Noble gases in a section across the vapor dominated geothermal field of Larderello,Italy

Noble gases were studied in six wells, located on a 4.5 km south to north section across the Larderello field. Depth of wells, flow and gas/steam ratios are known to increase from south to north. Exploitation progressed in the same direction. The following noble gas patterns are observable: (a) Atmospheric Ar, Kr and Xe reflect productions of gas-depleted water at Colombaia 2 and progressively more gas-enriched steam towards the Gabbro wells. (b) Radiogenic⁴He and⁴⁰Ar are observed in increasing concentrations from south to north. (c) The radiogenic and atmospheric gases reveal a positive correlation, indicating that the recharging water enters deep into the system, and gets well mixed with the radiogenic gases prior to the steam separation. (d) Gas contents and relative abundances of radiogenic argon decrease with production, thus supplying markers for the degree of exploitation in a well and a guide for optimum well spacing. (e) Excess neon over argon is observed and discussed in terms of crustal origin versus possible fractionation of atmospheric noble gases due to pertial steam separation.     

On gradings for one — dimensional seismologic predictions

This paper gives a complete commentary on some popular gradings which based on the 2×2 contingency table, for one—dimensional seismologic prediction. It contains:

1. In view of the statistical correlation, the Wallen gradingV=√QS is the most equitable one amomg all gradings.
2. Each one of the three gradings: Zhenchao Gu gradingS, Obuhov gradingQ and Shaoxie Xu gradingR, has its own inadequacy although they are so easy for use.
3. A set of gradings can be derived fromV. The harmonic mean ofS andQ, H(S,Q) and the Hedike gradingS _H are the members of this set. The order of some popular gradings are given in Theorem 5. 3.
4. In view of the measure of the overlapping part a gradingW is introduced. Another set of gradings may be derived from it. The index of efficiencyh is the severest one among this set.

     

Metavolcanic rocks and their origin,Southern Adirondack mountains,New York

One of the problems associated with massif-type anorthosite in high grade metamorphic terranes is the absence of anorthositic extrusives. However, if anorthosite formed by crystal segregation, volcanic equivalents of the final fluid differentiate might occur. Massive, stratiform hornblende-garnet granitic gneisses occur between two metasedimentary sequences in asynclinorium south of the main Adirondack anorthosite massif and north of the Thirteenth Lake anorthosite dome. The granitic gneisses are divided into three stratigraphic units on the basis of mineralogy. The entire stratigraphic configuration has been traced 70 kilometers laterally, and the interpretation of the literature indicates that it may extend for over 100 kilometers. Earlier workers considered the granitic gneisses to be sill-like intrusives. The following evidence suggests a volcanic origin for these gneisses:

1. A thin (3 to 5 meters) but continuous zone of cale-silicates and quartzite occurs within the sequence of granitic gneisses at the same horizon for some 25 kilometers laterally and does not appear to be truncated nor intruded by the gneisses. This observation virtually precludes an intrusive origin.
2. 2V, of plagioclase (An_24,25) in granulated, augen-shaped zones in the granitic gneisses variesfrom 109° to 120°, whereas 2V, for groundmass plagioclase (also An_{20, 25}) is 84° to 88°. According to the data of Slemmons, the 2V of the granulated augen is characteristic of volcanic (high temperature) plagioclase and that of the groundmass is characteristic of plutonic (low temperature) plagioclase.
3. The great lateral extent of the granitic gneisses suggests that the materials were deposited as volcanic ash or pyroclastics.
4. The stratigraphic coherency of metasedimentary sequences and granitic gneisses indicates that the gneisses are an integral part of the stratigraphy.

A jotunite-mangerite-charnockite suite of intrusives in this area is related to the main anorthosite massif. Since plagioclase augen or their remnants exist in both the granitic gneisses and in the intrusive suite, it is possible that the granitic gneisses and the intrusives were derived from the same magma. It has been suggested that differentiation of the anorthosite suite occurs at considerable depth whereas differentiation of the same magma at shallow depth produces the rapakivi-laboradorite porphyry association of the Fennoscandian region. If the stratiform granitic gneisses and the anorthosite suite in the Adirondacks are comagmatic, differentiation of the magma must have occurred at moderate depth and the parental magma may have been granodioritic and thus more silicic than presumed by most workers.     

