Masses of Fluid for Cylindrical Tanks in Rock With Partial Uplift of Bottom Plate

PubMed Central

Taniguchi, Tomoyo; Katayama, Yukihiro

2016-01-01

This study proposes the use of a slice model consisting of a set of thin rectangular tanks for evaluating the masses of fluid contributing to the rocking motion of cylindrical tanks; the effective mass of fluid for rocking motion, that for rocking–bulging interaction, effective moment inertia of fluid for rocking motion and its centroid. They are mathematically or numerically quantified, normalized, tabulated, and depicted as functions of the aspect of tanks for different values of the ratio of the uplift width of the tank bottom plate to the diameter of tank for the designer's convenience. PMID:27303110

Evaluation of CO 2 -Fluid-Rock Interaction in Enhanced Geothermal Systems: Field-Scale Geochemical Simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pan, Feng; McPherson, Brian J.; Kaszuba, John

Recent studies suggest that using supercritical CO 2 (scCO 2 ) instead of water as a heat transmission fluid in Enhanced Geothermal Systems (EGS) may improve energy extraction. While CO 2 -fluid-rock interactions at “typical” temperatures and pressures of subsurface reservoirs are fairly well known, such understanding for the elevated conditions of EGS is relatively unresolved. Geochemical impacts of CO 2 as a working fluid (“CO 2 -EGS”) compared to those for water as a working fluid (H 2 O-EGS) are needed. The primary objectives of this study are (1) constraining geochemical processes associated with CO 2 -fluid-rock interactions undermore » the high pressures and temperatures of a typical CO 2 -EGS site and (2) comparing geochemical impacts of CO 2 -EGS to geochemical impacts of H 2 O-EGS. The St. John’s Dome CO 2 -EGS research site in Arizona was adopted as a case study. A 3D model of the site was developed. Net heat extraction and mass flow production rates for CO 2 -EGS were larger compared to H 2 O-EGS, suggesting that using scCO 2 as a working fluid may enhance EGS heat extraction. More aqueous CO 2 accumulates within upper- and lower-lying layers than in the injection/production layers, reducing pH values and leading to increased dissolution and precipitation of minerals in those upper and lower layers. Dissolution of oligoclase for water as a working fluid shows smaller magnitude in rates and different distributions in profile than those for scCO 2 as a working fluid. It indicates that geochemical processes of scCO 2 -rock interaction have significant effects on mineral dissolution and precipitation in magnitudes and distributions.« less

Evaluation of CO 2 -Fluid-Rock Interaction in Enhanced Geothermal Systems: Field-Scale Geochemical Simulations

DOE PAGES

Pan, Feng; McPherson, Brian J.; Kaszuba, John

2017-01-01

Recent studies suggest that using supercritical CO 2 (scCO 2 ) instead of water as a heat transmission fluid in Enhanced Geothermal Systems (EGS) may improve energy extraction. While CO 2 -fluid-rock interactions at “typical” temperatures and pressures of subsurface reservoirs are fairly well known, such understanding for the elevated conditions of EGS is relatively unresolved. Geochemical impacts of CO 2 as a working fluid (“CO 2 -EGS”) compared to those for water as a working fluid (H 2 O-EGS) are needed. The primary objectives of this study are (1) constraining geochemical processes associated with CO 2 -fluid-rock interactions undermore » the high pressures and temperatures of a typical CO 2 -EGS site and (2) comparing geochemical impacts of CO 2 -EGS to geochemical impacts of H 2 O-EGS. The St. John’s Dome CO 2 -EGS research site in Arizona was adopted as a case study. A 3D model of the site was developed. Net heat extraction and mass flow production rates for CO 2 -EGS were larger compared to H 2 O-EGS, suggesting that using scCO 2 as a working fluid may enhance EGS heat extraction. More aqueous CO 2 accumulates within upper- and lower-lying layers than in the injection/production layers, reducing pH values and leading to increased dissolution and precipitation of minerals in those upper and lower layers. Dissolution of oligoclase for water as a working fluid shows smaller magnitude in rates and different distributions in profile than those for scCO 2 as a working fluid. It indicates that geochemical processes of scCO 2 -rock interaction have significant effects on mineral dissolution and precipitation in magnitudes and distributions.« less

Linking Serpentinite Geochemistry with Possible Alteration and Evolution of Supra-Subduction Wedge Mantle

NASA Astrophysics Data System (ADS)

Scambelluri, M.; Cannaò, E.; Agostini, S.; Gilio, M.

2016-12-01

Serpentinites are able to transport and release volatiles and fluid-mobile elements (FME) found in arc magmas. Constraining the trace element compositions of these rocks and of fluids released by de-serpentinization improves our knowledge of mass transfer from subduction zones to volcanic arcs, and of the role of slab and wedge mantle in this global process. Studies of high-pressure ultramafic rocks exhumed from plate interface settings reveal the fluid/rock interactions atop the slab and the processes that can affect the mantle wedge. Alpine eclogite-facies antigorite serpentinite (Voltri Massif) and fully de-serpentinized meta-peridotite (Cima di Gagnone) are enriched in sediment-derived As, Sb, U, Pb before peak dehydration. Their Sr, Pb and B isotopic compositions are reset during prograde (forearc) interaction with slab fluids. The eclogitic garnet and olivine from the Cima di Gagnone metaperidotite trap primary inclusions of the fluid released during breakdown of antigorite and chlorite. The inclusions display FME enrichments (high Cl, S; variable Cs, Rb, Ba, B, Pb, As, Sb) indicating element release from rocks to fluids during dehydration under subarc conditions. Our studies show that serpentinized mantle rocks from subduction zones sequester FME from slab fluids and convey these components and radiogenic isotopes into the mantle wedge upon dehydration. The geochemical processes revealed by such plate-interface rocks can apply to the supra-subduction mantle. Shallow element release from slabs to mantle wedge, downdrag of this altered mantle and its subsequent (subarc) dehydration transfers crust-derived FMEs to the arc magma sources without the need of concomitant subarc dehydration/melting of metasedimentary slab components. The slab signature detected in arc lavas can thus result from geochemical mixing of sediment, oceanic crust and ultramafic reservoirs into altered wedge-mantle rocks, rather than being attributed to multiple fluids.

Chlorine isotope constraints on fluid-rock interactions during subduction and exhumation of the Zermatt-Saas ophiolite

NASA Astrophysics Data System (ADS)

Selverstone, J.; Sharp, Z. D.

2013-10-01

Chlorine isotope compositions of high-pressure (˜2.3 GPa) serpentinite, rodingite, and hydrothermally altered oceanic crust (AOC) differ significantly from high- and ultrahigh-pressure (> 3.2 GPa) metasedimentary rocks in the Aosta region, Italy. Texturally early serpentinites, rodingites, and AOC have bulk δ37Cl values indistinguishable from those of modern seafloor analogues (δ37Cl = -1.0 to +1.0‰). In contrast, serpentinites and AOC samples that recrystallized during exhumation have low δ37Cl values (-2.7 to -0.5‰); 37Cl depletion correlates with progressive changes in bulk chemistry. HP/UHP metasediments have low δ37Cl values (median = -2.5‰) that differ statistically from modern marine sediments (median = -0.6‰). Cl in metasedimentary rocks is concentrated in texturally early minerals, indicating modification of seafloor compositions early in the subduction history. The data constrain fluid sources during both subduction and exhumation-related phases of fluid-rock interaction: (1) marine sediments at the top of the downgoing plate likely interacted with isotopically light pore fluids from the accretionary wedge in the early stages of subduction. (2) No pervasive interaction with externally derived fluid occurred during subsequent subduction to the maximum depths of burial. (3) Localized mixing between serpentinites and fluids released by previously isotopically modified metasediments occurred during exhumation in the subduction channel. Most samples, however, preserved protolith signatures during subduction to near-arc depths.

Thermodynamic modeling of non-ideal mineral-fluid equilibria in the system Si-Al-Fe-Mg-Ca-Na-K-H-O-Cl at elevated temperatures and pressures: Implications for hydrothermal mass transfer in granitic rocks

NASA Astrophysics Data System (ADS)

Dolejš, David; Wagner, Thomas

2008-01-01

We present the results of thermodynamic modeling of fluid-rock interaction in the system Si-Al-Fe-Mg-Ca-Na-H-O-Cl using the GEM-Selektor Gibbs free energy minimization code. Combination of non-ideal mixing properties in solids with multicomponent aqueous fluids represents a substantial improvement and it provides increased accuracy over existing modeling strategies. Application to the 10-component system allows us to link fluid composition and speciation with whole-rock mineralogy, mass and volume changes. We have simulated granite-fluid interaction over a wide range of conditions (200-600 °C, 100 MPa, 0-5 m Cl and fluid/rock ratios of 10-2-104) in order to explore composition of magmatic fluids of variable salinity, temperature effects on fluid composition and speciation and to simulate several paths of alteration zoning. At low fluid/rock ratios (f/r) the fluid composition is buffered by the silicate-oxide assemblage and remains close to invariant. This behavior extends to a f/r of 0.1 which exceeds the amount of exsolved magmatic fluids controlled by water solubility in silicate melts. With increasing peraluminosity of the parental granite, the Na-, K- and Fe-bearing fluids become more acidic and the oxidation state increases as a consequence of hydrogen and ferrous iron transfer to the fluid. With decreasing temperature, saline fluids become more Ca- and Na-rich, change from weakly acidic to alkaline, and become significantly more oxidizing. Large variations in Ca/Fe and Ca/Mg ratios in the fluid are a potential geothermometer. The mineral assemblage changes from cordierite-biotite granites through two-mica granites to chlorite-, epidote- and zeolite-bearing rocks. We have carried out three rock-titration simulations: (1) reaction with the 2 m NaCl fluid leads to albitization, chloritization and desilication, reproducing essential features observed in episyenites, (2) infiltration of a high-temperature fluid into the granite at 400 °C leads to hydrolytic alteration commencing with alkali-feldspar breakdown and leading to potassic, phyllic and argillic assemblages; this is associated with reduction and iron metasomatism as observed in nature and (3) interaction with a multicomponent fluid at 600 °C produces sodic-calcic metasomatism. Na, Ca and Fe are the most mobile elements whereas immobility of Al is limited by f/r ∼ 400. All simulations predict a volume decrease by 3.4-5.4%, i.e., porosity formation at f/r < 30. At higher fluid/rock ratios simulation (2) produces a substantial volume increase (59%) due to mineral precipitation, whereas simulation (3) predicts a volume decrease by 49% at the advanced albitization-desilication stage. Volume changes closely correlate with mass changes of SiO2 and are related to silica solubility in fluids. The combined effects of oxygen fugacity, fluid acidity and pH for breakdown of aqueous metal complexes and precipitation of ore minerals were evaluated by means of reduced activity products. Sharp increases in saturation indexes for oxidative breakdown occur at each alteration zone whereas reductive breakdown or involvement of other chloride complexes favor precipitation at high fluid/rock ratios only. Calculations of multicomponent aqueous-solid equilibria at high temperatures and pressures are able to accurately predict rock mineralogy and fluid chemistry and are applicable to diverse reactive flow processes in the Earth's crust.

Processes of high-T fluid-rock interaction during gold mineralization in carbonate-bearing metasediments: the Navachab gold deposit, Namibia

NASA Astrophysics Data System (ADS)

Dziggel, A.; Wulff, K.; Kolb, J.; Meyer, F. M.

2009-08-01

The Navachab gold deposit in the Damara belt of central Namibia is hosted by a near-vertical sequence of amphibolite facies shelf-type metasediments, including marble, calc-silicate rock, and biotite schist. Petrologic and geochemical data were collected in the ore, alteration halos, and the wall rock to evaluate transport of elements and interaction between the wall rock and the mineralizing fluid. The semi-massive sulfide lenses and quartz-sulfide veins are characterized by a complex polymetallic ore assemblage, comprising pyrrhotite, chalcopyrite, sphalerite, and arsenopyrite, native bismuth, gold, bismuthinite, and bismuth tellurides. Mass balance calculations indicate the addition of up to several orders of magnitude of Au, Bi, As, Ag, and Cu. The mineralized zones also record up to eightfold higher Mn and Fe concentrations. The semi-massive sulfide lenses are situated in the banded calc-silicate rock. Petrologic and textural data indicate that they represent hydraulic breccias that contain up to 50 vol.% ore minerals, and that are dominated by a high-temperature (T) alteration assemblage of garnet-clinopyroxene-K-feldspar-quartz. The quartz-sulfide veins crosscut all lithological units. Their thickness and mineralogy is strongly controlled by the composition and rheological behavior of the wall rocks. In the biotite schist and calc-silicate rock, they are up to several decimeters thick and quartz-rich, whereas in the marble, the same veins are only a few millimeters thick and dominated by sulfides. The associated alteration halos comprise (1) an actinolite-quartz alteration in the biotite schist, (2) a garnet-clinopyroxene-K-feldspar-quartz alteration in the marble and calc-silicate rock, and (3) a garnet-biotite alteration that is recorded in all rock types except the marble. The hydrothermal overprint was associated with large-scale carbonate dissolution and a dramatic increase in CO2 in the ore fluid. Decarbonation of wall rocks, as well as a low REE content of the ore fluid resulted in the mobilization of the REE, and the decoupling of the LREE from the HREE. The alteration halos not only parallel the mineralized zones, but may also follow up single layers away from the mineralization. Alteration is far more pronounced facing upward, indicating that the rocks were steep when veining occurred. The petrologic and geochemical data indicate that the actinolite-quartz- and garnet-clinopyroxene-K-feldspar-quartz alterations formed in equilibrium with a fluid (super-) saturated in Si, and were mainly controlled by the composition of the wall rocks. In contrast, the garnet-biotite alteration formed by interaction with a fluid undersaturated in Si, and was mainly controlled by the fluid composition. This points to major differences in fluid-rock ratios and changes in fluid composition during alteration. The alteration systematics and geometry of the hydrothermal vein system are consistent with cyclic fluctuations in fluid pressure during fault valve action.

GaMin’11 – an international inter-laboratory comparison for geochemical CO₂ - saline fluid - mineral interaction experiments

DOE PAGES

Ostertag-Henning, C.; Risse, A.; Thomas, B.; ...

2014-12-31

Due to the strong interest in geochemical CO₂-fluid-rock interaction in the context of geological storage of CO₂ a growing number of research groups have used a variety of different experimental ways to identify important geochemical dissolution or precipitation reactions and – if possible – quantify the rates and extent of mineral or rock alteration. In this inter-laboratory comparison the gas-fluid-mineral reactions of three samples of rock-forming minerals have been investigated by 11 experimental labs. The reported results point to robust identification of the major processes in the experiments by most groups. The dissolution rates derived from the changes in compositionmore » of the aqueous phase are consistent overall, but the variation could be reduced by using similar corrections for changing parameters in the reaction cells over time. The comparison of experimental setups and procedures as well as of data corrections identified potential improvements for future gas-fluid-rock studies.« less

Fast intraslab fluid-flow events linked to pulses of high pore fluid pressure at the subducted plate interface

NASA Astrophysics Data System (ADS)

Taetz, Stephan; John, Timm; Bröcker, Michael; Spandler, Carl; Stracke, Andreas

2018-01-01

A better understanding of the subduction zone fluid cycle and its chemical-mechanical feedback requires in-depth knowledge about how fluids flow within and out of descending slabs. Relicts of fluid-flow systems in exhumed rocks of fossil subduction zones allow for identification of the general relationships between dehydration reactions, fluid pathway formation, the dimensions and timescales of distinct fluid flow events; all of which are required for quantitative models for fluid-induced subduction zone processes. Two types of garnet-quartz-phengite veins can be distinguished in an eclogite-facies mélange block from the Pouébo Eclogite Mélange, New Caledonia. These veins record synmetamorphic internal fluid release by mineral breakdown reactions (type I veins), and infiltration of an external fluid (type II veins) with the associated formation of a reaction selvage. The dehydration and fluid migration documented by the type I veins likely occurred on a timescale of 105-106 years, based on average subduction rates and metamorphic conditions required for mineral dehydration and fluid flow. The timeframe of fluid-rock interaction between the external fluid and the wall-rock of the type II veins is quantified using a continuous bulk-rock Li-diffusion profile perpendicular to a vein and its metasomatic selvage. Differences in Li concentration between the internal and external fluid reservoirs resulted in a distinct diffusion profile (decreasing Li concentration and increasing δ7 Li) as the reaction front propagated into the host rock. Li-chronometric constraints indicate that the timescales of fluid-rock interaction associated with type II vein formation are on the order of 1 to 4 months (0.150-0.08+0.14 years). The short-lived, pulse-like character of this process is consistent with the notion that fluid flow caused by oceanic crust dehydration at the blueschist-to-eclogite transition contributes to or even dominates episodic pore fluid pressure increases at the plate interface, which in turn, may trigger slip events reported from many subduction zones.

European and Middle-East ferroan hydrothermal dolomites: lessons learnt with respect to crustal dynamics, fluid circulations and rock-fluid interactions

NASA Astrophysics Data System (ADS)

Nader, Fadi Henri; Gasparrini, Marta; Bachaud, Pierre

2016-04-01

Classical case studies of hydrothermal dolostones, which are known worldwide to provide excellent reservoirs for ores and hydrocarbons, often illustrate the presence of iron-rich dolomite phases. The world-class hydrothermal dolostones from the Basque-Cantabrian Basin (Northern Spain) exemplify the initiation of high temperature dolomitization (at about 200°C), with significant amount of ferroan dolomite phases (including up to 2% FeO). These dolomites are believed to be responsible for the pervasive replacement of the original limestone rocks - they are followed by non-ferroan dolomite phases. The associated fluids are supposed to have interacted with basement rocks, and travelled from deep-seated sources along major fault pathways. The geochemical traits of such fluids are also typically similar to, and probably associated with, mineralization fluids (e.g. Pb-Zn, MVT). In the Middle East, several observed dolostones show, on the contrary, a later phase of ferroan dolomite cements which occlude the inter-crystalline porosity of earlier non-ferroan matrix dolomites. Dolomitization occurred under increasingly higher temperatures (from 50 to 100°C) during burial. Here, the origin of iron-rich fluids and conditions of precipitation of associated dolomites do not necessarily involve interactions with basement rocks, but rather a relative Fe-enrichment with further reducing settings. Based on previous research projects concerning a variety of dolostones from Europe and the Middle-East, this contribution presents observational, analytical and computational results focused on ferroan dolomites. Recent numerical geochemical modelling emphasized the physico-chemical pre-requisites for crystallizing ferroan rather than non-ferroan dolomites (and vice-versa), allowing better understanding of related diagenetic processes. Besides, important larger-scale information on the crustal fluid circulations are demonstrated to be intimately associated to the parent-fluids sources and the conditions of mineral precipitation. By adopting this approach, ferroan dolomites are no longer considered simply as accessory diagenetic phases. They rather provide significant clues for understanding crustal dynamics and the impacts of evolving rock-fluid interactions on carbonate reservoir properties which are essential for ore and hydrocarbon exploitation, and for underground storage and gas sequestration.

Effect of Hydrothermal Alteration on Rock Properties in Active Geothermal Setting

NASA Astrophysics Data System (ADS)

Mikisek, P.; Bignall, G.; Sepulveda, F.; Sass, I.

2012-04-01

Hydrothermal alteration records the physical-chemical changes of rock and mineral phases caused by the interaction of hot fluids and wall rock, which can impact effective permeability, porosity, thermal parameters, rock strength and other rock properties. In this project, an experimental approach has been used to investigate the effects of hydrothermal alteration on rock properties. A rock property database of contrastingly altered rock types and intensities has been established. The database details horizontal and vertical permeability, porosity, density, thermal conductivity and thermal heat capacity for ~300 drill core samples from wells THM12, THM13, THM14, THM17, THM18, THM22 and TH18 in the Wairakei-Tauhara geothermal system (New Zealand), which has been compared with observed hydrothermal alteration type, rank and intensity obtained from XRD analysis and optical microscopy. Samples were selected from clay-altered tuff and intercalated siltstones of the Huka Falls Formation, which acts as a cap rock at Wairakei-Tauhara, and tuffaceous sandstones of the Waiora Formation, which is a primary reservoir-hosting unit for lateral and vertical fluid flows in the geothermal system. The Huka Falls Formation exhibits argillic-type alteration of varying intensity, while underlying Waiora Formations exhibits argillic- and propylithic-type alteration. We plan to use a tempered triaxial test cell at hydrothermal temperatures (up to 200°C) and pressures typical of geothermal conditions, to simulate hot (thermal) fluid percolation through the rock matrix of an inferred "reservoir". Compressibility data will be obtained under a range of operating (simulation reservoir) conditions, in a series of multiple week to month-long experiments that will monitor change in permeability and rock strength accompanying advancing hydrothermal alteration intensity caused by the hot brine interacting with the rock matrix. We suggest, our work will provide new baseline information concerning fluid-rock interaction processes in geothermal reservoirs, and their effects on rock properties, that will aid improved understanding of the evolution of high-temperature geothermal systems, provide constraints to parameterization of reservoir models and assist future well planning and design through prediction of rock properties in the context of drilling strategies.

Noble gases fingerprint a metasedimentary fluid source in the Macraes orogenic gold deposit, New Zealand

NASA Astrophysics Data System (ADS)

Goodwin, Nicholas R. J.; Burgess, Ray; Craw, Dave; Teagle, Damon A. H.; Ballentine, Chris J.

2017-02-01

The world-class Macraes orogenic gold deposit (˜10 Moz resource) formed during the late metamorphic uplift of a metasedimentary schist belt in southern New Zealand. Mineralising fluids, metals and metalloids were derived from within the metasedimentary host. Helium and argon extracted from fluid inclusions in sulphide mineral grains (three crush extractions from one sample) have crustal signatures, with no evidence for mantle input (R/Ra = 0.03). Xenon extracted from mineralised quartz samples provides evidence for extensive interaction between fluid and maturing organic material within the metasedimentary host rocks, with 132Xe/36Ar ratios up to 200 times greater than air. Similarly, I/Cl ratios for fluids extracted from mineralised quartz are similar to those of brines from marine sediments that have interacted with organic matter and are ten times higher than typical magmatic/mantle fluids. The Macraes mineralising fluids were compositionally variable, reflecting either mixing of two different crustal fluids in the metasedimentary pile or a single fluid type that has had varying degrees of interaction with the host metasediments. Evidence for additional input of meteoric water is equivocal, but minor meteoric incursion cannot be discounted. The Macraes deposit formed in a metasedimentary belt without associated coeval magmatism, and therefore represents a purely crustal metamorphogenic end member in a spectrum of orogenic hydrothermal processes that can include magmatic and/or mantle fluid input elsewhere in the world. There is no evidence for involvement of minor intercalated metabasic rocks in the Macraes mineralising system. Hydrothermal fluids that formed other, smaller, orogenic deposits in the same metamorphic belt have less pronounced noble gas and halogen evidence for crustal fluid-rock interaction than at Macraes, but these deposits also formed from broadly similar metamorphogenic processes.

Fluid-rock interaction during a large earthquake recorded in fault gouge: A case study of the Nojima fault, Japan

NASA Astrophysics Data System (ADS)

Bian, D.; Lin, A.

2016-12-01

Distinguishing the seismic ruptures during the earthquake from a lot of fractures in borehole core is very important to understand rupture processes and seismic efficiency. In particular, a great earthquake like the 1995 Mw 7.2 Kobe earthquake, but again, evidence has been limited to the grain size analysis and the color of fault gouge. In the past two decades, increasing geological evidence has emerged that seismic faults and shear zones within the middle to upper crust play a crucial role in controlling the architectures of crustal fluid migration. Rock-fluid interactions along seismogenic faults give us a chance to find the seismic ruptures from the same event. Recently, a new project of "Drilling into Fault Damage Zone" has being conducted by Kyoto University on the Nojima Fault again after 20 years of the 1995 Kobe earthquake for an integrated multidisciplinary study on the assessment of activity of active faults involving active tectonics, geochemistry and geochronology of active fault zones. In this work, we report on the signature of slip plane inside the Nojima Fault associated with individual earthquakes on the basis of trace element and isotope analyses. Trace element concentrations and 87Sr/86Sr ratios of fault gouge and host rocks were determined by an inductively coupled plasma mass spectrometer (ICP-MS) and thermal ionization mass spectrometry (TIMS). Samples were collected from two trenches and an outcrop of Nojima Fault which. Based on the geochemical result, we interpret these geochemical results in terms of fluid-rock interactions recorded in fault friction during earthquake. The trace-element enrichment pattern of the slip plane can be explained by fluid-rock interactions at high temperature. It also can help us find the main coseismic fault slipping plane inside the thick fault gouge zone.

