Geohazards analysis of Pisa tunnel in a fractured incompetent rocks in Zagros Mountains, Iran

The Pisa 2 tunnel with 740 m in length and 20° N trend is located along the Kazerun fault zone in Simply Folded Belt of Zagros, Iran. This tunnel has been excavated in the fractured incompetent marl layers with high expansive pressure of up to 2 kg/cm². In this study, the geological hazards along the tunnel have been recognized and categorized. This study revealed that, in the long-term usage of the tunnel, the lining did not endure against the loading and the secondary leakages. It is mainly attributed due to the non-efficiencies of drainage and isolation systems in the tunnel site. Therefore, it caused asphalt damage, drainage damage, and wall distortion. FLAC^3D software has been used in this research. We conducted various analyses for pre-excavation stress states, syn-excavation, and post-excavation strain states. The results showed no indication of instability and critical deformations during the excavation time. It also revealed that due to the non-efficiencies of drainage and isolation systems against secondary leakages and consequently marl expansion, the volumetric and shear strains (i.e., expansions and displacements) have exceeded from the critical states of strain along the tunnel. For various remedy purpose, this paper attempted several measures that can be taken in order to modify the drainage and isolation systems along the tunnel area. The reconstruction of drainage systems with suitable reinforced concrete and adequate slope has been proposed. The width of channel and isolation of backside of lining and implementation of multi-order outlets (i.e., backside of lining) for draining of groundwater into where the main drainage systems are located in the tunnel gallery were suggested.     

Simulation of groundwater drainage into a tunnel in fractured rock and numerical analysis of leakage remediation, Romeriksporten tunnel, Norway

Standard geostatistical methods for simulation of heterogeneity were applied to the Romeriksporten tunnel in Norway, where water was leaking through high-permeable fracture zones into the tunnel while it was under construction, causing drainage problems on the surface. After the tunnel was completed, artificial infiltration of water into wells drilled from the tunnel was implemented to control the leakage. Synthetic heterogeneity was generated at a scale sufficiently small to simulate the effects of remedial actions that were proposed to control the leakage. The flow field depends on the variance of permeabilities and the covariance model used to generate the heterogeneity. Flow channeling is the most important flow mechanism if the variance of the permeability field is large compared to the expected value. This condition makes the tunnel leakage difficult to control. The main effects of permeability changes due to sealing injection are simulated by a simple perturbation of the log-normal probability density function of the permeability. If flow channeling is the major transport mechanism of water into the tunnel, implementation of artificial infiltration of water to control the leakage requires previous chemical-sealing injection to be successful. Electronic Publication     

Rare earth element distributions in some Precambrian rocks and their phyllosilicates,Numedal, Norway

Mass spectrometric analyses for rare earth elements (REE) have been carried out on some Precambrian mica schists, gneisses and granites from the Precambrian Numedal area, Norway and on their phyllosilicates. The rocks, which are metamorphosed in the upper greenschist to amphibolite facies, were originally partly sedimentary, partly magmatic.The total REE contents for rocks varies from 145 to 761 ppm. An average of 16 phyllosilicate samples gave 417 ppm REE (max. of 1809 ppm, min. of ca. 50 ppm). Coexisting light and dark phyllosilicates have similar abundances of REE. For the micas of high REE content most of the REE was extractable by rinsing with EDTA. The data thus support the possibility of an extensive adsorption of REE ions on micaceous minerals. The REE distribution patterns do not provide a clear distinction between the sedimentary and magmatic origin for the rocks examined.     

Yield characteristics of fractured aquifers and their relation to lineaments in Precambrian crystalline rocks of Bharathapuzha river basin,Kerala

Data collected from bore wells drilled by Central Ground Water Board in Bharathapuzha river basin in Kerala have been analyzed to understand the spatial distribution of yields in Precambrian crystalline rock aquifers and their possible relation to lineaments in the area. Bore wells show wide variation in yields in both charnockites and migmatites. Bore wells in the depth range of 50 to 100 m are most productive in the area and drilling of wells below 150 m may not be economical due to the dying out of fractures at depth. Bore well yields showed a decrease with increasing distances from lineaments in the area. Analysis of the yield data of bore wells with respect to the lineament orientations indicated that bore wells drilled along N-S and SE-NW lineaments are the most productive, whereas those located along NNE-SSW and ESE-WNW lineaments are the least productive. Yields of bore wells, in general, are found to be influenced by the ruptural deformations in the geologic past, with the high yielding wells lying mostly on the lineaments along the directions of compression.     