Liparitic volcanism of some regional volcanic structures in Kazakhstan,Middle Asia and Caucasus

Liparitic volcanism is a typical feature of the orogenic phase giving rise to the Kazakhstan, Middle Asia and Caucasus folded systems. The main characteristics of the liparitic volcanism common to these three regions are the following:

1. Geo-structural zonation of the volcanic structures.
2. Dismembered Moho surface within the volcanic structures.
3. Synchronous, yet independent evolution of liparitic and andesitic volcanisms.
4. Ignimbritic character of the liparitic volcanism.
5. Lateral petrochemical zonation with some features common to the liparitic and andesitic rock series.

Geo-structural and petrochemical zonations are likely governed in the regions studied by a deep-seated plutonic body.     

Origin of rhyolites by anatectic melting of granitic crustal rocks

Rhyolitic pumice deposits on some East Aegean Islands are the remnants of a tuff sheet which covered formerly more than 2500 km². The rhyolites originated by melting of granitic crustal rocks. The petrological properties leading to this conclusion are as follows:

-mineralogical composition of the pumice being 60 wt % of glass and 40 % of relictic granitic minerals (quartz, plagioclase, potash feldspar, biotite) in «phenocrysts» up to 1 cm Ø.

-phenomena of strong corrosion, resorption and melting of all light colored «phenocrysts» in the rhyolitic pumice.

-mineralogical and chemical identity between pumice and granitic xenolites found in great quantity in the pumice tuff.

-structurally transitional types between pumice and the granites in different state of melting.

-eutectic composition of the pumice glass for a pressure of 2 kb.

     

Pétrologie de la Série Volcanique de l’île de Fayal (Açores)

Four volcanic units have been distinguished on the islanf of Fayal. In order of decreasing age, these are:

the eastern rift, and products of the activity preceding the collapse of the caldera visible at the summit of the stratovolcano, characterized by an alkaline series: basalt-hawaiite-mugearite-trachyte;

the products of the explosive and postcaldera activity where only evolved lavas occur (benmoreites and trachytes);

the recent basaltic activity of the Horta region;

the western fissural activity — recent and historical.

The two last units are characterized by exclusively basaltic, frequently picritic, eruptions. The lava groups cannot be distinguished by chemical criteria and have thus been treated as a single suite. Ninety samples have been analysed by X-ray fluorescence, and the mineralogy of 6 representative specimens has been determined by microprobe. The data were used to work out the evolution of the lava. The series is shown to have been produced by crystal fractionation under moderate water pressure from an alkali basalt. Moderate fractionation of amphibole during the last stages allow the liquids to remain weakly undersaturated from initial basalts until final trachytes. Mineralogical and chemical diversity between the most evolved lavas, benmoreites and trachytes, is an evidence of the strong influence ofpH₂O and/orfO₂ on the composition of such residua.     

Petrology of basaltic xenoliths in andesitic to dacitic host lavas from Martinique (lesser antilles): Evidence for magma mixing

Some recent calc-alkaline andesites and dacites from southern and central Martinique contain basic xenoliths belonging to two main petrographic types:

The most frequent one has a hyalodoleritic texture (« H type ») with hornblende + plagioclase + Fe-Ti oxides, set in an abundant glassy and vacuolar groundmass.

The other one exhibits a typical porphyritic basaltic texture (« B type ») and mineralogy (olivine + plagioclase + orthopyroxene + clinopyroxene + Fe-Ti oxides and scarce, or absent hornblende).