Sedimentary basin geochemistry and fluid/rock interactions workshop

DOE Office of Scientific and Technical Information (OSTI.GOV)

NONE

1991-12-31

Fundamental research related to organic geochemistry, fluid-rock interactions, and the processes by which fluids migrate through basins has long been a part of the U.S. Department of Energy Geosciences program. Objectives of this program were to emphasize those principles and processes which would be applicable to a wide range of problems associated with petroleum discovery, occurrence and extraction, waste disposal of all kinds, and environmental management. To gain a better understanding of the progress being made in understanding basinal fluids, their geochemistry and movement, and related research, and to enhance communication and interaction between principal investigators and DOE and othermore » Federal program managers interested in this topic, this workshop was organized by the School of Geology and Geophysics and held in Norman, Oklahoma in November, 1991.« less

Chlorine Isotope Evidence for Syn-Subduction Modification of Serpentinites by Interaction with Sediment-Derived Fluid

NASA Astrophysics Data System (ADS)

Selverstone, J.; Sharp, Z. D.

2012-12-01

High-pressure serpentinites and rodingites and high- to ultrahigh-pressure metasedimentary rocks from the Aosta region, Italy, preserve strikingly different chlorine isotope compositions that can be used to constrain the nature of fluid-rock interactions during subduction. Serpentinites and rodingitized gabbroic dikes subducted to 70-80 km have bulk δ37Cl values between -1.6 and +0.9‰ (median= -0.5‰, n=26 plus 5 replicates; one amphibole-vein outlier at -2.9‰). Serpentinite δ37Cl values are positively correlated with Cr ± Cl contents (r2= 0.97 and 0.58) and negatively correlated with CaO (r2=0.72). BSE imaging and X-ray mapping reveal up to three generations of compositionally distinct serpentine and chlorite in single samples. The youngest generation, which is most abundant, has the lowest chlorine content. Three rodingite samples contain abundant texturally early fluid inclusions. These samples were finely crushed and leached in 18 MΩ H2O to extract water-soluble chlorides. The leachates, which are assumed to record the compositions of the fluid inclusions, have δ37Cl values that are 0.7-1.5‰ lower than the corresponding bulk rock values. Leachate from the outlier amph-magnesite vein is indistinguishable from the bulk value at -2.7‰. There is almost no overlap between the Cl isotope compositions of HP serp/rod samples and associated HP/UHP metasedimentary rocks. Calcmica schists, diamond-bearing Mn nodules, and impure marbles subducted to >130 km and calcmica schists and Mn crusts transported to 70-80 km have δ37Cl values between -4.5 and -1.5‰ (median= -2.7‰, n=25 plus 7 replicates; two outlier points at -0.5‰). Primary fluid inclusions in the diamondiferous samples contain carbonate- and silicate-bearing aqueous fluids with very low chloride contents (Frezzotti et al., 2011, Nature Geosci). Taken together, these data record a history of progressive modification of serpentinites and rodingites by mixing with low-δ37Cl, low-Cl, high-Ca fluids during subduction and metamorphism. Serpentinites with the highest Cr contents have Cl isotopic compositions identical to those of modern seafloor serpentinites (δ37Cl=0.2-0.6‰), consistent with primary serpentinization by seawater (e.g., Barnes et al. 2009, Lithos). Low-Cr serpentinites record significant interaction with a Ca-rich fluid that shifted the rocks to lower δ37Cl values and diluted the original Cr and Cl contents. The fluid was likely derived from continuous devolatilization reactions in associated low-δ37Cl, calcareous metasedimentary rocks. These data have important implications for models of subduction mass transfer associated with antigorite breakdown. If serpentinites are commonly modified by interaction with metasedimentary fluids prior to antigorite dehydration, chemical signatures imparted during deserpentinization will reflect the integrated history of fluid-rock interaction in the subduction channel rather than an endmember "serpentinite signature". The data further suggest that Cl may be hydrophobic in HP/UHP carbonate-bearing aqueous fluids, resulting in generation of low-Cl fluid during metamorphic devolatilization.

Fully Coupled 3D Finite Element Model of Hydraulic Fracturing in a Permeable Rock Formation

NASA Astrophysics Data System (ADS)

Salimzadeh, S.; Paluszny, A.; Zimmerman, R. W.

2015-12-01

Hydraulic fracturing in permeable rock formations is a complex three-dimensional multi-physics phenomenon. Numerous analytical models of hydraulic fracturing processes have been proposed that typically simplify the physical processes, or somehow reduce the problem from three dimensions to two dimensions. Moreover, although such simplified models are able to model the growth of a single hydraulic fracture into an initially intact, homogeneous rock mass, they are generally not able to model fracturing of heterogeneous rock formations, or to account for interactions between multiple induced fractures, or between an induced fracture and pre-existing natural fractures. We have developed a numerical finite-element model for hydraulic fracturing that does not suffer from any of the limitations mentioned above. The model accounts for fluid flow within a fracture, the propagation of the fracture, and the leak-off of fluid from the fracture into the host rock. Fluid flow through the permeable rock matrix is modelled using Darcy's law, and is coupled with the laminar flow within the fracture. Fractures are discretely modelled in the three-dimensional mesh. Growth of a fracture is modelled using the concepts of linear elastic fracture mechanics (LEFM), with the onset and direction of growth based on stress intensity factors that are computed for arbitrary tetrahedral meshes. The model has been verified against several analytical solutions available in the literature for plane-strain (2D) and penny-shaped (3D) fractures, for various regimes of domination: viscosity, toughness, storage and leak-off. The interaction of the hydraulically driven fracture with pre-existing fractures and other fluid-driven fractures in terms of fluid leak-off, stress interaction and fracture arrest is investigated and the results are presented. Finally, some preliminary results are presented regarding the interaction of a hydraulically-induced fracture with a set of pre-existing natural fractures.

Geophysical aspects of underground fluid dynamics and mineral transformation process

NASA Astrophysics Data System (ADS)

Khramchenkov, Maxim; Khramchenkov, Eduard

2014-05-01

The description of processes of mass exchange between fluid and poly-minerals material in porous media from various kinds of rocks (primarily, sedimentary rocks) have been examined. It was shown that in some important cases there is a storage equation of non-linear diffusion equation type. In addition, process of filtration in un-swelling soils, swelling porous rocks and coupled process of consolidation and chemical interaction between fluid and particles material were considered. In the latter case equations of physical-chemical mechanics of conservation of mass for fluid and particles material were used. As it is well known, the mechanics of porous media is theoretical basis of such branches of science as rock mechanics, soil physics and so on. But at the same moment some complex processes in the geosystems lacks full theoretical description. The example of such processes is metamorphosis of rocks and correspondent variations of stress-strain state. In such processes chemical transformation of solid and fluid components, heat release and absorption, phase transitions, rock destruction occurs. Extensive usage of computational resources in limits of traditional models of the mechanics of porous media cannot guarantee full correctness of obtained models and results. The process of rocks consolidation which happens due to filtration of underground fluids is described from the position of rock mechanics. As an additional impact, let us consider the porous media consolidating under the weight of overlying rock with coupled complex geological processes, as a continuous porous medium of variable mass. Problems of obtaining of correct storage equations for coupled processes of consolidation and mass exchange between underground fluid and skeleton material are often met in catagenesi processes description. The example of such processes is metamorphosis of rocks and correspondent variations of stress-strain state. In such processes chemical transformation of solid and fluid components, heat release and absorption, phase transitions, rock destruction occurs. Extensive usage of computational resources in limits of traditional models of the mechanics of porous media cannot guarantee full correctness of obtained models and results. The present work is dedicated to the retrieval of new ways to formulate and construct such models. It was shown that in some important cases there is a governing equation of non-linear diffusion equation type (well-known Fisher equation). In addition, some geophysical aspects of filtration process in usual non-swelling soils, swelling porous rocks and coupled process of consolidation and chemical interaction between fluid and skeleton material, including earth quakes, are considered.

Fast fluid-flow events within a subduction-related vein system in oceanic eclogite: implications for pore fluid pressure at the plate interface

NASA Astrophysics Data System (ADS)

Taetz, Stephan; John, Timm; Bröcker, Michael; Spandler, Carl; Stracke, Andreas

2017-04-01

A better understanding of the subduction zone fluid cycle and its mechanical feedback requires in-depth knowledge of how fluids flow within and out of the descending slabs. In order to develop reliable quantitative models of fluid flow, the general relationship between dehydration reactions, fluid pathway formation, and the dimensions and timescales of distinct fluid flow events have to be explored. The high-pressure/low-temperature metamorphic rocks of the Pouébo Eclogite Mélange in New Caledonia provide an excellent opportunity to study the fluid flux in a subduction zone setting. Fluid dynamics are recorded by high-pressure veins that cross-cut eclogite facies mélange blocks from this occurrence. Two types of garnet-quartz-phengite veins can be distinguished. These veins record both synmetamorphic internal fluid release by mineral breakdown reactions (type I veins) as well as infiltration of an external fluid (type II veins) and the associated formation of a reaction halo. The overall dehydration, fluid accumulation and fluid migration documented by the type I veins occurred on a timescale of 10^5-106 years that is mainly given by the geometry and convergence rate of the subduction system. In order to quantify the timeframe of fluid-rock interaction between the external fluid and the wall-rock, we have applied Li-isotope chronology. A continuous profile was sampled perpendicular to a type II vein including material from the vein, the reaction selvage and the immediate host rock. Additional drill cores were taken from parts of the outcrop that most likely remained completely unaffected by fluid infiltration-induced alteration. Different Li concentrations in the internal and external fluid reservoirs produced a distinct diffusion profile of decreasing Li concentration and increasing δ7Li as the reaction front propagated into the host-rock. Li-chronometric constraints indicate that fluid-rock interaction related to the formation of the type II veins and had been completed within ca. 3 years. The short-lived, pulse-like character of this process is in accordance with the notion that fluid flow related to oceanic crust dehydration at the blueschist-to-eclogite transition contributes to or even dominates episodic pore fluid pressure increases at the plate interface which may trigger slip events reported from many subduction zones.

Sulfur isotopic disequilibrium and fluid-rock interaction during metamorphism of sulfidic black shales from the Waterville-Augusta area, Maine, USA

USGS Publications Warehouse

Oliver, N.H.S.; Hoering, T.C.; Johnson, T.W.; Rumble, D.; Shanks, Wayne C.

1992-01-01

Sulfur isotope ratios of pyrite (py) and pyrrhotite (po) from regionally metamorphosed graphitic sulfidic schists and related rocks from south-central Maine, USA, were analysed using SO2 and SF6 techniques. There is a broad range in ??34S values for both pyrite and pyrrhotite at most outcrops, up to 8%. and overall the values are isotopically light, averaging ~ -27??? for the entire data set, suggesting that the rocks have not been grossly isotopically disturbed by regional metamorphism from their inferred organic-rich sedimentary origins. At all temperatures from chlorite to sillimanite grades, sulfide analysed from veins and blebs within the schists show predominantly disequilibrium fractionations ranging from ??34Spy-po -3.0 to +3.5???, as do matrix sulfides from rocks that attained temperatures 500??C do matrix pyrite-pyrrhotite pairs with polygonal or aligned granoblastic microstructures approach isotopic equilibrium at millimeter to centimeter scales, suggesting that the process that favoured equilibration was recrystallization accompanying metamorphism and deformation. This disequilibrium may be a function of preferential interaction of one of the phases with an infiltrating fluid, but the lack of any systematic trends in the data, particularly with both negative and positive ??34Spy-po at some outcrops, does not permit ready identification of fluid sources, fluxes, or compositions. By combining published fluid fluxes for the area and a knowledge of the mass of sulfur contained in the rocks and the inferred infiltrating fluid, it appears that sulfur should have been homogenized over at least 10's to 1000's of meters, if equilibrium had been attained between rock sulfides and an infiltrating fluid of constant composition. That this did not occur was probably due to lack of equilibration between sulfides and the fluid but may also have arisen because of channelling of fluid flow along rather than across layers, or a lack of fluid infiltration through this unit. ?? 1992.

Effects of solid/liquid phase fractionation on pH and aqueous species molality in subduction zone fluids

NASA Astrophysics Data System (ADS)

Zhong, X.; Galvez, M. E.

2017-12-01

Metamorphic fluids are a crucial ingredient of geodynamic evolution, i.e. heat transfer, rock mechanics and metamorphic/metasomatic reactions. During crustal evolution at elevated P and T, rock forming components can be effectively fractionated from the reactive rock system by at least two processes: 1. extraction from porous rocks by liquid phases such as solute-bearing (e.g. Na+, Mg2+) aqueous fluids or partial melts. 2. isolation from effective bulk rock composition due to slow intragranular diffusion in high-P refractory phases such as garnet. The effect of phase fractionation (garnet, partial melt and aqueous species) on fluid - rock composition and properties remain unclear, mainly due to a high demand in quantitative computations of the thermodynamic interactions between rocks and fluids over a wide P-T range. To investigate this problem, we build our work on an approach initially introduced by Galvez et al., (2015) with new functionalities added in a MATLAB code (Rubisco). The fluxes of fractionated components in fluid, melt and garnet are monitored along a typical prograde P-T path for a model crustal pelite. Some preliminary results suggest a marginal effect of fractionated aqueous species on fluid and rock properties (e.g. pH, composition), but the corresponding fluxes are significant in the context of mantle wedge metasomatism. Our work provides insight into the role of high-P phase fractionation on mass redistribution between the surface and deep Earth in subduction zones. Existing limitations relevant to our liquid/mineral speciation/fractionation model will be discussed as well. ReferencesGalvez, M.E., Manning, C.E., Connolly, J.A.D., Rumble, D., 2015. The solubility of rocks in metamorphic fluids: A model for rock-dominated conditions to upper mantle pressure and temperature. Earth Planet. Sci. Lett. 430, 486-498.

Dissolution Rates and Reaction Products of Olivine Interaction with Ammonia-Rich Fluid

NASA Astrophysics Data System (ADS)

Zandanel, A. E.; Truche, L.; Hellmann, R.; Tobie, G.; Marrocchi, Y.

2018-05-01

Olivine dissolution rates and reaction products in NH3-rich fluids are determined from experiments simulating H2O-rock interaction on Enceladus. Kinetic rates are calculated from flow through experiments and reaction products from static experiments.

Effects of fluid-rock interactions on faulting within active fault zones - evidence from fault rock samples retrieved from international drilling projects

NASA Astrophysics Data System (ADS)

Janssen, C.; Wirth, R.; Kienast, M.; Yabe, Y.; Sulem, J.; Dresen, G. H.

2015-12-01

Chemical and mechanical effects of fluids influence the fault mechanical behavior. We analyzed fresh fault rocks from several scientific drilling projects to study the effects of fluids on fault strength. For example, in drill core samples on a rupture plane of an Mw 2.2 earthquake in a deep gold mine in South Africa the main shock occurred on a preexisting plane of weakness that was formed by fluid-rock interaction (magnesiohornblende was intensively altered to chlinochlore). The plane acted as conduit for hydrothermal fluids at some time in the past. The chemical influence of fluids on mineralogical alteration and geomechanical processes in fault core samples from SAFOD (San Andreas Fault Observatory at Depth) is visible in pronounced dissolution-precipitation processes (stylolites, solution seams) as well as in the formation of new phases. Detrital quartz and feldspar grains are partially dissolved and replaced by authigenic illite-smectite (I-S) mixed-layer clay minerals. Transmission Electron Microscopy (TEM) imaging of these grains reveals that the alteration processes and healing were initiated within pores and small intra-grain fissures. Newly formed phyllosilicates growing into open pore spaces likely reduced the fluid permeability. The mechanical influence of fluids is indicated by TEM observations, which document open pores that formed in-situ in the gouge material during or after deformation. Pores were possibly filled with formation water and/or hydrothermal fluids suggesting elevated fluid pressure preventing pore collapse. Fluid-driven healing of fractures in samples from SAFOD and the DGLab Gulf of Corinth project is visible in cementation. Cathodoluminescence microscopy (CL) reveals different generations of calcite veins. Differences in CL-colors suggest repeated infiltration of fluids with different chemical composition from varying sources (formation and meteoric water).

Fluids of the Lower Crust: Deep Is Different

NASA Astrophysics Data System (ADS)

Manning, Craig E.

2018-05-01

Deep fluids are important for the evolution and properties of the lower continental and arc crust in tectonically active settings. They comprise four components: H2O, nonpolar gases, salts, and rock-derived solutes. Contrasting behavior of H2O-gas and H2O-salt mixtures yields immiscibility and potential separation of phases with different chemical properties. Equilibrium thermodynamic modeling of fluid-rock interaction using simple ionic species known from shallow-crustal systems yields solutions too dilute to be consistent with experiments and resistivity surveys, especially if CO2 is added. Therefore, additional species must be present, and H2O-salt solutions likely explain much of the evidence for fluid action in high-pressure settings. At low salinity, H2O-rich fluids are powerful solvents for aluminosilicate rock components that are dissolved as polymerized clusters. Addition of salts changes solubility patterns, but aluminosilicate contents may remain high. Fluids with Xsalt = 0.05 to 0.4 in equilibrium with model crustal rocks have bulk conductivities of 10‑1.5 to 100 S/m at porosity of 0.001. Such fluids are consistent with observed conductivity anomalies and are capable of the mass transfer seen in metamorphic rocks exhumed from the lower crust.

Modeling and comparative study of fluid velocities in heterogeneous rocks

NASA Astrophysics Data System (ADS)

Hingerl, Ferdinand F.; Romanenko, Konstantin; Pini, Ronny; Balcom, Bruce; Benson, Sally

2013-04-01

Detailed knowledge of the distribution of effective porosity and fluid velocities in heterogeneous rock samples is crucial for understanding and predicting spatially resolved fluid residence times and kinetic reaction rates of fluid-rock interactions. The applicability of conventional MRI techniques to sedimentary rocks is limited by internal magnetic field gradients and short spin relaxation times. The approach developed at the UNB MRI Centre combines the 13-interval Alternating-Pulsed-Gradient Stimulated-Echo (APGSTE) scheme and three-dimensional Single Point Ramped Imaging with T1 Enhancement (SPRITE). These methods were designed to reduce the errors due to effects of background gradients and fast transverse relaxation. SPRITE is largely immune to time-evolution effects resulting from background gradients, paramagnetic impurities and chemical shift. Using these techniques quantitative 3D porosity maps as well as single-phase fluid velocity fields in sandstone core samples were measured. Using a new Magnetic Resonance Imaging technique developed at the MRI Centre at UNB, we created 3D maps of porosity distributions as well as single-phase fluid velocity distributions of sandstone rock samples. Then, we evaluated the applicability of the Kozeny-Carman relationship for modeling measured fluid velocity distributions in sandstones samples showing meso-scale heterogeneities using two different modeling approaches. The MRI maps were used as reference points for the modeling approaches. For the first modeling approach, we applied the Kozeny-Carman relationship to the porosity distributions and computed respective permeability maps, which in turn provided input for a CFD simulation - using the Stanford CFD code GPRS - to compute averaged velocity maps. The latter were then compared to the measured velocity maps. For the second approach, the measured velocity distributions were used as input for inversely computing permeabilities using the GPRS CFD code. The computed permeabilities were then correlated with the ones based on the porosity maps and the Kozeny-Carman relationship. The findings of the comparative modeling study are discussed and its potential impact on the modeling of fluid residence times and kinetic reaction rates of fluid-rock interactions in rocks containing meso-scale heterogeneities are reviewed.

Sulfur and carbon geochemistry of the Santa Elena peridotites: Comparing oceanic and continental processes during peridotite alteration

NASA Astrophysics Data System (ADS)

Schwarzenbach, Esther M.; Gill, Benjamin C.; Gazel, Esteban; Madrigal, Pilar

2016-05-01

Ultramafic rocks exposed on the continent serve as a window into oceanic and continental processes of water-peridotite interaction, so called serpentinization. In both environments there are active carbon and sulfur cycles that contain abiogenic and biogenic processes, which are eventually imprinted in the geochemical signatures of the basement rocks and the calcite and magnesite deposits associated with fluids that issue from these systems. Here, we present the carbon and sulfur geochemistry of ultramafic rocks and carbonate deposits from the Santa Elena ophiolite in Costa Rica. The aim of this study is to leverage the geochemistry of the ultramafic sequence and associated deposits to distinguish between processes that were dominant during ocean floor alteration and those dominant during low-temperature, continental water-peridotite interaction. The peridotites are variably serpentinized with total sulfur concentrations up to 877 ppm that is typically dominated by sulfide over sulfate. With the exception of one sample the ultramafic rocks are characterized by positive δ34Ssulfide (up to + 23.1‰) and δ34Ssulfate values (up to + 35.0‰). Carbon contents in the peridotites are low and are isotopically distinct from typical oceanic serpentinites. In particular, δ13C of the inorganic carbon suggests that the carbon is not derived from seawater, but rather the product of the interaction of meteoric water with the ultramafic rocks. In contrast, the sulfur isotope data from sulfide minerals in the peridotites preserve evidence for interaction with a hydrothermal fluid. Specifically, they indicate closed system abiogenic sulfate reduction suggesting that oceanic serpentinization occurred with limited input of seawater. Overall, the geochemical signatures preserve evidence for both oceanic and continental water-rock interaction with the majority of carbon (and possibly sulfate) being incorporated during continental water-rock interaction. Furthermore, there is evidence for microbial activity that was possibly stimulated by carbon sourced from water-rock interaction with adjacent sediments or fluid inclusions. This study provides detailed insight into the complex hydrothermal history of continental serpentinization systems and adds to our understanding of the carbon and sulfur cycling within peridotite-hosted hydrothermal systems.

Lithium isotope as a proxy for water/rock interaction between hydrothermal fluids and oceanic crust at Milos, Greece

NASA Astrophysics Data System (ADS)

Lou, U.-Lat; You, Chen-Feng; Wu, Shein-Fu; Chung, Chuan-Hsiung

2014-05-01

Hydrothermal activity at Milos in the Aegean island (Greece) is mainly located at rather shallow depth (about 5 m). It is interesting to compare these chemical compositions and the evolution processes of the hydrothermal fluids at deep sea hydrothermal vents in Mid-ocean Ridge (MOR). Lithium (Li) is a highly mobile element and its isotopic composition varies at different geological settings. Therefore, Li and its isotope could be used as an indicator for many geochemical processes. Since 6Li preferential retained in the mineral phase where 7Li is leached into fluid phase during basalt alteration, the Li isotopic fractionation between the rocks and the fluids reflect sensitively the degree of water-rock interaction. In this study, Bio-Rad AG-50W X8 cation exchange resin was used for purifying the hydrothermal fluids to separate Li from other matrix elements. The Li isotopic composition (δ7Li) was determined by Multi-collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS) with precision better than 0.2‰ (2σ, n=20). The Li concentration in the hydrothermal fluids falls between 0.02 to 10.31 mM. The δ7Li values vary from +1.9 to +29.7‰, indicating significant seawater contamination have occurred. These hydrothermal fluids fit well with seawater and brine two end-member binary mixing model. During phase separation, lithium, boron, chlorine, iodine, bromine, sodium and potassium were enriched in the brine phase. On the other hand, aluminum, sulphur and iron were enriched in the vapor phase. There is no significant isotope fractionation between the two phases. The water/rock ratio (W/R) calculated is low (about 1.5 to 1.8) for the Milos fluids, restricted seawater recharge into the oceanic crust. Moreover, the oceanic crust in the region becomes less altered since the W/R is low. The δ7Li value of the hydrothermal fluids can be used as a sensitive tool for studying water-rock interaction.

