Thermal and electric conductivity of three basaltic rocks of the Bohemian Massif under high temperatures

Summary The thermal, temperature and electric conductivities of three alkaline basalts are compared for temperatures ranging from 20 to 900 °C.     

Changes of electrical conductivity in the vicinity of the curie temperature of basaltic rocks — theoretical model

Summary Samples of basalts, haematites and magnetites display either temporary or permanent (magnetite) weakening of the increase of the electrical conductivity with increasing temperature in the vicinity of their Curie temperature. Using the second quantization, this paper explains the observed pattern of the electrical conductivity adequately for magnetite and approximately for the other rocks by means of a quantum theory model of ferromagnetic minerals. This theory describes only the electron component of the electrical conductivity, which is responsible for the Curie temperature effect.Dedicated to RNDr. Jan Pícha, CSc., on his 60th Birthday     

Chemical characteristics of some basaltic rocks of India

An analysis of the chemical characteristics of about 200 basaltic rocks of India indicate that the rocks of Pavagarh, Girnar, Rajmahal, Mundwara, Cuddapah and Panjal Trap form independent magmatic series of mixed type having entirely different chemical characteristics relative to the Deccan basalt. The tholeiitic and olivine or alkaline basalts do not seem to form independent magma types. The present study indicates that the rocks belonging to the above magma types coexist together and may represent differentiates of a single magma series.     

Petrology and geochemistry of basaltic rocks of the Lau Basin

The Lau Basin is a marginal sea, located between the Tonga and Lau Ridges, in the southwestern Pacific. The basin is on the “inner” or concave side of the Tonga Trench-Arc system and is situated above the deep seismic zone dipping westward from the Tonga Trench. The Tonga Trench-Arc system is undoubtedly located above a zone of crustal shortening as evidenced by the deep seismicity and vulcanism. However, the geological and geophysical data give strong support to the contention that the Lau Basin has formed by crustal dilation.Rocks dredged from ridges and seamounts in the basin are sub-alkaline basalt. The average major element composition of least altered samples is: SiO₂ 48.8%, TiO₂ 1.2%, K₂O 0.18%, P₂O₅ 0.08%, H₂O+ 0.30%, Fe^III/Fe^II = 0.26,CaO/Al₂O₃ = 0.77. The data for Lau Basin basalt (LBB) show close similarity to data of typical oceanic ridge basalt (ORB). Trace element abundances (ppm): Ni 160, Cr 390, Sr 100, Ba < 31, Rb < 1 also resemble ORB values. K/Rb in a least altered and unfractionated sample is 860, Ba/Sr is 0.1, Ba/Rb is 8. Strontium isotope data show the only marked variance from ORB chemistry with LBB values ranging from ⁸⁷Sr/⁸⁶Sr=0.7020 to 0.7051. The low Sr abundances in the samples suggest the possibility of crustal Sr contamination to explain the radiogenic Sr enrichment. An alternate possibility is that the mantle source rocks were enriched in ⁸⁷Sr. Variation within dredge hauls and between dredge sites may be explained by low-pressure fractional crystallization of magmas separated from the mantle at about 50 km depth.The basin probably began to open in middle to late Miocene time either by the disruption of a single andesitic island arc by splitting along its axis or by dilation of the area between two closely spaced concentric arcs. Mantle counterflow in the asthenosphere above the downgoing oceanic lithosphere slab is the probable driving force for dilation and has provided a continuous supply of parent material for the basalt of the basin floor.     

Variation trends in basaltic rocks of the canary islands

More than two hundred new analyses of basaltic rocks from the Canary Islands are presented. The available data show that the earlier successions have similar variation trends throughout the archipelago; these trends represent all the intermediate types between basic differentiates (oceanites, ankaramites) and more salic differentiates (trachy-basalts, hawaiites). In the more recent volcanic series, the study shows that there is a magmatic diversification with different variation trends in the Eastern than in the Central Canary Islands. In the latter the alkaline character becomes stronger in the successive periods of volcanic activity which have been established in each island. In the Eastern islands the basaltic evolution is, on the contrary, towards basaltic rocks with tholeiitic affinities.     

Numeric generalization of trends in rocks of basaltic composition

Relationship for the transformation of percentage values, plotted in a conventional regular tetrahedron, to 3-dimensional cartesian co-ordinates is derived to facilitate the calculation of statistical measures. Regression relationship is worked out using the recomputed values for six basalt compositions (data taken fromVemban, 1947) to numerically generalise the trend of crystallization.     

Radioactive and trace element distribution in basaltic rocks of Lower Silesia

Summary The distribution of radioactive(Th, U, K) and selected trace(Rb, Sr, Ba, Y, Zr, V, Cr, Ni) elements in volcanic rocks from the Opole and Jawor regions of the Lower Silesia has been studied. The behaviour of these elements in the studied rocks indicates that the Lower Silesian volcanic rocks are characterized by less differentiated type than other volcanic rocks of the Bohemian Massif, the Opole rock types probably having a less differentiated character than the Jawor rock types.

