Crystalline Rock Samples Research Articles

The electrical signature of rock samples exposed to hydrostatic and triaxial pressures

The electrical signature of sedimentary (carbonate) and crystalline rock samples was studied in hydrostatic and triaxial pressure experiments up to 300 MPa. The aim was to establish a relation between an electrical signal stimulated by an external pressure acting on the sample and the mechanical stability of the rock. Natural open fractures tend to be closed under hydrostatic pressure conditions, whereas in triaxial pressure experiments new fractures are generated. These contrary processes of either decrease or increase in crack density and geometry, cause a decrease or increase in the inner surface of the sample. Such pressure induced variations in pore geometry were investigated by an interpretation and modelling of the frequency dependence of the complex electrical conductivity. In a series of hydrostatic pressure experiments crack-closure was found in the electrical signature by a decrease of the model capacitor C being related to crack geometry. This capacitor increases in the triaxial experiments where new fractures were formed.

Transport and sorption of 85Sr and 125I in crushed crystalline rocks under dynamic flow conditions

Transport and sorption of water-soluble 85Sr2+ and 125I− in the columns with beds of crushed crystalline rocks from synthetic groundwater has been studied under dynamic flow conditions. Samples of crystalline rocks: diorite-I, diorite-II, gabbro, granite and tonalite, having the grain size between 0.25 and 0.80 mm, were used. Plastic syringes of 8.8 cm length and 2.1 cm in diameter were applied as columns. The synthetic groundwater was pumped downward through the columns with a seepage velocity of about 0.2 cm/min and the given radioactive nuclide was added into the water stream individually in a form of a short pulse. In case of 85Sr, desorption from diorite-I was also studied using an artificial acid rainfall and then, the longitudinal distribution of the residual 85Sr activity along the bed was measured. Retardation, distribution and hydrodynamic dispersion coefficients were determined by the evaluation of respective breakthrough curves. A corrected integral form of a simple advection–dispersion equation was derived and used for fitting the experimental data. The K d-parameters resulting from dynamic experiments were also compared with the results of static sorption experiments.

Presence of a Long‐Term Lithospheric Thermal Anomaly: Evidence from Apatite Fission‐Track Analysis in Northern New England

Abstract Apatite fission‐track (AFT) ages from 56 samples of Paleozoic and Mesozoic crystalline rocks in New Hampshire, northeastern Vermont, and western Maine range from 70 to 140 Ma and reflect widespread Early to Late Cretaceous cooling. The regional AFT age distributions determined in this study suggest that reactivation of preexisting orogen‐parallel faults and the presence of a long‐lived thermal anomaly in the lithospheric mantle controlled the late unroofing history of this part of the northern Appalachians. A northeast‐trending zone of young, dominantly Late Cretaceous AFT ages (70–118 Ma) extends from southwestern New Hampshire through the central White Mountain region and continues into northern New Hampshire, northeastern Vermont, and western Maine, providing evidence for regional NW‐SE extension and cooling at this time. Significantly older AFT ages (125–140 Ma) in the region bounded by the Bill Little, Ammonoosuc, and Northey Hill faults in northwestern New Hampshire suggest a normal‐sense r...

Migration and sorption of 137Cs and 152,154Eu in crushed crystalline rocks under dynamic conditions

In migration experiments, sorption of 137Cs and 152,154Eu in the columns of crushed crystalline rocks of 0.25–0.8 mm grain size under dynamic flow conditions from the synthetic groundwater (SGW) has been studied. Five samples of crystalline rocks from Cavernous Gas Reservoir near Přibram were taken. Plastic syringes of 8.8 cm length and 2.1 cm in diameter were used as columns. The water phase was pumped downward through the columns, using a multi-head peristaltic pump, with a seepage velocity of about 0.2 cm/min. The radioactive nuclides, containing chemical carriers, were added into the water stream individually in the form of a short pulse. Desorption experiments were carried out with 2:1 (v/v) mixture of H2SO4 and HNO3. In the columns the longitudinal distribution of the residual 137Cs and 152,154Eu activities was also determined. By the evaluation of respective breakthrough and displacement curves, the experimental and theoretical retardation factors, distribution coefficients and hydrodynamic dispersion coefficients were determined using the integrated analytical form of a simple advection-dispersion equation (ADE). Dynamic sorption experiments were also compared with the results of static sorption experiments.

