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Rock Interaction (rock + interaction)
Selected AbstractsRole of fluids in the metamorphism of the Alpine Fault Zone, New ZealandJOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2001J. K. Vry Abstract Models of fluid/rock interaction in and adjacent to the Alpine Fault in the Hokitika area, South Island, New Zealand, were investigated using hydrogen and other stable isotope studies, together with field and petrographic observations. All analysed samples from the study area have similar whole-rock ,D values (,DWR = ,56 to ,30,, average = ,45,, n = 20), irrespective of rock type, degree of chloritization, location along the fault, or across-strike distance from the fault in the garnet zone. The green, chlorite-rich fault rocks, which probably formed from Australian Plate precursors, record nearly isothermal fluid/rock interaction with a schist-derived metamorphic fluid at high temperatures near 450,500°C (,D of water in equilibrium with the green fault rocks (,DH2O, green) ,,,18,; ,D of water in equilibrium with the greyschists and greyschist-derived mylonites (,DH2O, grey) , ,19, at 500°C; ,DH2O, green , ,17,; ,DH2O, grey , ,14, at 450°C). There is no indication of an influx of a meteoric or mantle-derived fluid in the Alpine Fault Zone in the study area. The Alpine Fault Zone at the surface shows little evidence of late-stage retrogression or veining, which might be attributed to down-temperature fluid flow. It is probable that prograde metamorphism in the root zone of the Southern Alps releases metamorphic fluids that at some region rise vertically rather than following the trace of the Alpine Fault up to the surface, owing to the combined effects of the fault, the disturbed isotherms under the Southern Alps, and the brittle,ductile transition. Such fluids could mix with meteoric fluids to deposit quartz-rich, possibly gold-bearing veins in the region c. 5,10 km back from the fault trace. These results and interpretations are consistent with interpretations of magnetotelluric data obtained in the South Island GeopHysical Transects (SIGHT) programme. [source] Linear analysis of concrete arch dams including dam,water,foundation rock interaction considering spatially varying ground motionsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 7 2010Jin-Ting Wang Abstract The available substructure method and computer program for earthquake response analysis of arch dams, including the effects of dam,water,foundation rock interaction and recognizing the semi-unbounded size of the foundation rock and fluid domains, are extended to consider spatial variations in ground motions around the canyon. The response of Mauvoisin Dam in Switzerland to spatially varying ground motion recorded during a small earthquake is analyzed to illustrate the results from this analysis procedure. Copyright © 2009 John Wiley & Sons, Ltd. [source] Chemical modification of pyroclastic rock by hot water: an experimental investigation of mass transport at the fluid,solid interfaceGEOFLUIDS (ELECTRONIC), Issue 1 2009J. HARA Abstract Hydrothermal water,(pyroclastic) rock interactions were examined using flow-through experiments to deduce the effect of mass transport phenomena on the reaction process. A series of experiments were conducted over the temperature range 75,250°C, with a constant temperature for each experiment, and at saturated vapour pressure, to estimate the apparent rate constants as a function of temperature. Based on the chemistry of analysed solutions, the water,rock interaction in the experiments was controlled by diffusion from the reaction surface and by the existence of a surface layer at the rock,fluid interface, which regulated the chemical reaction rate. The reaction progress depended to a high degree on flow velocity and temperature conditions, with element abundances in the fluid significantly affected by these factors. Mass transport coefficients for diffusion from the rock surface to the bulk solution have been estimated. Ca is selectively depleted under lower temperature conditions (T < 150°C), whereas Na is greatly depleted under higher temperature conditions (T > 150°C), and K reaction rates are increased when flow velocity increases. Using these conditions, specific alkali and alkali earth cations were selectively leached from mineral surfaces. The ,surface layer' comprised a 0.5,1.8 mm boundary film on the solution side (the thickness of this layer has no dependence on chemical character) and a reaction layer. The reaction layer was composed of a Si, Al-rich cation-leached layer, whose thickness was dependent on temperature, flow velocity and reaction length. The reaction layer varied in thickness from about 10,4 to 10,7 mm under high temperature/low fluid velocity and low temperature/high fluid velocity conditions, respectively. [source] Isotopic and petrological evidence of fluid,rock interaction at a Tethyan ocean,continent transition in the Alps: implications for tectonic processes and carbon transfer during early ocean formationGEOFLUIDS (ELECTRONIC), Issue 4 2007A. ENGSTRÖM Abstract We report overprinting stable isotope evidence of fluid,rock interaction below two detachment faults along which mantle rocks were exhumed to the seafloor, between the respective landward and seaward limits of oceanic and continental crust, at a Tethyan ocean,continent transition (OCT). This OCT, which is presently exposed in the Tasna nappe (south-eastern Switzerland) is considered an on-land analogue of the well-studied Iberian OCT. We compare our results with the fault architecture (fault core,damage zone,protolith) described by Caine et al. [Geology (1996) Vol. 24, pp. 1025,1028]. We confirm the existence of a sharp boundary between the fault core and damage zone based on isotopic data, but the boundary between the damage zone and protolith is gradational. We identify evidence for: (1) pervasive isotopic modification to 8.4 ± 0.1, which accompanied or post-dated serpentinization of these mantle rocks at an estimated temperature of 67,109°C, (2) either (i) partial isolation of some highly strained regions [fault core(s) and