Gradual textural and mineralogical transitions occur between these two types (« I type ») with the progressive development of hornblende at the expense of olivine and pyroxenes. Mineralogical and chemical studies show no primary compositional correlations between the basaltic xenoliths and their host lavas, thus demonstrating that the former are not cognate inclusions; they are remnants of basaltic liquids intruded into andesitic to dacitic magma chambers. This interpretation is strengthened by the typical calc-alkaline basaltic composition of the xenoliths, whatever their petrographic type (« H », « I » or « B »). The intrusion of partly liquid, hot basaltic magma into colder water-saturated andesitic to dacitic bodies leads to drastic changes in physical conditions. The two components; the basaltic xenoliths are quenched and homogeneized with their host lavas with respect to T^o;fO₂ andpH₂O conditions. « H type » xenoliths represent original mostly liquid basalts in which such physical changes lead to the formation of hornblende and the development of a vacuolar and hyalodoleritic texture. The temperature increase of the acid magma depends on the amount of the intruding basalt and on the thermal contrast between the two components. The textural diversity which characterizes the xenoliths reflects the cooling rate of the basaltic fragments and/or their position relative to the basaltic bodies (chilled margins or inner, more crystallized, portions). In addition to physical equilibration (T, fO₂) between the magmas, mixing involves:

mechanical transfer of phenocrysts from one component to another, in both directions;

volatile transfer to the basaltic xenoliths, with chemical exchanges.

It is here demonstrated that a short period of time (some ten hours to a few days) separates the mixing event from the eruption, outlining the importance of magma mixing in the triggering of eruption. The common occurrence of basaltic xenoliths (generally of « H » type) in calc-alkaline lavas is emphasized, showing that this mechanism is of first importance in calc-alkaline magma petrogenesis.     

Distribution de l’uranium,du thorium et du potassium dans les roches volcaniques de l’Afar septentrional (Ethiopie)

Concentrations in uranium, thorium and potassium were determined by gamma spectrometry in more than 100 samples of volcanic rocks from the material obtained during the French-Italian expedition in Dankalia (Afar-Ethiopia) (December 1967 – February 1968). These samples were taken from two geographically distinct areas:

1. the danakile depression (Erta Ale range, Pierre Pruvost massif, Alayta, Afdera, Borawlu).
2. Ethiopian high lands (Adigrate — Axum).

The values we obtained give the following contents:

Dash

in the Erta Ale range, for basalts, K: 0,5%, U: 1,3 ppm, Th: 3,3 ppm, Th/U: 2,6.

for alkaline rhyolites, U: 4,1 ppm, K: 2,3%, Th: 15,2 ppm, Th/U: 3,7.

in the Pierre Pruvost massif, for acid rocks, K: 3,9%, U: 3,6 ppm, Th: 13,5 ppm, Th/U: 3,8.

in the Borawlu centre, K: 2,8%, U: 4,6 ppm, Th: 14,7, Th/U: 3,4 for the rhyolites, K: 0,6%, U: 0,9 ppm, Th: 3,1 ppm for the basalts.

on the Ethiopian high lands, for the Adigrate basaltic trap rocks, K: 0,6%, U: 0,6 ppm, Th: 1,1 ppm, Th/U: 1,7 and for the Axum zone of phonolitic pinnacles, K: 3,9%, U: 2,7 ppm, Th: 14,9 ppm, Th/U: 4,9.

The Th/K and U/K ratios are particularly high compared with the usual data, except for the Pierre Pruvost massif which seems to be different from the others. The difference of Th/U ratios for basic rocks and acid rocks is meaningful. For the magma which gave the volcanism of the studied area, one can think of an evolution more especially connected with transfers of volatile elements. The strong correlations existing between potassium, uranium and thorium probably indicate the presence of groups which are distinct from a geochemical point of view in the Dankalia lavas.     