Tracing subduction zone fluid-rock interactions using trace element and Mg-Sr-Nd isotopes

NASA Astrophysics Data System (ADS)

Wang, Shui-Jiong; Teng, Fang-Zhen; Li, Shu-Guang; Zhang, Li-Fei; Du, Jin-Xue; He, Yong-Sheng; Niu, Yaoling

2017-10-01

Slab-derived fluids play a key role in mass transfer and elemental/isotopic exchanges in subduction zones. The exhumation of deeply subducted crust is achieved via a subduction channel where fluids from various sources are abundant, and thus the chemical/isotopic compositions of these rocks could have been modified by subduction-zone fluid-rock interactions. Here, we investigate the Mg isotopic systematics of eclogites from southwestern Tianshan, in conjunction with major/trace element and Sr-Nd isotopes, to characterize the source and nature of fluids and to decipher how fluid-rock interactions in subduction channel might influence the Mg isotopic systematics of exhumed eclogites. The eclogites have high LILEs (especially Ba) and Pb, high initial 87Sr/86Sr (up to 0.7117; higher than that of coeval seawater), and varying Ni and Co (mostly lower than those of oceanic basalts), suggesting that these eclogites have interacted with metamorphic fluids mainly released from subducted sediments, with minor contributions from altered oceanic crust or altered abyssal peridotites. The positive correlation between 87Sr/86Sr and Pb* (an index of Pb enrichment; Pb* = 2*PbN/[CeN + PrN]), and the decoupling relationships and bidirectional patterns in 87Sr/86Sr-Rb/Sr, Pb*-Rb/Sr and Pb*-Ba/Pb spaces imply the presence of two compositionally different components for the fluids: one enriched in LILEs, and the other enriched in Pb and 87Sr/86Sr. The systematically heavier Mg isotopic compositions (δ26Mg = - 0.37 to + 0.26) relative to oceanic basalts (- 0.25 ± 0.07) and the roughly negative correlation of δ26Mg with MgO for the southwestern Tianshan eclogites, cannot be explained by inheritance of Mg isotopic signatures from ancient seafloor alteration or prograde metamorphism. Instead, the signatures are most likely produced by fluid-rock interactions during the exhumation of eclogites. The high Rb/Sr and Ba/Pb but low Pb* eclogites generally have high bulk-rock δ26Mg values, whereas high Pb* and 87Sr/86Sr eclogites have mantle-like δ26Mg values, suggesting that the two fluid components have diverse influences on the Mg isotopic systematics of these eclogites. The LILE-rich fluid component, possibly derived from mica-group minerals, contains a considerable amount of isotopically heavy Mg that has shifted the δ26Mg of the eclogites towards higher values. By contrast, the 87Sr/86Sr- and Pb-rich fluid component, most likely released from epidote-group minerals in metasediments, has little Mg so as not to modify the Mg isotopic composition of the eclogites. In addition, the influence of talc-derived fluid might be evident in a very few eclogites that have low Rb/Sr and Ba/Pb but slightly heavier Mg isotopic compositions. These findings represent an important step toward a broad understanding of the Mg isotope geochemistry in subduction zones, and contributing to understanding why island arc basalts have averagely heavier Mg isotopic compositions than the normal mantle.

Composition, Alteration, and Texture of Fault-Related Rocks from Safod Core and Surface Outcrop Analogs: Evidence for Deformation Processes and Fluid-Rock Interactions

NASA Astrophysics Data System (ADS)

Bradbury, Kelly K.; Davis, Colter R.; Shervais, John W.; Janecke, Susanne U.; Evans, James P.

2015-05-01

We examine the fine-scale variations in mineralogical composition, geochemical alteration, and texture of the fault-related rocks from the Phase 3 whole-rock core sampled between 3,187.4 and 3,301.4 m measured depth within the San Andreas Fault Observatory at Depth (SAFOD) borehole near Parkfield, California. This work provides insight into the physical and chemical properties, structural architecture, and fluid-rock interactions associated with the actively deforming traces of the San Andreas Fault zone at depth. Exhumed outcrops within the SAF system comprised of serpentinite-bearing protolith are examined for comparison at San Simeon, Goat Rock State Park, and Nelson Creek, California. In the Phase 3 SAFOD drillcore samples, the fault-related rocks consist of multiple juxtaposed lenses of sheared, foliated siltstone and shale with block-in-matrix fabric, black cataclasite to ultracataclasite, and sheared serpentinite-bearing, finely foliated fault gouge. Meters-wide zones of sheared rock and fault gouge correlate to the sites of active borehole casing deformation and are characterized by scaly clay fabric with multiple discrete slip surfaces or anastomosing shear zones that surround conglobulated or rounded clasts of compacted clay and/or serpentinite. The fine gouge matrix is composed of Mg-rich clays and serpentine minerals (saponite ± palygorskite, and lizardite ± chrysotile). Whole-rock geochemistry data show increases in Fe-, Mg-, Ni-, and Cr-oxides and hydroxides, Fe-sulfides, and C-rich material, with a total organic content of >1 % locally in the fault-related rocks. The faults sampled in the field are composed of meters-thick zones of cohesive to non-cohesive, serpentinite-bearing foliated clay gouge and black fine-grained fault rock derived from sheared Franciscan Formation or serpentinized Coast Range Ophiolite. X-ray diffraction of outcrop samples shows that the foliated clay gouge is composed primarily of saponite and serpentinite, with localized increases in Ni- and Cr-oxides and C-rich material over several meters. Mesoscopic and microscopic textures and deformation mechanisms interpreted from the outcrop sites are remarkably similar to those observed in the SAFOD core. Micro-scale to meso-scale fabrics observed in the SAFOD core exhibit textural characteristics that are common in deformed serpentinites and are often attributed to aseismic deformation with episodic seismic slip. The mineralogy and whole-rock geochemistry results indicate that the fault zone experienced transient fluid-rock interactions with fluids of varying chemical composition, including evidence for highly reducing, hydrocarbon-bearing fluids.

Accessory minerals and subduction zone metasomatism: a geochemical comparison of two mélanges (Washington and California, U.S.A.)

USGS Publications Warehouse

Sorensen, Sorena S.; Grossman, Jeffrey N.

1993-01-01

Data from the Gee Point and Catalina mélanges suggest that the accessory minerals titanite, rutile, apatite, zircon and REE-rich epidote play a significant role in the enrichment of trace elements in both mafic and ultramafic rocks during subduction-related fluid-rock interaction. Mobilization of incompatible elements, and deposition of such elements in the accessory minerals of mafic and ultramafic rocks may be fairly common in fluid-rich metamorphic environments in subduction zones.

Effect of fluid penetration on tensile failure during fracturing of an open-hole wellbore

NASA Astrophysics Data System (ADS)

Zeng, Fanhui; Cheng, Xiaozhao; Guo, Jianchun; Chen, Zhangxin; Tao, Liang; Liu, Xiaohua; Jiang, Qifeng; Xiang, Jianhua

2018-06-01

It is widely accepted that a fracture can be induced at a wellbore surface when the fluid pressure overcomes the rock tensile strength. However, few models of this phenomenon account for the fluid penetration effect. A rock is a typical permeable, porous medium, and the transmission of pressure from a wellbore to the surrounding rock temporally and spatially perturbs the effective stresses. In addition, these induced stresses influence the fracture initiation pressure. To gain a better understanding of the penetration effect on the initiation pressure of a permeable formation, a comprehensive formula is presented to study the effects of the in situ stresses, rock mechanical properties, injection rate, rock permeability, fluid viscosity, fluid compressibility and wellbore size on the magnitude of the initiation pressure during fracturing of an open-hole wellbore. In this context, the penetration effect is treated as a consequence of the interaction among these parameters by using Darcy’s law of radial flow. A fully coupled analytical procedure is developed to show how the fracturing fluid infiltrates the rock around the wellbore and considerably reduces the magnitude of the initiation pressure. Moreover, the calculation results are validated by hydraulic fracturing experiments in hydrostone. An exhaustive sensitivity study is performed, indicating that the local fluid pressure induced from a seepage effect strongly influences the fracture evolution. For permeable reservoirs, a low injection rate and a low viscosity of the injected fluid have a significant impact on the fracture initiation pressure. In this case, the Hubbert and Haimson equations to predict the fracture initiation pressure are not valid. The open-hole fracture initiation pressure increases with the fracturing fluid viscosity and fluid compressibility, while it decreases as the rock permeability, injection rate and wellbore size increase.

Upper mantle fluids evolution, diamond formation, and mantle metasomatism

NASA Astrophysics Data System (ADS)

Huang, F.; Sverjensky, D. A.

2017-12-01

During mantle metasomatism, fluid-rock interactions in the mantle modify wall-rock compositions. Previous studies usually either investigated mineral compositions in xenoliths and xenocrysts brought up by magmas, or examined fluid compositions preserved in fluid inclusions in diamonds. However, a key study of Panda diamonds analysed both mineral and fluid inclusions in the diamonds [1] which we used to develop a quantitative characterization of mantle metasomatic processes. In the present study, we used an extended Deep Earth Water model [2] to simulate fluid-rock interactions at upper mantle conditions, and examine the fluids and mineral assemblages together simultaneously. Three types of end-member fluids in the Panda diamond fluid inclusions include saline, rich in Na+K+Cl; silicic, rich in Si+Al; and carbonatitic, rich in Ca+Mg+Fe [1, 3]. We used the carbonatitic end-member to represent fluid from a subducting slab reacting with an excess of peridotite + some saline fluid in the host environment. During simultaneous fluid mixing and reaction with the host rock, the logfO2 increased by about 1.6 units, and the pH increased by 0.7 units. The final minerals were olivine, garnet and diamond. The Mg# of olivine decreased from 0.92 to 0.85. Garnet precipitated at an early stage, and its Mg# also decreased with reaction progress, in agreement with the solid inclusions in the Panda diamonds. Phlogopite precipitated as an intermediate mineral and then disappeared. The aqueous Ca, Mg, Fe, Si and Al concentrations all increased, while Na, K, and Cl concentrations decreased during the reaction, consistent with trends in the fluid inclusion compositions. Our study demonstrates that fluids coming from subducting slabs could trigger mantle metasomatism, influence the compositions of sub-lithospherc cratonic mantle, precipitate diamonds, and change the oxygen fugacity and pH of the upper mantle fluids. [1] Tomlinson et al. EPSL (2006); [2] Sverjensky, DA et al., GCA (2014), Huang, F, Ph. D. thesis, Johns Hopkins University, (2017); [3] Shirey et al., Rev. Mineral. Geochem. (2013)

Modelling of reactive fluid transport in deformable porous rocks

NASA Astrophysics Data System (ADS)

Yarushina, V. M.; Podladchikov, Y. Y.

2009-04-01

One outstanding challenge in geology today is the formulation of an understanding of the interaction between rocks and fluids. Advances in such knowledge are important for a broad range of geologic settings including partial melting and subsequent migration and emplacement of a melt into upper levels of the crust, or fluid flow during regional metamorphism and metasomatism. Rock-fluid interaction involves heat and mass transfer, deformation, hydrodynamic flow, and chemical reactions, thereby necessitating its consideration as a complex process coupling several simultaneous mechanisms. Deformation, chemical reactions, and fluid flow are coupled processes. Each affects the others. Special effort is required for accurate modelling of the porosity field through time. Mechanical compaction of porous rocks is usually treated under isothermal or isoentropic simplifying assumptions. However, joint consideration of both mechanical compaction and reactive porosity alteration requires somewhat greater than usual care about thermodynamic consistency. Here we consider the modelling of multi-component, multi-phase systems, which is fundamental to the study of fluid-rock interaction. Based on the conservation laws for mass, momentum, and energy in the form adopted in the theory of mixtures, we derive a thermodynamically admissible closed system of equations describing the coupling of heat and mass transfer, chemical reactions, and fluid flow in a deformable solid matrix. Geological environments where reactive transport is important are located at different depths and accordingly have different rheologies. In the near surface, elastic or elastoplastic properties would dominate, whereas viscoplasticity would have a profound effect deeper in the lithosphere. Poorly understood rheologies of heterogeneous porous rocks are derived from well understood processes (i.e., elasticity, viscosity, plastic flow, fracturing, and their combinations) on the microscale by considering a representative volume element and subsequent averaging of microscopic constitutive laws. Micromechanical and thermodynamic modelling is performed in such a way that the consistency of the obtained rheology and thermodynamically admissible closed system of equations with the exact Gassman's relationship and Terzaghi effective stress law in the simplified case of poroelasticity is guaranteed. In such environments as subduction zones or mid-ocean ridge, metamorphic rocks exhibit a lack of chemical homogenisation. Geochemistry suggests that in order to produce chemical heterogeneity, the fluids generated during high-pressure metamorphism must have been strongly channelled. The following three major mechanisms of fluid flow focusing have been proposed: fluid flow in open fractures and two different types of flow instabilities that do not require the pre-existing fracture network. Of the latter, the first represents a purely mechanical instability of Darcian flow through the deformable porous rock while the second is reactive infiltration instability. Both mechanical and reactive instabilities are expected to occur in the mantle and should probably reinforce each other. However, little research has been done in this direction. In order to investigate how the focusing of a fluid flow occurs, how mechanical and reactive infiltration instabilities influence each other, and what their relative importance in rocks with different rheologies is, linear and non-linear stability analysis is applied to derived governing equations.

Fault Weakening due to Erosion by Fluids: A Possible Origin of Intraplate Earthquake Swarms

NASA Astrophysics Data System (ADS)

Vavrycuk, V.; Hrubcova, P.

2016-12-01

The occurrence and specific properties of earthquake swarms in geothermal areas are usually attributed to a highly fractured rock and/or heterogeneous stress within the rock mass being triggered by magmatic or hydrothermal fluid intrusion. The increase of fluid pressure destabilizes fractures and causes their opening and subsequent shear-tensile rupture. The spreading and evolution of the seismic activity is controlled by fluid flow due to diffusion in a permeable rock and/or by the redistribution of Coulomb stress. The `fluid-injection model', however, is not valid universally. We provide evidence that this model is inconsistent with observations of earthquake swarms in West Bohemia, Czech Republic. Full seismic moment tensors of micro-earthquakes in the 1997 and 2008 swarms in West Bohemia indicate that fracturing at the starting phase of the swarm was not associated with fault openings caused by pressurized fluids but rather with fault compactions. This can physically be explained by a `fluid-erosion model', when the essential role in the swarm triggering is attributed to chemical and hydrothermal fluid-rock interactions in the focal zone. Since the rock is exposed to circulating hydrothermal, CO2-saturated fluids, the walls of fractures are weakened by dissolving and altering various minerals. If fault strength lowers to a critical value, the seismicity is triggered. The fractures are compacted during failure, the fault strength recovers and a new cycle begins.

Proceedings of the International Symposium on Dynamics of Fluids in Fractured Rocks: Concepts and Recent Advances

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faybishenko, B.

1999-02-01

This publication contains extended abstracts of papers presented at the International Symposium ''Dynamics of Fluids in Fractured Rocks: Concepts and Recent Advances'' held at Ernest Orlando Lawrence Berkeley National Laboratory on February 10-12, 1999. This Symposium is organized in Honor of the 80th Birthday of Paul A. Witherspoon, who initiated some of the early investigations on flow and transport in fractured rocks at the University of California, Berkeley, and at Lawrence Berkeley National Laboratory. He is a key figure in the development of basic concepts, modeling, and field measurements of fluid flow and contaminant transport in fractured rock systems. Themore » technical problems of assessing fluid flow, radionuclide transport, site characterization, modeling, and performance assessment in fractured rocks remain the most challenging aspects of subsurface flow and transport investigations. An understanding of these important aspects of hydrogeology is needed to assess disposal of nu clear wastes, development of geothermal resources, production of oil and gas resources, and remediation of contaminated sites. These Proceedings of more than 100 papers from 12 countries discuss recent scientific and practical developments and the status of our understanding of fluid flow and radionuclide transport in fractured rocks. The main topics of the papers are: Theoretical studies of fluid flow in fractured rocks; Multi-phase flow and reactive chemical transport in fractured rocks; Fracture/matrix interactions; Hydrogeological and transport testing; Fracture flow models; Vadose zone studies; Isotopic studies of flow in fractured systems; Fractures in geothermal systems; Remediation and colloid transport in fractured systems; and Nuclear waste disposal in fractured rocks.« less

Lithium isotopic systematics of submarine vent fluids from arc and back-arc hydrothermal systems in the western Pacific

NASA Astrophysics Data System (ADS)

Araoka, Daisuke; Nishio, Yoshiro; Gamo, Toshitaka; Yamaoka, Kyoko; Kawahata, Hodaka

2016-10-01

The Li concentration and isotopic composition (δ7Li) in submarine vent fluids are important for oceanic Li budget and potentially useful for investigating hydrothermal systems deep under the seafloor because hydrothermal vent fluids are highly enriched in Li relative to seawater. Although Li isotopic geochemistry has been studied at mid-ocean-ridge (MOR) hydrothermal sites, in arc and back-arc settings Li isotopic composition has not been systematically investigated. Here we determined the δ7Li and 87Sr/86Sr values of 11 end-member fluids from 5 arc and back-arc hydrothermal systems in the western Pacific and examined Li behavior during high-temperature water-rock interactions in different geological settings. In sediment-starved hydrothermal systems (Manus Basin, Izu-Bonin Arc, Mariana Trough, and North Fiji Basin), the Li concentrations (0.23-1.30 mmol/kg) and δ7Li values (+4.3‰ to +7.2‰) of the end-member fluids are explained mainly by dissolution-precipitation model during high-temperature seawater-rock interactions at steady state. Low Li concentrations are attributable to temperature-related apportioning of Li in rock into the fluid phase and phase separation process. Small variation in Li among MOR sites is probably caused by low-temperature alteration process by diffusive hydrothermal fluids under the seafloor. In contrast, the highest Li concentrations (3.40-5.98 mmol/kg) and lowest δ7Li values (+1.6‰ to +2.4‰) of end-member fluids from the Okinawa Trough demonstrate that the Li is predominantly derived from marine sediments. The variation of Li in sediment-hosted sites can be explained by the differences in degree of hydrothermal fluid-sediment interactions associated with the thickness of the marine sediment overlying these hydrothermal sites.

Aqueous geochemistry in icy world interiors: Equilibrium fluid, rock, and gas compositions, and fate of antifreezes and radionuclides

NASA Astrophysics Data System (ADS)

Neveu, Marc; Desch, Steven J.; Castillo-Rogez, Julie C.

2017-09-01

The geophysical evolution of many icy moons and dwarf planets seems to have provided opportunities for interaction between liquid water and rock (silicate and organic solids). Here, we explore two ways by which water-rock interaction can feed back on geophysical evolution: the production or consumption of antifreeze compounds, which affect the persistence and abundance of cold liquid; and the potential leaching into the fluid of lithophile radionuclides, affecting the distribution of a long-term heat source. We compile, validate, and use a numerical model, implemented with the PHREEQC code, of the interaction of chondritic rock with pure water and with C, N, S-bearing cometary fluid, thought to be the materials initially accreted by icy worlds, and describe the resulting equilibrium fluid and rock assemblages at temperatures, pressures, and water-to-rock ratios of 0-200 ° C, 1-1000 bar, and 0.1-10 by mass, respectively. Our findings suggest that water-rock interaction can strongly alter the nature and amount of antifreezes, resulting in solutions rich in reduced nitrogen and carbon, and sometimes dissolved H2, with additional sodium, calcium, chlorine, and/or oxidized carbon. Such fluids can remain partially liquid down to 176 K if NH3 is present. The prominence of Cl in solution seems to hinge on its primordial supply in ices, which is unconstrained by the meteoritical record. Equilibrium assemblages, rich in serpentine and saponite clays, retain thorium and uranium radionuclides unless U-Cl or U-HCO3 complexing, which was not modeled, significantly enhances U solubility. However, the radionuclide 40 K can be leached at high water:rock ratio and/or low temperature at which K is exchanged with ammonium in minerals. We recommend the inclusion of these effects in future models of the geophysical evolution of ocean-bearing icy worlds. Our simulation products match observations of chloride salts on Europa and Enceladus; CI chondrites mineralogies; the observation of serpentines, NH4-phyllosilicates, and carbonates on Ceres' surface; and of Na and NH4-carbonate and chloride in Ceres' bright spots. They also match results from previous modeling studies with similar assumptions, and systematically expand these results to heretofore unexplored physico-chemical conditions. This work involved the compilation and careful validation of a comprehensive PHREEQC database, which combines the advantages of the default databases phreeqc.dat (carefully vetted data, molar volumes) and llnl.dat (large diversity of species), and should be of broad use to anyone seeking to model aqueous geochemistry at pressures that differ from 1 bar with PHREEQC.

Hydrothermal mobilization of pegmatite-hosted REE and Zr at Strange Lake, Canada: A reaction path model

NASA Astrophysics Data System (ADS)

Gysi, Alexander P.; Williams-Jones, Anthony E.

2013-12-01

Petrological and geochemical observations of pegmatites in the Strange Lake pluton, Canada, have been combined with numerical simulations to improve our understanding of fluid-rock interaction in peralkaline granitic systems. In particular, they have made it possible to evaluate reaction paths responsible for hydrothermal mobilization and mineralization of rare earth elements (REE) and Zr. The focus of the study was the B-Zone in the northwest of the pluton, which contains a pegmatite swarm and is the target of exploration for an economically exploitable REE deposit. Many of the pegmatites are mineralogically zoned into a border consisting of variably altered primary K-feldspar, arfvedsonite, quartz, and zirconosilicates, and a core rich in quartz, fluorite and exotic REE minerals. Textural relationships indicate that the primary silicate minerals in the pegmatites were leached and/or replaced during acidic alteration by K-, Fe- and Al-phyllosilicates, aegirine, hematite, fluorite and/or quartz, and that primary zirconosilicates (e.g., elpidite) were replaced by gittinsite and/or zircon. Reaction textures recording coupled dissolution of silicate minerals and crystallization of secondary REE-silicates indicate hydrothermal mobilization of the REE. The mobility of the light (L)REE was limited by the stability of REE-F-(CO2)-minerals (basnäsite-(Ce) and fluocerite-(Ce)), whereas zirconosilicates and secondary gadolinite-group minerals controlled the mobility of Zr and the heavy (H)REE. Hydrothermal fluorite and fluorite-fluocerite-(Ce) solid solutions are interpreted to indicate the former presence of F-bearing saline fluids in the pegmatites. Numerical simulations show that the mobilization of REE and Zr in saline HCl-HF-bearing fluids is controlled by pH, ligand activity and temperature. Mobilization of Zr is significant in both saline HF- and HCl-HF-bearing fluids at low temperature (250 °C). In contrast, the REE are mobilized by saline HCl-bearing fluids, particularly at high temperature (400 °C). The LREE are more mobile than the HREE in saline HCl-bearing fluids due to the greater stability of LREE-chloride complexes. The simulated mineralogy is consistent with the zonation observed in the pegmatites and with fluid-rock interaction at conditions that were rock-buffered in the pegmatite borders (low fluid/rock ratio; and pH > 4) and fluid-buffered in the cores (high fluid/rock ratio; pH ⩽ 2). We propose a model in which saline HCl-HF-bearing fluids created pathways during acidic alteration from the pegmatite cores outward. This led to the mobilization of REE and Zr due to progressive alteration of primary silicate minerals and increased acidity upon cooling. The key requirement for REE and Zr mobilization in peralkaline igneous intrusions is the formation of an acidic subsystem with high fluid/rock ratios that increases the overall permeability of the rocks. In these zones, the extent of late stage hydrothermal redistribution and concentration of REE and Zr depends on the buffering capacity of the rocks and the availability of fluids that may produce autometasomatic rock alteration, interact with external rock units and/or mix with fluids from other sources. b The detection limits of Yb were 1043 ppm for zircon, 380 ppm for gadolinite-group minerals and 380 ppm for REE-F-(CO2)-minerals. bAja et al. (1995). cMigdisov et al. (2011). dTagirov et al. (1997). eTagirov and Schott (2001). fMigdisov et al. (2009) with REE (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu). b Calculated using the methods of the Chermak and Rimstidt (1989), Berman and Brown (1985) and Holland (1989) with molar volume of arfvedsonite from Hawthorne (1976). cZotov et al. (1998). d GEM-Selektor v.3 database (http://gems.web.psi.ch). eMigdisov et al. (2009).

Fluid-rock interaction recorded in fault rocks of the Nobeoka Thrust, fossilized megasplay fault in an ancient accretionary complex

NASA Astrophysics Data System (ADS)

Hasegawa, R.; Yamaguchi, A.; Fukuchi, R.; Kitamura, Y.; Kimura, G.; Hamada, Y.; Ashi, J.; Ishikawa, T.

2017-12-01

The relationship between faulting and fluid behavior has been in debate. In this study, we clarify the fluid-rock interaction in the Nobeoka Thrust by major/trace element composition analysis using the boring core of the Nobeoka Thrust, an exhumed analogue of an ancient megasplay fault in Shimanto accretionary complex, southwest Japan. The hanging wall and the footwall of the Nobeoka Thrust show difference in lithology and metamorphic grade, and their maximum burial temperature is estimated from vitrinite reflectance analysis to be 320 330°C and 250 270°C, respectively (Kondo et al., 2005). The fault zone was formed in a fluid-rich condition, as evidenced by warm fluid migration suggested by fluid inclusion analysis (Kondo et al., 2005), implosion brecciation accompanied by carbonate precipitation followed by formation of pseudotachylyte (Okamoto et al., 2006), ankerite veins coseismically formed under reducing conditions (Yamaguchi et al., 2011), and quartz veins recording stress rotation in seismic cycles (Otsubo et al., 2016). In this study, first we analyzed the major/trace element composition across the principal slip zone (PSZ) of the Nobeoka Thrust by using fragments of borehole cores penetrated through the Nobeoka Thrust. Many elements fluctuated just above the PSZ, whereas K increase and Na, Si decrease suggesting illitization of plagioclase, as well as positive anomalies in Li and Cs were found within the PSZ. For more detail understanding, we observed polished slabs and thin sections of the PSZ. Although grain size reduction of deformed clast and weak development of foliation were observed entirely in the PSZ by macroscopic observation, remarkable development of composite planar fabric nor evidence of friction melting were absent. In this presentation, we show the result of major/trace element composition corresponding to the internal structure of PSZ, and discuss fluid-rock interaction and its impact to megasplay fault activity in subduction zones.