mylonite] from this pervasive isotopic modification, because of permeability reduction (Caine et al.) or (ii) subsequent isotopic modification caused by structurally channelled flow of warm fluids within these highly strained regions, because of permeability enhancement, and (3) isotopic modification, which is associated with extensive calcification at T = 54,100°C, primarily beneath the younger of the two detachment faults and post-dating initial serpentinization. By comparing the volumetric extent of calcification with an experimentally verified model for calcite precipitation in veins, we conclude that calcification could have occurred in response to seawater infiltration, with a calculated flux rate of 0.1,0.2 m year,1 and a minimum duration of 0.2,4.0 × 104 years. The associated time-averaged uptake flux of carbon during this period was 8,120 mol m,2 year,1. By comparison with the estimated area of exhumed mantle rocks at the Iberian OCT, we calculate a maximum annual uptake flux for carbon of 2,30 Tg year,1. This is an order of magnitude greater than that for carbon exchange at the mid-ocean ridges and 0.1,1.4% of the global oceanic uptake flux for carbon. [source] Chemical and isotopic signatures of Na/HCO3/CO2 -rich geofluids, North PortugalGEOFLUIDS (ELECTRONIC), Issue 4 2006J. M. MARQUES Abstract Geochemical and isotopic studies have been undertaken to assess the origin of CO2 -rich waters issuing in the northern part of Portugal. These solutions are hot (76°C) to cold (17°C) Na,HCO3 mineral waters. The ,2H and ,18O signatures of the mineral waters reflect the influence of altitude on meteoric recharge. The lack of an 18O-shift indicates there has been no high temperature water,rock interaction at depth, corroborating the results of several chemical geothermometers (reservoir temperature of about 120°C). The low 14C activity (up to 9.9 pmC) measured in some of the cold CO2 -rich mineral waters (total dissolved inorganic carbon) is incompatible with the presence of 3H (from 1.7 to 4.1 TU) in those waters, which indicates relatively short subsurface circulation times. The ,13C values of CO2 gas and dissolved inorganic carbon range between ,6, and ,1, versus Vienna-Peedee Belemnite, indicating that the total carbon in the recharge waters is being diluted by larger quantities of CO2 (14C-free) introduced from deep-seated (upper mantle) sources, masking the 14C-dating values. The differences in the 87Sr/86Sr ratios of the studied thermal and mineral waters seem to be caused by water,rock interaction with different granitic rocks. Chlorine isotope signatures (,0.4, < ,37Cl < +0.4, versus standard mean ocean chloride) indicate that Cl in these waters could be derived from mixing of a small amount of igneous Cl from leaching of granitic rocks. [source] Sodic metasomatism in the Palaeoproterozoic Hotazel iron-formation, Transvaal Supergroup, South Africa: implications for fluid,rock interaction in the Kalahari manganese fieldGEOFLUIDS (ELECTRONIC), Issue 4 2005H. TSIKOS Abstract Petrological and geochemical evidence is presented on the occurrence of aegirine in the Palaeoproterozoic Hotazel iron-formation, which hosts the giant manganese deposits of the Kalahari manganese field, South Africa. The mineral has an essentially pure Na end-member composition and occurs sporadically in iron-formation immediately bordering the manganese ore beds. The development of aegirine appears to have taken place due to the action of late-infiltrating, saline hydrothermal fluids at the expense of a pre-existing, binary quartz,hematite assemblage. It is proposed that such a process would have overprinted (and therefore post-dated) a spatially more extensive, low-temperature alteration event which brought about thorough carbonate leaching, oxidation and residual enrichment of metals in the Hotazel iron,manganese rocks. [source] The upper continental crust, an aquifer and its fluid: hydaulic and chemical data from 4 km depth in fractured crystalline basement rocks at the KTB test siteGEOFLUIDS (ELECTRONIC), Issue 1 2005I. STOBER Abstract Detailed information on the hydrogeologic and hydraulic properties of the deeper parts of the upper continental crust is scarce. The pilot hole of the deep research drillhole (KTB) in crystalline basement of central Germany provided access to the crust for an exceptional pumping experiment of 1-year duration. The hydraulic properties of fractured crystalline rocks at 4 km depth were derived from the well test and a total of 23100 m3 of saline fluid was pumped from the crustal reservoir. The experiment shows that the water-saturated fracture pore space of the brittle upper crust is highly connected, hence, the continental upper crust is an aquifer. The pressure,time data from the well tests showed three distinct flow periods: the first period relates to wellbore storage and skin effects, the second flow period shows the typical characteristics of the homogeneous isotropic basement rock aquifer and the third flow period relates to the influence of a distant hydraulic border, probably an effect of the Franconian lineament, a steep dipping major thrust fault known from surface geology. The data analysis provided a transmissivity of the pumped aquifer T = 6.1 × 10,6 m2 sec,1, the corresponding hydraulic conductivity (permeability) is K = 4.07 × 10,8 m sec,1 and the computed storage coefficient (storativity) of the aquifer of about S = 5 × 10,6. This unexpected high permeability of the continental upper crust is well within the conditions of possible advective flow. The average flow porosity of the fractured basement aquifer is 0.6,0.7% and this range can be taken as a representative and characteristic values for the continental upper crust in general. The chemical composition of the pumped fluid was nearly constant during the 1-year test. The total of dissolved solids amounts to 62 g l,1 and comprise mainly a mixture of CaCl2 and NaCl; all other dissolved components amount to about 2 g l,1. The cation proportions of the fluid (XCa approximately 0.6) reflects the mineralogical composition of the reservoir rock and the high salinity results from desiccation (H2O-loss) due to the formation of abundant hydrate minerals during water,rock interaction. The constant fluid composition suggests that the fluid has been pumped from a rather homogeneous reservoir lithology dominated by metagabbros and amphibolites containing abundant Ca-rich plagioclase. [source] Strontium isotopic characterization of the Palmottu hydrosystem (Finland): water,rock interaction and geochemistry of groundwatersGEOFLUIDS (ELECTRONIC), Issue 3 2003Philippe Negrel Abstract The Palmottu hydrosystem is located in a granitic host rock in southern Finland. Along well-defined pathways in the fractured crystalline rock, strontium isotopes are used to trace the degree of water,rock interaction (WRI) and mixing processes in groundwaters. The 87Sr/86Sr ratios range between 0.716910 and 0.735606 in the surface waters and between 0.719991 and 0.750787 in the groundwaters, but are between 0.720 and 0.735 in most of the samples. Moreover, the results show a lack of correlation between the water chemistries determining the classification into different water-types (Na,Cl, Na,SO4, etc.) and the results of the strontium (Sr) contents and Sr isotopic ratios. From a WRI standpoint, this implies that the Sr behaviour is independent of the water chemistry; the occurrence of large 87Sr/86Sr variations is site specific and mainly dependent on the lithology. A model to determine the 87Sr/86Sr ratio of water after interaction with granite was developed. This model is based on the assumption that Sr was derived from three minerals: plagioclase, K-feldspar and biotite. The results of the calculation indicate that around half of the water analysed within the Palmottu hydrosystem can be explained by the weathering of the granites. However, clearly lower 87Sr/86Sr are observed in waters when compared to the calculated 87Sr/86Sr and other sources of Sr, with low 87Sr/86Sr, rather than the calculated granite,water interaction, which may be suspected. When comparing the 87Sr/86Sr and ion ratios (Ca/Na, Mg/Na, Sr/Na, Cl/Na), the scattering of the data can be explained by the presence of four end-members: a brine component (low 87Sr/86Sr and Ca/Na ratios,), a deep granitic component (high 87Sr/86Sr ratios and low Ca/Na ratios,), a subsurface component (intermediate 87Sr/86Sr ratios associated with high Ca/Na ratios,) and a surface end-member:snow and river drainage (low 87Sr/86Sr and low Ca/Na ratios,). These extreme end-members define a series of WRI-mixing line within a rather complex hydrosystem. [source] Origin of deep saline groundwaters in the Vienne granitic rocks (France): constraints inferred from boron and strontium isotopesGEOFLUIDS (ELECTRONIC), Issue 2 2001J. Casanova Abstract As part of a preliminary geological characterization programme to assess the feasibility of an underground laboratory in granitic rock, a series of 17 deep boreholes (maximum depth, 900 m) was drilled by ANDRA in the Vienne district, France. A salinity gradient was demonstrated in the granitic waters with concentrations varying from approximately 1 g L,1 at 150 m depth at the top of the basement (beneath the sedimentary cover) to 10 g L,1 in the deeper part (from 400 to 600 m depth). Sr and B isotope ratios were measured in order to better understand the origin of the salinity and to evaluate the degree of water,rock interaction in the system. The results obtained were compared to those of mineral spring waters emerging from the granitic basement in the Massif Central. Evidence in support of a significant marine contribution include: (i) the Cl,Br investigations agree with a marine origin for the saline groundwaters without evolution from seawater; (ii) the 87Sr/86Sr ratio of the Vienne deep groundwaters (0.7078,0.7084) is in agreement with a palaeo-seawater isotopic signature; (iii) measured ,11B values for the deepest brine samples are enriched in 11B (up to 36.1,) relative to the granitic springs. The combined use of ,11B, Cl, B, Br, Sr contents and 87Sr/86Sr ratios makes it possible to define and quantify a mixing model between marine and crustal end-members in order to explain the origin of the deep saline groundwaters in the Vienne granitic rocks. [source] Invasion of a karst aquifer by hydrothermal fluids: evidence from stable isotopic compositions of cave mineralizationGEOFLUIDS (ELECTRONIC), Issue 2 2001S. H. Bottrell Abstract Mineral deposits in the Cupp-Coutunn/Promeszutochnaya cave system (Turkmenia, central Asia) record a phase of hydrothermal activity within a pre-existing karstic groundwater conduit system. Hydrothermal fluids entered the caves through fault zones and deposited sulphate, sulphide and carbonate minerals under phreatic conditions. Locally, intense alteration of limestone wall rocks also occurred at this stage. Elsewhere in the region, similar faults contain economic quantities of galena and elemental sulphur mineralization. Comparisons between the Pb and S isotope compositions of minerals found in cave and ore deposits confirm the link between economic mineralization and hydrothermal activity at Cupp-Coutunn. The predominance of sulphate mineralization in Cupp-Coutunn implies that the fluids were more oxidized in the higher permeability zone associated with the karst aquifer. A slight increase in the ,34S of sulphate minerals and a corresponding ,34S decrease in sulphides suggest that partial isotopic equilibration occurred during oxidation. Carbonate minerals indicate that the hydrothermal fluid was enriched in 18O (,18OSMOW , + 10,) relative to meteoric groundwater and seawater. Estimated values for ,13CDIC (,13CPDB , , 13,) are consistent with compositions expected for dissolved inorganic carbon (DIC) derived from the products of thermal decomposition of organic matter and dissolution of marine carbonate. Values derived for ,13CDIC and ,18Owater indicate that the hydrothermal fluid was of basinal brine origin, generated by extensive water,rock interaction. Following the hydrothermal phase, speleothemic minerals were precipitated under vadose conditions. Speleothemic sulphates show a bimodal sulphur isotope distribution. One group has compositions similar to the