Groundwater in fractured crystalline rocks, the Clara mine, Black Forest (Germany)

The chemical composition of water sampled in a 700 m deep underground barite-fluorite mine in the crystalline basement of the Black Forest area (SW Germany) varies systematically with depth and the length of flow paths trough, the fracture porosity of the gneiss matrix. Calcium and sulfate increase as a result of a combined sulfide oxidation and plagioclase alteration reaction. The gneiss contains andesine–plagioclase (An₂₀–An₄₀) and is rich in primary sulfide. As an effect of Ca and SO₄ release by the prime water–rock reaction, dissolved oxygen decreases and the waters become more reduced. The waters have Cl/Br mass ratios of about 50, which is very close to that of experimentally leached gneiss powders indicating that the rock matrix is the source of the halogens. The waters are undersaturated with respect to calcite in the upper parts of the mine. With increasing reaction progress, calcite saturation is reached and carbonate forms as a reaction product of the prime reaction that also controls the partial pressure of CO₂ to progressively lower values. The chemical evolution of groundwater in fractured basement of the Clara mine suggests that the partial pressure of CO₂ is an internally buffered parameter rather than a controlling external variable.     

Partial eclogitisation of gabbroic rocks in a late Precambrian subduction zone (Zambia): prograde metamorphism triggered by fluid infiltration

Gabbros and eclogites occur closely associated in a 200-km-long and up to 40-km-wide area of the Zambezi Belt in central Zambia. This area is interpreted to represent part of a late Precambrian suture zone, with the mafic rocks being relics of subducted oceanic crust. Gradual stages of prograde transformation from gabbro to eclogite are preserved by disequilibrium textures of incomplete reactions. This resulted in kyanite–omphacite-bearing assemblages for eclogites that have Al-poor bulk compositions. Undeformed eclogites typically preserve features of a former gabbroic texture, reflected by replacements of plagioclase and magmatic pyroxene by eclogite facies minerals. Textures of deformed eclogites range from sheared porphyroclastic to porphyroblastic. Relics of magmatic pyroxene are common and complete eclogitisation occurred only in millimetre to centimetre-scale domains in most of the rocks. No evidence for prograde blueschist or amphibolite facies mineral assemblages was found in eclogites. In contrast, the fine grained intergrowth of omphacite, garnet, kyanite and quartz, which replace former plagioclase or was formed in the pressure shadow of magmatic pyroxene relics, indicates that eclogitisation might have affected the gabbroic protoliths directly without any significant intervening metamorphic reactions. Eclogitisation took place under P–T conditions of 630–690 °C and 26–28 kbar, suggesting a large overstepping (>10 kbar) of reaction boundaries. Eclogitisation was initialised and accompanied by a channelised fluid flow resulting in veins with large, subhedral grains of omphacite, kyanite and garnet. The gabbro-to-eclogite transformation was enhanced by a fluid which allowed the necessary material transport for the dissolution–precipitation mechanism that characterises the metamorphic mineral replacements. The process of eclogitisation was limited by reaction kinetics and dissolution–precipitation rates rather than by the metamorphic P–T conditions. Even though ductile deformation occurred and equilibrium phase boundaries were overstepped, the infiltration of fluids was necessary for triggering the gabbro-to-eclogite transformation.Editorial responsibility: J. Hoefs     

Petrogenesis of Carbonate-orthopyroxenites (Sagvandites) and related rocks from Troms, Northern Norway

Carbonate-orthopyroxenites from Troms consist of enstatite andmagnesite with variable amounts of olivine, talc, serpentine,chlorite, and phlogopite and include the ore minerals chromite,magnetite, pentlandite, pyrite, and in some cases pyrrhotite,heazlewoodite, millerite, and maucherite. Related rocks compriseolivine-magnesite-, talc-magnesite and olivine-orthopyroxene(saxonite)-assemblages. Allochemical replacement reactions,involving mobile CO₂, H₂O, and SiO₂, are shown to comprise themain petrogenetic mechanism. Saxonite, however, may representa possible source material. Discussion of the model system MgO-SiO₂-CO₂-H₂O for P_flukl =2 and 7 kb, respectively, indicates that best agreement withpetrographic evidence is reached assuming elevated pressuresand both gas-excess and gas-deficiency conditions by means oflocal equilibria. The gas-deficient assemblage enstatite+talc+forsterite+magnesiteis presumed to be stable at pressures above 5 kb. Recalculationof whole-rock analyses to a CO₂-free basis by several alternativemethods suggests that rock evolution could have followed thetrend dunite saxonite orthopyroxenite sagvandite+related rocks.A simple geometric method is used to outline possible schemesof rock evolution, involving gas-deficient phase assemblages.     