Dehydration reactions, mass transfer and rock deformation relationships during subduction of Alpine metabauxites: insights from LIBS compositional profiles between metamorphic veins

NASA Astrophysics Data System (ADS)

Verlaguet, A.; Brunet, F.; Goffe, B.; Menut, D.; Findling, N.; Poinssot, C.

2011-12-01

In subduction zones, the significant amounts of aqueous fluid released in the course of the successive dehydration reactions occurring during prograde metamorphism are expected to strongly influence the rock rheology, as well as kinetics of metamorphic reactions and mass transfer efficiency. Mineralized veins, ubiquitous in metamorphic rocks, can be seen as preserved witnesses of fluid and mass redistribution that partly accommodate the rock deformation (lateral segregation). However, the driving forces and mechanisms of mass transfer towards fluid-filled open spaces remain somewhat unclear. The aim of this study is to investigate the modalities of mass transfer during local fluid-rock interactions, and their links with fluid production and rock deformation. This study focuses on karstic pockets (metre scale) of Triassic metabauxites embedded in thick carbonate units, that have been isolated from large-scale fluid flow during HP-LT Alpine metamorphism (W. Vanoise, French Alps). These rocks display several generations of metamorphic veins containing various Al-bearing minerals, which give particular insights into mass transfer processes. It is proposed that the internally-derived fluid (~13 vol% produced by successive dehydration reactions) has promoted the opening of fluid-filled open spaces (euhedral habits of vein minerals) and served as medium for diffusive mass transfer from rock to vein. Based on mineralogical and textural features, two vein types can be distinguished: (1) some veins are filled with newly formed products of either prograde (chloritoid) or retrograde (chlorite) metamorphic reactions; in this case, fluid-filled open spaces seem to offer energetically favourable nucleation/growth sites; (2) the second vein type is filled with cookeite (Li-Al-rich chlorite) or pyrophyllite, that were present in the host rock prior to the vein formation. In this closed chemical system, mass transfer from rock to vein was achieved through the fluid, in a dissolution-transport-precipitation process, possibly stress-assisted. Cookeite is highly concentrated (40-70 vol%) in regularly spaced veins. Laser Induced Breakdown Spectroscopy profiles show that cookeite is evenly distributed in the rock matrix comprised between two veins. The absence of diffusion profiles suggests that the characteristic diffusion length for Li, Al and Si is greater than or equal to the distance separating two cookeite veins (3-6 cm). This is in agreement with characteristic diffusion lengths calculated from both grain boundary and pore fluid diffusion coefficients, for the estimated duration of the peak of metamorphism. Phyllosilicates have very different morphologies in the rock matrix (fibers) compared to veins (euhedral crystals): fluid-mineral interfacial energy may be maximal in the small matrix pores, which can maintain higher cookeite solubility than in fluid-filled open spaces. Therefore, as soon as veins open, chemical potential gradients may develop and drive cookeite transfer from rock matrix to veins.

Mobile Element Studies in Rocks (RAT) from Columbia Hills/West Spur at Gusev

NASA Technical Reports Server (NTRS)

Rao, M. N.; Nyquist, L. E.; Sutton, S. R.; Garrison, D. H.

2007-01-01

Using elemental abundances determined by SPIRIT APX spectrometer on rocks and soils at Gusev Plains and Columbia Hills/ West Spur regions, the Athena Team discussed the aqueous geochemical implications at these sites on Mars. They suggested that these rocks were exposed to variable degrees of aqueous alteration (low to high) at Gusev crater. Earlier, we developed analytical procedures for studying aqueous geochemical behavior of fluids on rocks at Meridiani. In the present study, we apply these methods to rocks at Columbia Hills/West Spur in order to understand the significance of the Gusev rock results in reference to aqueous geochemical processes on Mars . The data analysis procedure is based on treating SO3 ("a") and Cl ("b") as two variables and tracking the relationship between "a" and "b" when the fluids undergo evaporation. This process of evaporation leads to concentration changes in these two elements finally producing salt assemblages on Martian rocks. In some cases on plotting "a"/ "b" versus "b" in salt assemblages, they yield a hyperbolic distribution. The relationship is transformed into a straight line when "a"/"b" is again plotted against 1/"b" in the system. Earlier, we used this procedure in the case of Merdiani rock abrasion tool (RAT) rocks and in this study, we discuss the application of this procedure to Gusev rocks. This study shows that the Gusev Plains rocks were exposed to low SO3/Cl solutions (sulfate-poor) for short period of time (weak interaction), whereas solutions with high SO3/Cl ratios (sulfate-rich) seem to have pervasively interacted with Columbia Hills/ West Spur rocks (strong interaction) at Gusev crater. Our conclusions seem to be consistent with the Mossbauer results given for these rocks

Fluid flow in deforming media: interpreting stable isotope signatures of marbles

NASA Astrophysics Data System (ADS)

Bond, C. E.

2016-12-01

Fluid flow in the crust is controlled by permeable networks. These networks can be created and destroyed dynamically during rock deformation. Rock deformation is therefore critical in controlling fluid pathways in the crust and hence the location of mineral and other resources. Here, evidence for deformation-enhanced fluid infiltration shows that a range of deformation mechanisms control fluid flow and chemical and isotopic equilibration. The results attest to localised fluid infiltration within a single metamorphic terrain (12km) over a range of metamorphic grades; ecologite- blueschist to greenschist. For fluid infiltrating marbles during ductile deformation, chemical and isotopic signatures are now homogenous; whilst fluid infiltration associated with brittle deformation results in chemical and isotopic heterogeneity at a microscale. The findings demonstrate how ductile deformation enhances equilibration of δ18O at a grain scale whilst brittle deformation does not. The control of deformation mechanisms in equilibrating isotopic and chemical heterogeneities have implications for the understanding of fluid-rock interaction in the crust. Interpretation of bulk stable isotope data, particularly in the use of isotope profiles to determine fluid fluxes into relatively impermeable units that have been deformed need to be used with care when trying to determine fluid fluxes and infiltration mechanisms.

Fluid inclusion chemistry of adularia-sericite epithermal Au-Ag deposits of the southern Hauraki Goldfield, New Zealand

USGS Publications Warehouse

Simpson, Mark P.; Strmic Palinkas, Sabina; Mauk, Jeffrey L.; Bodnar, Robert J.

2015-01-01

LA-ICP-MS analyses show that in some cases different fluid inclusion assemblages (FIAs) within a single sample trapped fluids with variable chemistries. These differences likely reflect modification of a single parent fluid through mineral dissolution and precipitation, water/rock interactions, boiling and vapor loss, conductive cooling, and mixing.

Fluid Pocket Generation in Response to Heterogeneous Reactivity of a Rock Fracture Under Hydrothermal Conditions

NASA Astrophysics Data System (ADS)

Okamoto, A.; Tanaka, H.; Watanabe, N.; Saishu, H.; Tsuchiya, N.

2017-10-01

Fractures are the location of various water-rock interactions within the Earth's crust; however, the impact of the chemical heterogeneity of fractures on hydraulic properties is poorly understood. We conducted flow-through experiments on the dissolution of granite with a tensile fracture at 350°C and fluid pressure of 20 MPa with confining pressure of 40 MPa. The aperture structures were evaluated by X-ray computed tomography before and after the experiments. Under the experimental conditions, quartz grains dissolve rapidly to produce grain-scale pockets on the fracture surface, whereas altered feldspar grains act as asperities to sustain the open cavities. The fracture contained gouge with large surface area. The feedback between fluid flow and the rapid dissolution of gouge material produced large fluid pockets, whereas permeability did not always increase significantly. Such intense hydrological-chemical interactions could strongly influence the porosity-permeability relationship of fractured reservoirs in the crust.

Multiple stable isotope fronts during non-isothermal fluid flow

NASA Astrophysics Data System (ADS)

Fekete, Szandra; Weis, Philipp; Scott, Samuel; Driesner, Thomas

2018-02-01

Stable isotope signatures of oxygen, hydrogen and other elements in minerals from hydrothermal veins and metasomatized host rocks are widely used to investigate fluid sources and paths. Previous theoretical studies mostly focused on analyzing stable isotope fronts developing during single-phase, isothermal fluid flow. In this study, numerical simulations were performed to assess how temperature changes, transport phenomena, kinetic vs. equilibrium isotope exchange, and isotopic source signals determine mineral oxygen isotopic compositions during fluid-rock interaction. The simulations focus on one-dimensional scenarios, with non-isothermal single- and two-phase fluid flow, and include the effects of quartz precipitation and dissolution. If isotope exchange between fluid and mineral is fast, a previously unrecognized, significant enrichment in heavy oxygen isotopes of fluids and minerals occurs at the thermal front. The maximum enrichment depends on the initial isotopic composition of fluid and mineral, the fluid-rock ratio and the maximum change in temperature, but is independent of the isotopic composition of the incoming fluid. This thermally induced isotope front propagates faster than the signal related to the initial isotopic composition of the incoming fluid, which forms a trailing front behind the zone of transient heavy oxygen isotope enrichment. Temperature-dependent kinetic rates of isotope exchange between fluid and rock strongly influence the degree of enrichment at the thermal front. In systems where initial isotope values of fluids and rocks are far from equilibrium and isotope fractionation is controlled by kinetics, the temperature increase accelerates the approach of the fluid to equilibrium conditions with the host rock. Consequently, the increase at the thermal front can be less dominant and can even generate fluid values below the initial isotopic composition of the input fluid. As kinetics limit the degree of isotope exchange, a third front may develop in kinetically limited systems, which propagates with the advection speed of the incoming fluid and is, therefore, traveling fastest. The results show that oxygen isotope signatures at thermal fronts recorded in rocks and veins that experienced isotope exchange with fluids can easily be misinterpreted, namely if bulk analytical techniques are applied. However, stable isotope microanalysis on precipitated minerals may - if later isotope exchange is kinetically limited - provide a valuable archive of the transient thermal and hydrological evolution of a system.

Quantification of CO2-FLUID-ROCK Reactions Using Reactive and Non-Reactive Tracers

NASA Astrophysics Data System (ADS)

Matter, J.; Stute, M.; Hall, J. L.; Mesfin, K. G.; Gislason, S. R.; Oelkers, E. H.; Sigfússon, B.; Gunnarsson, I.; Aradottir, E. S.; Alfredsson, H. A.; Gunnlaugsson, E.; Broecker, W. S.

2013-12-01

Carbon dioxide mineralization via fluid-rock reactions provides the most effective and long-term storage option for geologic carbon storage. Injection of CO2 in geologic formations induces CO2 -fluid-rock reactions that may enhance or decrease the storage permanence and thus the long-term safety of geologic carbon storage. Hence, quantitative characterization of critical CO2 -fluid-rock interactions is essential to assess the storage efficiency and safety of geologic carbon storage. In an attempt to quantify in-situ fluid-rock reactions and CO2 transport relevant for geologic carbon storage, we are testing reactive (14C, 13C) and non-reactive (sodium fluorescein, amidorhodamine G, SF5CF3, and SF6) tracers in an ongoing CO2 injection in a basaltic storage reservoir at the CARBFIX pilot injection site in Iceland. At the injection site, CO2 is dissolved in groundwater and injected into a permeable basalt formation located 500-800 m below the surface [1]. The injected CO2 is labeled with 14C by dynamically adding calibrated amounts of H14CO3-solution into the injection stream in addition to the non-reactive tracers. Chemical and isotopic analyses of fluid samples collected in a monitoring well, reveal fast fluid-rock reactions. Maximum SF6 concentration in the monitoring well indicates the bulk arrival of the injected CO2 solution but dissolved inorganic carbon (DIC) concentration and pH values close to background, and a potentially lower 14C to SF6 ratio than the injection ratio suggest that most of the injected CO2 has reacted with the basaltic rocks. This is supported by δ13CDIC, which shows a drop from values close to the δ 13C of the injected CO2 gas (-3‰ VPDB) during breakthrough of the CO2 plume to subsequent more depleted values (-11.25‰ VPDB), indicating precipitation of carbonate minerals. Preliminary mass balance calculations using mixing relationships between the background water in the storage formation and the injected solution, suggest that approximately 85% of the injected CO2 must have reacted along the flow path from the injection well to the monitoring well within less than one year. Monitoring is still going on and we will extend the time series and the mass balance accordingly. Our study demonstrates that by combining reactive and non-reactive tracers, we are able to quantify CO2-fluid-rock interactions on a reservoir scale. [1] Gislason et al. (2010), Int. J. Greenh. Gas Con. 4, 537-545.

Regional hydrology of the Dixie Valley geothermal field, Nevada: preliminary interpretations of chemical and isotopic data

USGS Publications Warehouse

Nimz, Gregory; Janik, Cathy; Goff, Fraser; Dunlap, Charles; Huebner, Mark; Counce, Dale; Johnson, Stuart D.

1999-01-01

Chemical and isotopic analyses of Dixie Valley regional waters indicated several distinct groups ranging in recharge age from Pleistocene (1000a). Geothermal field fluids (~12-14 ka) appear derived from water similar in composition to non thermal groundwater observed today in valley artesian well (also ~14 ka). Geothermal fluid interaction with mafic rocks (Humboldt Lopolith) appears to be common, and significant reaction with granodiorite may also occur. Despite widespread occurrence of carbonate rocks, large scale chemical interaction appears minor. Age asymmetry of the range, more extensive interaction with deep seated waters in the west, and distribution of springs and artesian wells suggest the existence of a regional upward hydrologic gradient with an axis in proximity to the Stillwater range.

Fluid-Rock Characterization and Interactions in NMR Well Logging

DOE Office of Scientific and Technical Information (OSTI.GOV)

George J. Hirasaki; Kishore K. Mohanty

2005-09-05

The objective of this report is to characterize the fluid properties and fluid-rock interactions that are needed for formation evaluation by NMR well logging. The advances made in the understanding of NMR fluid properties are summarized in a chapter written for an AAPG book on NMR well logging. This includes live oils, viscous oils, natural gas mixtures, and the relation between relaxation time and diffusivity. Oil based drilling fluids can have an adverse effect on NMR well logging if it alters the wettability of the formation. The effect of various surfactants on wettability and surface relaxivity are evaluated for silicamore » sand. The relation between the relaxation time and diffusivity distinguishes the response of brine, oil, and gas in a NMR well log. A new NMR pulse sequence in the presence of a field gradient and a new inversion technique enables the T{sub 2} and diffusivity distributions to be displayed as a two-dimensional map. The objectives of pore morphology and rock characterization are to identify vug connectivity by using X-ray CT scan, and to improve NMR permeability correlation. Improved estimation of permeability from NMR response is possible by using estimated tortuosity as a parameter to interpolate between two existing permeability models.« less

Development and application of laser microprobe techniques for oxygen isotope analysis of silicates, and, fluid/rock interaction during and after granulite-facies metamorphism, highland southwestern complex, Sri Lanka

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elsenheimer, D.W.

1992-01-01

The extent of fluid/rock interaction within the crust is a function of crustal depth, with large hydrothermal systems common in the brittle, hydrostatically pressured upper crust, but restricted fluid flow in the lithostatically pressured lower crust. To quantify this fluid/rock interaction, a Nd-YAG/CO[sub 2] laser microprobe system was constructed to analyze oxygen isotope ratios in silicates. Developed protocols produce high precision in [sigma][sup 18]O ([+-]0.2, 1[sigma]) and accuracy comparable to conventional extraction techniques on samples of feldspar and quartz as small as 0.3mg. Analysis of sub-millimeter domains in quartz and feldspar in granite from the Isle of Skye, Scotland, revealsmore » complex intragranular zonation. Contrasting heterogeneous and homogeneous [sigma][sup 18]O zonation patterns are revealed in samples <10m apart. These differences suggest fluid flow and isotopic exchange was highly heterogeneous. It has been proposed that granulite-facies metamorphism in the Highland Southwestern Complex (HSWC), Sri Lanka, resulted from the pervasive influx of CO[sub 2], with the marbles and calc-silicates within the HSWC a proposed fluid source. The petrologic and stable isotopic characteristic of HSWC marbles are inconsistent with extensive decarbonation. Wollastonite calc-silicates occur as deformed bands and as post-metamorphis veins with isotopic compositions that suggest vein fluids that are at least in part magmatic. Post-metamorphic magmatic activity is responsible for the formation of secondary disseminated graphite growth in the HSWC. This graphite has magmatic isotopic compositions and is associated with vein graphite and amphibolite-granulite facies transitions zones. Similar features in Kerela Khondalite Belt, South India, may suggest a common metamorphic history for the two terranes.« less

Making a black shale shine: the interaction of hydrothermal fluids and diagenetic processes

NASA Astrophysics Data System (ADS)

Gleeson, Sarah; Magnall, Joe; Reynolds, Merilie

2016-04-01

Hydrothermal fluids are important agents of mass and thermal transfer in the upper crust. This is exemplified by shale-hosted massive sulphide deposits (SHMS), which are anomalous accumulations of Zn and Pb sulphides (± barite) in sedimentary basins created by hydrothermal fluids. These deposits occur in passive margin settings and, typically, there is no direct evidence of magmatic input. Recent studies of Paleozoic deposits in the North American Cordillera (MacMillan Pass and Red Dog Districts) have shown that the deposits are formed in a sub-seafloor setting, where the potential for thermal and chemical gradients is high. Mineralization is characterized by the replacement and displacement of unconsolidated, partially lithified and lithified biosiliceous mudstones (± carbonates), and commonly the sulphide mineralization post-dates, and replaces, bedded barite units in the sediments. The Red Dog District (Alaska, USA) contain some of the largest Zn-Pb deposits ever discovered. The host-rocks are dominantly carbonaceous mudstones, with carbonate units and some radiolarites. The ore forms massive sulphide bodies that replace pyritized mudstones, barite and carbonate units. Lithological and textural relationships provide evidence that much of the ore formed in bioturbated, biosiliceous zones that may have had high primary porosity and/or permeability. Sediment permeability may have been further modified by aging of the silica rich sediments and the dissolution/replacement of carbonate and barite beds. At the Tom and Jason deposits (MacMillan Pass, Yukon) the fault-controlled hydrothermal upflow zone is uniquely preserved as an unequivocal vent complex. Here, the metal bearing fluids are hot (300°C), low salinity (6 wt% NaCl equiv.) and acidic (pH < 4.5). These fluids were initially in thermal and chemical disequilibrium with a partially lithified organic rich host-rock but cooled rapidly during fluid rock interaction and the input of diagenetic pore fluids. Paragenetically-constrained sulphur isotope analyses provide evidence that at MacMillan Pass and in the Red Dog deposits, reduced sulphur was generated during open system diagenesis and euxinic conditions were not present at the time of mineralization. Furthermore, the formation of diagenetic barite provided an important mechanism of sulphur concentration into the host rock. Both features combined to produce an effective metal trap in the sub-surface. Ultimately, interactions between hydrothermal and diagenetic fluids within a permeable, chemically reactive medium contribute to the formation of SHMS deposits. Where these factors align, it is possible to produce world-class ore deposits (e.g. in the Red Dog district). The complex textures that are commonly encountered in these systems are the result of hydrothermal fluids interacting with their host-rocks in a heterogeneous and dynamic physical and chemical environment.

Simulating single-phase and two-phase non-Newtonian fluid flow of a digital rock scanned at high resolution

NASA Astrophysics Data System (ADS)

Tembely, Moussa; Alsumaiti, Ali M.; Jouini, Mohamed S.; Rahimov, Khurshed; Dolatabadi, Ali

2017-11-01

Most of the digital rock physics (DRP) simulations focus on Newtonian fluids and overlook the detailed description of rock-fluid interaction. A better understanding of multiphase non-Newtonian fluid flow at pore-scale is crucial for optimizing enhanced oil recovery (EOR). The Darcy scale properties of reservoir rocks such as the capillary pressure curves and the relative permeability are controlled by the pore-scale behavior of the multiphase flow. In the present work, a volume of fluid (VOF) method coupled with an adaptive meshing technique is used to perform the pore-scale simulation on a 3D X-ray micro-tomography (CT) images of rock samples. The numerical model is based on the resolution of the Navier-Stokes equations along with a phase fraction equation incorporating the dynamics contact model. The simulations of a single phase flow for the absolute permeability showed a good agreement with the literature benchmark. Subsequently, the code is used to simulate a two-phase flow consisting of a polymer solution, displaying a shear-thinning power law viscosity. The simulations enable to access the impact of the consistency factor (K), the behavior index (n), along with the two contact angles (advancing and receding) on the relative permeability.

Influence of magmatic volatiles on boron isotope compositions in vent fluids from the Eastern Manus Basin, Papua New Guinea

NASA Astrophysics Data System (ADS)

Wilckens, F. K.; Kasemann, S.; Bach, W.; Reeves, E. P.; Meixner, A.; Seewald, J.

2016-12-01

In this study we present boron (B), lithium (Li) and strontium (Sr) concentrations and isotopic composition of submarine hydrothermal fluids collected in 2006 and 2011 from PACMANUS, DESMOS and SuSu Knolls vent fields located in the Eastern Manus Basin [1,2]. Hydrothermal vent fluids within the Eastern Manus Basin range from high-temperature black smoker fluids to low-temperature diffuse fluids and acid-sulfate fluids. In general, the different fluid types show variable water-rock ratios during water-rock interaction and different inputs of magmatic volatiles. End-member black smoker fluids, which have in general high temperatures (mostly higher than 280°C) and pH values higher than 2 (measured at 25°C) are characterized by low δ7Li values (3.9 to 5.9‰) and 87Sr/86Sr ratios (0.704 to 0.705) similar to the values for island arc basalts. These results suggest low water-rock ratios during hydrothermal circulation. B concentrations and isotopic compositions in these fluids range from 1.0 to 2.6μM and 13 to 20‰, respectively. These data match with other vent fluids from island arc settings in the Western Pacific and plot in a B versus δ11B diagram on a two-component mixing line between seawater and island arc basalts [3]. Sr and Li isotopic composition of white smoker and acid-sulfate fluids overlap generally with the isotopic ratios for the black smoker fluids. However, in some fluids Sr isotope ratios are up to 0.709 near seawater composition suggesting higher water-rock ratios during water-rock interaction. B concentrations and isotope ratios in the white smoker and acid-sulfate fluids range from 0.6 to 2.2μM and 9 to 16‰, respectively which are lower compared with the values of black smoker fluids. In addition, these fluids do not fit on the mixing line between seawater and island arc basalt, and define another mixing trend in a B versus δ11B diagram. To explain this contradictory trend, a third mixing endmember is required that shifts B concentrations and δ11B to lower values. A possible mixing endmember is B volatized from magmatic gases. This endmember seems to be reasonable because it only influences B, whereas Li and Sr stay unaffected. [1] Reeves et al. (2011) GCA 75, 1088-1123 [2] Seewald et al. (2015) GCA 163, 178-199 [3] Yamaoka et al. (2015) CG 392, 9-18

Isotopic and noble gas geochemistry in geothermal research

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kennedy, B.M.; DePaolo, D.J.

1997-12-31

The objective of this program is to provide, through isotopic analyses of fluids, fluid inclusions, and rocks and minerals coupled with improved methods for geochemical data analysis, needed information regarding sources of geothermal heat and fluids, the spatial distribution of fluid types, subsurface flow, water-rock reaction paths and rates, and the temporal evolution of geothermal systems. Isotopic studies of geothermal fluids have previously been limited to the light stable isotopes of H, C, and O. However, other isotopic systems such as the noble gases (He, Ne, Ar, Kr and Xe) and reactive elements (e.g. B, N, S, Sr and Pb)more » are complementary and may even be more important in some geothermal systems. The chemistry and isotopic composition of a fluid moving through the crust will change in space and time in response to varying chemical and physical parameters or by mixing with additional fluids. The chemically inert noble gases often see through these variations, making them excellent tracers for heat and fluid sources. Whereas, the isotopic compositions of reactive elements are useful tools in characterizing water-rock interaction and modeling the movement of fluids through a geothermal reservoir.« less

Fluid and mass transfer at subduction interfaces-The field metamorphic record

NASA Astrophysics Data System (ADS)

Bebout, Gray E.; Penniston-Dorland, Sarah C.

