Triaxial compression testing of multicomponent geomaterials from quartz-poor (syenitic) systems

This paper focuses on mafic microgranular enclaves enclosed in quartz-poor igneous rocks and their effect on strength properties of the rock massif. The study examines host rock–enclave multicomponent geomaterials from enclave-bearing syenitic rocks from the Třebíč Massif exposed in the Královec quarry near Jaroměřice nad Rokytnou in the Czech Republic. A series of laboratory tests were performed to describe strength properties of individual constituents of the multicomponent geomaterials. We mainly focused on triaxial compression tests, however, rebound hardness, uniaxial compressive strength and indirect tensile strength were determined as well. The obtained results indicate that enclaves and even the contact zones between the enclaves and host rocks do not have any negative influence on the rock strength. In contrast, enclaves represent “stress concentrators” within such multicomponent systems. Strength properties of various multicomponent geomaterials are practically an unexplored topic in the field of rocks mechanics and future studies are needed to establish a robust database describing the behaviour of such geocomposites

Anisotropy of mechanical properties of greywacke

The paper brings description of the mechanical properties of greywacke sampled in Kobeřice quarry (Lower Carboniferous Culm Basin, Drahany Uplands, Bohemian Massif). Anisotropy of mechanical properties was identified from series of laboratory tests of oriented samples using following procedures: (1) indirect tensile testing, (2) uniaxial compressive testing and (3) triaxial compressive testing. Parameters of Mohr-Coulomb and Hoek-Brown failure criteria were determined by evaluation of the obtained laboratory data. The tested greywacke performed relatively high uniaxial compressive strength, roughly 200 MPa. Better fitting by Mohr-Coulomb criterion was identified than by Hoek-Brown one within the investigated interval of confining stresses (0-15 MPa). In addition, Schmidt hammer test was carried out with comparison of several correlation relationships to uniaxial compressive strength which were compared with directly obtained value from laboratory tests

Mechanical properties of granulite from Horní Bory in Bohemian massif

Granulite represents one of the favourite rock types for the construction of an underground nuclear waste repository in the Czech Republic. Granulite from the Bohemian Massif (locality Horní Bory) was investigated in this study, with a special focus on the evaluation of the rock anisotropy. Investigated rock represents typical fine-grained foliated felsic granulite with principal mineral association: quartz + feldspar (K-feldspar > plag ioclase) + garnet + biotite + kyanite and/or sillimanite. Anisotropy was identified in the rock fabric both at macroscopic and microscopic scale. During the laboratory testing, granulite reached considerable high uniaxial compressive strength (UCS) - up to 240 MPa; and brittle type (Class II) of failure occurred. We found that variability of the UCS and Young's modulus were relatively low. On the other hand, variability of the Poisson's ratio and the constants in Hoek-Brown failure criterion in triaxial loading were significantly hig

Post-collisional magmatic dyke from Dolní Údolí near Zlaté Hory (Hrubý Jeseník Mts.)

Devonian phyllites of the Vrbno Group located near village of Dolní Údolí (W of Zlaté Hory) are crosscut by undeformed 1 m thick mafic dyke. Using whole-rock geochemistry and composition of all main rock-forming minerals, we classified the rock as a porphyric microdiorite (with biotite and plagioclase phenocrysts). Trace elements of this dyke indicate post-collisional geotectonic setting. The dyke shows LREE enrichment with pronounced negative Eu anomaly. The chondrite-normalized spidergram patterns after Pearce (1983) reveal TNT (Ta-Nb-Ti) negative anomaly, which is typical for calc-alkaline lamprophyres (Rock 1991). The origin of calc-alkaline lamprophyres at the eastern margin of the Bohemian Massif (Moravo-Silesian region) may be connected with extensional gravitational collapse of the Hercynian orogen (Přichystal 1993). Cognate model can be supposed for the new microdiorite dyke.Devonian phyllites of the Vrbno Group located near village of Dolní Údolí (W of Zlaté Hory) are crosscut by undeformed 1 m thick mafic dyke. Using whole-rock geochemistry and composition of all main rock-forming minerals, we classified the rock as a porphyric microdiorite (with biotite and plagioclase phenocrysts). Trace elements of this dyke indicate post-collisional geotectonic setting. The dyke shows LREE enrichment with pronounced negative Eu anomaly. The chondrite-normalized spidergram patterns after Pearce (1983) reveal TNT (Ta-Nb-Ti) negative anomaly, which is typical for calc-alkaline lamprophyres (Rock 1991). The origin of calc-alkaline lamprophyres at the eastern margin of the Bohemian Massif (Moravo-Silesian region) may be connected with extensional gravitational collapse of the Hercynian orogen (Přichystal 1993). Cognate model can be supposed for the new microdiorite dyke

