Chondrules in the Murray CM2 meteorite and compositional differences between CM-CO and ordinary chondrite chondrules

Bulk compositions were determined by broad-beam electron microprobe analysis for thirteen of the least aqueously altered chondrules in Murray (CM2). These and literature data reveal compositional differences between CM-CO and ordinary chondrite (OC) chondrules:

• 1.(a) CO chondrules are richer in refractory lithophiles and poorer in Cr, Mn and volatile lithophiles than OC chondrules; much lower refractory lithophile abundances in CM chondrules resulted from aqueous alteration,
• 2.(b) in CM-CO chondrites, abundances of refractory lithophiles are higher in nonporphyritic than porphyritic chondrules, whereas in H-L-LL3 chondrites the converse is true,
• 3.(c) Cr ranges are greater and Cr and Mn correlate more strongly in chondrules in CM-CO than in H-L-LL3 chondrites.

We find evidence for two important lithophile precursor components of CM-CO chondrite chondrules:

• 1.(1) pyroxene- and refractory-rich, FeO-poor;
• 2.(2) olivine-rich, refractory and FeO-poor.

The occurrence of a few FeO-rich chondrules attests to a third component similar to matrix: olivine- and FeO-rich, refractories not characterized. The first two components differ from those inferred for OC chondrules, consistent with formation at different locations. The pyroxene- and refractory-rich, FeO-poor lithophile precursor component probably formed by an incomplete evaporation of presolar silicates that brought these materials into the enstatite stability field.     

Seismic patterns in Northern China and the characteristics of the epicentral distribution of the medium strong earthquakes before the large events

In this paper, the seismic pattern in Northern China from 30 ° to 42 ° N latitude and 104 ° to 125 ° E longitude, and the characteristics of the epicentral distribution before large events are presented. The results suggest that:

• 1.(1) the earthquakes in the region are mainly located in the orthogonal curvilinear network formed by the seismic belts;
• 2.(2) the larger earthquakes (M ⩾6) occurred mainly in the nodal regions of this grid:
• 3.(3) the strike of the fracture planes of the earthquakes coincided with the directions of the seismic belts;
• 4.(4) the pattern of medium strong earthquakes (M ⩾ 4.7) prior to thirteen large earthquakes (M⩾ 7) are analysed to be of three types:
  • 4.1.(a) mainly arranged along the two intersecting belts,
  • 4.2.(b) randomly distributed,
  • 4.3.(3) forming seismic gaps.

A theoretical basis and rules for drawing the orthogonal grid is presented, and an idea for the prediction of the sites of future earthquakes in Northern China is suggested.     

Coprecipitation of alkali metal ions with calcium carbonate

The coprecipitation of alkali metal ions (Li⁺, Na⁺, K⁺ and Rb⁺) with calcium carbonate has been studied experimentally and the following results have been obtained:

• 1.(1) Alkali metal ions are more easily coprecipitated with aragonite than with calcite.
• 2.(2) The relationship between the amounts of alkali metal ions coprecipitated with aragonite and their ionic radii shows a parabolic curve with a peak located at Na⁺ which has approximately the same ionic radius as Ca²⁺.
• 3.(3) However, the amounts of alkali metal ions coprecipitated with calcite decrease with increasing ionic radius of alkali metals.
• 4.(4) Our results support the hypothesis that
  • 4.1.(a) alkali metals are in interstitial positions in the crystal structure of calcite and do not substitute for Ca²⁺ in the lattice, but
  • 4.2.(b) in aragonite, alkali metals substitute for Ca²⁺ in the crystal structure.
• 5.(5) Magnesium ions in the parent solution increase the amounts of alkali metal ions (Li⁺, Na⁺, K⁺ and Rb⁺) coprecipitated with calcite but decrease those with aragonite.
• 6.(6) Sodium-bearing aragonite decreases the incorporation of other alkali metal ions (Li⁺, K⁺ and Rb⁺) into the aragonite.

     

A quantitative fluorescence technique for evaluating thermal maturity: Instrumentation and examples

Fluorescence microscopy is useful not only for identifying most of the oil-prone organic matter (macerals) in sedimentary rocks and coals but also for assessing their thermal maturities (ranks). This report introduces a violet-light excitation system which induces more than one order of magnitude stronger fluorescence intensity that the commonly used UV-light excitation system. The red/green quotient from violet-light excited fluorescence, Q_v, of sporinite can be easily measured using this system. Several examples using coal and cuttings samples are presented to demonstrate the use of this technique for evaluating the thermal maturities of coals and sedimentary rocks.From the results of our studies we conclude that:

• 1.(1) Violet-light excited fluorescence from sporinites can be routinely measured to assess thermal maturity.
• 2.(2) Spectral (Quantitative) fluorescence technique is useful for evaluating thermal maturity when samples are poorly polished or deficient in vitrinite.
• 3.(3) Visual (Strew-mounted) kerogen slides can not be used for fluorescence measurements unless a non-fluorescent mounting medium is used.