2016-01-01

The interface between subducting oceanic slabs and the hanging wall is a structurally and lithologically complex region. Chemically disparate lithologies (sedimentary, mafic and ultramafic rocks) and mechanical mixtures thereof show heterogeneous deformation. These lithologies are tectonically juxtaposed at mm to km scales, particularly in more intensely sheared regions (mélange zones, which act as fluid channelways). This juxtaposition, commonly in the presence of a mobile fluid phase, offers up huge potential for mass transfer and related metasomatic alteration. Fluids in this setting appear capable of transporting mass over scales of kms, along flow paths with widely varying geometries and P-T trajectories. Current models of arc magmatism require km-scale migration of fluids from the interface into mantle wedge magma source regions and implicit in these models is the transport of any fluids generated in the subducting slab along and ultimately through the subduction interface. Field and geochemical studies of high- and ultrahigh-pressure metamorphic rocks elucidate the sources and compositions of fluids in subduction interfaces and the interplay between deformation and fluid and mass transfer in this region. Recent geophysical studies of the subduction interface - its thickness, mineralogy, density, and H2O content - indicate that its rheology greatly influences the ways in which the subducting plate is coupled with the hanging wall. Field investigation of the magnitude and styles of fluid-rock interaction in metamorphic rocks representing "seismogenic zone" depths (and greater) yields insight regarding the roles of fluids and elevated fluid pore pressure in the weakening of plate interface rocks and the deformation leading to seismic events. From a geochemical perspective, the plate interface contributes to shaping the "slab signature" observed in studies of the composition of arc volcanic rocks. Understanding the production of fluids with hybridized chemical/isotopic compositions could improve models aimed at identifying the relative contributions of end-member rock reservoirs through analyses of arc volcanic rocks. Production of rocks rich in hydrous minerals, along the subduction interface, could stabilize H2O to great depths in subduction zones and influence deep-Earth H2O cycling. Enhancement of decarbonation reactions and dissolution by fluid infiltration facilitated by deformation at the interface could influence the C flux from subducting slabs entering the sub-arc mantle wedge and various forearc reservoirs. In this paper, we consider records of fluid and mass transfer at localities representing various depths and structural expressions of evolving paleo-interfaces, ranging widely in structural character, the rock types involved (ultramafic, mafic, sedimentary), and the rheology of these rocks. We stress commonalities in styles of fluid and mass transfer as related to deformation style and the associated geometries of fluid mobility at subduction interfaces. Variations in thermal structure among individual margins will lead to significant differences in not only the rheology of subducting rocks, and thus seismicity, but also the profiles of devolatilization and melting, through the forearc and subarc, and the element/mineral solubilities in any aqueous fluids or silicate melts that are produced. One key factor in considering fluid and mass transfer in the subduction interface, influencing C cycling and other chemical additions to arcs, is the uncertain degree to which sub-crustal ultramafic rocks in downgoing slabs are hydrated and release H2O-rich fluids.

Laboratory Simulations of Permeability Pertaining to Biosignature Development and Preservation Potential for Martian Subsurface Habitability

NASA Astrophysics Data System (ADS)

Perl, S. M.; Corsetti, F. A.; Berelson, W.; Nealson, K. H.; Bhartia, R.

2014-12-01

Sedimentological and mineralogical observations indicate that sandstones within the Eagle and Endurance crater sections of the Burns Formation of Meridiani Planum, Mars, were derived from sulfate-bearing altered basalt, possibly from a playa lake, and deposited by eolian and locally subaqueous processes in a eolian dune - sand sheet - interdune setting. Abrasion of rocks within the outcrop outlining Endurance Crater by the MER rover Opportunity revealed void spaces later determined to be secondary pore space created from the dissolution of soluble minerals from multiple groundwater movement (recharge) events. Previous investigations into the secondary porosity and permeability of rocks within the Karatepe section showed that the ability for fluid movement through the vertical sedimentary section was greatest between the Upper and Middle units at the Whatanga contact within Endurance Crater, where secondary porosity was measured to be ~40% of the rock. Our investigations into quantifying subsurface habitability involve simulating the paleo-groundwater environments on the micro-to-mesoscale (sub mm-scale to cm-scale) to determine how preservation potential changes with repeated water-rock interaction, varying fluid chemistry (pH, salinity, T, others), and pressure changes under Earth and Mars conditions. In addition to fluids, microbes (extremophiles) will be introduced into our simulation to observe how changing experimental input conditions impact the growth and development of biotic interactions and eventually biosignatures left behind within sedimentary microtextures. Moreover, detection of biosignatures using visual and UV methods will help inform the M2020 rover mission regarding in-situ analysis of abraded rock outcrops. Finally, results of this work will use terrestrial rocks and fluids from a known Mars analogue (the Rio Tinto basin) in order to aid in determining habitability and survivability in acidic and high saline conditions that are similar to Meridiani Planum, Mars.

Environmental consequences of shale gas exploitation and the crucial role of rock microfracturing

NASA Astrophysics Data System (ADS)

Renard, Francois

2015-04-01

The growing exploitation of unconventional gas and oil resources has dramatically changed the international market of hydrocarbons in the past ten years. However, several environmental concerns have also been identified such as the increased microseismicity, the leakage of gas into freshwater aquifers, and the enhanced water-rock interactions inducing the release of heavy metals and other toxic elements in the produced water. In all these processes, fluids are transported into a network of fracture, ranging from nanoscale microcracks at the interface between minerals and the kerogen of the source rock, to well-developed fractures at the meter scale. Characterizing the fracture network and the mechanisms of its formation remains a crucial goal. A major difficulty when analyzing fractures from core samples drilled at depth is that some of them are produced by the coring process, while some other are produced naturally at depth by the coupling between geochemical and mechanical forces. Here, I present new results of high resolution synchrotron 3D X-ray microtomography imaging of shale samples, at different resolutions, to characterize their microfractures and their mechanisms of formation. The heterogeneities of rock microstructure are also imaged, as they create local stress concentrations where cracks may nucleate or along which they propagate. The main results are that microcracks form preferentially along kerogen-mineral interfaces and propagate along initial heterogeneities according to the local stress direction, connecting to increase the total volume of fractured rock. Their lifetime is also an important parameter because they may seal by fluid circulation, fluid-rock interactions, and precipitation of a cement. Understanding the multi-scale processes of fracture network development in shales and the coupling with fluid circulation represents a key challenge for future research directions.

Volatile (Li, B, F and Cl) mobility during amphibole breakdown in subduction zones

NASA Astrophysics Data System (ADS)

Debret, Baptiste; Koga, Kenneth T.; Cattani, Fanny; Nicollet, Christian; Van den Bleeken, Greg; Schwartz, Stephane

2016-02-01

Amphiboles are ubiquitous minerals in the altered oceanic crust. During subduction, their breakdown is governed by continuous reactions up to eclogitic facies conditions. Amphiboles thus contribute to slab-derived fluid throughout prograde metamorphism and continuously record information about volatile exchanges occurring between the slab and the mantle wedge. However, the fate of volatile elements and especially halogens, such as F and Cl, in amphibole during subduction is poorly constrained. We studied metagabbros from three different localities in the Western Alps: the Chenaillet ophiolite, the Queyras Schistes Lustrés and the Monviso meta-ophiolitic complexes. These samples record different metamorphic conditions, from greenschist to eclogite facies, and have interacted with different lithologies (e.g. sedimentary rocks, serpentinites) from their formation at mid-oceanic ridge, up to their devolatilization during subduction. In the oceanic crust, the initial halogen budget is mostly stored in magmatic amphibole (F = 300-7000 ppm; Cl = 20-1200 ppm) or in amphibole corona (F = 100-7000 ppm; Cl = 80-2000 ppm) and titanite (F = 200-1500 ppm; Cl < 200 ppm) formed during hydrothermal seafloor alteration. It is thus the fate of these phases that govern the halogen fluxes between the crust and the overlying mantle and/or the plate interface in subduction zones. Li and B are poorly stored in the oceanic crust (< 5 ppm). In subduction zones, prograde metamorphism of metagabbros is first marked by the crystallization of glaucophane at the expense of magmatic and amphibole coronas. This episode is accompanied with a decrease of halogen concentrations in amphiboles (< 200 ppm of F and Cl) suggesting that these elements can be transferred to the mantle wedge by fluids. In the Queyras Schistes Lustrés complex, the intense deformation and the abundant devolatilization of metasedimentary rocks produce large fluid flows that promote rock chemical hybridization (metasomatic mixing with hybrid composition between metasedimentary rock and metagabbro) at the metasedimentary rock/metagabbro contacts. Such fluid/rock interactions result in a strong addition of Li in glaucophane (up to 600 ppm) whereas halogen concentrations are unaffected. At eclogite facies conditions, metagabbros display low halogens concentrations (< 20 ppm of F and < 100 ppm of Cl) relative to altered oceanic crust (F = 40-650 ppm; Cl = 40-1400 ppm) suggesting that these elements are continuously released by fluids during the first 30-80 km of subduction whatever the tectonic environment (e.g. slab, plate interface) and the considered fluid/rock interactions.

Mass transfer and fluid evolution in late-metamorphic veins, Rhenish Massif (Germany): insight from alteration geochemistry and fluid-mineral equilibria modeling

NASA Astrophysics Data System (ADS)

Marsala, Achille; Wagner, Thomas

2016-08-01

Element mobility and fluid-rock interaction related to the formation of late-metamorphic quartz veins have been studied by combination of mineral chemistry, whole-rock geochemistry, mass balance analysis and fluid-mineral equilibria modeling. The quartz veins are hosted by very low-grade metasedimentary rocks of the fold-and-thrust belt of the Rhenish Massif (Germany). The veins record two stages of evolution, a massive vein filling assemblage with elongate-blocky quartz, chlorite, apatite and albite, and a later open space filling assemblage with euhedral crystals of quartz, ankerite-dolomite and minor calcite and sulfides. Detailed mass balance analysis of an alteration profile adjacent to a representative quartz vein demonstrates that element mobility is restricted to the proximal zone. The most important element changes are gain of Ca, Fe, Mg, Mn, P and CO2, and loss of Si, K and Na. The data demonstrate that wall-rock carbonation is one of the main alteration features, whereas mobility of Si, K and Na are related to dissolution of quartz and destruction of detrital feldspar and muscovite. The whole-rock geochemical data, in conjunction with fluid composition data and pressure-temperature estimates, were used as input for fluid-mineral equilibria modeling in the system Si-Al-Fe-Mg-Ca-Na-K-C-S-O-H-B-F-Cl. Modeling involved calculation of rock-buffered fluid compositions over the temperature interval 100-500 °C, and reaction-path simulations where a rock-buffered high-temperature fluid reacts with fresh host-rocks at temperatures of 400, 300 and 200 °C. Calculated rock-buffered fluid compositions demonstrate that retrograde silica solubility is a strong driving force for quartz leaching in the temperature-pressure window of 380-450 °C and 0.5 kbar. These conditions overlap with the estimated temperatures for the initial stage of vein formation. Reaction-path models show that high-temperature alteration can produce the observed silica leaching, suggesting that fast advection of external hot fluids from deeper crustal levels was essential for the early stage of vein formation. Fluid advection must have occurred as multiple pulses, which allowed for periods of influx of fluids that leached quartz, alternating with periods of cooling and quartz precipitation in the veins. Reaction-path models at high temperatures (300-400 °C) do not produce carbonate alteration, whereas fluid-rock reaction at 200 °C produces carbonate alteration, consistent with the temperature estimates for the late-stage vein carbonate assemblage. Comparison between modeling results and geochemical data suggests that the observed alteration features are the product of fluid-rock reaction under conditions where the external fluid gradually cooled down and evolved with time. The results of this study highlight the importance of late-orogenic fluid migration for the formation of quartz vein arrays in fold-and-thrust belts.

Paleozoic fluid history of the Michigan Basin: Evidence from dolomite geochemistry in the Middle Ordovician St. Peter Sandstone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Winter, B.L.; Johnson, C.M.; Simo, J.A.

1995-04-03

The isotope (Sr and O) and elemental (Mg, Ca, Mn, Fe, and Sr) compositions of the various dolomites in the Middle Ordovician St. Peter Sandstone in the Michigan Basin are determined and the variations are modeled in terms of fluid-rock interaction or as mixing relations. These geochemical models, combined with the paragenetic sequence of the dolomites and late anhydrite cement, suggest the existence of at least four distinct diagenetic fluids in the St. Peter Sandstone during the paleozoic. Fluid 1 has a composition consistent with a modified older (pre-Middle Ordovician) seawater origin, which indicates that the flow path for thismore » fluid had a major upward component. This fluid resulted in the first and volumetrically most important burial dolomitization event, producing dolomite in both carbonate and quartz sandstone lithofacies in the St. Peter Sandstone. Fluid 2 has a composition consistent with a modified Middle to early Late Ordovician seawater origin, suggesting a major downward component for fluid flow. Fluid 2 produced dolomite cement in the carbonate lithofacies that postdates Fluid 1 dolomite. The composition of Fluid 3 is best interpreted to reflect a heated, deep basinal brine that had previously interacted with the K-feldspar-rich rocks near the Cambrian-Precambrian unconformity in the Michigan Basin, indicating a major upward component for fluid flow. Fluid 3 produced dolomite cement in quartz sandstone lithofacies that postdates Fluid 1 dolomite. Fluid 4 resulted in precipitation of late anhydrite in fractures. The {sup 87}Sr/{sup 86}Sr ratio of the anhydrite is consistent with Fluid 4 originating as a dilute fluid that interacted extensively with Silurian gypsum in the Michigan Basin; this indicates that the flow path of Fluid 4 had a major downward component.« less

Sources of Matter and Ore-Producing Fluid of the Tamunyer Gold-Sulfide Deposit (Northern Urals): Isotope Results

NASA Astrophysics Data System (ADS)

Zamyatina, D. A.; Murzin, V. V.

2018-02-01

The Tamunyer deposit is a typical example of gold-sulfide mineralization located in the lower lithologic-stratigraphic unit (S2-D1) of the Auerbach volcanic-plutonic belt. The latter comprises island-arc andesitic volcano-sediments, volcanics, and comagmatic intrusive formations. Carbonates have demonstrated intermediate values of δ13C between marine limestone and mantle. The quartz δ18O is in the range of 15.3-17.2‰. The δ34S of sulfides from the beresitized volcano-sedimentary rocks and ores varies widely from -7.5 to 12‰. The calculated isotope compositions of H2O, CO2, and H2S of the ore-bearing fluid imply two major sources of matter contributing to ore genesis: local rocks and foreign fluid. The ore-bearing fluid was formed by interaction and isotope equilibration between a deep magmatic fluid and marine carbonates (W/R 1), with the contribution of sulfur from the volcano-sedimentary rocks.

Geochemistry of hydrothermal vent fluids and its implications for subsurface processes at the active Longqi hydrothermal field, Southwest Indian Ridge

NASA Astrophysics Data System (ADS)

Ji, Fuwu; Zhou, Huaiyang; Yang, Qunhui; Gao, Hang; Wang, Hu; Lilley, Marvin D.

2017-04-01

The Longqi hydrothermal field at 49.6°E on the Southwest Indian Ridge was the first active hydrothermal field found at a bare-rock ultra-slow spreading mid-ocean ridge. Here we report the chemistry of the hydrothermal fluids, for the first time, that were collected from the S zone and the M zone of the Longqi field by gas-tight isobaric samplers by the HOV "Jiaolong" diving cruise in January 2015. According to H2, CH4 and other chemical data of the vent fluid, we suggest that the basement rock at the Longqi field is dominantly mafic. This is consistent with the observation that the host rock of the active Longqi Hydrothermal field is dominated by extensively distributed basaltic rock. It was very interesting to detect simultaneously discharging brine and vapor caused by phase separation at vents DFF6, DFF20, and DFF5 respectively, in a distance of about 400 m. Based on the end-member fluid chemistry and distance between the vents, we propose that there is a single fluid source at the Longqi field. The fluid branches while rising to the seafloor, and two of the branches reach S zone and M zone and phase separate at similar conditions of about 28-30.2 MPa and 400.6-408.3 °C before they discharge from the vents. The end-member fluid compositions of these vents are comparable with or within the range of variation of known global seafloor hydrothermal fluid chemical data from fast, intermediate and slow spreading ridges, which confirms that the spreading rate is not the key factor that directly controls hydrothermal fluid chemistry. The composition of basement rock, water-rock interaction and phase separation are the major factors that control the composition of the vent fluids in the Longqi field.

Dehydration reactions, mass transfer and rock deformation relationships during subduction of Alpine metabauxites: insights from LIBS compositional profiles between metamorphic veins

NASA Astrophysics Data System (ADS)

Verlaguet, Anne; Brunet, Fabrice; Goffé, Bruno; Menut, Denis; Findling, Nathaniel; Poinssot, Christophe

2013-04-01

In subduction zones, the significant amounts of aqueous fluid released in the course of the successive dehydration reactions occurring during prograde metamorphism are expected to strongly influence the rock rheology, as well as kinetics of metamorphic reactions and mass transfer efficiency. Mineralized veins, ubiquitous in metamorphic rocks, can be seen as preserved witnesses of fluid and mass redistribution that partly accommodate the rock deformation (lateral segregation). However, the driving forces and mechanisms of mass transfer towards fluid-filled open spaces remain somewhat unclear. The aim of this study is to investigate the vein-forming processes and the modalities of mass transfer during local fluid-rock interactions, and their links with fluid production and rock deformation, with new insights from Laser Induced Breakdown Spectroscopy (LIBS) profiles. This study focuses on karstic pockets (metre scale) of Triassic metabauxites embedded in thick carbonate units, that have been isolated from large-scale fluid flow during HP-LT Alpine metamorphism (W. Vanoise, French Alps). These rocks display several generations of metamorphic veins containing various Al-bearing minerals, which give particular insights into mass transfer processes. It is proposed that the internally-derived fluid (~13 vol% produced by successive dehydration reactions) has promoted the opening of fluid-filled open spaces (euhedral habits of vein minerals) and served as medium for diffusive mass transfer from rock to vein. Based on mineralogical and textural features, two vein types can be distinguished: (1) some veins are filled with newly formed products of either prograde (chloritoid) or retrograde (chlorite) metamorphic reactions; in this case, fluid-filled open spaces seem to offer energetically favourable nucleation/growth sites; (2) the second vein type is filled with cookeite (Li-Al-rich chlorite) or pyrophyllite, that were present in the host rock prior to the vein formation. In this closed chemical system, mass transfer from rock to vein was achieved through the fluid, in a dissolution-transport-precipitation process, possibly stress-assisted. To investigate the modalities of mass transfer towards this second vein type, LIBS profiles were performed in the rock matrix, taking Li concentration as a proxy for cookeite distribution. Cookeite is highly concentrated (40-70 vol%) in regularly spaced veins, and the LIBS profiles show that cookeite is evenly distributed in the rock matrix comprised between two veins. The absence of diffusion profiles suggests that the characteristic diffusion length for Li, Al and Si is greater than or equal to the distance separating two cookeite veins (3-6 cm). This is in agreement with characteristic diffusion lengths calculated from both grain boundary and pore fluid diffusion coefficients, for the estimated duration of the peak of metamorphism. Concerning mass transfer driving forces, phyllosilicates have very different morphologies in the rock matrix (fibers) compared to veins (euhedral crystals): fluid-mineral interfacial energy may be maximal in the small matrix pores, which can maintain higher cookeite solubility than in fluid-filled open spaces. Therefore, as soon as veins open, chemical potential gradients may develop and drive cookeite transfer from rock matrix to veins.

Using SEM Analysis on Ion-Milled Shale Surface to Determine Shale-Fracturing Fluid Interaction

NASA Astrophysics Data System (ADS)

Lu, J.; Mickler, P. J.; Nicot, J. P.

2014-12-01

It is important to document and assess shale-fluid interaction during hydraulic fracturing (HF) in order to understand its impact on flowback water chemistry and rock property. A series of autoclave experiments were conducted to react shale samples from major oil and gas shales with synthetic HF containing various additives. To better determine mineral dissolution and precipitation at the rock-fluid interface, ion-milling technique was applied to create extremely flat rock surfaces that were examined before and after the autoclave experiments using a scanning electron microscope (SEM) coupled with energy dispersive spectroscopy (EDS) detectors. This method is able to reveal a level of detail not observable on broken surface or mechanically polished surface. It allows direct comparison of the same mineral and organic matter particles before and after the reaction experiments. Minerals undergone dissolution and newly precipitated materials are readily determined by comparing to the exact locations before reaction. The dissolution porosity and the thickness of precipitates can be quantified by tracing and measuring the geometry of the pores and precipitates. Changes in porosity and permeability were confirmed by mercury intrusion capillary tests.

Geochemistry of continental subduction-zone fluids

NASA Astrophysics Data System (ADS)

Zheng, Yong-Fei; Hermann, Joerg

2014-12-01

The composition of continental subduction-zone fluids varies dramatically from dilute aqueous solutions at subsolidus conditions to hydrous silicate melts at supersolidus conditions, with variable concentrations of fluid-mobile incompatible trace elements. At ultrahigh-pressure (UHP) metamorphic conditions, supercritical fluids may occur with variable compositions. The water component of these fluids primarily derives from structural hydroxyl and molecular water in hydrous and nominally anhydrous minerals at UHP conditions. While the breakdown of hydrous minerals is the predominant water source for fluid activity in the subduction factory, water released from nominally anhydrous minerals provides an additional water source. These different sources of water may accumulate to induce partial melting of UHP metamorphic rocks on and above their wet solidii. Silica is the dominant solute in the deep fluids, followed by aluminum and alkalis. Trace element abundances are low in metamorphic fluids at subsolidus conditions, but become significantly elevated in anatectic melts at supersolidus conditions. The compositions of dissolved and residual minerals are a function of pressure-temperature and whole-rock composition, which exert a strong control on the trace element signature of liberated fluids. The trace element patterns of migmatic leucosomes in UHP rocks and multiphase solid inclusions in UHP minerals exhibit strong enrichment of large ion lithophile elements (LILE) and moderate enrichment of light rare earth elements (LREE) but depletion of high field strength elements (HFSE) and heavy rare earth elements (HREE), demonstrating their crystallization from anatectic melts of crustal protoliths. Interaction of the anatectic melts with the mantle wedge peridotite leads to modal metasomatism with the generation of new mineral phases as well as cryptic metasomatism that is only manifested by the enrichment of fluid-mobile incompatible trace elements in orogenic peridotites. Partial melting of the metasomatic mantle domains gives rise to a variety of mafic igneous rocks in collisional orogens and their adjacent active continental margins. The study of such metasomatic processes and products is of great importance to understanding of the mass transfer at the slab-mantle interface in subduction channels. Therefore, the property and behavior of subduction-zone fluids are a key for understanding of the crust-mantle interaction at convergent plate margins.

Dissolution and secondary mineral precipitation in basalts due to reactions with carbonic acid

NASA Astrophysics Data System (ADS)

Kanakiya, Shreya; Adam, Ludmila; Esteban, Lionel; Rowe, Michael C.; Shane, Phil

2017-06-01

One of the leading hydrothermal alteration processes in volcanic environments is when rock-forming minerals with high concentrations of iron, magnesium, and calcium react with CO2 and water to form carbonate minerals. This is used to the advantage of geologic sequestration of anthropogenic CO2. Here we experimentally investigate how mineral carbonation processes alter the rock microstructure due to CO2-water-rock interactions. In order to characterize these changes, CO2-water-rock alteration in Auckland Volcanic Field young basalts (less than 0.3 Ma) is studied before and after a 140 day reaction period. We investigate how whole core basalts with similar geochemistry but different porosity, permeability, pore geometry, and volcanic glass content alter due to CO2-water-rock reactions. Ankerite and aluminosilicate minerals precipitate as secondary phases in the pore space. However, rock dissolution mechanisms are found to dominate this secondary mineral precipitation resulting in an increase in porosity and decrease in rigidity of all samples. The basalt with the highest initial porosity and volcanic glass volume shows the most secondary mineral precipitation. At the same time, this sample exhibits the greatest increase in porosity and permeability, and a decrease in rock rigidity post reaction. For the measured samples, we observe a correlation between volcanic glass volume and rock porosity increase due to rock-fluid reactions. We believe this study can help understand the dynamic rock-fluid interactions when monitoring field scale CO2 sequestration projects in basalts.

Oxygen and Hydrogen Isotope Values for Unaltered and Hydrothermally Altered Samples from the Cretaceous Linga Plutonic Complex of the Peruvian Coastal Batholith near Ica.