Petrological and geochemical characteristics of Palaeogene low-rank coal on the Faroe Islands: restricted effects of alteration by basaltic lava flows

The first combined petrographic and geochemical investigation of coal from the Faroe Islands was performed as a case study to understand thermal effects from basaltic lavaflows on immature coal. The samples were divided into two distinct groups:“normal”coal (xylite and detroxylite) and“altered organic matter”(charcoal and organic particles dispersed in samples rich in altered clastic mineral components or enriched via hydrothermal fluids). The“normal”coal consists primarily of huminite-group material dominated by ulminite. The proportions of material from inertinite and liptinite groups vary from sample to sample. The studied macerals are anisotropic with no observed reaction rims or vacuoles. According to the mean ulminite reflectance in combination with ultimate and proximate analyses, the coal reached the lignite and subbituminous stages. The maceral compositions together with coal palynology indicate a predominance of gelified wood-derived tissues and demonstrate that the coal evolved in wet forest swamps under limno-telmatic to telmatic conditions. Alteration effects on immature coals from overlying basalt flows were relatively limited. Due to relatively rapid heat loss from the basaltic lava, as verified by the presence of volcanic glass (tachylyte), its imposed thermal effects resulted only in development of a thin“anthracite-like”crust on samples with no elevated coal rank. Associated hydrothermal fluids induced coal hydrofracturing with subsequent mineral precipitation and decomposition of the ambient feldspar-rich volcaniclastic sediments. Altered organic matter is enriched in SiO2, Al2O3 and FeOtot, as well as in trace elements such as Ni and Cr. In contrast, these samples are depleted in Hg (<10 ppb).Jedná se o první kombinovaný petrografický a geochemický výzkum uhlí na Faerských ostrovech, který byl proveden jako klíčová studie k pochopení termálního efektu výlevů bazaltových láv v blízkosti slojí nevyzrálého uhlí. Vzorky byly rozděleny do dvou odlišných skupin: „normální“ uhlí (xylit a detroxylit) a „alterovaná organická hmota“ (dřevěné uhlí a organické částice rozptýlené ve vzorcích bohatých na alterované klastické minerální komponenty nebo obohacených hydrotermálními fluidy). „Normální“ uhlí je tvořeno převážně macerály huminitové skupiny, z nichž dominuje ulminit. Zastoupení macerálů skupiny inertinitu a liptinitu je variabilní. Studované macerály jsou anizotropní, bez pozorovaných reakčních lemů či vakuol. Na základě světelné odraznosti ulminitu a chemicko-technologických parametrů vykazuje uhlí nízký stupeň prouhelnění. Macerálové složení společně s palynologií indikují převahu dřevních pletiv a ukazují na vývoj uhlí v prostředí občasně zaplavovaných lesních mokřadů. Efekt alterace nevyzrálého uhlí nadložními bazaltovými výlevy byl poměrně omezený. Vzhledem k relativně rychlému zchladnutí bazaltové lávy, prokázanému přítomností vulkanického skla (tachylytu), se termální efekt projevil pouze vyvinutím tenké vrstvičky antracitového vzhledu na vzorcích bez celkového zvýšení stupně prouhelnění. Hydrotermální fluida spojená s vulkanickou aktivitou způsobila mechanickou desintegraci uhlí a následné vysrážení minerálů doprovázené rozkladem okolních vulkanoklastických sedimentů bohatých na živce. Alterovaná organická hmota je obohacena jednak o SiO2, Al2O3 a FeOtot, jednak o stopové prvky, jako například Ni a Cr. Naopak, tyto vzorky jsou ochuzeny o Hg (<10 ppb)

PRVNÍ NÁLEZ ŽÍLY LAMPROFYRU NA DRAHANSKÉ VRCHOVINĚ

Up to the present times, sporadic lamprophyric dykes have been described from almost all basic geological units at the eastern margin of the Bohemian Massif excluding large area of Culmian sediments in the Drahany Upland. Our first finding of such rock was ascertained in the active quarry at the village of Rozstání - Baldovec in the central part of the Drahany Upland (Fig. 1). The magmatic rock forms only about 2 m thick dyke with a very steep dip (8590 °) and the NW - SE orientation. Besides phenocrysts of pyroxene and amygdales filled by chlorite and calcite, there are conspicuous phenocrysts of dark mica. The igneous rock has also substantially higher magnetic susceptibility (up to 35×10-3 SI units) comparing surrounding Culmian graywackes, conglomerates and shales of the Rozstání formation (only about 0,10,2 ×10-3 SI units). Using determination of major and trace elements, the composition of all basic rock-forming minerals by means of microprobe, we classified the rock as a minette. We suppose its Late CarboniferousPermian age because of typical geochemical signs of Hercynian lapmprophyres in the whole Europe (both incompatible element enrichment and abundant transition elements see Turpin, Velde, Pinte 1988). The origin of lamprophyric rocks at the eastern margin of the Bohemian Massif is connected with extensional gravitational collapse of the Hercynian orogeny (Přichystal 1993, 1995)

