Metamorphic Rock Samples Research Articles

ANALÝZA LABORATORNÍCH HODNOT RADIOAKTIVITY HORNIN NA MAPOVÉM LISTU 15-11 ZLATÉ HORY

Natural radioactive elements (potassium, uranium and thorium) abundances were measured in 769 samples of metamorphic and igneous rocks and pre-Cenozoic sedimentary rocks from all geological units on the map sheet 15-11 Zlaté Hory, using a laboratory gamma-ray spectrometer. Metamorphic rocks belong to two geological units of the Silesicum: to the Vrbno Group (a volcanosedimentary complex composed mainly of phyllites, quartzites, amphibolites, greenschists, acid to intermediate metavolcanites and their metatuff s) and the Desná Group (metagranites and blastomylonites). Unmetamorphosed pre-Cenozoic sedimentary rocks are represented by three Variscan flysch formations – the Andělská Hora, Horní Benešov, and Moravice Fms. (rocks of the first formation are unmetamorphosed to anchimetamorphosed), only in small areas by Cretaceous sandstones of the Peruc-Korycany Formation and Devonian limestones of the Líšeň Formation. Unmetamorphosed magmatites are represented by granitoids, lamprophyres andmicrogabbro. From calculated values of mass activity of 226Ra equivalent it is evident that natural radioactivity of most of the studied rocks is low. Slightly increased mass activity values were found in feldspar-rich quartzites (186 Bq.kg-1 on average), metakeratophyres (200 Bq.kg-1) and felsic metatuff s (229 Bq.kg-1) of the Vrbno Group.

Geochemistry, Hydrothermal alteration and Ore mineralogy of Skarn Mineralization at Wethey-Pheshey area, Thabeikkyin Township, Mandalay Region, Myanmar

Wethey-Pheshy area is located 80 km north of Mandalay at Thabeikkyin Township, Mandalay Region. X-ray Diffraction (XRD) Analysis and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) were applied in this study. Geochemical studies on the host rocks indicate that major and minor oxides compositions of metamorphicrocks show some degree of variation. CaO, MgO, FeO, TiO2 and P2O5 concentration of the metamorphic rock samples show a coherent negative correlation with SiO2 whereas Na2O is positively correlated with SiO2. The metamorphic rocks are strongly enriched in light rare earth elements (LREE) and relatively depleted in heavy rare earth element (HREE). The depleted Eu-nomalies in the chondrite-normalized REE diagrams indicate a plagioclase-depleted Eu crustal source or fractionation during magmatic differentiation. Intrusion of granitic rocks in the diopside marble caused the base metal ore mineralization and associated skarn alterations. Granite shows the sub-alkaline nature and peraluminous character. It is identified as I-type granite (magnetite series) developed in the volcanic arc setting. Hydrothermal alteration types associated with gold and skarn mineralization in the study area include calc-silicate alteration, propylitization, sericitization (argillitization) and hematization. Based on the nature and characteristics of host rocks, mineralization and alteration style and geochemical characteristics in the study area is identified as intrusion-related skarn mineralization. Common ore minerals include chalcopyrite, galena, sphalerite, pyrite, gold and Fe-oxides.

An Examination of the Physio-mechanical Properties of Rock Lump and Aggregates in Three Leading Quarry Sites Near Accra

In recent times, there has been an increasing indiscrimination in the choice of aggregate for the casting of concrete in the construction industry. The nearest available material is used without looking into its properties and strength. The source of aggregates and its physio-mechanical properties have an effect on the final product depending on the design mix. This study focusses on the determination of dry density, water content of rock materials, porosity, compressive strength of parent rock lumps material, rock aggregates and the grading of aggregates. Samples were picked from three leading quarries near Accra, Ghana and were tested quantitatively at the laboratory. Analysis shows that air spaces in rock lump samples with valued percentages varied from 29% to 34% and 41% for igneous, sedimentary and metamorphic rocks respectively, with a direct proportional effect on the water content of the rock lump. Invariably, the dry density for sampled igneous, sedimentary and metamorphic rocks lump varied from 1.12g/cm3 to 1.57g/cm3 and 2.03g/cm3 respectively. There was a direct correlation between the impact resistance and load resistance results of the samples. Igneous rock recorded the highest impact resistance of 802 mm followed by sedimentary and then metamorphic rocks with 602mm and 201mm respectively with a corresponding load resistance of 57kn, 29kn and 13kn. The studies revealed rock aggregate moisture contents as 8.1%, 7.6% and 10.7% translating into its water absorption and porosity of 10.25%, 14.11% and 7.55% for igneous, sedimentary and metamorphic rocks respectively. The laboratory results with respect to grading of the aggregates for particle size distribution shows that sedimentary crush rocks showed a well graded particle size distribution, best suited for concrete works. Based on comparative laboratory analysis of the physio-mechanical properties of the three rocks, igneous rocks showed properties best suited for concrete mix design, whilst metamorphic rock samples proved to be the poorest.