     

Mineralogy and petrology of alkaline granophyric xenoliths from the Thorsmörk ignimbrite,southern Iceland

The Thorsmörk ignimbrite, southern Iceland, contains a suite of granophyre xenoliths displaying magmatic or high-temperature sub-solidus mineral assemblages. These granophyres are consanguineous with the erupting comenditic magma. Four types of mineral assemblages are distinguished:

• 1.(A) oligoclase, edenitic hornblende, salitic pyroxene, magnesian biotite, magnetite and sphene;
• 2.(B) oligoclase, manganoan to sodic ferro-augite, fayalite, richterite, ilmenite and magnetite;
• 3.(C) anorthoclase, ferrohedenbergite to aegirine hedenbergite, ilmenite, magnetite and (riebeckite);
• 4.(D) cryptoperthite, aegirine hedenbergite to (aegirine), aenigmatite, arfvedsonite, ilmenite and magnetite.

Geothermometry shows that the xenoliths have crystallized between 900°C and 500°C at moderate oxygen fugacities, just above the FMQ buffer. It is further demonstrated that a hot vapour phase heavily charged with sodium and halogens, played a major role in the late sub-solidus crystallization of the different types.     

Aridification — Climate change in South-Eastern Europe

Climatic change in SE Europe can be characterized by the term aridification, which means increasing semi-aridity, manifested in an increase of mean annual temperature and at the same time in a decrease in the yearly precipitation.The paper deals with research results obtained within the framework of the MEDALUS II project (funded by the Commission of the European Communities). The project had the following objectives:

• 1.(i) Assessment of the impact of global change on the climate of the investigated area, including possible future climates.
• 2.(ii) Physical processes of aridification, including studies of groundwater level change, soil moisture profile dynamics, soil development, vegetation change and soil erosion.
• 3.(iii) Land use change, involving research on present land use and suggestions for the future.

Various methods were applied with respect to the different research objectives.

• 1.(i) Statistical analysis of climatic oscillations and computer runs of climatic scenarios,
• 2.(ii) Analysis of ground water data, mapping and analysis of soils and vegetation, assessment of present and future soil, and
• 3.(iii) Land capability assessment through ranking environmental conditions according to the demands of the most widely grown arable crops in Hungary.

According to our results i) the average annual warming during the last 110 years was +0.0105 °C, and precipitation decreased by 0.917 mm/year; ii) a decline of −2 to −4 m in the annual mean groundwater level can be detected in the most sensitive areas, with gradual lowering of the water table in alkali ponds; complete desiccation of some of them severs the direct contact between groundwater and salt-affected soils, the solonchak soil dynamics cease, helophile and hygrophile plant associations disappear, and consequent changes in the soil erosion regime are likely to lead to disastrous erosion in the future; iii) the climatic changes induce a transformation in land use from arable crops to plantations, starting with orchards.     

The geothermal gradient map of Central Tunisia: Comparison with structural,gravimetric and petroleum data

Five hundred and fifty temperature values, initially measured as either bottom-hole temperatures (BHT) or drill-stem tests (DST), from 98 selected petroleum exploration wells form the basis of a geothermal gradient map of central Tunisia. A “global-statistical” method was employed to correct the BHT measurements, using the DST as references. The geothermal gradient ranges from 23° to 49°C/km. Comparison of the geothermal gradient with structural, gravimetric and petroleum data indicates that:

• 1.(1) the general trend of the geothermal gradient curves reflects the main structural directions of the region,
• 2.(2) zones of low and high geothermal gradient are correlated with zones of negative and positive Bouguer anomalies and
• 3.(3) the five most important oil fields of central Tunisia are located near the geothermal gradient curve of 40° C/km.

Such associations could have practical importance in petroleum exploration, but their significance must first be established through further investigation and additional data.     

Great earthquakes,seismicity gaps and potential for earthquake disaster along the Himalaya plate boundary

Analysis of the space-time patterns of seismicity in the Himalaya plate boundary has established the existence of three seismic gaps:

• 1.(1) The “Kashmir gap” lying west of the 1905 Kangra earthquake;
• 2.(2) the “Central gap”, situated between the 1905 Kangra and the 1934 Bihar earthquakes;
• 3.(3) the “Assam gap” between the 1897 and 1950 Assam earthquakes.