NASA Astrophysics Data System (ADS)

Gonzalez, L. U.; Holk, G. J.; Clausen, B. L.; Poma Porras, O. A.

2015-12-01

A portion of the Peruvian Coastal Batholith near Ica, Peru is being studied using stable isotopes to determine the source of hydrothermal fluids that caused propylitic, phyllic, and potassic alteration in the mineralized Linga plutonic complex. Sources of hydrothermal fluids and water/rock ratios are estimated to understand the role of such fluids in alteration during cooling. A set of 64 mineral analysis from 18 igneous samples, 7 unaltered and 11 altered, were analyzed for D/H and 18O/16O isotopes. The δ18O values for whole rocks with no apparent alteration vary from +6.8‰ to +7.9‰, with sets of δ18O mineral values indicating isotopic equilibrium at closure temperatures from 571°C to 651°C, and no interaction with meteoric water. This conclusion is bolstered by hornblende (-87‰ to -64‰) and biotite (-81‰ to -74‰) δD values Most δ18O values for samples with hydrothermal alteration suggest that alteration results from magmatic fluids; however, several analyses indicate interaction with other fluids. The high δ18O values for plagioclase (+9.3‰) and hornblende (+6.3‰) from a metamorphic aureole in volcanic host rock near a plutonic intrusion may be due to interaction with metamorphic or low temperature magmatic fluids. Plagioclase (+2.6‰) and biotite (+0.1‰) δ18O values in a sample from the Jurassic volcanic envelope indicate a significant effect from meteoric-hydrothermal fluids. An altered monzonite yielded δ18O values for quartz (+5.5‰), K-spar (+5.6‰), and magnetite (+0.4‰), also suggesting interaction with meteoric fluids. A diorite from an area with strong epidotization produced an epidote δD value of -25.8‰ and a monzonite from a highly veined area has an epidote δD value of -36.1‰ suggesting interaction with sea water. This new data indicate that the Linga complex was primarily influenced by magmatic hydrothermal fluids, but metamorphic, meteoric, and sea water may have had some influence in producing alteration assemblages and in cooling the magmatic complex.

Oxygen and hydrogen isotopic composition of the fluid during formation of anthophyllite metaultramafic rocks in the Sysert metamorphic complex, central Urals

NASA Astrophysics Data System (ADS)

Murzin, V. V.

2014-12-01

The oxygen (δ18O) and hydrogen (δD) isotopic composition of H2O-bearing minerals was studied for the ore-bearing amphibole metaultramafic rocks, which are the products of the early regional (435 ± 44 Ma) and late local (260 ± 6 Ma) silicic metasomatose in the Sysert metamorphic complex. The gold-sulfide mineralization of the Karas'evogorskoe deposit and anthophyllite-asbestos bodies of the Tersut deposit are related to the regional and local metasomatose combined with plagiogranitization and potassium granitization, respectively. The H2O-bearing minerals of metasomatites (anthophyllite, tremolite, talc) of the Karas'evogorskoe and Tersut deposits are characterized by heavier δ18O (9.8 to 12.2 and 7.6 to 9.4‰, respectively) and lighter ·D (87 to -91 and -56 to -67‰, respectively) values. The calculated isotopic composition of the fluid in equilibrium with these minerals indicates a heterogeneous source of water for the fluids related to the formation of metasomatites and the metamorphic origin of fluids. During the regional metasomatose, this fluid was a result of equilibrium of the deep fluid with volcanosedimentary rocks enriched in the heavy oxygen isotope. At the local metasomatose, the metamorphic fluid was formed by interaction of magmatic water produced by potassium granitization with ultramafic rocks.

Authigenic potassium feldspar: a tracer for the timing of palaeofluid flow in carbonate rocks, Northern Calcareous Alps, Austria

USGS Publications Warehouse

Spotl, C.; Kunk, Michael J.; Ramseyer, K.; Longstaffe, F.J.

1998-01-01

This paper is included in the Special Publication entitled 'Dating and duration of fluid flow and fluid-rock interaction', edited by J. Parnell. Feldspar is a common authigenic constituent in Permian carbonate rocks which occur as tectonically isolated blocks within the evaporitic Haselgebirge melange in the Northern Calcareous Alps (NCA). Coexisting with pyrite, anhydrite, (saddle) dolomite, magnesite, fluorite and calcite, K-feldspar and minor albite record an event of regionally extensive interaction of hot brines with carbonate rocks. Detailed petrographic, crystallographic and geochemical studies reveal a variability in crystal size and shape, Al-Si ordering, elemental and stable isotopic compositions of the K-feldspar, which is only partially consistent with the traditional view of authigenic feldspar as a well-ordered, compositionally pure mineral. 40Ar-39Ar step- heating measurements of authigenic potassium feldspar from several localities yield two age populations, an older one of 145-154 Ma, and a younger one of c.90-97 Ma. Most age spectra reflect cooling through the argon retention temperature interval, which was rapid in some localities (as indicated by plateau ages) and slower in others. Rb-Sr isotope data are more difficult to interpret, because in many K-feldspar samples they are controlled largely by Sr-bearing inclusions. The Jurassic 40Ar-39Ar dates are interpreted as minimum ages of feldspar growth and hence imply that fluid-rock interaction is likely to be simultaneous with or to slightly predate melange formation. Deformation associated with the closure and subduction of the Meliata-Hallstatt ocean south of the NCA during the Upper Jurassic is regarded as the principal geodynamic driving force for both enhanced fluid circulation and melange formation. Some localities were reheated beyond the argon retention temperature for microcline during mid-Cretaceous nappe stacking of the NCA, thus obliterating the older signal.

Aqueous Alteration of Endeavour Crater Rim Apron Rocks

NASA Technical Reports Server (NTRS)

Mittlefehldt, David W.; Ming, Douglas W.; Gellert, Ralf; Clark, Benton C.; Morris, Richard V.; Yen, Albert S.; Arvidson, Raymond E.; Crumpler, Larry S.; Farrand, William H.; Grant, John A.;

Aqueous Alteration of Endeavour Crater Rim Apron Rocks

NASA Astrophysics Data System (ADS)

Ming, D. W.; Mittlefehldt, D. W.; Gellert, R.; Clark, B. C.; Morris, R. V.; Yen, A. S.; Arvidson, R. E.; Crumpler, L. S.; Farrand, W. H.; Grant, J. A., III; Jolliff, B. L.; Parker, T. J.; Peretyazhko, T.

2014-12-01

Mars Exploration Rover Opportunity is exploring Noachian age rocks of the rim of 22 km diameter Endeavour crater. Overlying the pre-impact lithologies and rim breccias is a thin apron of fine-grained sediments, the Grasberg fm, forming annuli on the lower slopes of rim segments. Hesperian Burns fm sandstones overly the Grasberg fm. Grasberg rocks have major element compositions that are distinct from Burns fm sandstones, especially when comparing interior compositions exposed by the Rock Abrasion Tool. Grasberg rocks are also different from Endeavour rim breccias, but have general compositional similarities to them. Grasberg sediments are plausibly fine-grained materials derived from the impact breccias. Veins of CaSO4 transect Grasberg fm rocks demonstrating post-formation aqueous alteration. Minor/trace elements show variations consistent with mobilization by aqueous fluids. Grasberg fm rocks have low Mn and high Fe/Mn ratios compared to the other lithologies. Manganese likely was mobilized and removed from the Grasberg host rock by redox reactions. We posit that Fe2+ from acidic solutions associated with formation of the Burns sulfate-rich sandstones acted as an electron donor to reduce more oxidized Mn to Mn2+. The Fe contents of Grasberg rocks are slightly higher than in other rocks suggesting precipitation of Fe phases in Grasberg materials. Pancam spectra show that Grasberg rocks have a higher fraction of ferric oxide minerals than other Endeavour rim rocks. Solutions transported Mn2+ into the Endeavour rim materials and oxidized and/or precipitated it in them. Grasberg has higher contents of the mobile elements K, Zn, Cl, and Br compared to the rim materials. Similar enrichments of mobile elements were measured by the Spirit APXS on West Spur and around Home Plate in Gusev crater. Enhancements in these elements are attributed to interactions of hydrothermal acidic fluids with the host rocks. Interactions of fluids with the Grasberg fm postdate the genesis of the Endeavour rim phyllosilicates. The aqueous alteration history of Endeavour rim rocks is complicated by different styles of alteration that have spanned the Noachian and Hesperian. Late stage acidic aqueous alteration of Grasberg fm materials is likely penecontemporaneous with the diagenesis of the sulfate-rich sediments of Meridiani Planum.

Origin of high-grade gold ore, source of ore fluid components, and genesis of the Meikle and neighboring Carlin-type deposits, Northern Carlin Trend, Nevada

USGS Publications Warehouse

Emsbo, P.; Hofstra, A.H.; Lauha, E.A.; Griffin, G.L.; Hutchinson, R.W.

2003-01-01

The Meikle mine exploits one of the world's highest grade Carlin-type gold deposits with reserves of ca. 220 t gold at an average grade of 24.7 g/t. Locally, gold grades exceed 400 g/t. Several geologic events converged at Meikle to create these spectacular gold grades. Prior to mineralization, a Devonian hydrothermal system altered the Bootstrap limestone to Fe-rich dolomite. Subsequently the rocks were brecciated by faulting and Late Jurassic intrusive activity. The resulting permeability focused flow of late Eocene Carlin-type ore fluids and allowed them to react with the Fe-rich dolomite. Fluid inclusion data and mineral assemblages indicate that these fluids were hot (ca. 220??C),of moderate salinity (400 g/t. Petrographic observations, geochemical data, and stable isotope results from the Meikle mine and other deposits at the Goldstrike mine place important constraints on genetic models for Meikle and other Carlin-type gold deposits on the northern Carlin trend. The ore fluids were meteoric water (??D = -135???, ??18O = -5???) that interacted with sedimentary rocks at a water/rock ratio of ca. 1 and temperatures of ca. 220??C. The absence of significant silicification suggests that there was little cooling of the ore fluids during mineralization. These two observations strongly suggest that ore fluids were not derived from deep sources but instead flowed parallel to isotherms. The gold was transported by H2S (??34S = 9???), which was derived from Paleozoic sedimentary rocks. The presence of auriferous sedimentary exhalative mineralization in the local stratigraphic sequence raises the possibility that preexisting concentrations of gold contributed to the Carlin-type deposits. Taken together our observations suggest that meteoric water evolved to become an ore fluid by shallow circulation through previously gold- and sulfur-enriched rocks. Carlin-type gold deposits formed where these fluids encountered permeable, reactive Fe-rich rocks.

Metal transports and enrichments in iron depositions hosted in basaltic rocks. II: Metal rich fluids and Fe origin

NASA Astrophysics Data System (ADS)

Zhang, Ronghua; Zhang, Xuetong; Hu, Shumin

2015-12-01

This study focuses on revealing the mechanism of metal transport, enrichment and Fe origin of iron deposition during water basalt interactions occurred in basaltic rocks. Observations of the iron deposits (anhydrite-magnetite-pyroxene type deposits) hosted in K-rich basaltic rocks in the Mesozoic volcanic area of the Middle-Lower Yangtze River valley, China, indicate that the mechanism of metal transport and enrichment for those deposits are significant objective to scientists, and the Fe origin problem is not well resolved. Here the metal transport, enrichment and iron origin have been investigated in high temperature experiments of water basaltic interactions. These deposits were accompanying a wide zone with metal alteration. The effects of hydrothermal alteration on major rock-forming element concentrations in basaltic rock were investigated by systematically comparing the chemical compositions of altered rocks with those of fresh rocks. In the deposits, these metals are distributed throughout altered rocks that exhibit vertical zoning from the deeper to the shallow. Then, combined with the investigations of the metal-alterations, we performed kinetic experiments of water-basaltic rock interactions using flow-through reactors in open systems at temperatures from 20 °C to 550 °C, 23-34 MPa. Release rates for the rock-forming elements from the rocks have been measured. Experiments provide the release rates for various elements at a large temperature range, and indicate that the dissolution rates (release rates) for various elements vary with temperature. Si, Al, and K have high release rates at temperatures from 300 °C to 500 °C; the maximum release rates (RMX) for Si are reached at temperatures from 300 °C to 400 °C. The RMXs for Ca, Mg, and Fe are at low temperatures from 20 °C to 300 °C. Results demonstrate that Fe is not released from 400 °C to 550 °C, and indicate that when deep circling fluids passed through basaltic rocks, Fe was not mobile, and fixed in the rocks at temperatures from 400 °C to 550 °C. Significance of the results is to provide evidence that the Fe of ores originated from basalt, and Fe-oxides precipitated across the critical state of water. Simultaneously, Ca, Mg and Fe are fixed in the deeper altered rocks (mafic minerals). But, Fe was dissolved at relatively low temperatures (100-300 °C). Si, Al, and K were easily mobile from basalt by upward flowing fluids from 300 °C to 400 °C and transported to the upper part (silicified and argillized rock).

Estimation of the reactive mineral surface area during CO2-rich fluid-rock interaction: the influence of neogenic phases

NASA Astrophysics Data System (ADS)

Scislewski, A.; Zuddas, P.

2010-12-01

Mineral dissolution and precipitation reactions actively participate to control fluid chemistry during water-rock interaction. It is however, difficult to estimate and well normalize bulk reaction rates if the mineral surface area exposed to the aqueous solution and effectively participating on the reactions is unknown. We evaluated the changing of the reactive mineral surface area during the interaction between CO2-rich fluids and Albitite/Granitoid rocks (similar mineralogy but different abundances), reacting under flow-through conditions. Our methodology, adopting an inverse modeling approach, is based on the estimation of dissolution rate and reactive surface area of the different minerals participating in the reactions by the reconstruction the chemical evolution of the interacting fluids. The irreversible mass-transfer processes is defined by a fractional degree of advancement, while calculations were carried out for Albite, Microcline, Biotite and Calcite assuming that the ion activity of dissolved silica and aluminium ions was limited by the equilibrium with quartz and kaolinite. Irrespective of the mineral abundance in granite and albitite, we found that mineral dissolution rates did not change significantly in the investigated range of time where output solution’s pH remained in the range between 6 and 8, indicating that the observed variation in fluid composition depends not on pH but rather on the variation of the parent mineral’s reactive surface area. We found that the reactive surface area of Albite varied by more than 2 orders of magnitude, while Microcline, Calcite and Biotite surface areas changed by 1-2 orders of magnitude. We propose that parent mineral chemical heterogeneity and, particularly, the stability of secondary mineral phases may explain the observed variation of the reactive surface area of the minerals. Formation of coatings at the dissolving parent mineral surfaces significantly reduced the amount of surface available to react with CO2-rich fluids, decreasing the effective reactive surface area. Predictive models of CO2 sequestration under geological conditions should take into account the inhibiting role of surface coating formation. The CO2 rich fluid-rock interactions may also have significant consequences on metal mobilization. Our results indicated that the formation of stable carbonate complexes enhances the solubility of uranium minerals of both albitite and granite, facilitating the U(IV) oxidation, and limiting the extent of uranium adsorption onto particles in oxidized waters. This clearly produces an increase of the uranium mobility with significant consequences for the environment.

A comparison/validation of a fractional derivative model with an empirical model of non-linear shock waves in swelling shales

NASA Astrophysics Data System (ADS)

Droghei, Riccardo; Salusti, Ettore

2013-04-01

Control of drilling parameters, as fluid pressure, mud weight, salt concentration is essential to avoid instabilities when drilling through shale sections. To investigate shale deformation, fundamental for deep oil drilling and hydraulic fracturing for gas extraction ("fracking"), a non-linear model of mechanic and chemo-poroelastic interactions among fluid, solute and the solid matrix is here discussed. The two equations of this model describe the isothermal evolution of fluid pressure and solute density in a fluid saturated porous rock. Their solutions are quick non-linear Burger's solitary waves, potentially destructive for deep operations. In such analysis the effect of diffusion, that can play a particular role in fracking, is investigated. Then, following Civan (1998), both diffusive and shock waves are applied to fine particles filtration due to such quick transients , their effect on the adjacent rocks and the resulting time-delayed evolution. Notice how time delays in simple porous media dynamics have recently been analyzed using a fractional derivative approach. To make a tentative comparison of these two deeply different methods,in our model we insert fractional time derivatives, i.e. a kind of time-average of the fluid-rocks interactions. Then the delaying effects of fine particles filtration is compared with fractional model time delays. All this can be seen as an empirical check of these fractional models.

Origin, evolution and geothermometry of the thermal waters in the Gölemezli Geothermal Field, Denizli Basin (SW Anatolia, Turkey)

NASA Astrophysics Data System (ADS)

Alçiçek, Hülya; Bülbül, Ali; Brogi, Andrea; Liotta, Domenico; Ruggieri, Giovanni; Capezzuoli, Enrico; Meccheri, Marco; Yavuzer, İbrahim; Alçiçek, Mehmet Cihat

2018-01-01

The Gölemezli Geothermal Field (GGF) is one of the best known geothermal fields in western Anatolia (Turkey). The exploited fluids are of meteoric origin, mixed with deep magmatic fluids, which interacted with the metamorphic rocks of the Menderes Massif. The geothermal fluids are channeled along Quaternary faults belonging to the main normal faults system delimiting the northern side of the Denizli Basin and their associated transfer zones. In this study, hydrochemical and isotopic analyses of the thermal and cold waters allow us to determine water-rock interactions, fluid paths and mixing processes. Two groups of thermal waters have been distinguished: (i) Group 1A, comprising Na-SO4 type and Ca-SO4 type and (ii) Group 1B, only consisting Ca-HCO3 type waters. Differently, two groups were recognized in the cold waters: (i) Group 2A, corresponding to Ca-HCO3 type and (ii) Group 2B, including Mg-HCO3 type. Their geochemical characteristics indicate interactions with the Paleozoic metamorphic rocks of the Menderes Massif and with the Neogene lacustrine sedimentary rocks. Dissolution of host rock and ion-exchange reactions modify thermal water composition in the reservoir of the GGF. High correlation in some ionic ratios and high concentrations of some minor elements suggest an enhanced water-rock interaction. None of the thermal waters has been reached a complete chemical re-equilibrium, possibly as a result of mixing with cold water during their pathways. Geothermal reservoir temperatures are calculated in the range of 130-210°C for the Gölemezli field. Very negative δ18O and δ2H isotopic ratios are respectively between -8.37 and -8.13‰ and -61.09 and -59.34‰ for the SO4-rich thermal waters, and ca. - 8.40 and -8.32‰ and - 57.80 and -57.41‰ for the HCO3-rich thermal waters. Low tritium (< 1 TU) and low oxygen isotope values reflect a deep circuit and fluids of meteoric origin. Positive δ13CDIC ratios (+ 5.11 to + 7.54‰) of all thermal waters imply a contribution of metamorphic origin. Heating is guaranteed by a deep circuit within an overheated continental crust, mainly affected by damaged rock volumes. Volatile ascent from deep magmatic sources through crustal structures can explain the occurrence of mantle volatiles at shallow depth in the Denizli Basin. The NW- and NE-trending fault systems, associated with their related fractures, played as hydraulic conduits underlining the strict link existing between fractures and fluid convection in the extensional settings. In this view, the GGF is a very good example of geothermal field associated to active tectonic setting and magmatism, as it is the case of the other geothermal fields occurring in the Denizli Basin.

Concomitant skarn and syenitic magma evolution at the margins of the Zippa Mountain pluton

NASA Astrophysics Data System (ADS)

Coulson, I. M.; Westphal, M.; Anderson, R. G.; Kyser, T. K.

2007-07-01

Zippa Mountain pluton is a Mesozoic concentrically-zoned intrusion, located within the Canadian Cordillera of British Columbia. An extensive phase of K-feldspar bearing syenite grades towards its margins to mela-syenite and clinopyroxenite. This simple pattern of petrological zonation is overprinted by localised occurrences of silica-undersaturated, peralkaline rock types. High-purity wollastonite skarns occur within and peripheral to the intrusion and result from extensive interaction between intrusion-related fluids and Permian limestone/marble, at shallow crustal levels. Field, chemical and isotopic studies provide insights into interaction between a parental syenitic magma and these country rocks. To achieve this, petrological studies of four of the skarn bodies present have been combined with chemical and isotopic data from the pluton, and from drill core through the skarn into the pluton, to reconstruct the stages in the development of wollastonite skarn and progressive magma-country rock interaction. Derivation of peralkaline compositions from the syenitic magma requires either a loss of Si and Al, or addition of Na and/or K. Our studies preclude the addition of alkali elements but highlight extensive Si-infiltration into the limestone, while the conversion of marble to grossular-andradite skarn, indicates Al-infiltration. Fluid egress resulted in de-silicification/de-alumination of the Zippa Mountain magmas, and increased peralkalinity; wollastonite and garnet-bearing skarn formed as a by-product. Hence, the development of peralkaline rock compositions at Zippa Mountain required a parental syenitic magma, and reaction and/or interaction with calcareous country rocks.

Detachment of particulate iron sulfide during shale-water interaction

NASA Astrophysics Data System (ADS)

Emmanuel, S.; Kreisserman, Y.

2017-12-01

Hydraulic fracturing, a commonly used technique to extract oil and gas from shales, is controversial in part because of the threat it poses to water resources. The technique involves the injection into the subsurface of large amounts of fluid, which can become contaminated by fluid-rock interaction. The dissolution of pyrite is thought to be a primary pathway for the contamination of fracturing fluids with toxic elements, such as arsenic and lead. In this study, we use direct observations with atomic force microscopy to show that the dissolution of carbonate minerals in Eagle Ford shale leads to the physical detachment of embedded pyrite grains. To simulate the way fluid interacts with a fractured shale surface, we also reacted rock samples in a flow-through cell, and used environmental scanning electron microscopy to compare the surfaces before and after interaction with water. Crucially, our results show that the flux of particulate iron sulfide into the fluid may be orders of magnitude higher than the flux of pyrite from chemical dissolution. This result suggests that mechanical detachment of pyrite grains could be the dominant mode by which arsenic and other inorganic elements are mobilized in the subsurface. Thus, during hydraulic fracturing operations and in groundwater systems containing pyrite, the transport of many toxic species may be controlled by the transport of colloidal iron sulfide particles.

Fluid flow and water-rock interaction in the East Rift Zone of Kilauea Volcano, Hawaii

NASA Astrophysics Data System (ADS)

Conrad, Mark E.; Thomas, Donald M.; Flexser, Steven; Vennemann, Torsten W.

1997-07-01

The East Rift Zone of Kilauea Volcano in Hawaii represents a major area of geothermal activity. Fluid inclusion and stable isotope analyses of secondary hydrothermal minerals in core samples from three scientific observation holes (SOH) drilled into the rift zone indicate that the geothermal system is dominated by meteoric waters to depths of as much as 1500 m below sea level. Calculated δ18O and δD values for fluids on the north side of the rift zone indicate that the deep meteoric fluids may be derived from precipitation on the upper slopes of Mauna Loa Volcano. In the interior of the rift zone, recharge is dominated by seawater mixed with local meteoric water. Water/rock ratios in the rift area are approximately 2, but strongly 18O-enriched fluids in the deeper parts of the SOH-2 and SOH-4 drill holes (on the north side of the rift) indicate that the fluids underwent extensive interaction with rocks prior to reaching this part of the rift zone. Marine carbonates at the subaerial to submarine transition (between 1700 and 1780 m depth) in SOH-4 have not fully equilibrated with the fluids, suggesting that the onset of hydrothermal activity in this area was relatively recent (<2000 years). This may represent increased volcanic activity along the rift after the end of the Ai La'au phase of eruptive activity at the Kilauea summit approximately 1000 years ago, or it may reflect progressive evolution of the hydrothermal system in response to southward migration of intrusive activity within the rift.

K-Ar constraints on fluid-rock interaction and dissolution-precipitation events within the actively creeping shear zones from SAFOD cores

NASA Astrophysics Data System (ADS)

Ali, S.; Hemming, S. R.; Torgersen, T.; Fleisher, M. Q.; Cox, S. E.; Stute, M.