Comment on “John’s stone: A possible fragment of the 1908 Tunguska meteorite” (Anfinogenov et al., 2014, Icarus 243, 139–147)

Anfinogenov et al. (Anfinogenov et al. [2014]. Icarus 243, 139–147) argue that a highly silicified gravelite sandstone referred to as “John’s stone” could be a fragment of the long-sought-after impactor from the 1908 Tunguska event. We have analyzed the oxygen isotopic composition of two distinct samples of John’s stone both kindly provided by Dr Yana Anfingenova. Both samples had very similar isotopic compositions, such that the average of the two was as follows: δ17O=6.67±0.15‰; δ18O=12.78±0.28‰; Δ17O=−0.01±0.01 (errors 1SD). This value is well within the range for samples of terrestrial quartz-bearing sedimentary and metamorphic rocks. John’s stone has an oxygen isotope composition and mineralogy that is unlike any known group of meteorites. If John’s stone is extraterrestrial this would imply that it represents a previously unknown type of meteorite, as suggested by Anfinogenov et al. However, since sandstones can only form on a parent body with liquid water and by inference, also an atmosphere, we argue that there are only two possible parent bodies in the Solar System: the Earth and Mars. Mars can be ruled out for several reasons, including the oxygen isotopic and noble gas composition of John’s stone, which is clearly distinct from martian meteorites. Consistent with the O study, the noble gases do not provide any evidence for an extraterrestrial origin of the samples. The lack of any cosmogenic noble gases (particularly striking in 3He, 21Ne, 38Ar) is consistent with a terrestrial origin or an extraterrestrial origin under large shielding.Based on the combined evidence obtained in this study we infer that John’s stone is a terrestrial rock unrelated to the Tunguska impactor.

Experimental studies on hydro-mechanical properties of metamorphic rock under hydraulic pressures

The research on the hydro-mechanical coupling of metamorphic rock is of great importance in rock engineering. The main purpose of this study was to investigate the hydro-mechanical properties of metamorphic rock based on the experimental data from triaxial compression tests. Metamorphic rock samples taken from an underground oil storage facility were tested under different hydraulic pressures using a rock servo-controlled triaxial rheology test system. The results indicated that hydraulic pressure had impact on the strength, deformation and permeability of the metamorphic rock. Based on the test results, the stress–strain behaviour and permeability evolution of the rock samples show three stages. The mechanical properties of the metamorphic rock are presented in detail for the three stages in the whole stress–strain process. The derived mechanical parameters are correlated to the division of the phases. The relationship between hydraulic pressure and axial strain, lateral strain, volumetric strain and permeability are analysed and discussed, especially the influence of hydraulic pressure on various parameters in the hydro-mechanical process. The influence of the hydraulic pressure on the failure mode of the rock under coupled conditions is described.

A comparative assessment of indirect methods for estimating the uniaxial compressive and tensile strength of rocks

The uniaxial compressive and tensile strength of rocks are crucial parameters in the design stage of geotechnical structures. However, direct determination of these parameters is expensive, troublesome, time consuming, and sometimes requires high-quality core samples for tests. Therefore, this study aimed to determine the applicability of the point load strength index and Schmidt hammer hardness values to estimate the uniaxial compressive strength and tensile strength of rocks based on the regression analyses. Further, multiple regression analysis was used on datasets obtained from tested rocks. For these purposes, representative samples of volcanic, sedimentary, and metamorphic rocks were collected from 37 different points along a tunnel alignment in Northeast Turkey where hundreds of underground projects are being constructed. Results from the regression analyses showed the existence of satisfactory correlations. The results were also compared and discussed with the results obtained by other researchers conducted on different types of rocks.

Results of studying metamorphic rock samples (Outokumpu, Finland Borehole) by the acoustic polarization method

When studying the elastic properties of anisotropic solid media, it is necessary to determine the spatial orientation of the elastic symmetry elements. This is particularly important for randomly inhomogeneous elastically anisotropic media, such as rock. By applying the acoustic polarization method, the possibility of determining the direction of the symmetry elements of deep rock samples extracted from the Outokumpu, Finland borehole was demonstrated. The anisotropy indices of samples were obtained, calculated from the velocity values of longitudinal and transverse waves. Additional inelastic effects were revealed that are widespread in rock.