This study has shown that the above great earthquakes were preceded as well as followed by long periods (⩾ 19 years) of decreased levels of seismic activity in the epicentral regions. Remarkable decrease in the seismicity following the year 1970 has been observed in the western half of the Central gap as well as in the Assam gap. Local seismic investigation in the Assam gap confirms this feature and the seismicity suggests the existence there of an asperity.The local seismic investigations in Garhwal Himalaya have shown that the small earthquakes are confined to the upper 6–8 km of the crust and may have strike-slip motions. These earthquakes occur in a region where teleseismically recorded events were few.     

Development of engineering geology in western United States

Geologic concepts and scientific-technical guidance for the planning-design and construction of engineered works was recognized in Europe by the 1800s and by the early 1900s in North America. This early geologic knowledge and experience provided the rudimentary principles that guided practitioners of the 19th century in serving the emerging projects in western United States. Case studies review the scientific-technical lessons learned and the legacy of geologic principles established in the planning and construction of major civil, mining, and military engineered works in the western states. These contributions to GeoScience knowledge and engineering geology practice include:

• •Tunnels and aqueducts across active fault zones, beneath young volcanic features, groundwater-charged faults, and land subsidence mitigation.
• •Controversial foundation design, Folsom and Auburn dams, Golden Gate Bridge.
• •Protective underground construction chambers, safety dependent geologic setting.
• •Geologic mapping as database management leasing, maintenance railroad trackway.
• •Causeway Great Salt Lake, geo-risks calculated, mitigated ‘as-constructed’.
• •Nuclear powerplants seismic design.
• •Urban Land-Use, on-going processes, acceptable geo-risks.
• •Dwelling Insurance, insuree's responsibilities.
• •Selecting technique/method to mitigate risk, preferably based on extensive database, evaluation of characteristics and historical origin adverse features/conditions that constitute a geo-risk.

     

Nature of particulate organic matter in the River Indus,Pakistan

Suspended sediments from the Indus River collected during 1981 through 1983 were analyzed for POC and its constituent fractions including amino acids, amino sugars and sugars. Percentage of POC decreased with increasing suspended matter concentrations, which suggested dilution of organic matter by mineral matter.The concentrations of amino acids, amino sugars and sugars varied, respectively, between 180 and 2000 μg/l, 5 and 125 μg/l, and 60 and 1100 μg/l. Their contributions to POC varied between 2 and 60% for amino acids and amino sugars, and between 2 and 15% for sugars. They were high during low sediment discharge (February to June), and low during high sediment discharge (August and September). Suspended sediments associated with high sediment discharge periods were characterized by low ratios of:

• 1.(i) aspartic acid:β-alanine
• 2.(ii) glutamic acid:γ-aminobutyric acid
• 3.(iii) amino acids:amino sugars
• 4.(iv) hexoses:pentoses. These and the relative distribution pattern of the monosaccharides such as galactose, arabinose, mannose and xylose indicated that, not only dilution, but also differences in the sources and processes affect the POC transport in the Indus River. These result in transport of biodegraded organic matter during high sediment discharge periods: this appears to be common to other major rivers of the region, with depositional centers in deep sea areas. These rivers, with their high sediment loads, could contribute up to 8 to 11% of the global annual organic carbon burial in marine sediments.

     

Tectonoelectric zonation in the Hellenic Arc

The electrical (apparent) resistivities ρ were measured by means of the magnetotelluric effect at twenty sites in Greece and in two directions, E-W and N-S. In most of the sites, ρ_EW differs considerably from ρ_NS. These results allow the following three zones to be distinguished:

• 1.(1) an external zone along western Greece with ρ_EW >ρ_NS;
• 2.(2) an intermediate zone along the main mountain chain in continental Greece where ρ_Ns >ρ_EW and
• 3.(3) an internal zone in the northern Aegean where ρ_EW >ρ_NS.

The above resistivity zones are compared to data from geotectonic, neotectonic, seismotectonic and in situ stress measurements which all show a similar geometry of zonation almost parallel to the active Hellenic Arc.     

Evaluation of the thermal regime of the Valles Caldera,New Mexico,U.S.A., by downward continuation of temperature data

Downward continuation of temperature data from 73 wells extending to depths of 250 ft (76 m) provides constraints on the thermal regime of the Valles Caldera. Surface-temperature gradient data and bottom-hole temperatures were used as constraints in the downward continuation. Three factors were found to control the shallow thermal regime:

• 1.(1) heat associated with the main geothermal source;
• 2.(2) local topography; and
• 3.(3) west-southwest groundwater flow. Although the well density is relatively high, comparison with the topography shows that the wells are not randomly distributed and tend to be clustered in valleys. Many details in the thermal regime appear to be related to groundwater drainage in these valleys. Temperature gradients and temperatures generally increase in the same direction as the regional drainage of the caldera suggesting a long-wavelength, shallow component to this regional gradient trend. Inversion of gradient and temperature data show additional deep heat input in the west-southwest sector of the caldera which appears to be spatially associated to the youngest volcanism. A previously reported northeast displacement of the main heat source from the surface anomaly has not been confirmed.