Temperature dependence of the relationship of thermal diffusivity versus thermal conductivity for crystalline rocks

Thermal diffusivity governs the transient heat transport equation. Thus, a realistic characterisation of this parameter and its temperature dependence is crucial for geothermal modelling. Due to sparse information from boreholes, lack of samples, and elaborate measurement procedures, there is often insufficient data on thermal diffusivity at elevated temperatures. We make use of existing data on crystalline (metamorphic and magmatic) rock samples from the Kola Peninsula and the Eastern Alps and develop a general relationship for the temperature dependence of thermal diffusivity up to 300°C. The temperature dependence of thermal conductivity is parameterised itself, using an empirical relationship which is set up for both data sets as well. Hence, only thermal conductivity at ambient temperatures is required for determining the temperature dependence of thermal diffusivity. We obtain different coefficients for both data sets which can be explained by different geological settings, and therefore different mineral compositions and internal structures. Comparisons with other expressions for these rock physical parameters show a good agreement at ambient conditions. General relations for thermal diffusivity at elevated temperatures are rare. A comparison of our results with data from two crystalline samples from the KTB and data from the Southern Indian Granulite Province highlights the need for further data, which will help to quantify uncertainties.

Very high slip rates on continental extensional faults: new evidence from (U–Th)/He thermochronometry of the Buckskin Mountains, Arizona

New (U–Th)/He in apatite ages suggest rapid slip rates on the Tertiary Buckskin–Rawhide detachment fault, which crops out in the Buckskin and Rawhide Mountains of western Arizona. Single-crystal (U–Th)/He in apatite ages were determined for a suite of crystalline rock samples from the footwall to this detachment. The samples were collected from a transect parallel to the fault slip direction, and proximal to the fault zone; they show a linear decrease in age with distance, from ∼14 to ∼11 Ma over ∼15 km. The age versus distance relationship is interpreted to show a slip rate of 4.2 (+1.2/−0.8) mm/yr, continuing for a period of >3 Myr. This rate is more-or-less in agreement with, but more precise than, previously published slip rates from this and other large-offset extensional detachments. Such slip rates are alarmingly high, being roughly 5–10 times faster than rates commonly observed on active structures at the Earth’s surface. These rapid slip rates suggest that significant seismic hazard might be posed by some extensional structures, and they raise questions regarding the relationship between such rapidly slipping, large-offset structures and the slower, smaller offset faults that are more commonly observed at the Earth’s surface.

Relationship between Fluctuations of Arrival Time and Energy of Seismic Waves and Scale Length of Heterogeneity: An Inference from Experimental Study

In order to study the effect of heterogeneity on the arrival time and energy fluctuations of seismic waves, we made laboratory-scale physical model experiments by observing elastic waves propagating through crystalline rock samples having different scales of heterogeneity. A laser Doppler vibrometer was used to measure the waveforms. About 100 waveforms were obtained over a square grid with a spacing of 1 mm in linear profiles for Westerly and Oshima granite samples, which correspond to small and large scales of heterogeneity, respectively. The same measurement was done for steel block, which is a homogeneous medium. Characteristic scale length of heterogeneity of Westerly and Oshima granites are found to be 0.22 mm and 0.46 mm, respectively; the values were obtained from spatial autocorrelation function of velocity fluctuation based on microstructure photo image. The arrival time of P wave was determined by searching the best-fit point that divides the waveform into two different autoregressive (AR) models based on Akaike information criterion (AIC). This method automatically yields the arrival time of P waves, and the fluctuation of arrival time can be studied as a statistical distribution. We also calculated logarithmic values of the wave energy and studied their fluctuation. The observed fluctuations of the arrival time and the log of wave energy show nonsymmetric distributions. Both the variances of arrival time and log-energy distributions increase with increasing scale length of heterogeneity. This indicates a positive correlation between the variances of the fluctuation and the scale length of heterogeneity. The study also reveals that the correlation coefficient between fluctuations of arrival time and energy of seismic wave increases with increasing length of heterogeneity.