The use of sagebrush (Artemisia) as a biogeochemical indicator of base-metal deposits in Precambrian rocks of west-central Colorado

The efficacy of sagebrush (Artemisia) as a biogeochemical indicator of base-metal mineralization in stratabound Precambrian ore deposits in west-central Colorado was investigated by collecting new (mostly flowering) growth from several sagebrush shrubs over and near five such deposits in three different areas. These are the Sedalia mine and two mines in the Turret district near Salida, and two mines in the Cochetopa district southeast of Gunnison. Two species were used, A. tridentata and A. frigida, depending on the area. Sagebrush clippings were separated into two subsamples consisting of (1) stems, and (2) leaves and blossoms stripped from the stems. These subsamples were ashed separately and the ash analyzed with an emission spectrograph for 30 elements. There appear to be no appreciable differences in the analyses of the two subsamples, indicating that composite samples would provide adequate information for further investigations. Eight of these elements, Ag, Bi, Cu, Pb, Sn, Y, Zn, and Zr, are present in notably higher concentrations in the ash of samples growing over mineralized ground than in that of control samples growing over barren ground. Although the distribution pattern, and the number of these anomalous elements, differs at each of the five localities, three of them, silver, copper, and lead, show good contrast and close association with subjacent mineralization in all five study areas.     

Molybdenum distribution in Precambrian rocks of the Colorado Mineral Belt

The average Mo content of more than one hundred rock samples from the Precambrian basement of the Colorado Mineral Belt corresponds well to the global molybdenum content of crustal rocks of 1.0 ppm. There are no indications of a regional geochemical molybdenum anomaly in that part of the crust or upper mantle.     

Prehnite-pumpellyite facies metamorphism in Precambrian basement rocks of S Sweden

Very small amounts of prehnite and pumpellyite have been found, often as lenses in biotite crystals, in otherwise quite ordinary quartzo-feldspathic gneisses and granitoid rocks forming common components of the Precambrian basement of S Sweden. It is concluded that both minerals belong to the same metamorphic paragenesis, which also includes quartz, K-feldspar, albite, epidote, colourless mica and chlorite. The presence of this paragenesis, in however slight amounts, signifies that the rocks bear the imprint of a phase of metamorphism belonging to the prehnite-pumpellyite facies.     

桂北前寒武纪花岗岩类岩石的地球化学与成因

桂北广泛发育前寒武纪花岗岩类岩石，按岩石组合特征可区分为二类，一类为花岗闪长质岩石，另一类为黑云母花岗质岩石。二类岩石的A／NKC值均在1．10以上，属铝过饱和岩石，但花岗闪长质岩石相对贫硅、钾，富铁，镁，贫铷，富锶、钡，并具有较高的稀土元素总量和轻重稀土元素比值；黑云母花岗质岩石则具更显著的铕负异常，二类岩石εNd(T)值的变化范围与四堡群基底相近，但花岗闪长岩石更接近四堡群基底中的变质镁铁质－超镁铁质杂岩，黑云母花岗质岩石则更靠近四堡群基底中的浅变质沉积岩，对岩石产出动力地质背景的全面分析表明，区内二类花岗质岩石是华夏地块与扬子地块碰撞俯冲作用的不同阶段由成熟度不同的四堡群变质基底在不同深度经部分熔融作用的产物。     

Long-term impacts of dust storms on transport systems in south-eastern Iran

Natural Hazards - Dust storms are frequent in the Sistan region of south-eastern Iran and cause a wide range of problems, but few studies have assessed their negative impacts. This paper makes an...     