2009-12-01

The San Andreas Fault Observatory at Depth (SAFOD) was drilled to study the physical and chemical processes responsible for faulting and earthquake generation along an active, plate-bounding fault at depth. SAFOD drill cores show multiple zones of alteration and deformation due to fluid-rock interaction in the fault rocks(Schleicher et al. 2008). In context of fluid studies in the SAFZ, noble gas and potassium measurements were performed on solid samples of sedimentary rocks obtained from drill cores across the fault (3050-4000m-MD). We used a combination of 40Ar/39Ar and K-Ar methods on crushed samples of mudrock with variable amounts of visible slickensides to constrain the degree of resetting of the K-Ar system across the San Andreas Fault zone. 40Ar/39Ar was analyzed from small fragments (sand sized grains) while K-Ar was measured in crushed bulk rock samples (100-250 mg for Ar, and 5-10 mg for K analyses). The apparent 40Ar/39Ar ages based on single step laser fusion of small fragments corresponding to the detrital component in the coarse fraction, show varying ages ranging from the provenance age to <13Ma. Although more data are needed to make detailed comparisons, the apparent K-Ar ages of bulk samples in the fault zone are biased toward authigenic materials contained in the fine fraction, similar to the 40Ar/39Ar ages reported for mineralogical separates from very fine size fractions of samples obtained from 3065.98m-MD and 3294.89m-MD (Schleicher et al., submitted to Geology). The small samples measured for 40Ar/39Ar show scatter in the apparent ages, generally bracketing the bulk ages. However they are picked from sieved portions of the samples, and it is likely that there may be a loss of the younger (finer) material. Detrital provenance ages appear to be 50-60Ma in the Pacific Plate, and 100Ma in the North American Plate. 40Ar/39Ar ages within the SAFZ, as defined by geophysical logs (3200-3400m MD), are dominated by apparent detrital ages of ˜100Ma. More work is needed to test whether this is a real provenance age, or if there could be some systematic process that could lead to age bias towards older values. We observe nearly complete resetting of K-Ar ages, indicating that the K content is dominated by newly formed authigenic minerals as a result of fluid rock interaction in the SAFZ. Because the authigenic minerals are subject to successive dissolution-precipitation events over a range of time (3 to 0 Ma) and because the detrital component may not be fully reset, the K-Ar apparent ages (<300,000 years) in the SAFZ provide a maximum age on the resetting event. Similar trends of relatively young ages across the SAFZ compared to the surrounding country rock in the Pacific and North American Plates are also observed in the apparent fluid ‘ages’, corresponding to the fluid event responsible for the fluid-rock interaction in the fault (Ali et al. this session).

Digital Rock Simulation of Flow in Carbonate Samples

NASA Astrophysics Data System (ADS)

Klemin, D.; Andersen, M.

2014-12-01

Reservoir engineering has becomes more complex to deal with current challenges, so core analysts must understand and model pore geometries and fluid behaviors at pores scales more rapidly and realistically. We introduce an industry-unique direct hydrodynamic pore flow simulator that operates on pore geometries from digital rock models obtained using microCT or 3D scanning electron microscope (SEM) images. The PVT and rheological models used in the simulator represent real reservoir fluids. Fluid-solid interactions are introduced using distributed micro-scale wetting properties. The simulator uses density functional approach applied for hydrodynamics of complex systems. This talk covers selected applications of the simulator. We performed microCT scanning of six different carbonate rock samples from homogeneous limestones to vuggy carbonates. From these, we constructed digital rock models representing pore geometries for the simulator. We simulated nonreactive tracer flow in all six digital models using a digital fluid description that included a passive tracer solution. During the simulation, we evaluated the composition of the effluent. Results of tracer flow simulations corresponded well with experimental data of nonreactive tracer floods for the same carbonate rock types. This simulation data of the non-reactive tracer flow can be used to calculate the volume of the rock accessible by the fluid, which can be further used to predict response of a porous medium to a reactive fluid. The described digital core analysis workflow provides a basis for a wide variety of activities, including input to design acidizing jobs and evaluating treatment efficiency and EOR economics. Digital rock multiphase flow simulations of a scanned carbonate rock evaluated the effect of wettability on flow properties. Various wetting properties were tested: slightly oil wet, slightly water wet, and water wet. Steady-state relative permeability simulations yielded curves for all three ranges of wetting properties. The wetting variation affected phase mobility and residual phase saturations for primary oil flood and floods with varying ratios of oil and water.

Driving forces for metamorphic vein filling during bauxite dehydration: insights from Li and Al transfer illustrated by LIBS compositional profiles (Western Alps)

NASA Astrophysics Data System (ADS)

Verlaguet, Anne; Brunet, Fabrice; Goffé, Bruno; Menut, Denis; Findling, Nathaniel; Poinssot, Christophe

2015-04-01

In subduction zones, the significant amounts of aqueous fluid released in the course of the successive dehydration reactions occurring during prograde metamorphism are expected to strongly influence the rock rheology, as well as kinetics of metamorphic reactions and mass transfer efficiency. Mineralized veins, ubiquitous in metamorphic rocks, can be seen as preserved witnesses of fluid and mass redistribution that partly accommodate the rock deformation (lateral segregation). However, the driving forces and mechanisms of mass transfer towards fluid-filled open spaces remain somewhat unclear. The aim of this study is to investigate the vein-forming processes and the modalities of mass transfer during local fluid-rock interactions, and their links with fluid production and rock deformation, with new insights from Laser Induced Breakdown Spectroscopy (LIBS) profiles. This study focuses on karstic pockets (metre scale) of Triassic metabauxites embedded in thick carbonate units, that have been isolated from large-scale fluid flow during HP-LT Alpine metamorphism (W. Vanoise, French Alps). These rocks display several generations of metamorphic veins containing various Al-bearing minerals, which give particular insights into mass transfer processes. It is proposed that the internally-derived fluid (~13 vol% produced by successive dehydration reactions) has promoted the opening of fluid-filled open spaces (euhedral habits of vein minerals) and served as medium for diffusive mass transfer from rock to vein. Based on mineralogical and textural features, two vein types can be distinguished: (1) some veins are filled with newly formed products of either prograde (chloritoid) or retrograde (chlorite) metamorphic reactions; in this case, fluid-filled open spaces seem to offer energetically favourable nucleation/growth sites; (2) the second vein type is filled with cookeite (Li-Al-rich chlorite) or pyrophyllite, which were present in the host-rock prior to the vein formation. In this closed chemical system, mass transfer from rock to vein was achieved through the fluid, in a dissolution-transport-precipitation process. To investigate the modalities of mass transfer towards this second vein type, LIBS profiles were performed in the host-rock, taking Li concentration as a proxy for cookeite distribution. Cookeite is highly concentrated (45-65 vol%) in regularly spaced veins, and the LIBS profiles show that cookeite is evenly distributed in the host-rock comprised between two veins. The absence of diffusion profiles suggests that the characteristic diffusion distance for Li, Al and Si is greater than or equal to the distance separating two cookeite veins (2-4 cm). This is in agreement with characteristic diffusion lengths calculated from both grain boundary and pore fluid diffusion coefficients, for the estimated duration of the peak of metamorphism. Which driving forces are responsible for cookeite selective transfer towards veins? Chemical potential gradients between host-rock pores and veins may have developed in response to either (1) a stress difference: thermochemical calculations show that pressure-solution processes may affect preferentially cookeite and pyrophyllite; (2) a difference in interfacial energy, phyllosilicates showing very different morphologies in host-rocks (fibers) compared to veins (euhedral crystals); fluid-mineral interfacial energy may be maximal in the small host-rock pores, which can maintain higher cookeite solubility than large fluid-filled open spaces (i.e., veins).

Using Digital Computer Field Mapping of Outcrops to Examine the Preservation of High-P Rocks During Pervasive, Retrograde Greenschist Fluid Infiltration, Tinos, Cyclades Archipelago, Greece

NASA Astrophysics Data System (ADS)

Breeding, C. M.; Ague, J. J.; Broecker, M.

2001-12-01

Digital field mapping of outcrops on the island of Tinos, Greece, was undertaken to investigate the nature of retrograde fluid infiltration during exhumation of high-P metamorphic rocks of the Attic-Cycladic blueschist belt. High-resolution digital photographs of outcrops were taken and loaded into graphics editing software on a portable, belt-mounted computer in the field. Geologic features from outcrops were drawn and labeled on the digital images using the software in real-time. The ability to simultaneously identify geologic features in outcrops and digitize those features onto digital photographs in the field allows the creation of detailed, field-verified, outcrop-scale maps that aid in geologic interpretation. During Cretaceous-Eocene subduction in the Cyclades, downgoing crustal material was metamorphosed to eclogite and blueschist facies. Subsequent Oligocene-Miocene exhumation of the high-P rocks was accompanied by pervasive, retrograde fluid infiltration resulting in nearly complete greenschist facies overprinting. On Tinos, most high-P rocks have undergone intense retrogression; however, adjacent to thick marble horizons with completely retrograded contact zones, small (sub km-scale) enclaves of high-P rocks (blueschist and minor eclogite facies) were preserved. Field observations suggest that the remnant high-P zones consist mostly of massive metabasic rocks and minor adjacent metasediments. Within the enclaves, detailed digital outcrop maps reveal that greenschist retrogression increases in intensity outward from the center, implying interaction with a fluid flowing along enclave perimeters. Permeability contrasts could not have been solely responsible for preservation of the high-P rocks, as similar rock suites distal to marble contacts were completely overprinted. We conclude that the retrograded contacts of the marble units served as high-permeability conduits for regional retrograde fluid flow. Pervasive, layer-parallel flow through metasediments would have been drawn into these more permeable flow channels. Deflections in fluid flow paths toward the high flux contacts likely caused retrograde fluids to flow around the enclaves, preserving the zones of "dry," unretrograded high-P rocks near marble horizons. Digital mapping of outcrops is a unique method for direct examination of the relationships between geologic structure, lithology, and mineral assemblage variation in the field. Outcrop mapping in the Attic-Cycladic blueschist belt has revealed that regional fluid flow along contacts can have important implications for the large-scale distribution of mineral assemblages in metamorphic terranes.

Modeling of Propagation of Interacting Cracks Under Hydraulic Pressure Gradient

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Hai; Mattson, Earl Douglas; Podgorney, Robert Karl

A robust and reliable numerical model for fracture initiation and propagation, which includes the interactions among propagating fractures and the coupling between deformation, fracturing and fluid flow in fracture apertures and in the permeable rock matrix, would be an important tool for developing a better understanding of fracturing behaviors of crystalline brittle rocks driven by thermal and (or) hydraulic pressure gradients. In this paper, we present a physics-based hydraulic fracturing simulator based on coupling a quasi-static discrete element model (DEM) for deformation and fracturing with conjugate lattice network flow model for fluid flow in both fractures and porous matrix. Fracturingmore » is represented explicitly by removing broken bonds from the network to represent microcracks. Initiation of new microfractures and growth and coalescence of the microcracks leads to the formation of macroscopic fractures when external and/or internal loads are applied. The coupled DEM-network flow model reproduces realistic growth pattern of hydraulic fractures. In particular, simulation results of perforated horizontal wellbore clearly demonstrate that elastic interactions among multiple propagating fractures, fluid viscosity, strong coupling between fluid pressure fluctuations within fractures and fracturing, and lower length scale heterogeneities, collectively lead to complicated fracturing patterns.« less

A THC Simulator for Modeling Fluid-Rock Interactions

NASA Astrophysics Data System (ADS)

Hamidi, Sahar; Galvan, Boris; Heinze, Thomas; Miller, Stephen

2014-05-01

Fluid-rock interactions play an essential role in many earth processes, from a likely influence on earthquake nucleation and aftershocks, to enhanced geothermal system, carbon capture and storage (CCS), and underground nuclear waste repositories. In THC models, two-way interactions between different processes (thermal, hydraulic and chemical) are present. Fluid flow influences the permeability of the rock especially if chemical reactions are taken into account. On one hand solute concentration influences fluid properties while, on the other hand, heat can affect further chemical reactions. Estimating heat production from a naturally fractured geothermal systems remains a complex problem. Previous works are typically based on a local thermal equilibrium assumption and rarely consider the salinity. The dissolved salt in fluid affects the hydro- and thermodynamical behavior of the system by changing the hydraulic properties of the circulating fluid. Coupled thermal-hydraulic-chemical models (THC) are important for investigating these processes, but what is needed is a coupling to mechanics to result in THMC models. Although similar models currently exist (e.g. PFLOTRAN), our objective here is to develop algorithms for implementation using the Graphics Processing Unit (GPU) computer architecture to be run on GPU clusters. To that aim, we present a two-dimensional numerical simulation of a fully coupled non-isothermal non-reactive solute flow. The thermal part of the simulation models heat transfer processes for either local thermal equilibrium or nonequilibrium cases, and coupled to a non-reactive mass transfer described by a non-linear diffusion/dispersion model. The flow process of the model includes a non-linear Darcian flow for either saturated or unsaturated scenarios. For the unsaturated case, we use the Richards' approximation for a mixture of liquid and gas phases. Relative permeability and capillary pressure are determined by the van Genuchten relations. Permeability of rock is controlled by porosity, which is itself related to effective stress. The theoretical model is solved using explicit finite differences, and runs in parallel mode with OpenMP. The code is fully modular so that any combination of current THC processes, one- and two-phase, can be chosen. Future developments will include dissolution and precipitation of chemical components in addition to chemical erosion.

Zinc isotope systematics of subduction-zone magmas

NASA Astrophysics Data System (ADS)

Huang, J.; Zhang, X. C.; Huang, F.; Yu, H.

2016-12-01

Subduction-zone magmas are generated by partial melting of mantle wedge triggered by addition of fluids derived from subducted hydrothermally altered oceanic lithosphere. Source of the fluids may be sediment, altered oceanic crust and serpentinized peridotite/serpentinite. Knowledge of the exact fluid source can facilitate our better understanding of the mechanism of fluid flux, element cycling and crust-mantle interaction in subduction zones. Zinc isotopes have the potential to place a constraint on this issue, because (1) Zn has an intermediate mobility during fluid-rock interaction and is enriched in subduction-zone fluids (e.g., Li et al., 2013); (2) sediment, altered oceanic crust and serpentinite have distinct Zn isotopic compositions (Pons et al., 2011); and (3) the mantle has a homogeneous Zn isotope composition (δ66Zn = 0.28 ± 0.05‰, Chen et al., 2013). Thus, the Zn isotopic composition of subduction-zone magmas reflects the characteristics of slab-derived fluids of different sources. Here, high-precision Zn isotope analyses were conducted on igneous rocks from arcs of Central America, Kamchatka, South Lesser Antilles, and Aleutian. One rhyolite with 75.1 wt.% SiO2 and 0.2 wt.% FeOT displays the heaviest δ66Zn value of 0.394‰ (relative to JMC Lyon) that probably results from the crystallization of Fe-Ti oxides during the late-stage differentiation. The rest of rocks have Zn isotopic compositions (0.161 to 0.339‰) similar to or lighter than those of the mantle. In an individual arc, the δ66Zn values of rocks show broad negative correlations with Ba/Th and 87Sr/86Sr ratios, suggesting that the slab-derived fluids should have lighter δ66Zn as well as higher Ba/Th and 87Sr/86Sr ratios relative to the mantle. These features are in accordance with those of serpentinites. Thus, addition of serpentinite-derived 66Zn-depleted fluids into the mantle wedge can explain the declined δ66Zn of subduction-zone magmas. ReferenceChen et al. (2013) EPSL 369-370:34-42; Li et al. (2013) GCA 120:326-362; Pons et al. (2011) PNAS 108:17639-17643.

A Chlorine-Centric Perspective on Fluid-Mediated Processes at Convergent Plate Boundaries

NASA Astrophysics Data System (ADS)

Selverstone, J.

2014-12-01

The release and migration of metamorphic fluids from subducting slabs into overlying mantle is widely recognized as a major mechanism in producing arc geochemical signatures and returning fluid-mobile elements to earth's crust and surface environments. Although the magnitudes of many geochemical fluxes are well constrained, the processes whereby mass transfer occurs in different portions of the subduction system are less well known. Chlorine stable isotopes provide a new perspective on some of these processes: Cl is hydrophilic, but decarbonation reactions favor Cl retention in minerals. Cl also shows less isotopic fractionation than other fluid-sensitive systems and may thus preserve evidence of specific fluid sources and/or fluid mixing events. Detailed studies of sedimentary sequences show that individual beds are isotopically homogeneous but large heterogeneities in δ37Cl exist across beds on a cm to m scale and vary as a function of depositional environment. Compositionally correlative medium-, high-, and ultrahigh-pressure metamorphic sequences in the Alps record decreases of 30-50% in Cl contents in the earliest stages of metamorphism, but little change thereafter. No statistically significant change in isotopic composition occurs during prograde metamorphism of individual horizons, and the same large degree of isotopic heterogeneity (up to 6‰) persists throughout the prograde devolatilization history of the rocks. Likewise, analysis of HP/UHP serpentinites and altered oceanic crust show that heterogeneous protolith compositions are preserved during transport to sub-arc depths, despite large-scale devolatilization. However, upward transport of rocks within the subduction channel results in highly localized interaction with isotopically distinct, Cl-bearing fluid packets. Overlying forearc wedge rocks also record heterogeneous and channelized interaction with distinct fluid components with different δ37Cl. Within-layer fluid compartmentalization during continuous devolatilization reactions must thus be reconciled with discontinuous, cross-layer fluid percolation out of the slab and into the wedge. The resulting implications of the chlorine data for recent mechanical models of slab-to-wedge fluid transport will be discussed.

Alpine Serpentinite Geochemistry As Key To Define Timing Of Oceanic Lithosphere Accretion To The Subduction Plate Interface

NASA Astrophysics Data System (ADS)

Gilio, M.; Scambelluri, M.; Agostini, S.; Godard, M.; Pettke, D. T.; Angiboust, S.

2016-12-01

Isotopic (Pb, Sr and B) and trace element (B, Be, As, Sb, U, Th) signatures of serpentinites are useful geochemical tools to assess element exchange and fluid-rock interactions in subduction zone settings. They help to unravel geological history and tectonic evolution of subduction serpentinites and associated meta-oceanic crust. Sedimentary-derived fluid influx within HP plate interface environments strongly enriches serpentinites in As, Sb, B, U and Th and resets their B, Sr and Pb isotopic compositions. This HP metasomatic signature is preserved during exhumation and/or released at higher PT through de-serpentinization, fueling partial melting in the sub-arc mantle and recycling such fingerprint into arc magmas. This study focuses on the subduction recrystallization, geochemical diversity and fluid-rock interaction recorded by high- to ultra-high pressure (HP, UHP) Alpine serpentinites from the subducted oceanic plate (Cignana Unit, Zermatt-Saas Complex, Monviso and Lanzo Ultramafic Massifs). The As and Sb compositions of the HP-UHP Alpine ophiolitic rocks reveal the interaction between serpentinite and crust-derived fluids during their emplacement along the plate interface. This enables to define a hypothetical architecture of the Alpine subduction interface, considering large ultramafic slices. In this scenario, the Lanzo peridotite and serpentinite retain an As-Sb composition comparable to DM and PM: i.e. they experienced little exchange with sediment-derived fluids. Lanzo thus belonged to sections of the subducting plate, afar from the plate interface. Serpentinites from the Lago di Cignana Unit and Monviso and Voltri are richer in As and Sb, showing moderate to strong interaction with sediment- and crust-derived fluids during subduction (i.e. they behaved as open systems). These serpentinite slices accreted at the plate interface and exchanged with slab-derived fluids at different depths during Alpine subduction: Voltri accreted at shallower conditions (50-60 km) than Monviso Unit (around 80 km depth) and Lago di Cignana (about 100 km depth), and exchanged with sedimentary and crustal systems during the entire burial history. Their relatively lower density might act as buoyancy force, triggering the exhumation of much denser lithologies (eclogite and peridotite).

Linking the tectonic evolution with fluid history in magma-poor rifted margins: tracking mantle- and continental crust-related fluids

NASA Astrophysics Data System (ADS)

Pinto, V. H. G.; Manatschal, G.; Karpoff, A. M.

2014-12-01

The thinning of the crust and the exhumation of subcontinental mantle is accompanied by a series of extensional detachment faults. Exhumation of mantle and crustal rocks is intimately related to percolation of fluids along detachment faults leading to changes in mineralogy and chemistry of the mantle, crustal and sedimentary rocks. Field observation, analytical methods, refraction/reflection and well-core data, allowed us to investigate the role of fluids in the Iberian margin and former Alpine Tethys distal margins and the Pyrenees rifted system. In the continental crust, fluid-rock interaction leads to saussuritization that produces Si and Ca enriched fluids found in forms of veins along the fault zone. In the zone of exhumed mantle, large amounts of water are absorbed in the first 5-6 km of serpentinized mantle, which has the counter-effect of depleting the mantle of elements (e.g., Si, Ca, Mg, Fe, Mn, Ni and Cr) forming mantle-related fluids. Using Cr-Ni-V and Fe-Mn as tracers, we show that in the distal margin, mantle-related fluids used detachment faults as pathways and interacted with the overlying crust, the sedimentary basin and the seawater, while further inward parts of the margin, continental crust-related fluids enriched in Si and Ca impregnated the fault zone and may have affected the sedimentary basin. The overall observations and results enable us to show when, where and how these interactions occurred during the formation of the rifted margin. In a first stage, continental crust-related fluids dominated the rifted systems. During the second stage, mantle-related fluids affected the overlying syn-tectonic sediments through direct migration along detachment faults at the future distal margin. In a third stage, these fluids reached the seafloor, "polluted" the seawater and were absorbed by post-tectonic sediments. We conclude that a significant amount of serpentinization occurred underneath the thinned continental crust, that the mantle-related fluids might have modified the chemical composition of the sediments and seawater. We propose that the chemical signature of serpentinization that occurs during the mantle exhumation is recorded in the sediments and may serve as a proxy to date serpentinization and mantle exhumation in present day magma-poor rifted margins.

Pore Characterization of Shale Rock and Shale Interaction with Fluids at Reservoir Pressure-Temperature Conditions Using Small-Angle Neutron Scattering

NASA Astrophysics Data System (ADS)

Ding, M.; Hjelm, R.; Watkins, E.; Xu, H.; Pawar, R.

2015-12-01

Oil/gas produced from unconventional reservoirs has become strategically important for the US domestic energy independence. In unconventional realm, hydrocarbons are generated and stored in nanopores media ranging from a few to hundreds of nanometers. Fundamental knowledge of coupled thermo-hydro-mechanical-chemical (THMC) processes that control fluid flow and propagation within nano-pore confinement is critical for maximizing unconventional oil/gas production. The size and confinement of the nanometer pores creates many complex rock-fluid interface interactions. It is imperative to promote innovative experimental studies to decipher physical and chemical processes at the nanopore scale that govern hydrocarbon generation and mass transport of hydrocarbon mixtures in tight shale and other low permeability formations at reservoir pressure-temperature conditions. We have carried out laboratory investigations exploring quantitative relationship between pore characteristics of the Wolfcamp shale from Western Texas and the shale interaction with fluids at reservoir P-T conditions using small-angle neutron scattering (SANS). We have performed SANS measurements of the shale rock in single fluid (e.g., H2O and D2O) and multifluid (CH4/(30% H2O+70% D2O)) systems at various pressures up to 20000 psi and temperature up to 150 oF. Figure 1 shows our SANS data at different pressures with H2O as the pressure medium. Our data analysis using IRENA software suggests that the principal changes of pore volume in the shale occurred on smaller than 50 nm pores and pressure at 5000 psi (Figure 2). Our results also suggest that with increasing P, more water flows into pores; with decreasing P, water is retained in the pores.

Effects of fluids on rock deformation and fault slip: From nature to societal impact (Louis Néel Medal Lecture)

NASA Astrophysics Data System (ADS)

Spiers, Christopher J.

2017-04-01

Understanding the effects of fluid-rock interaction on rock and fault mechanical behaviour is central not only to understanding natural tectonic and seismogenic processes, and phenomena such as resource trapping, but also to evaluating the impact of industrial operations in the Earth's crust. These include activities ranging from extraction of geo-energy to geological storage of fuels, CO2 and wastes. For the assessment of both natural and induced geohazards, a physics-based approach to quantifying rock mechanical behaviour is unmissable. Microstructural studies of rocks deformed naturally in the mid and upper crust, or at seismogenic depths in subduction zones, show widespread evidence for brittle deformation (cataclasis), dissolution-precipitation transfer, fluid-related reactions producing weak minerals, and dilatation/cementation of fractures, cracks and pores. In addition, experimental work on rocks and simulated fault gouges has shown that the presence of water strongly influences their mechanical and transport properties. This implies the operation of fluid-assisted deformation mechanisms, such as stress corrosion cracking and diffusive mass transfer (pressure solution). More recently, other fluid-coupled deformation processes have been recognised, in rocks from peridotites and granites to sandstones, limestones and shales. In this lecture, I will give an overview of progress in this area. I will address the physics of pressure solution and stress corrosion cracking and how they contribute to the deformation and compaction of sandstone, carbonate and evaporite rocks in the mid and upper crust, under natural conditions and in the context of deformation caused by geo-resources production and geo-storage. New results on how these processes are affected by pore fluid salinity, gas content and CO2 activity will also be considered, as will data on the effects of mineral-fluid reactions and associated volume changes on rock deformation, fracturing and transport. The effects of gas and CO2 sorption on the stress-strain behaviour and permeability of clay and shale caprocks, recently reported in relation to seal integrity, will be addressed too, and compared with similar phenomena familiar in seen in coal seams. Lastly, I will address the effects of fluid-rock interaction on the frictional behaviour of faults. Recent low velocity friction experiments (<100 μm/s) performed on simulated carbonate, evaporite and quartz gouges, with varying phyllosilicate content, indicate that pressure solution is key to determining whether frictional slip is velocity-strengthening (stable) or velocity weakening (potentially seismogenic). An important trend seen is a transition from velocity strengthening at low temperatures, to velocity weakening at intermediate temperatures, and back to velocity strengthening at high temperatures. This behaviour and the restrengthening observed when shearing is stopped are strongly influenced by water content. It is inferred that mechanistic models for the frictional behaviour of gouge-filled faults, under crustal conditions, must account for diffusion and stress corrosion cracking, and for slip on grain boundaries. First attempts to do this, assuming diffusive mass transfer as the fluid-assisted mechanism, successfully predict the steady state and transient behaviour seen in experiments and offer new perspectives for providing friction laws as for modelling earthquake rupture nucleation and evaluating seismic hazard, in the context of both natural and induced seismicity.