Evidence for Differential Unroofing in the Adirondack Mountains, New York State, Determined by Apatite Fission‐Track Thermochronology

Apatite fission-track ages of 168-83 Ma for 39 samples of Proterozoic crystalline rocks, three samples of Cambrian Potsdam sandstone, and one Cretaceous lamprophyre dike from the Adirondack Mountains in New York State indicate that unroofing in this region occurred from Late Jurassic through Early Cretaceous. Samples from the High Peaks section of the Adirondack massif yielded the oldest apatite fission-track ages (168-135 Ma), indicating that it was exhumed first. Unroofing along the northern, northwestern, and southwestern margins of the Adirondacks began slightly later, as shown by younger apatite fission-track ages (146-114 Ma) determined for these rocks. This delay in exhumation may have resulted from burial of the peripheral regions by sediment shed from the High Peaks. Apatite fission-track ages for samples from the southeastern Adirondacks are distinctly younger (112-83 Ma) than those determined for the rest of the Adirondack region. These younger apatite fission-track ages are from a section of the Adirondacks dissected by shear zones and post-Ordovician north-northeast-trending normal faults. Differential unroofing may have been accommodated by reactivation of the faults in a reverse sense of motion with maximum compressive stress, sigma1, oriented west-northwest. A change in the orientation of the post-Early Cretaceous paleostress field is supported by a change in the trend of Cretaceous lamprophyre dikes from east-west to west-northwest.

Early Tertiary thermotectonic history of the northern Yukon and adjacent Northwest Territories, Arctic Canada

Apatite fission-track data from 16 sedimentary and crystalline rock samples indicate rapid regional Early Eocene denudation within the onshore Beaufort–Mackenzie region of northwestern Canada. Rocks exposed in the area of the Big Fish River, Northwest Territories, cooled rapidly from paleotemperatures of >80–110 °C to <6 0°C at ca. 56 ± 2 Ma, probably in response to kilometre-scale denudation associated with regional structuring. The data suggest the region experienced a geothermal gradient of ~28 °C/km prior to rapid cooling, with ~2.7 km of section having been removed from the top of the exposed section in the Moose Channel Formation and ~3.8 km from the top of the exposed Cuesta Creek Member. Farther to the west, rocks exposed in the headwaters of the Blow River in the Barn Mountains, Yukon Territories, were exposed to paleotemperatures above 110 °C in the Late Paleocene prior to rapid cooling from these elevated paleotemperatures due to kilometre-scale denudation at ca. 56 ± 2 Ma. Exposure of these samples at the surface today requires that a minimum of ~3.8 km of denudation occurred since they began cooling below ~110 °C. The apatite analyses indicate that rocks exposed in the northern Yukon and Northwest Territories experienced rapid cooling during the Early Eocene in response to kilometre-scale denudation, associated with early Tertiary folding and thrusting in the northern Cordillera. Early Eocene cooling–uplift ages for onshore sections are slightly older than the Middle Eocene ages previously documented for the adjacent offshore foldbelt and suggest that the deformation progressed toward the foreland of the foldbelt through time.