Prediction of water inflow into underground excavations in fractured rocks using a 3D discrete fracture network (DFN) model

Groundwater flow is a major issue in underground opening in fractured rocks. Because of finding the fracture connectivity, contribution of each fracture in flow, and fracture connectivity to excavation boundary, the prediction of water flow to underground excavations is difficult. Simulation of fracture characteristics and spatial distribution is necessary to obtain realistic estimation of inflow quantity to tunnel and underground excavations. In this research, a computer code for three-dimensional discrete fracture network modeling of water inflow into underground excavations was developed. In this code, the fractures are simulated as ellipsoid while geometrical properties of the fractures are reproduced using a stochastic method. Properties such as the size, orientation, and density of the fractures are modeled by their respective probability distributions, which are obtained from field measurements. According to the fracture condition, the flow paths in rock mass are determined. The flow paths are considered as channels with rectangular sections in which channel width and fracture aperture determine geometry of channel section. Inflow into excavation is predicted ignoring matrix permeability and considering the hydrogeological conditions. To verify presented model, simulation results were compared to a part of the Cheshmeh-Roozieh water transfer tunnel in Iran. The results obtained from this research are in good agreement with the field data. Thus, the average of the predicted inflow has just an approximation error equal to 17.8%, and its standard deviation is 8.6 l/s, which is equal to 21% of the observed value that demonstrates low dispersion of the predicted values.     

The Precambrian metamorphic rocks of Ceylon: A critique of a radical interpretation

Zusammenfassung Die neue Hypothese von M. B.Katz (1971), da\ die Vijaya-Gneise und -Migmatite das ursprüngliche Grundgebirge unter den metamorphen Sedimenten der Highland-Serie sind, hÄlt einer kritischen Prüfung nicht stand. Die Ältere Auffassung, die Vijaya-Gesteine seien durch retrograd-metamorphe Amphibolit-Fazies-überprÄgung aus der vorher in Granulit-Fazies entwickelten Highland-Serie hervorgegangen, ist aufrechtzuerhalten und kann durch neue Explorationskartierung und strukturelle und isotopische Analysen wesentlich gestützt werden.

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A critical review leads to the rejection of the recent hypothesis of M. B.Katz (1971) according to which the Vijayan gneisses and migmatites formed an original basement to the Highland Series metasediments. An earlier synthesis which interpreted the Vijayan rocks as the result of a retrograde amphibolite facies metamorphism superimposed upon pre-existing granulite facies Highland Series is upheld and is strongly supported by new reconnaissance mapping and structural and isotopic analyses.

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Résumé Un examen critique montre qu'il faut rejeter la nouvelle hypothèse de M. B.Katz (1971) selon laquelle les gneiss et migmatites du Vijáya constituent le socle original sous les sédiments métamorphisés de la série du Highland. De nouveaux levés de reconnaissance et des analyses structurelles et isotopiques soutiennent au contraire la vue antérieure selon laquelle les roches vijayiennes seraient issues de roches de la série du Highland antérieurement à faciès granulitique, et ce, à la suite d'un rétrométamorphisme qui leur aurait surimposé le faciès amphibolitique.

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(M. B. Katz, 1971), Vijaya Highland, , . , Vijaya Highland , , .

     

Early Precambrian high-grade metamorphosed terrigenous rocks of granulite-gneiss terranes of the Sharyzhalgai uplift (southwestern Siberian craton)