Natural gas geochemistry and its origins in Kuqa depression

According to gas compositional and carbon isotopic measurement of 114 gas samples from the Kuqa depression, accumulation of the natural gases in the depression is dominated by hydrocarbon gases, with high gas dryness (C₁/C_1–4) at the middle and northern parts of the depression and low one towards east and west sides and southern part. The carbon isotopes of methane and its homologues are relatively enriched in ¹³C, and the distributive range of δ ¹³C₁, δ ¹³C₂ and δ ¹³C₃ is ?32‰–?36‰, ?22‰–?24‰ and ?20‰–?22‰, respectively. In general, the carbon isotopes of gaseous alkanes become less negative with the increase of carbon numbers. The δ ¹³ \(C_{CO_2 } \) value is less than ?10‰ in the Kuqa depression, indicating its organogenic origin. The distributive range of ³He/⁴He ratio is within n × 10^?8 and a decrease in ³He/⁴He ratio from north to south in the depression is observed. Based on the geochemical parameters of natural gas above, natural gas in the Kuqa depression is of characteristics of coal-type gas origin. The possible reasons for the partial reversal of stable carbon isotopes of gaseous alkanes involve the mixing of gases from one common source rock with different thermal maturity or from two separated source rock intervals of similar kerogen type, multistages accumulation of natural gas under high-temperature and over-pressure conditions, and sufficiency and diffusion of natural gas.     

Geophysical aspects of man-made electromagnetic noise in the earth—A review

The paper gives a summary of geophysical aspects of man-made electromagnetic noise in the Earth as follows:

- EM distortion effects of man-made constructions below and over the Earth's surface defined as ‘passive-noise’,

- field observation of EM disturbances due to ‘active’ man-made sources,

- EM source mechanism of some important active sources from a geophysical point of view,

- efforts in order to improve the signal-to noise ratio by instrumental, methodological and dataprocessing ways,

- application of man-made EM noise for geophysical prospecting.

The paper is based on world-wide EM noise survey studies published mainly in geophysical journals.     

Seismic sources and attenuation properties at the Campi Flegrei volcanic area

Microearthquake digital data collected at Campi Flegrei during the recent (1982–1985) ground uplift episode have been analyzed in order to infer source and medium seismic properties. The main results obtained from these analyses are:

1. Hypocenter distribution and the size of the seismic zone do not change with time and do not depend on the ground uplift rate. Events occurred clustered in time with no simple causal relations between the cluster occurrences and their energy.
2. Anelastic attenuation does not depend strongly on frequency, showing a constant pattern at high frequencies. The observed values of low and high frequency attenuation, due to the short source receiver distances, do not seriously affect the spectral content of signals radiated by the sources.
3. A constant Brune stress drop pattern (～4–5 bars) as a function of seismic moment is observed. This indicates that the manner of fracturing is almost independent on magnitude of earthquakes (hypothesis of self-similarity (Aki, 1967)). Seismic processes in a prefractured medium can explain the observed small stress drop values.
4. Focal mechanisms from moment tensor estimates show that radiation patterns are mostly well interpreted in terms of double couple source models.
5. The scaling of peak ground motion parameters (A _max andV _max vs seismic moment) can be explained by an ω² source model (constant stress drop) multiplied by an exponential function with a small decay parameter, which takes into account the measured attenuation.

These results support the hypothesis of earthquakes generated by simple shear fractures along prefractured structures as a response to changes in the stress field due to the ground deformation.     

The microseismic network of the Ridracoli Dam,North Italy: Data and interpretations

The Ridracoli Dam has been operating since 1981. Around the reservoir ISMES installed and operated for 10 years a seismic network, now reduced to a 3-D station. Earthquakes were recorded with completeness from magnitude 0.8 onwards. In the same period, all the parameters relevant to the dam and the environment were measured. This provided a complete data base for RIS studies, unique in its kind in Italy. The main findings of the analyses performed are the following:

1. The filling of the reservoir has not influenced the seismicity of the area for most significant events (M _L>3.5).
2. Lesser seismicity around the reservoir seems to be correlated with water level in the reservoir, but also shows to be dependent on regional seismicity.
3. b value shows a slight increase with time. This may indicate an increase in rock fracturing, which is known to precede the disappearing of Type II RIS.

