic adjustment and/or settlement),
4. permafrost-related aureoles and mega-aureoles (as result of migration above thawing permafrost in areas with high relief).

The spatial distribution of these different types of aureoles indicates the predominant type of relief-forming dynamics in the area of their distribution (impact-related aureoles occur predominantly in the area of the Southern Uplands; volcanic, tectonic and permafrost-related aureoles in the area of large-scale updomings-TaNoVa, Elysiumand their volcanic provinces).     

华北地台与秦岭地槽构造关系初探

边界问题或构造关系问题,一直是地质学家最为关心的问题之一。华北地台与秦岭地槽构造关系的实质是洋壳与陆壳的矛盾统一和相互转化。中晚元古代时,秦岭地槽为洋壳演化区,华北地台为陆壳区,幸岭洋壳板块俯冲至华北陆壳板块之下:黑沟—铁炉子断裂相当俯冲带,其北洛南—栾川断隆是陆壳被改造而具陆缘弧性质;陆缘弧发展晚期在其南缘发育有弧前坳陷;陆缘弧之北的熊耳断坳则为弧后裂陷盆地;陆缘弧与弧后裂陷盆地之间的马超营—石门断裂为前陆断裂带。因此,秦岭地槽与华北地台的具体界线应以中晚元古代时大洋与大陆的分界线——黑沟—铁炉子断裂为准,而马超营—石门断裂仅为陆壳改造区内次级单位的分界.     

The origin of basaltic rocks in Niutoushan area— high pressure differentiation

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:

1. Both early subalkali and late alkali bali basalts are formed under the same geological environment.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.

Basaltic rocks in Niutoushan were formed through the so-called “high pressure differentiation”, that is, at about 20 kb the crystallization of clinopyroxene and orthpyroxene resulted in the separation of subalkaline basaltic magma from the primary olivine tholeiitic magma, and then the residue gradually became alkaline olivine basaltic magma.     

The Araguainha astrobleme/Central Brazil

The following facts have supported the origin of the Araguainha circular structure in Central Brazil by a meteoritic impact:

1. the almost circular contour
2. the impact-morphologic sequence including a central uplift, ring walls and a basin rim of escarpments
3. outcrops of suevites and mixed breccias
4. the evidence of shock metamorphism
5. the presence of shatter cones, and
6. negative anomalies of the total intensity of the magnetic field at the center of the ring structure.

     

Kyanite eclogites

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.

1. Kyanite-free magmatic eclogites, rich in magnesium, from:
2. kimberlites
3. dunites and serpentinites.
4. Kyanite-bearing eclogites and grosspydites rich in CaO and low in FeO with intermediate MgO from:
5. kimberlites
6. gneisses.
7. Kyanite-free eclogites of metamorphic origin rich in iron with low magnesium and intermediate amounts of calcium from:
8. glaucophane schists
9. gneisses.

     

Geologic and fluid inclusion studies of ten types of tungsten ore deposits in South China

There are 10 types of tungsten ore deposits in South China: granite, porphyry, volcanic, pegmatite, skarn, greisen, wolframite-quartz ± microcline veins, stratabound, ferberite-quartz veins and placer. Most are chronologically related to Yenshanian granites. Integrated field, mineralogic, fluid inclusion and geochemical studies were undertaken to determine the characteristics and origin of the ores. Most of the tungsten ore deposits are also spatially related to Yenshanian granites. These granites include several intrusions, isotopically dated at 160–180 m. y. and 70–100 m. y. The concentration of trace elements, especially W Mo, Sn, Ta, Nb, Li, and F are relatively high in the granites. In the granites of South China, the average WO₃ is 4.35 ppm, but in Yenshanian granites, which are the youngest of these, the average WO₃ is 5.16 ppm. In the youngest of Yenshanian granites, a light mica-albite granite has been identified, whose average WO₃ is as high as 242.3 ppm. From this line of evidence, the tungsten ore deposits in South China are considered to be genetically related to Yenshanian granites. Wolframite-sulfide-quartz veins and scheelite skarns provide the bulk of the reserves and production. There are many different kinds of alteration associated with the different tungsten ore deposits, but the principal ones are silicification, greisenization, potash-feldspathization and chloritization. Four types of fluid inclusions were found:

1. Liquid-rich;
2. Gas-rich;
3. Liquid CO₂-bearing;
4. Polyphase with daughter minerals.

Most common are type I inclusions. Type IV fluid inclusions only appeared in the porphyry and skarns. In skarns, type IV inclusions are evidently confined to the early stage, i.e., the simple silicate stage, but in the later scheelite mineralization stage, only types I and III inclusions occurred. Types II and III were found in the wolframite-quartz-sulfide veins, especially at the top of the veins. Homogenization temperature and salinity were determined on the inclusions, and the pressure of formation was estimated from the inclusions. The homogenization temperatures of some of these types of tungsten ore deposits are as follows: porphyry, 386°C; greisen, 244–301°C; granite, 220°C; wolframite-sulfide-quartz veins, 240–310°C; wolframite-microcline-quartz veins, 267–325°C; stratabound, 219°C; and ferberite-quartz veins. 142°C. The salinity of fluid inclusions in the wolframite-sulfide-quartz veins type was only 5–10% equiv. NaCl. The pressures of formation, determined from the tomperature of homogenization, volume and density of phases in H₂O-CO₂ inclusions, from veins in three different wolframite-sulfide-quartz deposits, were 450, 550, and 750 atm., respectively. Most of the tungsten ore deposits were formed between 220°C and 390°C, with the porphyry highest and the ferberite-quartz veins type lowest. In the wolframite sulfide-quartz veins, four stages can be recognized: oxide-silicate; wolframitequartz-beryl; wolframite-quartz-sulfide; and carbonate. Throughout this sequence, the salinity and temperature decrease, e. g., from 293°C to 129°C. It is concluded that these particular tungsten deposits were formed from a dilute water solution at moderate to high temperatures and at moderate pressures.     

Antimoniferous mineralization from the Mid-European Saxothuringian Zone: mineralogy,geology, geochemistry and ensialic origin

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:

1. Stratabound and stratiform fahlore (Fahlerz) mineralization in Silurian and Lower Devonian black shales.
2. Sulphosalt- and stibnite-bearing veins (partly associated with native gold) in wall rocks of the Late Variscan granites.
3. Monometallic and monomineralic antimony lodes along anticlinal structures.
4. Sulphosalt-bearing lead-zinc veins.

Antimony in the black shales was concentrated during late diagenetic cementation along with copper. The sulpho-salt-bearing stibnite veins in the metamorphic country rocks of the granites are genetically associated with the granitic intrusions nearby. This is proved by trace element chemistry and structural as well as mineralogical features of those veins. U/Pb age dating of contemporaneous pitchblende from the »polymetallic uranium paragenesis« from Hoehensteinweg uranium deposit yielded a late Variscan age of formation for these veins of type 2. Early Paleozoic rocks (metavolcanics) are suggested to have been the parent material for these granite-related Sb concentrations. However the monotonous Sb veins are more akin to the basic protore in deeper crustal sections. The thermal aureole of a deep-seated heat source is preserved by the Ag/Sb ratio of galena in Pb-Zn veins (type 4), which shows a marked variation along the SW plunging Berga Anticline from increased Ag/Sb ratios near the core of the anticline towards reduced values in mining sites more peripheral to this fold structure. Pb isotopes of stibnite as well as Pb sulphides point to a crustal derivation of both elements. An in-situ re-deposition and leaching of Sb from the wall rocks as well as antimoniferous black shales may be ruled out. It has to be emphasized that intra-crustal mass movements (A subduction) and the late Vanscan igneous activity are the major factors controling release of Sb from the Early Paleozoic low metal concentrations within metavolcanic rocks and subsequent discharge of Sb-bearing fluids within joints and fractures related to late Variscan tectonic movements. A schematic exploration concept is outlined.     

Charriage crustal,anatexie et decrochements ductiles dans les Maures orientales (Var,France) au cours de l'orogenese varisque

The kinematics of the deformational events recorded in the catazonal gneisses within the eastern part of the Maures massif (Variscan basement of Provence, southeastern France) has been established. These events can be correlated with both the metamorphic and the magmatic evolution, and the orogenic history of the eastern Maures then consists of the following stages:

1. -HP-metamorphism preserved only in relict eclogites and quartzites rich in calc-silicates,
2. -Catazonal metamorphism involving anatectic melting, broadly contemporaneous with large-scale horizontal transport towards the NNE. During this event, the lithologic units were disrupted and intensively mylonitized.
3. -Intrusion of a first generation of anatectic granitoids.
4. -A second tectonic event under epi-to mesozonal metamorphism conditions is responsible for the northward displacement of the eastern Maures relative to the western part along a sinistral strike-slip fault 4 km wide (Ramatuelle — Plan de la Tour fault) in which the early anatectic granitoids have been mylonitized. Outside the fault zone, this event is marked by upright to W-vergent open folds trending N-S, i.e. parallel to the transport direction.
5. -A moderate cataclastic reactivation of the Ramatuelle — Plan de la Tour fault with a dextral sense of shear, locally accompanied in the eastern part of the area by minor lowtemperature thrusting towards the south.
6. -Intrusion of a second generation of anatectic granites about 320 Ma ago.

The metamorphic, magmatic and tectonic evolution of the eastern Maures suggests a continuous orogenic history in an area of rapid crustal thickening by large-scale thrusting within the continental crust. This evolution may be related to the development of continental subduction during the continent/continent collision responsible for the Variscan orogeny in southern Europe.     