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Geochemistry of the Mesozoic basaltic rocks in southern Hunan Province

Southern Hunan Province is famous for its intensive rare, radioactive and other metal elements’ mineralizations. There is a relation between the basaltic rocks and mineralizations in space, time and ore-forming elements. The Jurassic-Cretaceous (204–81 Ma) basaltic rocks consists mainly of alkali-basalt and tholeiitic basalt formed in plate environment. Trace elements and Sr, Nd, Pb isotopic compositions show that the regional mantle source was metasomatized shortly before the partial melting. The alkali basalt and tholeiitic basalt might be 3%–5% and 10%–15% of the partial melting of the enriched mantle source respectively. Obviously the enrichment of the regional mantle played an important role in formation of the large and super-large deposits in southern Hunan Province.     

Electric conductivity of Fe-Ti minerals

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Geochemistry of basaltic and gabbroic rocks from the West Mariana basin and the Mariana trench

This paper describes the chemistry of 33 basaltic rocks dredged from the West Mariana basin and from the Mariana trench during the R/V “Dmitry Mendeleev” 1976 cruise in the western Pacific.The shipboard investigations were carried out by an international working group of 66 earth scientists under the IGCP Project “Ophiolites” and sponsored by the U.S.S.R. Academy of Sciences, Moscow. The purpose of the expedition was to investigate the structure and composition of the oceanic crust of marginal basins, remnant island arcs and deep-sea trenches. Tholeiitic basalts and gabbros as well as ultramafic rocks in various stages of alteration were dredged from the central part of the West Mariana basin demonstrating the presence of oceanic crust.The Pacific slope of the Mariana trench yielded altered basaltic rocks of tholeiitic and alkalic (? trachybasaltic to shoshonitic) composition. The lower part of the island arc slope contains typical tholeiitic basalts, dolerites and gabbros as well as ultramafics associated with flysch-type sediments. This is strong evidence for the formation of an “ophiolite-schuppenzone”, probably due to subduction of Pacific oceanic crust.Associated with these rocks are amygdaloidal, highly magnesian lavas (similar to boninites), which have not been recognized previously in oceanic ridge basalts.These rocks (together with the dolerites) are interpreted as parts of the Mariana island arc and are thought to be the first stage of island arc development (an immature island arc).     

Electrical conductivity of ultramafic rocks to 1820 kelvin

Electrical conductivity, σ, of six ultramafic rocks (garnet-bearing peridotites and an eclogite) has been investigated in the temperature range 670–1820 K under known environment. Between 670 and ～1320 K σ increases with 1/T monotonically, first slowly, by 1–1.5 orders of magnitude. Above 1320 K σ increases sharply; an increase of 3–4 orders of magnitude is observed between 1320 and 1670 K. In the same temperature range the σ values for all the six rocks fall within 1.5 orders of magnitude, the lowest conductivity being for a spinel lherzolite. The range of σ values is narrowed at higher temperatures. The differences in σ values above 1470 K may be explained on the basis of varying degrees of partial melting in the rocks. Over the entire range of temperature, the σ values for the ultramafic rocks are lower than those reported for basalts but higher (by 1–2 orders of magnitude) than those for single-crystal olivines.     

Electrical conductivity of igneous rocks: Composition and temperature relations

The conductivity of four igneous rocks with, 49, 65, 77, and 84% SiO₂ was measured as a function of temperature in the interval from 20° to 1280°C; measurements were made in a vacuum of 10^?3 torr. No simple relationships were found between conductivity and SiO₂ content or versus major element groupings such as Na₂O=K₂O=CaO and TiO₂=Cr₂O₃=Al₂O₃=Fe₂O₃=FeO. An analytical expression was obtained between conductivity and the albite-quartz ratio, valid for temperatures between 300° and 1200°C. It was necessary to compute the CIPW norm in order to obtain the albite and quartz percentages. The onset of melting apparently occurred between 600° and 700°C. Petrography performed on two samples after cooling showed 70 and 85% partial melting. Three conduction regions were identified: 1) below 300°C, 2) between 300°C and 600°C, and 3) above 600°C. Different activation energies obtained for the heating and cooling intervals confirm that the sample undergoes textural changes in the heating-cooling cycle. Activation energy increments of 0.1 and 0.2 eV per decade of albite-quartz ratio were obtained.     

Measurements of thermal conductivity and specific heat in volcanogenic rocks

A laboratory installation has been developed together with a technique for determining thermo-physical properties (thermal conductivity and specific heat) in cylindrical rock specimens. The technique is based on iTOUGH2-EOS3 inversion modeling using temperature measurements inside specimens as a result of their short-term heating and subsequent return to the initial temperature. We estimated the thermal conductivity and specific heat for a collection of volcanogenic petrotypes that reflect the rocks that compose the Rogozhnikovskii volcanogenic oil reservoir (29 specimens). The average thermal conductivity of the dry rocks is 1.47 W/m °C and the average specific heat is 754 kJ/kg °C; the reproducibility of this estimation is 2.2% for thermal conductivity and 0.7% for specific heat.     