     

Buckling loads of fully embedded vertical piles

Determination of critical buckling loads of columns in a medium which offers resistance to lateral deflections depend on:

• (a) Length of the pile, L.
• (b) Flexural stiffness of the pile, EI.
• (c) Stiffness of the soil, K, and
• (d) Boundary conditions of the pile, both at the top and the tip.

In this paper, solutions for buckling loads have been obtained in closed form by energy methods for fully embedded vertical piles for boundary conditions, pinned top-pinned tip, fixed top-fixed tip, and a linear variation of soil stiffness. The effects of pile length, soil stiffness, and boundary conditions on buckling loads and mode of buckling have been studied for pile lengths up to 24 m with EI of 477 tm², K₀ [A] from 0 to 2000 t/m² and N_h [B] from 0 to 2000 t/m³.     

An alternative view of the Bayesian probabilistic prediction of strong shocks in the Hellenic Arc

A Bayesian discrete distribution, as developed by Ferraes (1985), is applied to predict the inter-arrival times for strong shocks in the Hellenic Arc on the basis of nine samples of shocks with seismotectonic locations very different from those used by Ferraes. The results suggest an alternative view of the Bayesian probabilistic prediction of strong earthquakes in the Hellenic Arc, and can be summed up as follows:

• 1.(a) Maximum final Bayesian probabilities of various inter-arrival times in a given seismotectonic segment are very dependent on the data set used and particularly on its time length.
• 2.(b) When using this method to determine the time intervals during which large shocks are to be expected in the Western and Eastern Hellenic arcs, it is very difficult to estimate intervals of less than a decade. The determination of the occurrence time, even in the long-term sense, remains the major problem in the prediction of these shocks.
• 3.(c) Bayesian probabilities in conjunction with seismicity observations indicate that large intermediate depth earthquakes in the Hellenic Arc are long overdue. Shocks of this sort can be expected to occur in the next few years.

It is also pointed out that although Bayesian-type predictions may be useful for engineering purposes, they are not a suitable basis for making specific predictions or taking special precautions.     

Ore mineralization related to geological evolution of the Karkonosze–Izera Massif (the Sudetes,Poland) — Towards a model

The Karkonosze–Izera Massif is a large tectonic unit located in the northern periphery of the Bohemian Massif. It includes the Variscan Karkonosze Granite (about 328–304 Ma) surrounded by the following four older units:

• -Izera–Kowary (the Early Paleozoic continental crust of the Saxothuringian Basin),
• -Ještĕd (the Middle Devonian to Lower Viséan sedimentary succession deposited on the NE passive margin of the Saxothuringian Terrane), out of the present study area,
• -Southern Karkonosze (metamorphosed sediments and volcanics filling the Saxothuringian Basin), out of the present study area,
• -Leszczyniec (Early Ordovician, obducted fragment of Saxothuringian Basin sea floor).

The authors present a genetic model of ore mineralization in the Karkonosze–Izera Massif, in which ore deposits and ore minerals occurrences are related to the successive episodes of the geological history of the Karkonosze–Izera Massif:

• -formation of the Saxothuringian Basin and its passive continental margin (about 500–490 Ma)
• -Variscan thermal events:
  • -regional metamorphism (360–340 Ma)
  • -Karkonosze Granite intrusion (328–304 Ma)
• -Late Cretaceous and Neogene-to-Recent hypergenic processes.

The oldest ore deposits and ore minerals occurrences of the Karkonosze–Izera Massif are represented by pyrite and magnetite deposits hosted in the Leszczyniec Unit as well as by magnetite deposit and, presumably, by a small part of tin mineralization hosted in the Izera–Kowary Unit. All these deposits and occurrences were subjected to the pre-Variscan regional metamorphism.Most of the Karkonosze–Izera Massif ore deposits and occurrences are related to the Karkonosze Granite intrusion. This group includes a spatially diversified assemblage of small ore deposits and ore mineral occurrences of: Fe, Cu, Sn, As, U, Co, Au, Ag, Pb, Ni, Bi, Zn, Sb, Se, S, Th, REE, Mo, W and Hg located within the granite and in granite-related pegmatites, in the close contact aureole of the granite and within the metamorphic envelope, at various distances from the granite. Assuming world standards, all these deposits are now uneconomic. Various age determinations indicated that ore formation connected with the Karkonosze Granite might have taken place mostly between about 326 and 270 Ma.The last ore-forming episode in the Karkonosze–Izera Massif is related to hypergenic processes, particularly important in the northern part of the massif, in the Izera–Kowary Unit where some uranium deposits and occurrences resulted from the infiltration of ore solutions that originated from the weathering of pre-existing accumulations of uranium minerals. A separate problem is the presence of oxidation zones of ore deposits and occurrences, both the fossil and the recent.A full list of ore minerals identified in described deposits and occurrences of the Karkonosze–Izera Massif together with relevant, key references is presented in the form of an appendix.     