Crustal features of some main suture zones along the European Geotraverse

The European Geotraverse (EGT) crosses along a 4000 km profile from the North Cape to Tunisia the following main suture zones:

the Tornquist-Teisseyre zone between the Baltic Shield and the Variscan realm,

the transition zones between Rhenohercynian and Saxothuringian as well as between Saxothuringian and Moldanubian zones in the Variscan part of central Europe, and

the collision zone between the European continent and the Adriatic microplate.

Some structural aspects of these suture zones are described.     

Field and petrological evidence for the development of an ensialic marginal basin related to the Hercynian orogeny in the Massif Central,France

Six lithologic units in tectonic contact with each other have been defined during mapping of the Devonian in the Beaujolais area of the northeastern Massif Central. Five main igneous suites have been recognized:

1. A transitional basaltic suite restricted to a single unit.
2. An acid volcanic-plutonic suite the members of which are related by fractional crystallization and magma mixing.
3. Low-TiO₂ volcanic rocks with calc-alkaline affinities.
4. A TiO₂-rich tholeiitic suite related to an ophiolitic complex.
5. A plutonic suite with close resemblances to Alaskantype intrusions.

The transitional metabasalts (1) form the oldest igneous suite and could represent either an intraplate magmatic forerunner of rifting or tectonic slices of weakly metamorphosed rocks representing a pre-Acadian event. The next three suites may be related to a short-lived ensialic marginal basin that developed between the Acadian and Bretonian orogenies. The basin is asymmetric, with the ophiolite of the central part flanked by an acid ridge on one side and a passive continental margin on the other. Quartz-keratophyres (2) and calc-alkalic basic volcanic rocks (3) were intercalated in varying proportions to form a bimodal volcanic pile before the rifting event that led to the formation of the ophiolites (4). The acid ridge (2) may be due to the reactivation of a continental basement. Cumulate rocks with Alaskan-type affinities occur as olistoliths, emplaced before the formation of the rift basin, supporting a comparison of the Hercynian belt with accreted magmatic arc terranes.     

Some examples of the Middle-Triassic Marine transgression in South-Western Mediterranean Europe

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:

1. margin with a narrow shelf sloping toward a very shallow restricted basin (Central and Southwestern Sardinia);
2. margin with a broad shelf gently sloping toward a shallow basin (NE Spain, Monti Pisani, NW Sardinia);
3. margin with a narrow shelf and steep slope marked by tectonic and volcanic activity (Punta Bianca).

     

Near-field ground motion during earthquake preparation process

Wave number discretization method is applied to study the near-field of seismic sources embedded in a cracked elastic solid. Near-field solutions are obtained for horizontal and vertical line forces. Effects of modifications in cracks of focal region on ground motion, in the near-field, are studied numerically for different

? values of crack density

? saturation of cracks

? width of cracks, and

? regimes of connection between cracks.

An earthquake process is assumed to be going through five major stages. These stages represent continuous accumulation of stress, interconnections between cracks leading to eventual failure and drainage of fluid from cracks after the major shock. Variations in the velocity ratio of waves noted from accelerograms verify the process of preparation of an earthquake.P wave contribution to vertical acceleration is negligible when the source is a vertical line force andS wave contributes only a little to horizontal acceleration when the source is a horizontal line force.     

Die Ultrabasitmassive im Präkambrium des Staates Goiäs/Brasilien

The Brazilian state of Goiás and parts of Mato Grosso represent the centre of the Brazilian shield, between the Guaporé craton in the west and the São Francisco craton in the east. In contrast to opinions before, early Precambrian gneisses and migmatites form only small parts of the shield complex whereas middle and late Precambrian sequences dominate. From tectonic position, an eugeosynclinal central zone can be distinguished accompanied by younger miogeosynclinal series to the east and west. The ultrabasic massifs of Goiás can be differentiated into following types:

1. alpinotype serpentinised dunites and peridotites,
2. gabbro-pyroxenite-peridotite associations,
3. pyroxenite-metagabbro associations,
4. dunite-pyroxenite-alkalisyenite associations,
5. lamprophyre dykes.

Nos. 1, 2 and 3 are of Precambrian age whereas 4 and 5 are surely of post-Devonian, probably of Cretaceous age and can be attributed to the phase of Paraná volcanism. The most economic types at the moment (Nos. 1 and 2) yield Ni, Cu and Co in lateritic enrichment, Cr, Pt and related elements as primary constituents. Latest, the types 4 and 5 cause special interest. From their association with carbonatites they are related to the Araxá complex of Minas Gerais and anticipate mineralizations of Nb, Ta, Ti and P.     

Forest condition and forest damages — contribution of remote sensing to different inventory approaches

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