Objev a genetický význam porfyrického alkaliCkoživcového mikrodioritu (dioritového porfyritu) v Olšanech na Drahanské vrchovině

From large area of Culmian sediments in the Drahany Upland we described first finding of magmatic dyke (lamprophyre/minette) at the village of Rozstání-Baldovec in the last year (Krmíček - Přichystal 2005). Our second finding of magmatic dyke was ascertained in the active quarry at the village of Olšany. The igneous rock has higher magnetic susceptibility (up to 35×10-3 SI units). Using complex petrologic study we classified the rock as a porphyric alkali feldspar microdiorite. Chondrite normalized REE patterns for our dyke show good correlation with Hercynian lamprophyres at the eastern margin of the Bohemian Massif (Moravo-Silesian Region) and slightly different composition from porphyric microdiorites of the Brno Massif (Fig. 4)

Determination of Rock Parameters Used for Calibration of Constitutive Model

Mathematical modelingis an important part of designing underground and other structures.However, the accuracy of the obtained results is strongly dependent on the input parameters quality of the selected material (constitutive) model. An insight into this issueis outlined in this article.Special emphasis was placed on various possibilities of laboratory determination of the necessary parameters for calibration of the Mohr-Coulomb and Hoek-Brown constitutive models. Described procedure was also applied to a selected rock type –Čeřínek-type granite of the Moldanubian pluton, a candidate rock in which a deep geological repository for used nuclear fuel and high-level radioactive nuclear waste might be built in a future

Lead isotope evolution of the upper mantle beneath the Bohemian Massif

The main focus of the lead isotope study is on Cretaceous to Quaternary volcanic and subvolcanic rocks of the Ohře/Eger Rift, which allows to map the upper mantle heterogenity on a regional scale, but also at depth and through time.Studie izotopů olova je zaměřena na křídové až kvartérní vulkanické a subvulkanické horniny oháreckého riftu, které umožňují mapovat heterogenitu svrchního pláště v regionálním měřítku, ale také v závislosti na hloubce a v průběhu času

Basic dykes with pyroxene in the vicinity of Blansko

Three mafic dykes found in the vicinity of Blansko were examined petrographically. One of them was studied geochemically. All three dykes contain clinopyroxene as phenocrysts (sometimes pseudomorphosed by hornblende) or in the groundmass with lathy plagioclases in the central parts of the dykes. Plagioclase usually takes the form of euhedral phenocrysts toward the contact with the host rock. Also, the structure changes from ophitic in the central parts to porphyric along the contact. Studied dykes display modal composition of microdiorites and porphyric microdiorites respectively. The dyke from Čertův Hrádek (no. 1) shows a noticeable geochemical similarity compared with the Hercynian dykes of porphyric microdiorites (diorite porphyrites) of the eastern granodiorite part of the Brno Massif studied by Hanžl et al. (1995). The dyke is formed by basaltic andesite based on the alkali/SiO2 ratio with features of calc-alkaline within plate basalt due to content of some trace elements or non-orogenic basalt account on content of Ti in pyroxenes (Leterrier et al. 1982).Three mafic dykes found in the vicinity of Blansko were examined petrographically. One of them was studied geochemically. All three dykes contain clinopyroxene as phenocrysts (sometimes pseudomorphosed by hornblende) or in the groundmass with lathy plagioclases in the central parts of the dykes. Plagioclase usually takes the form of euhedral phenocrysts toward the contact with the host rock. Also, the structure changes from ophitic in the central parts to porphyric along the contact. Studied dykes display modal composition of microdiorites and porphyric microdiorites respectively. The dyke from Čertův Hrádek (no. 1) shows a noticeable geochemical similarity compared with the Hercynian dykes of porphyric microdiorites (diorite porphyrites) of the eastern granodiorite part of the Brno Massif studied by Hanžl et al. (1995). The dyke is formed by basaltic andesite based on the alkali/SiO2 ratio with features of calc-alkaline within plate basalt due to content of some trace elements or non-orogenic basalt account on content of Ti in pyroxenes (Leterrier et al. 1982)