hydrothermal sulphates, whilst the second group is characterized by higher ,34S values. This latter group may either record the effects of microbial sulphate reduction, or reflect the introduction of sulphate-rich groundwater generated by the dissolution of overlying evaporites. Oxygen isotope compositions show that calcite speleothems were precipitated from nonthermal groundwater of meteoric origin. Carbonate speleothems are relatively enriched in 13C compared to most cave deposits, but can be explained by normal speleothem-forming processes under thin, arid-zone soils dominated by C4 vegetation. However, the presence of sulphate speleothems, with isotopic compositions indicative of the oxidation of hydrothermal sulphide, implies that CO2 derived by reaction of limestone with sulphuric acid (,condensation corrosion') contributed to the formation of 13C-enriched speleothem deposits. [source] Contribution to the study of thermal waters in Greece: chemical patterns and origin of thermal water in the thermal springs of LesvosHYDROLOGICAL PROCESSES, Issue 2 2008N. J. Lambrakis Abstract The occurrence of thermal/spa waters on Lesvos Island is related to the presence of a major faulting system. Thermal waters are the result of mixing of meteoric and infiltrating seawater at great depth, and their total salinity depends on the percentage of seawater in their composition. According to the diagrams of main elements, trace elements and environmental isotopes, most of the components that determine the chemical composition of thermal waters such as sodium, chloride and sulphates originate from seawaters. On the other hand, the concentration of calcium, magnesium, boron, lithium, etc., was affected by water,rock interaction under high temperature conditions. Moving towards the surface, thermal waters may become polluted by influx of recent seawater, allowing their chemical composition to become similar to that of seawater. The thermal waters of Lesvos Island present relatively high concentrations of ammonia and redox sensitive metals because they are hosted in a reducing environment. They also exhibit low nitrate concentrations due to their mixture with recent fresh water. Finally, they show increased radon concentrations, ranging from 20 to 60 kBq m,3 in the eastern and southern parts of the island, and about 230 kBq m,3 in the north, in the area of Eftalou,Argenos. Copyright © 2007 John Wiley & Sons, Ltd. [source] Water quality and hydrogeochemical characteristics of the River Buyukmelen, Duzce, TurkeyHYDROLOGICAL PROCESSES, Issue 20 2005Rustem Pehlivan Abstract The River Buyukmelen is located in the province of Duzce in northwest Turkey and its water basin is approximately 470 km2. The Aksu, Kucukmelen and Ugursuyu streams flow into the River Buyukmelen. It flows into the Black Sea with an output of 44 m3 s,1. The geological succession in the basin comprises limestone and dolomitic limestone of the Y,lanl, formation, sandstone, clayey limestone and marls of the Akveren formation, clastics and volcano-clastics of the Caycuma formation, and cover units comprised of river alluvium, lacutrine sediments and beach sands. The River Buyukmelen is expected to be a water source that can supply the drinking water needs of Istanbul until 2040; therefore, it is imperative that its water quality be preserved. The samples of rock, soil, stream water, suspended, bed and stream sediments and beach sand were collected from the Buyukmelen river basin. They were examined using mineralogical and geochemical methods. The chemical constituents most commonly found in the stream waters are Na+, Mg2+, SO2,4, Cl, and HCO3, in the Guz stream water, Ca2+ in the Abaza stream water, and K+ in the Kuplu stream water. The concentrations of Na+, K+, Ca2+, Mg2+, SO2,4, HCO,3, Cl,, As, Pb, Ni, Mn, Cr, Zn, Fe and U in the Kuplu and Guz stream waters were much higher than the world average values. The Dilaver, Gubi, Tepekoy, Maden, Celik and Abaza streams interact with sedimentary rocks, and the Kuplu and Guz streams interact with volcanic rocks. The amount of suspended sediment in the River Buyukmelen in December 2002 was 120 mg l,1. The suspended and bed sediments in the muddy stream waters are formed of quartz, calcite, plagioclase, clay (kaolinite, illite and smectite), muscovite and amphibole minerals. As, Co, Cd, Cr, Pb, Ni, Zn and U have all accumulated in the Buyukmelen river-bed sediments. The muddy feature of the waters is related to the petrographic features of the rocks in the basin and their mineralogical compositions, as most of the sandstones and volcanic rocks (basalt, tuffite and agglomerate) are decomposed to a clay-rich composition at the surface. Thus, the suspended sediment in stream waters increases by physical weathering of the rocks and water,rock interaction. Owing to the growing population and industrialization, water demand is increasing. The plan is to bring water from the River Buyukmelen to Istanbul's drinking-water reservoirs. According to the Water Pollution Regulations, the River Buyukmelen belongs to quality class 1 based on Hg, Cd, Pb, As, Cu, Cr, Zn, Mn, Se, Ba, Na+, Cl,, and SO2,4; and to quality class 3 based on Fe concentration. The concentration of Fe in the River Buyukmelen exceeds the limit values permitted by the World Health Organization and the Turkish Standard. Because water from the River Buyukmelen will be used as drinking water, it will have an adverse effect on water quality and humans if not treated in advance. In addition, the inclusion of Mn and Zn in the Elmali drinking-water reservoir of Istanbul and Fe in the River Buyukmelen water indicates natural inorganic contamination. Mn, Zn and Fe contents in the waters are related to geological origin. Moreover, the River Buyukmelen flow is very muddy in the rainy seasons and it is inevitable that this will pose problems during the purification process. Copyright © 2005 John Wiley & Sons, Ltd. [source] Hydrogeochemistry of seepage water collected within the Youngcheon diversion tunnel, Korea: source and evolution of SO4 -rich groundwater in sedimentary terrainHYDROLOGICAL PROCESSES, Issue 9 2001Gi-Tak Chae Abstract In