Crack initiation stress in low porosity crystalline and sedimentary rocks

The stress–strain data from 376 laboratory tests carried out on samples of igneous, sedimentary and metamorphic rocks were analyzed to establish the onset of microcracking in compression, referred to as the Crack Initiation (CI) stress. A statistical approach was used to find the geological parameters influencing crack initiation stress. Among various rock properties such as grain size and mineralogy, the proportion of the hardest constituent mineral were found to correlate with CI stress. Foliation induced anisotropy was found to affect the peak strength but its effect on CI stress was less pronounced. The CI stress to peak stress ratio ranged from 0.42 to 0.47 regardless of the material properties in uniaxial compression whereas this ratio ranged from 0.50 to 0.54 when confined. The crack initiation parameters for the Hoek–Brown spalling criterion for igneous rocks can be expressed in terms of the CI stress ratio and the tensile strength. A comparison of tensile strength from the Brazilian and Direct tension tests showed that the Direct tensile strength was approximately 0.77 of the Brazilian tensile strength.

Assessment of relationships between drilling rate index and mechanical properties of rocks

This paper examines the relationships between drilling rate index (DRI) and some mechanical properties of rocks in order to evaluate the effect of strength and indexes of rock on rock drillability. For this purpose, some index properties (in situ Schmidt rebound hardness (SRH), Shore scleroscope hardness (SSH), and point load strength (PLS)) and strength properties (uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS)) values of 32 sedimentary, igneous and metamorphic rock samples were determined. The relationships between DRI and both strength and indexes properties were evaluated using regression analysis and statistical methods. As a result, decreasing linear relationships were found between DRI and uniaxial compressive strength, Schmidt rebound hardness, Shore scleroscope hardness, diametral and axial point load strength.

P-wave velocity changes in freezing hard low-porosity rocks: a laboratory-based time-average model

Abstract. P-wave refraction seismics is a key method in permafrost research but its applicability to low-porosity rocks, which constitute alpine rock walls, has been denied in prior studies. These studies explain p-wave velocity changes in freezing rocks exclusively due to changing velocities of pore infill, i.e. water, air and ice. In existing models, no significant velocity increase is expected for low-porosity bedrock. We postulate, that mixing laws apply for high-porosity rocks, but freezing in confined space in low-porosity bedrock also alters physical rock matrix properties. In the laboratory, we measured p-wave velocities of 22 decimetre-large low-porosity (< 10%) metamorphic, magmatic and sedimentary rock samples from permafrost sites with a natural texture (> 100 micro-fissures) from 25 °C to −15 °C in 0.3 °C increments close to the freezing point. When freezing, p-wave velocity increases by 11–166% perpendicular to cleavage/bedding and equivalent to a matrix velocity increase from 11–200% coincident to an anisotropy decrease in most samples. The expansion of rigid bedrock upon freezing is restricted and ice pressure will increase matrix velocity and decrease anisotropy while changing velocities of the pore infill are insignificant. Here, we present a modified Timur's two-phase-equation implementing changes in matrix velocity dependent on lithology and demonstrate the general applicability of refraction seismics to differentiate frozen and unfrozen low-porosity bedrock.

Cathodolumenescence Spectra of Quartz As Provenance Indicators Revisited

Abstract We present a discrimination scheme for cathodoluminescence (CL) spectra of quartz as a tool in provenance studies. We analyzed > 1000 quartz crystals from 58 samples of different plutonic, volcanic, metamorphic, and pegmatitic rocks. The technique is based on the measurement of the relative intensity of the two main emission centers in visible light at 470–490 nm and 600–640 nm. The results confirm a red, violet, or bright to medium blue luminescence for volcanic phenocrysts, mainly bright blue colors for felsic plutonic and high-temperature metamorphic quartz, as well as brown to dark blue CL for quartz of low-temperature metamorphic origin. These and additional results for mafic plutonic (dark blue) and pegmatitic quartz (bright blue) lead to a possible discrimination with the following rock grouping: (1) volcanic quartz, (2) low-temperature metamorphic and mafic plutonic quartz, and (3) felsic plutonic, high-temperature metamorphic, and pegmatitic quartz. In the proposed scheme, 87% of the spectra are classified correctly. The three quartz groups can be taken as an estimate for the amount of volcanic, metamorphic, and plutonic quartz in sediments, unless major input from plutonic, high-temperature metamorphic, or pegmatitic quartz has taken place. Hence, despite criticism within the literature during the last decades, the CL colors of detrital quartz still can be used as provenance indicators. We finally conclude that the measurement of wavelength spectra is a fast and straightforward method to determine quartz-bearing source rocks of siliciclastic sediments.