Neutron radiographic measurement of porosity of crystalline rock samples: a feasibility study: H. Pleinert & C. Degueldre, Journal of Contaminant Hydrology, 19(1), 1995, pp 29–46

Neutron radiographic measurement of porosity of crystalline rock samples: a feasibility study: H. Pleinert & C. Degueldre, Journal of Contaminant Hydrology, 19(1), 1995, pp 29–46

Geophysical research on the Kärdla impact structure, Hiiumaa Island, Estonia

Abstract— The 4 km wide and 500 m deep circular Kärdla impact structure in Hiiumaa Island, Estonia, of middle Ordovician age (∼455 Ma), is buried under Upper Ordovician and Quaternary sediments. To constrain the geophysical models of the structure, petrophysical properties such as magnetic susceptibility, natural remanent magnetization (NRM), density, electrical conductivity, porosity and P‐wave velocity were measured on samples of crystalline and sedimentary rocks collected from drill cores in different parts of the structure and the surrounding area. The results were used to interpret the central gravity anomaly of −3 mGal and the magnetic anomaly of −100 nT and also the surrounding weak positive anomalies revealed by high precision survey data.The unshocked granitic rocks outside the structure have a mean density of ∼2630 kgm−3. Their shocked counterparts have densities of ∼2400 kgm−3 at a depth of ∼500 m, increasing up to 2550 kgm−3 at a depth of 850 m. Porosity and electrical conductivity decrease, but P‐wave velocity increases as density increases away from the impact point. Thus, the gradual changes in the physical properties of the rocks as a function of radial distance from the crater centre are consistent with an impact origin for Kärdla. As in many other impact structures, the magnetization of the shocked rocks are also clearly lower than those of unshocked target rocks.A new geophysical and geological model of the Kärdla structure is presented based on geophysical field measurements and data on gradual changes in petrophysical parameters of the shocked target and overlying rocks, together with structural data from numerous boreholes. An important feature of this model is the lack of an observable geophysical signature of the central uplift observed in drillcores.

Measurements of Water Potential and Water Content in Unsaturated Cystalline Rock

A water desaturation zone develops around a tunnel in water‐saturated rock when the evaporative water loss at the rock surface is larger than the water flow from the surrounding saturated region of restricted permeability. We describe the methods with which such water desaturation processes in rock materials can be quantified. The water retention characteristic θ (ψ) of crystalline rock samples was determined with a pressure membrane apparatus. The negative water potential, identical to the capillary pressure, ψ, below the tensiometric range (ψ < −0.1 MPa) can be measured with thermocouple psychrometers (TP), and the volumetric water contents, θ, by means of time domain reflectometry (TDR). These standard methods were adapted for measuring the water status in a macroscopically unfissured granodiorite with a total porosity of approximately 0.01. The measured water retention curve of granodiorite samples from the Grimsel test site (central Switzerland) exhibits a shape which is typical for bimodal pore size distributions. The measured bimodality is probably an artifact of a large surface ratio of solid/voids. The thermocouples were installed without a metallic screen using the cavity drilled into the granodiorite as a measuring chamber. The water potentials observed in a cylindrical granodiorite monolith ranged between −0.1 and −3.0 MPa; those near the wall in a ventilated tunnel between −0.1 and −2.2 MPa. Two types of three‐rod TDR probes were used, one as a depth probe inserted into the rock, the other as a surface probe using three copper stripes attached to the surface for detecting water content changes in the rock‐to‐air boundary. The TDR signal was smoothed with a low‐pass filter, and the signal length determined based on the first derivative of the trace. Despite the low porosity of crystalline rock these standard methods are applicable to describe the unsaturated zone in solid rock and may also be used in other consolidated materials such as concrete.

Neutron radiographic measurement of porosity of crystalline rock samples: a feasibility study

Neutron radiography (NR) provides a sensitive and quantitative technique for the determination of hydrogen. NR can therefore be used to determine the porosity of rocks impregnated with a hydrogen-containing material: in this feasibility study, the water content of granodiorite and mylonite samples was determined by quantitative NR combined with densitometric scanning. For a sample of 1-cm thickness, this technique allows porosity detection down to 0.015 with a resolution of 1 mm 2, down to 0.005 with a resolution of 1 cm 2, and is applicable for porosities higher than 0.05 with a precision of ±0.5% at a resolution of 1 cm 2. 3-D information may be gained by combination of 2-D radiographs. The accuracy of the technique was estimated by comparing the NR results with those obtained by gravimetry. Extension to resin-impregnated porosity and to other types of rock is discussed.