the Youngcheon Diversion Tunnel area, South Korea, 46 samples of tunnel seepage water (TSW) and borehole groundwater were collected from areas with sedimentary rocks (mainly sandstone and shale) and were examined for hydrogeochemical characteristics. The measured SO4 concentrations range widely from 7·7 to 942·0 mg/l, and exceed the Korean Drinking Water Standard (200 mg/l) in about half the samples. The TDS (total dissolved solid) content generally is high (171,1461 mg/l) from more shale-rich formations and also reflects varying degrees of water,rock interaction. The water is classified into three groups: Ca SO4 type (61% of the samples collected), Ca SO4 HCO3 type (15%) and Ca HCO3 type (24%). The Ca HCO3 type water (mean concentrations=369 mg/l Ca, 148 mg/l HCO3 and 23 mg/l SO4) reflected the simple reaction between CO2 -recharged water and calcite, whereas the more SO4 -rich nature of Ca SO4 type water (mean concentrations=153 mg/l Ca, 66 mg/l HCO3 and 416 mg/l SO4) reflected the oxidation of pyrite in sedimentary rocks and fracture zones. Pyrite oxidation resulted in precipitation of amorphous iron hydroxide locally within the tunnel as well as in high concentrations of Ca (mean 153 mg/l) and Na (mean 49 mg/l) for TSW, and is associated with calcite dissolution resulting in pH buffering. The pyrite oxidation required for the formation of Ca SO4 type water was enhanced by the diffusion of oxygenated air through the fractures related to the tunnel's construction. The subsequent outgassing of CO2 into the tunnel resulted in precipitation of iron-bearing carbonate. Copyright © 2001 John Wiley & Sons, Ltd. [source] Numerical simulation of the fracture process in cutting heterogeneous brittle materialINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2002H. Y. Liu Abstract The process of cutting homogeneous soft material has been investigated extensively. However, there are not so many studies on cutting heterogeneous brittle material. In this paper, R-T2D (Rock and Tool interaction), based on the rock failure process analysis model, is developed to simulate the fracture process in cutting heterogeneous brittle material. The simulated results reproduce the process involved in the fragmentation of rock or rock-like material under mechanical tools: the build-up of the stress field, the formation of the crushed zone, surface chipping, and the formation of the crater and subsurface cracks. Due to the inclusion of heterogeneity in the model, some new features in cutting brittle material are revealed. Firstly, macroscopic cracks sprout at the two edges of the cutter in a tensile mode. Then with the tensile cracks releasing the confining pressure, the rock in the initially high confining pressure zone is compressed into failure and the crushed zone gradually comes into being. The cracked zone near the crushed zone is always available, which makes the boundary of the crushed zone vague. Some cracks propagate to form chipping cracks and some dip into the rock to form subsurface cracks. The chipping cracks are mainly driven to propagate in a tensile mode or a mixed tensile and shear mode, following curvilinear paths, and finally intersect with the free surface to form chips. According to the simulated results, some qualitative and quantitative analyses are performed. It is found that the back rake angle of the cutter has an important effect on the cutting efficiency. Although the quantitative analysis needs more research work, it is not difficult to see the promise that the numerical method holds. It can be utilized to improve our understanding of tool,rock interaction and rock failure mechanisms under the action of mechanical tools, which, in turn, will be useful in assisting the design of fragmentation equipment and fragmentation operations. Copyright © 2002 John Wiley & Sons, Ltd. [source] Melt,wall rock interaction in the mantle shown by silicate melt inclusions in peridotite xenoliths from the central Pannonian Basin (western Hungary)ISLAND ARC, Issue 2 2009Csaba Szabó Abstract In this paper we present a detailed textural and geochemical study of two equigranular textured amphibole-bearing spinel lherzolite xenoliths from Szigliget, Bakony,Balaton Highland Volcanic Field (BBHVF, western Hungary) containing abundant primary silicate melt inclusions (SMIs) in clinopyroxene rims and secondary SMIs in orthopyroxene (and rarely spinel) along healed fractures. The SMIs are dominantly composed of silicate glass and CO2 -rich bubbles. Clinopyroxene and orthopyroxene are zoned in both studied xenoliths, especially with respect to Fe, Mg, Na, and Al contents. Cores of clinopyroxenes in both xenoliths show trace element distribution close to primitive mantle. Rims of clinopyroxenes are enriched in Th, U, light rare earth elements (LREEs) and medium REEs (MREEs). Amphiboles in the Szg08 xenolith exhibit elevated Rb, Ba, Nb, Ta, LREE, and MREE contents. The composition of silicate glass in the SMIs covers a wide range from the basaltic trachyandesite and andesite to phonolitic compositions. The glasses are particularly rich in P2O5. Both primary and secondary SMIs are strongly enriched in incompatible trace elements (mostly U, Th, La, Zr) and display a slight negative Hf anomaly. The development of zoned pyroxenes, as well as the entrapment of primary SMIs in the clinopyroxene rims, happened after partial melting and subsequent crystallization of clinopyroxenes, most probably due to an interaction between hot volatile-bearing evolved melt and mantle wall-rocks. This silicate melt filled microfractures in orthopyroxenes (and rarely spinels) resulting in secondary SMIs. [source] Zeolites in fissures of granites and gneisses of the Central AlpsJOURNAL OF METAMORPHIC GEOLOGY, Issue 8 2010T. WEISENBERGER Abstract Six different Ca-zeolite minerals are widespread in various assemblages in late fissures and fractures in granites and gneisses of the Swiss Alps. The zeolites formed as a result of water,rock interaction at relatively low temperatures (<250 °C) in the continental upper crust. The zeolites typically overgrow earlier minerals of the fissure assemblages, but zeolites also occur