Correlating P-wave Velocity with the Physico-Mechanical Properties of Different Rocks

In mining and civil engineering projects, physico-mechanical properties of the rock affect both the project design and the construction operation. Determination of various physico-mechanical properties of rocks is expensive and time consuming, and sometimes it is very difficult to get cores to perform direct tests to evaluate the rock mass. The purpose of this work is to investigate the relationships between the different physico-mechanical properties of the various rock types with the P-wave velocity. Measurement of P-wave velocity is relatively cheap, non-destructive and easy to carry out. In this study, representative rock mass samples of igneous, sedimentary, and metamorphic rocks were collected from the different locations of India to obtain an empirical relation between P-wave velocity and uniaxial compressive strength, tensile strength, punch shear, density, slake durability index, Young’s modulus, Poisson’s ratio, impact strength index and Schmidt hammer rebound number. A very strong correlation was found between the P-wave velocity and different physico-mechanical properties of various rock types with very high coefficients of determination. To check the sensitivity of the empirical equations, Students t test was also performed, which confirmed the validity of the proposed correlations.

Petrophysical analysis of a mid-crustal reflector in the IBERSEIS profile, SW Spain

The origin of strong crustal reflectors in vertical incidence reflection seismic data is generally attributed to either rock layering, deformation fabrics in shear zones, fluids, or igneous intrusions. The IBERSEIS normal incidence reflection and wide-angle seismic profiles in SW Spain imaged a large, high velocity, subhorizontal reflector in the middle crust (the IBERSEIS Reflective Body) whose origin has been attributed to a mafic intrusion. In order to test this hypothesis, in this paper we present laboratory measurements of Vp, Vs, and density from 17 samples of mafic igneous and metamorphic rocks, and metasediments that are thought to be equivalent to the proposed IBERSEIS Reflective Body. These measurements are then corrected to 400°C at 600MPa and used to calculate Poisson's ratio and to compare it, Vp, and Vs to values measured in situ by wide-angle data. Finally, normal incidence reflection coefficients are calculated to test if the measured lithologies could reproduce the reflectivity imaged in the vertical incidence reflection seismic data for the IBERSEIS Reflective Body. Our physical property measurements are very similar to those modeled from the wide-angle data, and our reflection coefficients are sufficiently high to cause strong mid-crustal reflectivity. Our data indicate, therefore, that previous interpretations of the IBERSEIS Reflective Body as a mafic sill are quite reasonable.

The effect of mechanical rock properties and brittleness on drillability

This paper examines the relationships between drilling rate index (DRI) and some mechanical properties of rocks in order to evaluate the effect of properties of strength, indexes, and brittleness of rock on rock drillability. For this purpose, some index properties (Shore scleroscope hardness (SSH), and point load strength (PLS) and geomechanical (uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS)) values of 32 sedimentary, igneous and metamorphic rock samples were determined. Then, the brittleness concepts which use the uniaxial compressive strength and tensile strength of rocks were determined for calculations. Four different brittleness concepts were used in the statistical analysis. In this study, a new brittleness concept (B4) which was found as a result of laboratory studies has proposed by authors for percussive drilling and rotary drilling. The relationships among of DRI and both mechanical rock properties and brittleness concepts were evaluated using regression analysis and statistical methods. As a result, decreasing linear relationships were found among of DRI and uniaxial compressive strength, shore scleroscope hardness, diametral and axial point load strength. In additional to meaningful relations were obtained between drillability of rocks and brittleness of B3 and B4.

On the correlation between the acoustic anisotropy and the magnetic susceptibility anisotropy of the rocks.

Using resonant acoustic spectroscopy technique, we studied several rock samples. Acoustic data were compared with the data for magnetic susceptibility of the same samples. The correlation between the acoustic anisotropy and the magnetic susceptibility anisotropy has been revealed for samples of metamorphic and sedimentary rocks. The existence of this correlation points to the same origin for both magnetic and acoustic anisotropy. The origin is the rock texture created during long tectonic history of the rock samples analyzed. The value of acoustic anisotropy allows evaluating the rock fracturing or the amplitude of tectonic stresses. Under additional calibration, it makes possible the use of the magnetic susceptibility value as a measure of tectonic processes intensity. The latter can be very useful to create express diagnostics of tectonic history in the field conditions.