We present results of geochemical and Sm-Nd isotope studies of high-grade metaterrigenous rocks of the Kitoi and northwestern Irkut terranes of the Sharyzhalgai uplift on the Siberian Platform in comparison with paragneisses of the southeastern Irkut terrane. The metasedimentary rocks of the first region are high-alumina garnet-sillimanite-cordierite-bearing paragneisses; their protoliths were mostly mudstones and pelitic mudstones by major-element composition. The low-alumina biotite gneisses of the Kitoi terrane formed, most likely, from magmatic protoliths similar in petrochemical features to intraplate volcanics. The major factor controlling the composition of the studied high-alumina paragneisses is precipitation of most of incompatible trace elements in the clay fraction of sediments, as evidenced from the positive correlation between trace-element and Al₂O3 contents. The Cr and Ni contents, showing a positive correlation with MgO and no correlation with Al₂O3, are an indicator of the contribution of the mafic-source material to the formation of high-alumina rocks. The contribution of a mafic source-derived material to the formation of terrigenous rocks increases in passing from Kitoi to northwestern Irkut terrane. The high-alumina and garnet-biotite paragneisses of the southeastern Irkut terrane are similar in trace-element patterns to the analogous rocks of the Kitoi terrane and northwestern part of the Irkut terrane but show higher Th contents and a distinct negative Eu anomaly related to the change in the composition of the felsic source. The participation of felsic potassic igneous rocks in the formation of the southeastern terrigenous sediments is consistent with their deposition after the Neoarchean collision processes (metamorphism and granite magmatism), whereas sedimentation in the Kitoi and northwestern Irkut terranes preceded them. The Sm-Nd isotope characteristics indicate that the latter sediments formed mostly as a result of the erosion of the Paleo-Mesoarchean crust, whereas the metasediments of the southeastern Irkut terrane formed with the participation of Paleoproterozoic juvenile rocks. Thus, the variations in the trace-element and isotope compositions of the high-grade metamorphosed terrigenous rocks reflect recycling and growth of the continental crust of the Sharyzhalgai uplift during the Neoarchean-Pa- leoproterozoic transition.     

Geochronology of Precambrian rocks in the Laramie Range and implications for the tectonic framework of Precambrian southern Wyoming

From Casper Mountain; at its northern end, to the northwestern margin of the Laramie anorthosite—syenite complex, in its central parts, the Laramie Range is underlain by granite and granitic gneiss that has a minimum age of 2.54 ± 0.04 Ga (Rb/Sr whole-rock isochron) and by metasedimentary rocks, including marble and quartzite, that appear to overlie the granitic gneiss nonconformably (minimum age: 1.7 Ga based on several horn-blende K/Ar dates). Southward from the anorthosite—syenite complex into Colorado, the Range is underlain chiefly by the Sherman Granite (1.41 Ga; Peterman and Hedge, 1968) and scattered patches of gneiss that are not dated, but are tentatively correlated wit similar gneiss in the southern Medicine Bow Mountains and in the Colorado Front Range, where they are dated as ? 1.7 Ga (Peterman and Hedge, 1968).The Laramie anorthosite—syenite complex (minimum age: ? 1.42 Ga or ? 1.51 Ga if a hornblende K/Ar date is accepted) apparently intruded the suture separating the old (? 2.5 Ga) continental edge from younger (? 1.7 Ga) geosynclinal rocks. The suture, which manifests itself as the Mullen Creek—Nash Fork shear zone in the Medicine Bow Mountains, also is the boundary between ensialic and ensimatic geosynclinal deposition that occurred during the interval 1.7–2.5 Ga ago.K/Ar dates on biotite and muscovite from rocks north of the anorthosite—syenite complex grade from 2.5 Ga on Casper Mountain down to 1.38 Ga near the complex. Near its northern tip, the Laramie Range is crossed by a geochronologic front, separating 2.5 Ga old gneiss whose K/Ar dates were not lowered by subsequent metamorphism from 2.5 Ga old gneiss whose mica dates were reset between 1.4 and 1.6 Ga ago.     

U---Pb and Rb---Sr systematics in a polyorogenic segment of the Precambrian shield, central southern Norway

U---Pb analyses of zircon, monazite and sphene as well as Rb---Sr analyses of whole rocks and minerals have been carried out in an attempt to elucidate the evolution of the Precambrian shield underlying the Caledonian Jotun-nappe in central southern Norway. The earliest event recognized in the area is a high grade metamorphism at 1518 ± 17 m.y. which followed intense magma formation, igneous activity, erosion and sedimentation over a period of maximum 300 m.y. The Sveconorwegian cycle is characterized by the intrusion of two anatectic magma generations at 1014 ± 35 m.y. and 930±10 m.y. that disturbed and partly reset the isotopic systems of the country rocks. A post-magmatic fracturing stage at 875 m.y. concludes this cycle. Rb---Sr mineral systems were not completely equilibrated in the undeformed shield during the Caledonian event in contrast to new grown minerals in strongly deformed overlying Lower Paleozoic sediments which record the main deformation at 384±18 m.y. Zircon lower intercept ages ranging between 330–370 m.y. show that lead loss of zircon in rocks subjected to low grade metamorphic conditions may be the result of such processes as annealing, alteration, dilation or a combination of them.