Progress in the study and modelling of similar fold interferences

Similar fold interferences are examined in two different ways.

• 1.(1) We show the importance of taking into account the original position of the stratification with respect to the orientations of two interfering fold phases. Basin and dome cases correspond to particular orientations of the interfering phases with respect to each other. In all other cases, coaxiality may be achieved for particular positions of the original stratification.
• 2.(2) We have achieved a computer-aided modelling which allows the visualization by means of sections and block-diagrams of any two or three similar fold interferences. The program allows us to define the stratification, orientations of the various phases and their profiles (sinusoidal or drawn by hand), and orientations and dimensions of the selected section or block diagram. Faults may also be represented.This modelling method is a powerful research tool that we hope to apply in future to detailed studies of fold interferences, to achieve quantitative field models of multiply folded and faulted terranes.

     

Chemical modelling of kerogens

Models of kerogens belonging to the three classical Types have been represented at the following evolution stages:

• •-beginning of diagenesis (sensu-stricto),
• •-beginning of catagenesis,
• •-end of catagenesis.

Chemical models are drawn, using analytical data obtained on natural samples: elemental analysis, electron microscopy, ¹³C NMR, thermogravimetry, functional analysis and pyrolysis.In order both to get a statistical representation and make comparisons easier, the same molecular weight of about 25,000 has been chosen for the different models of kerogens at the beginning of the diagenesis stage.     

Effects of composition and high pressures on the electrical conductivity of Fe-rich (Mg,Fe)2SiO4 olivines and spinels

Synthetic olivines, with composition Fa₅₀, Fa₇₅ and Fa₁₀₀, have been transformed into spinel in a laser-heated diamond-cell at pressures from 70 to 200 kbar and at a luminance temperature of about 1,200° C. The electrical conductivity σ was measured, at room temperature and up to 200 kbar, on olivine (Lacam 1982; 1983) and spinel (present study). The data obtained permit the following conclusions:

1. Sample nature effect: under the same conditions (composition, pressure), the σ of spinel is more than three orders of magnitude of the σ of olivine.
2. Composition effect: there are more than three orders of magnitude between the values of σ for spinels derived from initial compositions of Fa₅₀ and Fa₁₀₀, respectively.
3. Pressure effect: The P-effect on σ is greater for olivines than for spinels.

Besides, as in the case of olivine, in spinel the σ obeys an empirical Boltzmann relation: $$\log {\text{ }}\sigma = n \times x + S \times P + const$$ where the first and second term are the composition and pressure contributions, respectively; x the ratio Fa/Fo in mole percent. In spinel, the activation volume, in direct connection with S, was found to be in the order of 0.3 cm³/mol, about one half of that for olivine.     

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.

     

Origin of biotite-hornblende-garnet coronas between oxides and plagioclase in olivine metagabbros,Adirondack region,New York

Complex multivariant reactions involving Fe-Ti oxide minerals, plagioclase and olivine have produced coronas of biotite, hornblende and garnet between ilmenite and plagioclase in Adirondack olivine metagabbros. Both the biotite (6–10% TiO₂) and the hornblende (3–6% TiO₂) are exceptionally Titanium-rich. The garnet is nearly identical in composition to the garnet in coronas around olivine in the same rocks. The coronas form in two stages:

1. Plagioclase+Fe-Ti Oxides+Olivine+water =Hornblende+Spinel+Orthopyroxene±Biotite +more-sodic Plagioclase
2. Hornblende+Orthopyroxene±Spinel+Plagioclase =Garnet+Clinopyroxene+more-sodic Plagioclase

The Orthopyroxene and part of the clinopyroxene form adjacent to olivine. Both reactions are linked by exchange of Mg²⁺ and Fe²⁺ with the reactions forming pyroxene and garnet coronas around olivine in the same rocks. The reactions occur under granulite fades metamorphic conditions, either during isobaric cooling or with increasing pressure at high temperature.