Petrophysical properties (density and magnetization) of rocks from the northern part of the Baltic Shield

Density, magnetic susceptibility and remanent magnetization of more than 30,000 samples of crystalline rocks from the northern part of the Baltic Shield have been measured by the national geological surveys of the Nordic countries. These data were compiled into a database as part of a project involving Finland, Norway and Sweden — the Nordkalott Project. In addition, more than 20,000 in-situ susceptibility measurements are available for a large part of the Baltic Shield. From all these measurements, a number of general conclusions can be drawn regarding the distribution of magnetic minerals in the different lithologies: 1. (1) The Precambrian metasupracrustal rocks show a rather typical bimodal distribution in susceptibility. The spatial distribution of these susceptibility modes gives rise to the banded patterns observed in high-resolution (low-altitude) aeromagnetic measurements. 2. (2) The amount of remanence in the various rock types is generally low, as indicated by Q-values (Königsberger ratios) of around 0.2 on average. Thus, magnetization is parallel to the Earth's magnetic field, simplifying the interpretation ol the total field magnetic survey results. 3. (3) Plutonic rocks as a whole have the same bimodal susceptibility distribution, but individual plutons have usually unimodal susceptibility distributions and thereby create characteristic local anomaly patterns. 4. (4) Metamorphic processes significantly affect the distribution of magnetite. Well-documented examples include the amphibolite-granulite facies transition (Tectonophysics, Vol. 192). the serpentinization of ultramafic rocks (Pure Appl. Geophys., Vol. 114) and oxidation in fracture zones (Geoexploration, 15). The metamorphic development of magnetite appears to reflect in many cases the variation in primary composition. 5. (5) The range in density variation and magnetic susceptibility in crystalline rocks is now well defined. In local structures it is, however, always necessary to determine the actual petrophysical contrasts in order to minimize the ambiguity in quantitative interpretation of potential field anomalies.

Composition of the Crystalline Basement and Shock Metamorphism of Crystalline and Sedimentary Target Rocks at the Haughton Impact Crater, Devon Island, Canada

Abstract— About 100 cobble‐sized samples collected from the surface of the central polymict breccia formation of Haughton impact crater, Canada, have been studied microscopically and chemically. Breccia clasts derived from the 1700 m deep Precambian basement consist of 13 rock types which can be grouped into sillimanite‐ and garnet‐bearing gneiss; alkali feldspar‐rich aplitic or biotite‐hornblende‐bearing gneiss; biotite and hornblende gneiss; apatite‐rich biotite and biotite‐hornblende gneiss; calcitediopside gneiss; amphibolite; tonalitic orthogneiss; and basalts. The range of chemical compositions of these rocks is wide: e.g., SiO2 ranges from 40–85 wt.%; Al2O3 from 7–20 wt.%; CaO from 0.01–25 wt.%; or P2Os from <0.01–5 wt.%. Nearly all samples of crystalline rocks are shock metamorphosed up to about 60 GPa. Most conspicuous is the absence of whole‐rock melts and the very rare occurrence of unshocked rocks. The 45 samples examined can be classified into the following shock stages: stage 0 (<5 GPa): 4.5%, stage Ia (10–20 GPa): 9.0%, stage Ib (20–35 GPa): 33%, stage II (35–45 GPa): 29%, stage III (45–55 GPa): 18%, stage III–IV (55–60 GPa): 6.5%. Among Paleozoic sedimentary rock clasts higher degrees of shock than within crystalline rocks were observed such as highly vesiculated, whole‐rock melts of sandstones and shales. Within the northern and eastern sectors of the allochthonous breccia no distinct radial variation of the cobble‐sized lithic clasts regarding abundance, rock type, and degree of shock was observed, with the exception that clasts of shock‐melted sedimentary rocks and of highly shocked basement rocks (stage III–IV) are strongly concentrated near the center of the crater. Based on our field and laboratory investigations we conclude that vaporization and melting due to the Haughton impact affected the lower section of the sedimentary strata from about 900 to 1700 m depth (Eleanor River limestones and dolomites, Lower Ordovician and Cambrian limestones, dolomites, shales, and sandstones). The 60‐GPa shock pressure isobar reached only the uppermost basement rocks so that whole rock melting of the crystalline rocks was not possible.