as monomineralic fissure fillings. They represent the youngest fissure minerals formed during uplift and exhumation of the Alpine orogen. A systematic study of zeolite samples showed that the majority of finds originate from three regions particularity rich in zeolite-bearing fissures: (i) in the central and eastern part of the Aar- and Gotthard Massifs; (2) Gibelsbach/Fiesch, in a fissure breccia located at the boundary of Aar Massif and Permian sedimentary rocks; and (3) in Penninic gneisses of the Simano nappe at Arvigo (Val Calanca). Rail and road tunnel construction across the Aar- and Gotthard Massif provided excellent data on zeolite frequency in Alpine fissures. It was found that 32% (Gotthard NEAT rail base tunnel, Amsteg section) and 18% (Gotthard road tunnel) of all studied fissures are filled with zeolites. The number of different zeolites is limited to six species: laumontite, stilbite and scolecite are abundant and common, whereas heulandite, chabazite and epistilbite occur occasionally. Calcium is the dominant extra-framework cation, with minor K and Na. Heulandite and chabazite contain Sr up to 29 and 10 mol.% extra-framework cations respectively. Na and K contents in zeolites tend to increase during growth as a result of changes in fluid composition and/or temperature. The K enrichment of stilbite found in surface outcrops compared to subsurface samples may indicate late stage cation exchange with surface water. Texture data, relative age sequences derived from fissure assemblages and equilibrium calculations show that the Ca-dominated zeolites precipitated from fluid with decreasing temperature in the order (old to young = hot to cold): scolecite, laumontite, heulandite, chabazite and stilbite. The necessary components for zeolite formation are derived from dissolving primary granite and gneiss minerals. The nature of these minerals depends, among other factors, on the metamorphic history of the host rock. Zeolites in the Aar Massif derived from the dissolution of epidote, secondary calcite and albite that were originally formed during Alpine greenschist metamorphism from primary granite and gneiss assemblages. Zeolite fissures occur in areas of H2O-dominated fluids. This is consistent with equilibrium calculations that predict a low CO2 tolerance of zeolite assemblages, particularly at low temperature. [source] Progress of actinolite-forming reactions in mafic schists during retrograde metamorphism: an example from the Sanbagawa metamorphic belt in central Shikoku, JapanJOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2005A. OKAMOTO Abstract Hydration reactions are direct evidence of fluid,rock interaction during regional metamorphism. In this study, hydration reactions to produce retrograde actinolite in mafic schists are investigated to evaluate the controlling factors on the reaction progress. Mafic schists in the Sanbagawa belt contain amphibole coexisting with epidote, chlorite, plagioclase and quartz. Amphibole typically shows two types of compositional zoning from core to rim: barroisite , hornblende , actinolite in the high-grade zone, and winchite , actinolite in the low-grade zone. Both types indicate that amphibole grew during the exhumation stage of the metamorphic belt. Microstructures of amphibole zoning and mass-balance relations suggest that: (1) the actinolite-forming reactions proceeded at the expense of the preexisting amphibole; and (2) the breakdown reaction of hornblende consumed more H2O fluid than that of winchite, when one mole of preexisting amphibole was reacted. Reaction progress is indicated by the volume fraction of actinolite to total amphibole, Yact, with the following details: (1) reaction proceeded homogeneously in each mafic layer; (2) the extent of the hornblende breakdown reaction is commonly low (Yact < 0.5), but it increases drastically in the high-grade part of the garnet zone (Yact,>,0.7); and (3) the extent of the winchite breakdown reaction is commonly high (Yact,>,0.7). Many microcracks are observed within hornblende, and the extent of hornblende breakdown reaction is correlated with the size reduction of the hornblende core. Brittle fracturing of hornblende may have enhanced retrograde reaction progress by increasing of influx of H2O and the surface area of hornblende. In contrast to high-grade rocks, the winchite breakdown reaction is well advanced in the low-grade rocks, where reaction progress is not associated with brittle fracturing of winchite. The high extent of the reaction in the low-grade rocks may be due to small size of winchite before the reaction. [source] Geochemical and stable isotope resetting in shear zones from Täschalp: constraints on fluid flow during exhumation in the Western AlpsJOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2003I. Cartwright Abstract Fluid flow at greenschist facies conditions during exhumation of the western Alps occurred in several penecontemporaneous systems, including shear zones at lithological contacts, deformed contacts between serpentinite bodies and metabasalts, albite veins within metabasalts, and calcite + quartz veins within calcareous schists. Fluid flow in shear zones that juxtapose metasediments and ophiolitic rocks within the Piemonte Unit reset O and H isotope ratios. ,18O values are buffered by the wall rocks; however, calculated fluid ,2H values are similar within all the shear zones suggesting that they formed an interconnected network. The similarity of ,2H values of the sheared rocks and those of unsheared calcareous schists suggests that the fluids were derived from, or had equilibrated with, the schists that envelop the ophiolite rocks. Time-integrated fluid fluxes at the sheared contacts estimated from changes in Si in metabasalts were up to 105 m3 m,2, with the fluid flowing up temperature driven either by topography or seismic pumping. Individual shear zones were active for c. 2,3 Myr, implying average fluid fluxes of up to 10,9 m3 m,2 s,1. Rocks in shear zones within the ophiolite away from contacts with the metasediments show much less marked isotopic and geochemical changes, implying that fluid volumes decreased into the