     

Turbidity and mass concentration of suspended matter in lake water: A comparison of two calibration methods

Turbidity measurements by foreward scattering nephelometer have been regularly conducted on the north basin of Lake Lugano (Switzerland/Italy) since September 1992. In order to determine mass concentrations from these data, both, in-situ and laboratory calibration experiments have been performed in November and December 1992 on suspended matter of the hypolimnion. Results show:

1. Mass concentration/turbidity ratios are different in the two turbidity zones examined due to variation in the optical signature of the suspended matter.
2. Laboratory calibrations using suspended matter originating from the water depths of interest give representative results provided that physical and chemical alterations occuring during the particle transfer process remain negligible.

     

Small scale arcuate intrusions on Saint Helena,South Atlantic

Sixteen arcuate intrusions have been emplaced at extremely high levels into the basaltic shield volcanoes of Saint Helena. These intrusions are of special interest because of their small size and modes of emplacement. The arcuate masses are of three distinctive types:

1. Irregular, steeply inward-dipping, basic sheets with diameters of 150 m to 450 m infill tensional fractures originating at depths of about 500 m beneath the volcano surface.
2. Strongly curved sheets from 25 m to 750 m in diameter are cross-sections of inclined intrusions which in three dimensions resemble single sticks of celery. These intrusions, varying from basalt to trachyte in composition, are infilled tensional fractures originating at « point » pressure sources, inclined to the horizontal, at depths of about 500 m below the surface.
3. Salic intrusions with near-vertical sides and gently inclined roof-infillings have outer diameters of 350 m to 1070 m. Pressure exerted onto the flanks of the volcano by domed, convex upwards, areas of a magma chamber roof, at a depth of about 2 km, caused near-vertical ring fractures to form. Formation of a sub-horizontal cross fracture and subsequent intrusion of magma produced the « roof-infillings » by updoming the overlying basalts or sinking of the enclosed block, or combinations of the two processes. Two intrusions of this third type are multiple.

     

On the reduction of time variations for geomagnetic repeat station measurements

For most previous geomagnetic surveys, the time variations of the observatory closest to the site of observation have been used for reduction. The accuracy of repeat station measurements depends upon the distance between the station and the observatory. Nowadays, the requirements for the accuracy of repeat station measurements are much higher, especially with respect to local secular variation anomalies. On the other hand, transportable variograph stations are available, by means of which time variations can be recorded closer to the station site. The reduction steps for this method are:

1. Reduction of measured values to the base-line of the nearby variograph station;
2. Computation of the nearest quiet night value using the baseline of the variograph;
3. Computation of the difference between this value and the corresponding one at the observatory.

The problems are:

- the stability of the base-line values of the variographs;

- the question as to what degree a quiet night value represents the normal value at that time (e.g. influence of aD _st field and/or other fields).

A repeat station survey of the Federal Republic of Germany was carried out in 1982. During the same time, eleven stations recorded the time variations in that area. We discuss the aforementioned aspects by way of an example taken from this survey.     

On conditions for the unique inversion of seismic travel-time curves

It is shown that when the travel-time curve of a refracted wave from a surface source is known and at least one of the following conditions is satisfied, i.e. when

1. the travel-time curve of a wave reflected from a horizontal interface lying below the deepest low velocity layer is known, or
2. the travel-time curve of a wave from a deep source situated below the deepest low velocity layer is known, or
3. the measureH(u)=mes {z∶z≥0,v ^?1 (z)≥u} is analytical in some segment [c, d], where \(0< c< d< \infty , c< a_n , H(a_n ) = \bar z_n ,\bar z_n\) is the depth of the lower end of the deepest low velocity layer and in the interval [c, ∞) an analytical functionH(u)) exists which providesH(u)≡H(u)) ifu∈[c, d], then (1) velocityv(z) outside the low velocity layers and (2) the measureH _k (u)=mes {z∶z∈L _k,v ^?1 (z)≥u} for each low velocity layerL _k,k=1, 2, ..., n, are defined unambiguously.