X-ray fluorescence determination of the FeO/Fe2O 3 tot ratio in rocks

Chances for estimating the FeO/Fe2O 3 tot ratio in rocks by the K and L series of X-ray fluorescence spectra are studied. The errors in the determination of FeO/Fe2O 3 tot by the intensity ratio of the Kβ2,5/Kβ1,3 and Lβ/Lα1,2 lines are compared. The relative standard deviation of determining FeO using a set of 49 standard samples of eruptive rocks varies in the range 5–16%, depending on the ratio FeO/Fe2O 3 tot and the concentration of FeO. The better precision is attainable for a ratio above 0.45 at a FeO concentration in the range 5–15%. For samples of andesites and basalts, the relative standard deviation is better than 4%, for rocks of the granite family it is 23% at FeO concentrations below 3%. For samples of metamorphic and sedimentary rocks, the error of FeO determination is higher than that for the eruptive ones. For samples with the ratio FeO/Fe/Fe2O 3 tot < 0.25, the deviation may exceed 30 rel %. In contrast to chemical analysis, the X-ray fluorescence method appears advantageous in time and cost of sample preparation and can be used for routine analysis in geochemical research.

Components and episodic growth of Precambrian crust in the Cathaysia Block, South China: Evidence from U–Pb ages and Hf isotopes of zircons in Neoproterozoic sediments

Detailed LAM-ICPMS U–Pb dating and LAM-MC-ICPMS Lu–Hf isotope analysis were carried out on zircons from nine samples of basement metamorphic rocks in the southern Cathaysia Block, South China. The chemical compositions of these metamorphic rocks and zircon morphology indicate that their protoliths were sedimentary; zircon U–Pb dating results show they mainly formed during the late Neoproterozoic. The Precambrian crust of the Cathaysia Block can be divided into two distinct tectonic domains, the Wuyishan terrane to the northeast and the Nanling-Yunkai terrane to the southwest. The nearly E–W boundary between these two terranes is also supported by geophysical, petrological and geochemical evidence, and the basement rocks of the two terranes are comprised of different components. The Wuyishan terrane is characterized by dominant Paleoproterozoic (1.86 Ga) and lesser Neoarchean magmatism, and the southern-central part of the terrane suffered strong Neoproterozoic and early Paleozoic tectonothermal reworking. The zircon data suggest that there were five important episodes of juvenile crust generation (3.6 Ga, 2.8 Ga, 2.6–2.4 Ga, 1.85 Ga and 0.8–0.7 Ga) in the Wuyishan terrane. Strong Paleoproterozoic (1.85 Ga) magmatism in northern Wuyishan and Neoproterozoic (0.8–0.7 Ga) magmatism in central and southern Wuyishan both principally involved the remelting of old crust with minor input of juvenile material. In contrast, the Nanling-Yunkai terrane contains abundant Neoarchean and Grenvillian zircons, some evidence of Mesoproterozoic activity and rare Paleo- to Meso-Archean and Neoproterozoic zircons. U–Pb ages and Hf-isotopic compositions of the detrital zircons from the late Neoproterozoic to early Paleozoic meta-sedimentary rocks in the Nanling-Yunkai area suggest that the growth of juvenile crust mainly occurred at ∼3.6 Ga, ∼3.3 Ga, 2.5–2.6 Ga, ∼1.6 Ga, ∼1.0 Ga and 0.8–0.7 Ga. Neoarchaean (2.6–2.5 Ga), Grenvillian (∼1.0 Ga) and Neoproterozoic (0.8–0.7 Ga) magmatism mainly involved the recycling of old crust. Minor remnants of ∼4.1 Ga crust may remain in the terrane. This crustal history is distinct from that of the Wuyishan terrane and analogous to those recorded for the eastern India–East Antarctic domain of northern Gondwanaland, suggesting that they probably were once linked.