Geochemical characteristics of Cretaceous basaltic rocks in South China and constraints on Pacific plate subduction

The South China, including Yangzi Craton and the Cathaysian Block, belongs to the southern part of East Asia continent. It borders Pacific plate on the east side and Qinling-Dabie Orogen on the north side. During the middle-late Cretaceous, a number of downfaulted red basins (the terrestrial sedimentary basins in Fig. 1) and volcanic- sedimentary basins had been developed in South China[1,2], in which the con-temporaneous basaltic rocks were generally distributed (Fig. 1). Although the …     

Electrical conductivity of rocks in the heating and cooling cycle

Summary The values of the electrical conductivity, recorded during the heating and cooling cycle, of eclogites and basalts are compared. The observed difference in the values is explained by reversible and irreversible changes which take place in the samples.     

Petrography and geochemistry of basaltic rocks from the Conrad fracture zone on the America-Antarctica Ridge

Intrusive and extrusive basaltic rocks have been dredged from the Conrad fracture zone (transecting the slow-spreading America-Antarctica Ridge). The majority of rocks recovered are holocrystalline with the dominant mineral assemblage being plagioclase plus clinopyroxene with or without minor Fe-Ti oxides (olivine occurs in only three samples) and many of the samples show evidence of extensive alteration. Secondary minerals include chlorite, actinolite, K- and Na-feldspar, analcite and epidote. In terms of bulk chemistry the rocks are characterized by their generally evolved and highly variable compositions (e.g.Mg^*=0.65?0.35;TiO₂=0.7?3.6%;Zr=31?374ppm;Nb=<3?21ppm;Y=17?96ppm;Ni=100?9ppm), but with respect to the immobile incompatible element ratios (e.g. Zr/Nb, Y/Nb, La/Sm) are similar to “normal” or depleted mid-oceanic ridge basalts.Quantitative major and trace element modelling indicate that most of the variation observed can be attributed to low-pressure fractional crystallization of plagioclase plus clinopyroxene in approximately equal proportions with or without minor Fe-Ti oxides. The range in composition can be accounted for by up to 76% fractional crystallization. Although ferrobasalts have not frequently been associated with slow spreading ridges, the extreme differentiation observed in the Conrad fracture zone basalts implies some additional constraint other than spreading rate on the formation of ferrobasalt and reaffirms the importance of extensive crustal differentiation during the production of this basalt type.     

Effect of hydrostatic pressure upto 1.5 GPa on the magnetic parameters of basaltic rocks

Summary The effect of hydrostatic pressure upto 1.5 GPa on the remanent magnetic polarization of samples, representing three groups of basalts with different ratios of the reversible and irreversible component of overall changes is studied. It is shown that, as a result of permanent changes of the transfer properties of the non-magnetic matrix, the patterns of pressure changes of the remanent magnetic polarization differ after applying a pressure of 1.5 GPa, however, the ratio of the reversible and irreversible component does not change.     

Origin of magnetic minerals and natural remanent magnetization of basaltic rocks from Lower Silesia,Poland

Summary Two groups of basaltic rocks with normal and reversed NRM were examined. It was found that in both groups the primary NRM, synchronous with the period of rock formation, is preserved. Relations of the primary NRM to the origin and the degree of oxidation of magnetic minerals were considered in detail.     

Complete and partial self-reversal of natural remanent magnetization of basaltic rocks from Lower Silesia,Poland

Summary Experiments of heating-cooling cycles in zero magnetic field were performed in order to study self-reversal of NRM in basaltic rocks from Lower Silesia. Complete self-reversal occurred in one sample containing titanomagnetite withT _c of 170°C and a small amount of a phase with higher Curie point. During consecutive heat treatments the phenomenon became less conspicuous. In three samples of higher oxidation level, containing several magnetic phases, only partial self-reversal of NRM occurred. For the most oxidized sample no changes of direction of NRM were observed. We suggest that the investigated phenomenon of self-reversal of NRM is due to a negative magnetic interaction between primary titanomagnetite and products of its oxidation. It seems that complete self-reversal can take place in a restricted state of oxidation.     

Correlation between magnetic and mineralogical properties of some tertiary basaltic rocks from qatrani-fayum area,Egypt

This paper reports clear correlation between the magnetic and mineralogical properties of some basaltic rocks from Egypt. Although all the measured samples are reversely magnetized lavas, yet clear differences were found between them. A four-fold classification based on the nature of both titanomagnetite and discrete ilmenite grains is given. The classification is based mainly on the differentiation between the different stages of oxidation and these were found to be in accordance with the intensity of magnetization and susceptibility values.