ophiolite unit, consistent with the source of fluids being the metasediments. Fluids were generated by dehydration reactions that were intersected during exhumation and, while many rocks show the affects of fluid,rock interaction, large-scale fluid flow between major units was not common. [source] Distinguishing between seafloor alteration and fluid flow during subduction using stable isotope geochemistry: examples from Tethyan ophiolites in the Western AlpsJOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2000Miller Large amounts of fluid, bound up in the hydrated upper layers of the ocean crust, are consumed at convergent margins and released in subduction zones through devolatilization. The liberated fluids may play an integral role in subduction zone processes, including the generation of arc-magmas. However, exhumed subduction zone rocks often record little evidence of large-scale fluid flow, especially at deeper levels within the subduction zone. Basaltic pillows from the high-pressure Corsican and Zermatt-Saas ophiolites show a range of ,18O values that overall reflect seafloor alteration prior to subduction. However, comparison between the ,18O values of the cores and rims of the pillows suggests that the ,18O values of the pillow rims at least have been modified during subduction and high-pressure metamorphism. Pillows that have not undergone high-pressure metamorphism generally have rims with higher ,18O values than their cores, whereas the converse is the case in pillows that have undergone high-pressure metamorphism. This reversal in the core to rim oxygen isotope relationship between unmetamorphosed and metamorphosed pillows is strong evidence for fluid,rock interaction occurring during subduction and high-pressure metamorphism. However, the preservation of different ,18O values in the cores and rims of individual pillows and within and between different pillows suggests that fluid flow within the subduction zone was strongly channelled. Resetting of the ,18O values in the pillow rims was probably due to fluid-hosted diffusion that occurred over relatively short time-scales (<1 Myr). [source] Isotopic climate record in a Holocene stalagmite from Ursilor Cave (Romania)JOURNAL OF QUATERNARY SCIENCE, Issue 4 2002Bogdan Petroniu Onac Abstract The PU-2 stalagmite from Ursilor Cave provides the first dated Romanian isotope record for the Holocene. The overall growth rate of the speleothem was 3.5 cm kyr,1, corresponding to a temporal resolution of 142 y between each isotope analysis. The ,Hendy' tests indicate that isotopic equilibrium conditions occurred during the formation of PU-2, and hence that it is suitable for palaeoclimatic studies. The relationship between ,18O and temperature was found to be positive. This can be interpreted either as rain-out with distance from the west-northwest ocean source of evaporation or shifts in air mass source with changing North Atlantic Oscillation indices. Applying five U,Th thermal ionisation mass spectrometric (TIMS) dates to a 17.5 cm isotope profile (,18O and ,13C) along the stalagmite growth axis enabled a tentative interpretation of the palaeoclimate signal over the past 7.1 kyr. Spikes of depleted isotopic ,18O values are centred near ca. 7, ca. 5.2 and ca. 4 ka, reflecting cool conditions. The record shows two warm intervals between ca. 3.8 and ca. 3.2 ka (the maximum warmth) and from ca. 2 to ca. 1.4 ka, when the ,18O values were less negative than present. The ,Holocene Climate Optimum' spanning the time interval from ca. 6.8 to ca. 4.4 ka is not well expressed in the PU-2 stalagmite. Individual spikes of lighter ,13C are interpreted as indicative of periods of heavy rainfall, at ca. 7, ca. 5.5, and ca. 3.5 ka. The overall trend to lighter ,13C in the PU-2 stalagmite may reflect a gradual decrease in water,rock interaction. The results demonstrate that the effect of North Atlantic oceanic changes extended to the investigated area. Nevertheless, some differences in temporal correlation and intensity of stable isotopic response to these climatic events have been found, but the exact nature of these differences and the underlying mechanism is yet to be determined. Copyright © 2002 John Wiley & Sons, Ltd. [source] Chemical modification of pyroclastic rock by hot water: an experimental investigation of mass transport at the fluid,solid interfaceGEOFLUIDS (ELECTRONIC), Issue 1 2009J. HARA Abstract Hydrothermal water,(pyroclastic) rock interactions were examined using flow-through experiments to deduce the effect of mass transport phenomena on the reaction process. A series of experiments were conducted over the temperature range 75,250°C, with a constant temperature for each experiment, and at saturated vapour pressure, to estimate the apparent rate constants as a function of temperature. Based on the chemistry of analysed solutions, the water,rock interaction in the experiments was controlled by diffusion from the reaction surface and by the existence of a surface layer at the rock,fluid interface, which regulated the chemical reaction rate. The reaction progress depended to a high degree on flow velocity and temperature conditions, with element abundances in the fluid significantly affected by these factors. Mass transport coefficients for diffusion from the rock surface to the bulk solution have been estimated. Ca is selectively depleted under lower temperature conditions (T < 150°C), whereas Na is greatly depleted under higher temperature conditions (T > 150°C), and K reaction rates are increased when flow velocity increases. Using these conditions, specific alkali and alkali earth cations were selectively leached from mineral surfaces. The ,surface layer' comprised a 0.5,1.8 mm boundary film on the solution side (the thickness of this layer has no dependence on chemical character) and a reaction layer. The reaction layer was composed of a Si, Al-rich cation-leached layer, whose thickness was dependent on temperature, flow velocity and reaction length. The reaction layer varied in thickness from about 10,4 to 10,7 mm under high temperature/low fluid velocity and low temperature/high fluid velocity