Velocities of elastic waves andv P/v S ratios in dry and water-saturated rock samples at high pressure

Elastic wave velocities and the ratiov P/v S were studied for dry and initially saturated samples of carbonate and crystalline rocks at pressures to 2 kbar. In initially saturated samplesv P increases in crystalline rock, whereas in sedimentary rock it may either increase or decrease with increasing pressure. Under the same conditionsv S remains approximately constant in crystalline rocks and decreases in sedimentary samples. The ratiov P/v S as a function of pressure increases in dry rocks and decreases in saturated ones. Saturated samples always have higherv P/v S ratios than dry ones. It appears that the geometry of the pore space influences the acoustic properties of saturated crystalline rocks.

The residual permanent magnetic dipole moment of the moon

The residual dipole moment of the outer spherical shell of the Moon, magnetized in the field of an internal dipole is calculated for the case when the permeability of the shell differs from unity. It is shown that, using an average value of surface magnetization from returned lunar crystalline rock samples and a global figure for the lunar permeability of 1.012, that a residual moment of the order of 1015 to 1016 Am2 is expected. This value is some two or three orders of magnitude lower than the moment for a shell magnetized in an external uniform field and is of the same order as the upper limit of the residual moment detected by Russellet al. (1974). At present the magnetic data and the thermal state of the Moon are not known with sufficient accuracy to distinguish between a crust magnetized in an internal dipole field of constant polarity and a crust magnetized in the dipole field of a self-reversing core dynamo. Refined measurements of the relevant parameters together with the theory presented in this paper could enable these two possibilities to be distinguished.

Mineralogy and Deformation in Some Lunar Samples

Observations on the mineralogy and deformation in samples of crystalline rocks, breccias, and fines from Tranquillity Base provide evidence for magmatic and impact processes. Overall homogeneity, igneous textures, and absence of xenoliths in the crystalline rocks indicate derivation from a common titanium-rich magma by internal, anorogenic volcanism rather than by impact. Crystallization conditions allowed strong compositional variation in pyroxenes, olivine, and plagioclase and the growth of a new mineral, the iron analog of pyroxmangite. Subsequently, impact produced breccias containing shock-deformed crystals and glasses of varying compositions.

Mineralogy and Petrology of Coarse Particulate Material from Lunar Surface at Tranquillity Base

Five grams of coarse fines (10085,11) contains 1227 grains, mostly mafic holocrystalline rock fragments, microbreccia, and glass spatter and agglomerates with less abundant anorthosite fragments and regularly shaped glass. The crystalline lithic fragments in the coarse fines and microbreccias represent a closely related suite of gabbroid igneous rocks that have a wider range of modal analyses and textures than seen in the larger crystalline rock samples returned by Apollo 11. Petrographic evidence of shock metamorphism is common, and the abundant glass is almost all shock-produced. None of the glass observed is similar to tektite glass.

Argon-40/ Argon-39 Dating of Lunar Rock Samples

Seven crystalline rock samples returned by Apollo 11 have been analyzed in detail by means of the (40)Ar-(-39)Ar dating technique. The extent of radiogenic argon loss in these samples ranges from 7 percent to >/= 48 percent. Potassium-argon ages, corrected for the effects of this loss, cluster relatively closely around the value of 3.7 x 10(9) years. Most of the vulcanism associated with the formation of the Mare Tranquillitatis presumably occurred around 3.7 x 10(9) years ago. A major cause of the escape of gas from lunar rock is probably the impact event which ejected the rock from its place of origin to its place of discovery. Upper limits for the times at which these impact events occurred have been estimated.