MetPetDB: A database for metamorphic geochemistry

We present a data model for the initial implementation of MetPetDB, a geochemical database specific to metamorphic rock samples. The database is designed around the concept of preservation of spatial relationships, at all scales, of chemical analyses and their textural setting. Objects in the database (samples) represent physical rock samples; each sample may contain one or more subsamples with associated geochemical and image data. Samples, subsamples, geochemical data, and images are described with attributes (some required, some optional); these attributes also serve as search delimiters. All data in the database are classified as published (i.e., archived or published data), public or private. Public and published data may be freely searched and downloaded. All private data is owned; permission to view, edit, download and otherwise manipulate private data may be granted only by the data owner; all such editing operations are recorded by the database to create a data version log. The sharing of data permissions among a group of collaborators researching a common sample is done by the sample owner through the project manager. User interaction with MetPetDB is hosted by a web‐based platform based upon the Java servlet application programming interface, with the PostgreSQL relational database. The database web portal includes modules that allow the user to interact with the database: registered users may save and download public and published data, upload private data, create projects, and assign permission levels to project collaborators. An Image Viewer module provides for spatial integration of image and geochemical data. A toolkit consisting of plotting and geochemical calculation software for data analysis and a mobile application for viewing the public and published data is being developed. Future issues to address include population of the database, integration with other geochemical databases, development of the analysis toolkit, creation of data models for derivative data, and building a community‐wide user base. It is believed that this and other geochemical databases will enable more productive collaborations, generate more efficient research efforts, and foster new developments in basic research in the field of solid earth geochemistry.

High efficiency of natural lamellar remanent magnetisation in single grains of ilmeno-hematite calculated using Mössbauer spectroscopy

Rocks from large remanent magnetic anomalies on Earth have been found to contain exsolved rhombohedral oxides, which also have been proposed as earth analogues for the rocks creating the observed large remanent anomalies on Mars. Theoretical considerations and previous case studies of natural rocks have shown that the natural magnetisation is carried by lamellar magnetism due to uncompensated moments at the interface between antiferromagnetic hematite and paramagnetic ilmenite. Here, single grains (≈ 250 µm) of titanohematite with ferri-ilmenite exsolution lamellae from Mesoproterozoic metamorphic rock samples in southwest Sweden and the Adirondack Mountains, USA, are studied using room-temperature Mössbauer spectroscopy to identify possible characteristic magnetic signatures of lamellar magnetism. Mössbauer spectra of synthetic samples of titanohematite (Fe 0.95Ti 0.05O 3 and Fe 0.9Ti 0.1O 3) were collected for comparison and showed a dominant six-line magnetic spectrum due to Fe 3+ in titanohematite with a weak sextet due to Fe 2 +–Fe 3+ charge transfer. Mössbauer spectra of the natural ilmeno-hematite grains are similar to those for synthetic titanohematite, but contain additionally two paramagnetic doublets corresponding to Fe 2+ and Fe 3+ in ilmenite. However, several grains also contain an additional weak, broad magnetic component that we assign to iron in contact layers according to the lamellar magnetism model. Similar to the previous Mössbauer results for natural hemo-ilmenite, there is no evidence for superparamagnetic behaviour of the nanoscale titanohematite lamellae contained within coarser ferri-ilmenite lamellae, and no evidence for single-domain or superparamagnetic magnetite. The compositions of titanohematite and ferri-ilmenite in the individual ilmeno-hematite grains calculated from the Mössbauer area ratios show that compositions are closer to end-member values than the compositions inferred from electron microprobe and transmission electron microscopy on the same grains, consistent with observations that lamella thicknesses are as small as a few nm. Bulk compositions of ilmeno-hematite grains calculated from the Mössbauer data confirm that the Swedish samples are significantly more ilmenite-rich than the Adirondack samples, and agree with an estimation of bulk composition through point counting of electron backscatter images. The Mössbauer data allow a quantitative estimation of contact layer abundance, which is used to determine the efficiency of lamellar natural remanent magnetisation acquisition. Because minerals with a high natural remanent magnetisation efficiency are expected to create larger remanent magnetic anomalies, contact layer abundance determination by Mössbauer spectroscopy provides a valuable new tool for mineral-based magnetic anomaly interpretation on Earth and other planetary bodies.

Epithermal neutron activation, radiometric, correlation and principal component analysis applied to the distribution of major and trace elements in some igneous and metamorphic rocks from Romania

Six major (Na, Al, K, Ca, Ti, Fe) and 28 trace (Sc, Cr, V, Mn, Co, Zn, Cu, As, Br, Sr, Rb, Zr, Mo, Sn, Sb, Ba, Cs, La, Ce, Nd, Eu, Sm, Tb, Hf, Ta, W, Th and U) elements were determined by epithermal neutron activation analysis (ENAA) in nine Meridional Carpathian and Macin Mountains samples of igneous and metamorphic rocks. Correlation and principal factor analysis were used to interpret data while natural radionuclides radiometry shows a good correlation with ENAA results.