     

Reoccurrence formulas for the largest earthquake magnitudes based on the modified cumulative frequency-magnitude relationship

A modified formula of the cumulative frequency-magnitude relation has been formulated and tested in a previous paper by the authors of this study. Based on the modified relationship, the following reoccurrence formulas have been obtained.

1. For the ‘T-years period’ larger earthquake magnitude,M _T $$M_T = \frac{1}{{A_3 }}ln\frac{{A_2 }}{{(1/T) + A_1 }}.$$
2. For the value of the maximum earthquake magnitude, which is exceeded with probabilityP inT-years period,M _PT $$M_{PT} = \frac{{ln(A_2 .T)}}{{A_3 }} - \frac{{ln[A_1 .T - ln(1 - P)]}}{{A_3 }}.$$
3. For the probability of occurrence of an earthquake of magnitudeM in aT-years period,P _MT $$P_{MT} = 1 - \exp [ - T[ - A_1 + A_2 \exp ( - A_3 M)]].$$

The above formulas provide estimates of the probability of reoccurrence of the largest earthquake events which are significantly more realistic than those based on the Gutenberg-Richter relationships; at least for numerous tested earthquake samples from the major area of Greece.     

Die Einschichtung der Rhone im Genfersee: Ergebnisse von Strömungsmessungen im August 1983

Results obtained by means of an ultrasonic current meter in the plume of the Rhone river are summarized as follows:

1. Currents of Rhone river water entering the lake were clearly discernible up to a distance of about 1 km from the river mouth. The interflow was observed at depth of 10 to 30 m.
2. Interflow velocities decreased with increasing distance from the river mouth: from 40cm/s at a distance of 350 m to about 15 cm/s at 1 km.
3. Short-term variations of current velocities and directions documented the highly turbulent nature of the interflow.
4. The entering river water (inflow direction to the NNW) interfered with a persisting northeastward current of the lake water. At a distance of 1–2 km from the mouth the interflow gradually assumed the same direction, possibly due to deflection by Coriolis forces.
5. Current velocities showed considerable variations within a time scale in the order of hours at the same measuring position. The reasons for these fluctuations remain unclear. Possible causes may be lateral oscillations of the entering river water or its deviation by river mouth bars during periods of reduced river discharge. Variations of the discharge alone cannot explain these current fluctuations.

     

Characteristics of afferent activity of ampullary electroreceptors in catfishParasilurus asotus

The spontaneous and evoked activity of electroreceptors were electrophysiologically studied. The results are:

1. The spontaneous discharge rate ranged from 15 to 85 imp/s with a mode of 50 imp/s for 126 organs of 18 animals.
2. By analysis of periodic histograms and interspike interval histograms of responses to sinusoidal electric stimulations, the frequency response characteristic was determined. The frequency response curve shows a band pass type, the band width ranged from 5 Hz to 30 Hz and the best frequency is around 15 Hz.
3. The thresholds of responses for 47 organs were measured by injection of sinusoidal current into the organs. The threshold values were less than 0.1nA (61µV/cm) for 35 organs (74%), and less than 0.01nA (6.1 µV/cm) for the rest of 9 organs (19%).

     

Petrology of the volcanic rocks of martinique,West Indies

Volcanological differences between the old and the recent lavas from Martinique, Lesser Antilles, are presented, showing that two volcanic series exist in this island:

Dash

a high-alumina basalt series generally mafic, line-grained, partly pillowed, with clinopyroxene-rich lavas which show iron enrichment tendancies en an A.F.M. plot;

a calc-alkaline (slightly potassic) series much more siliceous as a group, porphyric, predominantly sub-aerially erupted with orthopyroxene-rich lavas which show no iron enrichment.

The high-alumina basalt series is considered as having originated from a differentiation trend by fractionation of olivine, clinopyroxene and plagioclase. Lavas range from olivine basalt to tridymite-rich dacite. The calc-alkaline series probably derives from the contamination of the first suite but the occurence of hornblende-rich cumulates indicates the process of fractionation takes place too. Lavas range from orthopyroxene andesite and hornblende andesite to quartz-hornblende dacite and quartz-biotite dacite.