conditions, respectively. [source] Geochemistry of the Bagnères-de-Bigorre thermal waters from the North Pyrenean Zone (France)GEOFLUIDS (ELECTRONIC), Issue 1 2002S. Levet Abstract Thermal springs are poorly known in the sedimentary sites of the Pyrenees. In this paper, we describe the ,Bagnères-de-Bigorre' springs which occur in a remarkably active seismotectonic context. A chemical and isotopic study of 15 spring waters (both cold and thermal, ranging in temperature from 7.0 to 49.9°C), and continuous monitoring of a single spring allow us to characterise water,rock interactions, fluids paths and mixing processes. Three groups of waters are distinguished: (I) SO42+,Ca2+,Cl, thermal waters (II) SO42+,Cl,,Ca2+ thermal waters and (III) HCO3,,Ca2+ cold shallow waters. Their characteristics suggest interactions with Mesozoic evaporite and carbonate formations. O and D isotopes from thermal waters indicate a local meteoric origin of Atlantic signature and a recharge elevation of 800 to 1000 m, which corresponds to a single feeding area. Their ,13C values (,2.8 to ,9.6,) are consistent with carbonate dissolution, slight fractionation and a surficial organic input leading to ,13C depletion. Sr isotopes (0.70751 to 0.70777), Na+/Cl, and (Ca2+ + Mg2+)/SO42, ratios as well as thermodynamic calculations show that the dissolution of anhydrite and halite-bearing Triassic layers control the chemical composition of group-I and -II waters. The contrasting trends of cation/Cl, ratios and TDS of waters from groups I and II suggest the existence of two different circulation paths at depth as well as dilution with surficial waters similar to group III. Calculated mixing proportions show that three waters from group I are diluted from 17 to 66%, whereas all waters from group II are mixed. The aquifer temperature is estimated to be in the range 55,64°C using the retrograde and prograde solubilities of anhydrite and chalcedony, respectively. Accordingly, the mean depth of the reservoir is around 1.7 km, which allows us to constrain the depth of the Triassic layer. [source] Geochemical constraints of the eclogite and granulite facies metamorphism as recognized in the Raobazhai complex from North Dabie Shan, ChinaJOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2001Y. L. Xiao Abstract A combined study of major and trace elements, fluid inclusions and oxygen isotopes has been carried out on garnet pyroxenite from the Raobazhai complex in the North Dabie Terrane (NDT). Well-preserved compositional zoning with Na decreasing and Ca and Mg increasing from the core to rim of pyroxene in the garnet pyroxenite indicates eclogite facies metamorphism at the peak metamorphic stage and subsequent granulite facies metamorphism during uplift. A P,T path with substantial heating (from c. 750 to 900 °C) after the maximum pressure reveals a different uplift history compared with most other eclogites in the South Dabie Terrane (SDT). Fluid inclusion data can be correlated with the metamorphic grade: the fluid regime during the peak metamorphism (eclogite facies) was dominated by N2 -bearing NaCl-rich solutions, whereas it changed into CO2 -dominated fluids during the granulite facies retrograde metamorphism. At a late retrograde metamorphic stage, probably after amphibolite facies metamorphism, some external low-salinity fluids were involved. In situ UV-laser oxygen isotope analysis was undertaken on a 7 mm garnet, and impure pyroxene, amphibole and plagioclase. The nearly homogeneous oxygen isotopic composition (,18OVSMOW = c. 6.7,) in the garnet porphyroblast indicates closed fluid system conditions during garnet growth. However, isotopic fractionations between retrograde phases (amphibole and plagioclase) and garnet show an oxygen isotopic disequilibrium, indicating retrograde fluid,rock interactions. Unusual MORB-like rare earth element (REE) patterns for whole rock of the garnet pyroxenite contrast with most ultra-high-pressure (UHP) eclogites in the Dabie-Sulu area. However, the age-corrected initial ,Nd(t) is ,,2.9, which indicates that the protolith of the garnet pyroxenite was derived from an enriched mantle rather than from a MORB source. Combined with the present data of oxygen isotopic compositions and the characteristic N2 content in the fluid inclusions, we suggest that the protolith of the garnet pyroxenite from Raobazhai formed in an enriched mantle fragment, which has been exposed to the surface prior to the Triassic metamorphism. [source] 3D seismic technology: the geological ,Hubble'BASIN RESEARCH, Issue 1 2005Joe Cartwright The proliferation of three-dimensional (3D) seismic technology is one of the most exciting developments in the Earth Sciences over the past century. 3D reflection seismic data provide interpreters with the ability to map structures and stratigraphic features in 3D detail to a resolution of a few tens of metres over thousands of square kilometres. It is a geological ,Hubble', whose resolving power has already yielded some fascinating (and surprising) insights and will continue to provide a major stimulus for research into geological processes and products for many decades to come. Academic and other research institutions have a major role to play in the use of this data by exploiting the enormous volume of geological information contained in 3D seismic surveys. This paper reviews some of the recent advances in basin analysis made using the medium of 3D seismic data, focusing on the fields of structural and sedimentary geology, fluid,rock interactions and igneous geology. It is noted that the increased resolution of the 3D seismic method provided the essential catalyst necessary to stimulate novel observations and discover new geological structures such as mud diapir feeders, km-long gas blow-out pipes, giant pockmarks and sandstone intrusions, and to capture the spatial variability of diagenetic fronts. The UKs first impact crater was also discovered using 3D seismic data. The potential for future developments in this field of geophysical interpretation is considerable, and we anticipate that new discoveries will be made in many years to come. [source] | |||||||||||||