Anomalously low strength of serpentinite sheared against granite and implications for creep on the Hayward and Calaveras Faults

USGS Publications Warehouse

Moore, Diane E.; Lockner, David A.; Ponce, David A.

2010-01-01

Serpentinized ophiolitic rocks are juxtaposed against quartzofeldspathic rocks at depth across considerable portions of the Hayward and Calaveras Faults. The marked compositional contrast between these rock types may contribute to fault creep that has been observed along these faults. To investigate this possibility, we are conducting hydrothermal shearing experiments to look for changes in frictional properties resulting from the shear of ultramafic rock juxtaposed against quartzose rock units. In this paper we report the first results in this effort: shear of bare-rock surfaces of serpentinite and granite, and shear of antigorite-serpentinite gouge between forcing blocks of granitic rock. All experiments were conducted at 250°C. Serpentinite sheared against granite at 50 MPa pore-fluid pressure is weaker than either rock type separately, and the weakening is significantly more pronounced at lower shearing rates. In contrast, serpentinite gouge sheared dry between granite blocks is as strong as the bare granite surface. We propose that the weakening is the result of a solution-transfer process involving the dissolution of serpentine minerals at grain-to-grain contacts. Dissolution of serpentine is enhanced by modifications to pore-fluid chemistry caused by interaction of the fluid with the quartz-bearing rocks. The compositional differences between serpentinized ultramafic rocks of the Coast Range Ophiolite and quartzofeldspathic rock units such as those of the Franciscan Complex may provide the mechanism for aseismic slip (creep) in the shallow crust along the Hayward, Calaveras, and other creeping faults in central and northern California.

Fluid-rock geochemical interaction for modelling calibration in geothermal exploration in Indonesia

NASA Astrophysics Data System (ADS)

Deon, Fiorenza; Barnhoorn, Auke; Lievens, Caroline; Ryannugroho, Riskiray; Imaro, Tulus; Bruhn, David; van der Meer, Freek; Hutami, Rizki; Sibarani, Besteba; Sule, Rachmat; Saptadij, Nenny; Hecker, Christoph; Appelt, Oona; Wilke, Franziska

2017-04-01

Indonesia with its large, but partially unexplored geothermal potential is one of the most interesting and suitable places in the world to conduct geothermal exploration research. This study focuses on geothermal exploration based on fluid-rock geochemistry/geomechanics and aims to compile an overview on geochemical data-rock properties from important geothermal fields in Indonesia. The research carried out in the field and in the laboratory is performed in the framework of the GEOCAP cooperation (Geothermal Capacity Building program Indonesia- the Netherlands). The application of petrology and geochemistry accounts to a better understanding of areas where operating power plants exist but also helps in the initial exploration stage of green areas. Because of their relevance and geological setting geothermal fields in Java, Sulawesi and the sedimentary basin of central Sumatra have been chosen as focus areas of this study. Operators, universities and governmental agencies will benefit from this approach as it will be applied also to new green-field terrains. By comparing the characteristic of the fluids, the alteration petrology and the rock geochemistry we also aim to contribute to compile an overview of the geochemistry of the important geothermal fields in Indonesia. At the same time the rock petrology and fluid geochemistry will be used as input data to model the reservoir fluid composition along with T-P parameters with the geochemical workbench PHREEQC. The field and laboratory data are mandatory for both the implementation and validation of the model results.

Serpentinization and fluid-rock interaction in Jurassic mafic and ultramafic sea-floor: constraints from Ligurian ophiolite sequences

NASA Astrophysics Data System (ADS)

Vogel, Monica; Früh-Green, Gretchen L.; Boschi, Chiara; Schwarzenbach, Esther M.

2014-05-01

The Bracco-Levanto ophiolitic complex (Eastern Liguria) represents one of the largest and better-exposed ophiolitic successions in the Northern Apennines. It is considered to be a fragment of heterogeneous Jurassic lithosphere that records tectono-magmatic and alteration histories similar to those documented along the Mid-Atlantic Ridge, such as at the 15°20'N area and the Atlantis Massif at 30°N. Structural and petrological studies on these rocks provide constraints on metamorphic/deformation processes during formation and hydrothermal alteration of the Jurassic oceanic lithosphere. We present a petrological and geochemical study of deformation processes and fluid-rock interaction in the Bracco-Levanto ophiolitic complex and compare these to modern oceanic hydrothermal systems, such as the Lost City Hydrothermal Field hosted in ultramafic rocks on the Atlantis Massif. A focus is on investigating mass transfer and fluid flow paths during high and low temperature hydrothermal activity, and on processes leading to hydrothermal carbonate precipitation and the formation of ophicalcites, which are characteristic of the Bracco-Levanto sequences. Major element and mineral compositional data allow us to distinguish a multiphase history of alteration characterized by: (1) widespread SiO2 metasomatism during progressive serpentinization, and (2) multiple phases of veining and carbonate precipitation associated with circulation of seawater and high fluid-rock ratios in the shallow ultramafic-dominated portions of the Jurassic seafloor. We observe regional variations in MgO, SiO2 and Al2O3, suggesting Si-flux towards stratigraphically higher units. In general, the ophicalcites have higher Si, Al and Fe concentrations and lower Mg than the serpentinite basement rocks or serpentinites with minimal carbonate veins. Bulk rock trace element data and Sr isotope ratios indicate seawater reacting with rocks of more mafic composition, then channeled towards stratigraphically higher units, leading to Si metasomatism in the serpentinites and ophicalcites. Channelling of Si-rich fluids is also indicated by amphibole and talc growth in shear zones and wall rock around the ophicalcites. δ18O-values of the carbonate veins indicate temperatures up to 150°C and document a decrease in temperature with ongoing serpentinization. Comparison with serpentinites from the Atlantis Massif and 15°20'N indicates a similar degree of Si enrichment in the modern seafloor and suggests that Si-metasomatism may be a fundamental process associated with serpentinization at slow-spreading ridge environments.

Boiling vapour-type fluids from the Nifonea vent field (New Hebrides Back-Arc, Vanuatu, SW Pacific): Geochemistry of an early-stage, post-eruptive hydrothermal system

NASA Astrophysics Data System (ADS)

Schmidt, Katja; Garbe-Schönberg, Dieter; Hannington, Mark D.; Anderson, Melissa O.; Bühring, Benjamin; Haase, Karsten; Haruel, Christy; Lupton, John; Koschinsky, Andrea

2017-06-01

In 2013, high-temperature vent fluids were sampled in the Nifonea vent field. This field is located within the caldera of a large shield-type volcano of the Vate Trough, a young extensional rift in the New Hebrides back-arc. Hydrothermal venting occurs as clear and black smoker fluids with temperatures up to 368 °C, the hottest temperatures measured so far in the western Pacific. The physico-chemical conditions place the fluids within the two-phase field of NaCl-H2O, and venting is dominated by vapour phase fluids with Cl concentrations as low as 25 mM. The fluid composition, which differs between the individual vent sites, is interpreted to reflect the specific geochemical fluid signature of a hydrothermal system in its initial, post-eruptive stage. The strong Cl depletion is accompanied by low alkali/Cl ratios compared to more evolved hydrothermal systems, and very high Fe/Cl ratios. The concentrations of REY (180 nM) and As (21 μM) in the most Cl-depleted fluid are among the highest reported so far for submarine hydrothermal fluids, whereas the inter-element REY fractionation is only minor. The fluid signature, which has been described here for the first time in a back-arc setting, is controlled by fast fluid passage through basaltic volcanic rocks, with extremely high water-rock ratios and only limited water-rock exchange, phase separation and segregation, and (at least) two-component fluid mixing. Metals and metalloids are unexpectedly mobile in the vapour phase fluids, and the strong enrichments of Fe, REY, and As highlight the metal transport capacity of low-salinity, low-density vapours at the specific physico-chemical conditions at Nifonea. One possible scenario is that the fluids boiled before the separated vapour phase continued to react with fresh glassy lavas. The mobilization of metals is likely to occur by leaching from fresh glass and grain boundaries and is supported by the high water/rock ratios. The enrichment of B and As is further controlled by their high volatility, whereas the strong enrichment of REY is also a consequence of the elevated concentrations in the host rocks. However, a direct contribution of metals such as As from magmatic degassing cannot be ruled out. The different fluid end-member composition of individual vent sites could be explained by mixing of vapour phase fluids with another fluid phase of different water/rock interaction history.

DOE workshop: Sedimentary systems, aqueous and organic geochemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1993-07-01

A DOE workshop on sedimentary systems, aqueous and organic geochemistry was held July 15-16, 1993 at Lawrence Berkeley Laboratory. Papers were organized into several sections: Fundamental Properties, containing papers on the thermodynamics of brines, minerals and aqueous electrolyte solutions; Geochemical Transport, covering 3-D imaging of drill core samples, hydrothermal geochemistry, chemical interactions in hydrocarbon reservoirs, fluid flow model application, among others; Rock-Water Interactions, with presentations on stable isotope systematics of fluid/rock interaction, fluid flow and petotectonic evolution, grain boundary transport, sulfur incorporation, tracers in geologic reservoirs, geothermal controls on oil-reservoir evolution, and mineral hydrolysis kinetics; Organic Geochemistry covered new methodsmore » for constraining time of hydrocarbon migration, kinetic models of petroleum formation, mudstones in burial diagenesis, compound-specific carbon isotope analysis of petroleums, stability of natural gas, sulfur in sedimentary organic matter, organic geochemistry of deep ocean sediments, direct speciation of metal by optical spectroscopies; and lastly, Sedimentary Systems, covering sequence stratigraphy, seismic reflectors and diagenetic changes in carbonates, geochemistry and origin of regional dolomites, and evidence of large comet or asteroid impacts at extinction boundaries.« less

Summaries of FY 1995 geosciences research

DOE Office of Scientific and Technical Information (OSTI.GOV)

NONE

1995-12-01

The summaries in this document, prepared by the investigators, describe the scope of the individual programs. The Geosciences Research Program includes research in geophysics, geochemistry, resource evaluation, solar-terrestrial interactions, and their subdivisions including earth dynamics, properties of earth materials, rock mechanics, underground imaging, rock-fluid interactions, continental scientific drilling, geochemical transport, solar/atmospheric physics, and modeling, with emphasis on the interdisciplinary areas. All such research is related either direct or indirect to the Department of Energy`s long-range technological needs.

Contrasting fluid/rock interaction between the Notch Peak granitic intrusion and argillites and limestones in western Utah: evidence from stable isotopes and phase assemblages

USGS Publications Warehouse

Nabelek, P.I.; Labotka, T.C.; O'Neil, J.R.; Papike, J.J.

1984-01-01

The Jurassic Notch Peak granitic stock, western Utah, discordantly intrudes Cambrian interbedded pure limestones and calcareous argillites. Contact metamorphosed argillite and limestone samples, collected along traverses away from the intrusion, were analyzed for ??18O, ??13C, and ??D. The ??13C and ??18O values for the limestones remain constant at about 0.5 (PDB) and 20 (SMOW), respectively, with increasing metamorphic grade. The whole rock ??18O values of the argillites systematically decrease from 19 to as low as 8.1, and the ??13C values of the carbonate fraction from 0.5 to -11.8. The change in ??13C values can be explained by Rayleigh decarbonation during calcsilicate reactions, where calculated {Mathematical expression} is about 4.5 permil for the high-grade samples and less for medium and low-grade samples suggesting a range in temperatures at which most decarbonation occurred. However, the amount of CO2 released was not anough to decrease the whole rock ??18O to the values observed in the argillites. The low ??18O values close to the intrusion suggest interaction with magmatic water that had a ??18O value of 8.5. The extreme lowering of ??13C by fractional devolatilization and the lowering of ??18O in argillites close to the intrusion indicates oxgen-equivalent fluid/rock ratios in excess of 1.0 and X(CO2)F of the fluid less than 0.2. Mineral assemblages in conjunction with the isotopic data indicate a strong influence of water infiltration on the reaction relations in the argillites and separate fluid and thermal fronts moving thru the argillites. The different stable isotope relations in limestones and argillites attest to the importance of decarbonation in the enhancement of permeability. The flow of fluids was confined to the argillite beds (argillite aquifers) whereas the limestones prevented vertical fluid flow and convective cooling of the stock. ?? 1984 Springer-Verlag.

Si-Metasomatism During Serpentinization of Jurassic Ultramafic Sea-floor: a Comparative Study

NASA Astrophysics Data System (ADS)

Vogel, M.; Frueh-Green, G. L.; Boschi, C.; Schwarzenbach, E. M.

2014-12-01

The Bracco-Levanto ophiolitic complex (northwestern Italy) represents one of the largest and better-exposed ophiolitic successions in the Northern Apennines. It is considered to be a fragment of heterogeneous Jurassic lithosphere that records tectono-magmatic and alteration histories similar to those documented along the Mid-Atlantic Ridge (MAR), such as at the 15°20'N area and the Atlantis Massif at 30°N. Structural and petrological studies on these rocks provide constraints on metamorphic/deformation processes during formation and hydrothermal alteration of the Jurassic oceanic lithosphere. We present a petrological and geochemical study of serpentinization processes and fluid-rock interaction in the Bracco-Levanto ophiolitic complex and compare these to published data from modern oceanic hydrothermal systems, such as the Lost City hydrothermal field hosted in serpentinites on the Atlantis Massif. Major element and mineral compositional data allow us to distinguish a multiphase history of alteration characterized by: (1) widespread Si-metasomatism during progressive serpentinization, and (2) multiple phases of veining and carbonate precipitation associated with circulation of seawater in the shallow ultramafic-dominated portions of the Jurassic seafloor, resulting in the formation of ophicalcites. In detail, regional variations in Si, Mg and Al content are observed in zones of ophicalcite formation, indicating metasomatic reactions and Si-Al transport during long-lived fluid-rock interaction and channelling of hydrothermal fluids. Rare earth element and isotopic analysis indicate that the Si-rich fluids are derived from alteration of pyroxenes to talc and tremolite in ultramafic rocks at depth. Comparison with serpentinites from the Atlantis Massif and 15°20'N indicates a similar degree of Si-enrichment in the modern seafloor and suggests that Si-metasomatism may be a fundamental process associated with serpentinization at slow-spreading ridge environments. However, in contrast to metasomatic processes at the MAR, we find no geochemical evidence for a gabbroic source of the fluids, and thus, processes leading to Si-rich fluids can be variable in these environments.

Possibilities of the particle finite element method for fluid-soil-structure interaction problems

NASA Astrophysics Data System (ADS)

Oñate, Eugenio; Celigueta, Miguel Angel; Idelsohn, Sergio R.; Salazar, Fernando; Suárez, Benjamín

2011-09-01

We present some developments in the particle finite element method (PFEM) for analysis of complex coupled problems in mechanics involving fluid-soil-structure interaction (FSSI). The PFEM uses an updated Lagrangian description to model the motion of nodes (particles) in both the fluid and the solid domains (the later including soil/rock and structures). A mesh connects the particles (nodes) defining the discretized domain where the governing equations for each of the constituent materials are solved as in the standard FEM. The stabilization for dealing with an incompressibility continuum is introduced via the finite calculus method. An incremental iterative scheme for the solution of the non linear transient coupled FSSI problem is described. The procedure to model frictional contact conditions and material erosion at fluid-solid and solid-solid interfaces is described. We present several examples of application of the PFEM to solve FSSI problems such as the motion of rocks by water streams, the erosion of a river bed adjacent to a bridge foundation, the stability of breakwaters and constructions sea waves and the study of landslides.

Studying physical properties of deformed intact and fractured rocks by micro-scale hydro-mechanical-seismicity model

NASA Astrophysics Data System (ADS)

Raziperchikolaee, Samin

The pore pressure variation in an underground formation during hydraulic stimulation of low permeability formations or CO2 sequestration into saline aquifers can induce microseismicity due to fracture generation or pre-existing fracture activation. While the analysis of microseismic data mainly focuses on mapping the location of fractures, the seismic waves generated by the microseismic events also contain information for understanding of fracture mechanisms based on microseismic source analysis. We developed a micro-scale geomechanics, fluid-flow and seismic model that can predict transport and seismic source behavior during rock failure. This model features the incorporation of microseismic source analysis in fractured and intact rock transport properties during possible rock damage and failure. The modeling method considers comprehensive grains and cements interaction through a bonded-particle-model. As a result of grain deformation and microcrack development in the rock sample, forces and displacements in the grains involved in the bond breakage are measured to determine seismic moment tensor. In addition, geometric description of the complex pore structure is regenerated to predict fluid flow behavior of fractured samples. Numerical experiments are conducted for different intact and fractured digital rock samples, representing various mechanical behaviors of rocks and fracture surface properties, to consider their roles on seismic and transport properties of rocks during deformation. Studying rock deformation in detail provides an opportunity to understand the relationship between source mechanism of microseismic events and transport properties of damaged rocks to have a better characterizing of fluid flow behavior in subsurface formations.

The saltiest springs in the Sierra Nevada, California

USGS Publications Warehouse

Moore, James G.; Diggles, Michael F.; Evans, William C.; Klemic, Karin

2017-07-20

The five saltiest springs in the Sierra Nevada in California are found between 38.5° and 38.8° N. latitude, on the South Fork American River; on Caples Creek, a tributary of the Silver Fork American River; and on the North Fork Mokelumne River. The springs issue from Cretaceous granitic rocks in the bottoms of these major canyons, between 1,200- and 2,200-m elevation. All of these springs were well known to Native Americans, who excavated meter-sized basins in the granitic rock, within which they produced salt by evaporation near at least four of the five spring sites. The spring waters are dominated by Cl, Na, and Ca; are enriched relative to seawater in Ca, Li, and As; and are depleted in SO4, Mg, and K. Tritium analyses indicate that the spring waters have had little interaction with rainfall since about 1954. The waters are apparently an old groundwater of meteoric origin that resided at depth before moving up along fractures to the surface of the exhumed granitic rocks. However, along the way these waters incorporated salts from depth, the origin of which could have been either from marine sedimentary rocks intruded by the granitic magmas or from fluid inclusions in the granitic rocks. Prolonged storage at depth fostered water-rock interactions that undoubtedly modified the fluid compositions.

Final Report: Development of a Chemical Model to Predict the Interactions between Supercritical CO2, Fluid and Rock in EGS Reservoirs

DOE Office of Scientific and Technical Information (OSTI.GOV)

McPherson, Brian J.; Pan, Feng

2014-09-24

This report summarizes development of a coupled-process reservoir model for simulating enhanced geothermal systems (EGS) that utilize supercritical carbon dioxide as a working fluid. Specifically, the project team developed an advanced chemical kinetic model for evaluating important processes in EGS reservoirs, such as mineral precipitation and dissolution at elevated temperature and pressure, and for evaluating potential impacts on EGS surface facilities by related chemical processes. We assembled a new database for better-calibrated simulation of water/brine/ rock/CO2 interactions in EGS reservoirs. This database utilizes existing kinetic and other chemical data, and we updated those data to reflect corrections for elevated temperaturemore » and pressure conditions of EGS reservoirs.« less

Fluid involvement in normal faulting

NASA Astrophysics Data System (ADS)

Sibson, Richard H.

2000-04-01

Evidence of fluid interaction with normal faults comes from their varied role as flow barriers or conduits in hydrocarbon basins and as hosting structures for hydrothermal mineralisation, and from fault-rock assemblages in exhumed footwalls of steep active normal faults and metamorphic core complexes. These last suggest involvement of predominantly aqueous fluids over a broad depth range, with implications for fault shear resistance and the mechanics of normal fault reactivation. A general downwards progression in fault rock assemblages (high-level breccia-gouge (often clay-rich) → cataclasites → phyllonites → mylonite → mylonitic gneiss with the onset of greenschist phyllonites occurring near the base of the seismogenic crust) is inferred for normal fault zones developed in quartzo-feldspathic continental crust. Fluid inclusion studies in hydrothermal veining from some footwall assemblages suggest a transition from hydrostatic to suprahydrostatic fluid pressures over the depth range 3-5 km, with some evidence for near-lithostatic to hydrostatic pressure cycling towards the base of the seismogenic zone in the phyllonitic assemblages. Development of fault-fracture meshes through mixed-mode brittle failure in rock-masses with strong competence layering is promoted by low effective stress in the absence of thoroughgoing cohesionless faults that are favourably oriented for reactivation. Meshes may develop around normal faults in the near-surface under hydrostatic fluid pressures to depths determined by rock tensile strength, and at greater depths in overpressured portions of normal fault zones and at stress heterogeneities, especially dilational jogs. Overpressures localised within developing normal fault zones also determine the extent to which they may reutilise existing discontinuities (for example, low-angle thrust faults). Brittle failure mode plots demonstrate that reactivation of existing low-angle faults under vertical σ1 trajectories is only likely if fluid overpressures are localised within the fault zone and the surrounding rock retains significant tensile strength. Migrating pore fluids interact both statically and dynamically with normal faults. Static effects include consideration of the relative permeability of the faults with respect to the country rock, and juxtaposition effects which determine whether a fault is transmissive to flow or acts as an impermeable barrier. Strong directional permeability is expected in the subhorizontal σ2 direction parallel to intersections between minor faults, extension fractures, and stylolites. Three dynamic mechanisms tied to the seismic stress cycle may contribute to fluid redistribution: (i) cycling of mean stress coupled to shear stress, sometimes leading to postfailure expulsion of fluid from vertical fractures; (ii) suction pump action at dilational fault jogs; and, (iii) fault-valve action when a normal fault transects a seal capping either uniformly overpressured crust or overpressures localised to the immediate vicinity of the fault zone at depth. The combination of σ2 directional permeability with fluid redistribution from mean stress cycling may lead to hydraulic communication along strike, contributing to the protracted earthquake sequences that characterise normal fault systems.

Attenuation and Dispersion Analysis in Laboratory Measured Elastic Properties in the Middle East Carbonate Reservoir Rocks

NASA Astrophysics Data System (ADS)

Sharma, R.

2016-12-01

Carbonate rocks are sensitive to circulation of fluid types that leads to diagenetic alterations and therefore to heterogeneity in distribution of porosity and permeability. These heterogeneities in turn, lead to heterogeneity in saturations varying from partial to patchy to uniform. Depending on the interaction between fluids and rock matrix, a weakening or strengthening in shear modulus of carbonate rocks can also develop (Eberli et al., 2003; Adam et al., 2006; Sharma et al., 2009; Sharma et al., 2013). Thus the elastic response over the production life of the carbonate reservoirs can change considerably. Efforts to couple fluid flow with varying seismic properties of these reservoirs are limited in success due to the differences between static elastic properties derived from reservoir simulation and dynamic elastic properties derived from inverted seismic. An additional limitation arises from the assumption that shear modulus does not change with fluid type and saturations. To overcome these limitations, we need to understand the relationships between the static and the dynamic elastic properties using laboratory measurements made at varying pressures, frequencies and with varying saturants. I will present the following results: 1) errors associated with using dynamic (2 - 2000 Hz and 1 MHz) elastic properties data for static ( 0 Hz) reservoir properties, 2) shear modulus variation in carbonates upon saturation with varying saturants The results will enable us to estimate, 1) distribution of stress-strain relations in reservoir rocks and 2) modulus dispersion to correct seismic-derived moduli as inputs for reservoir simulators. The results are critical to estimate, 1) modulus dispersion correction and 2) occurrence and amount of shear modulus variation with fluid change vital for rock stability analysis

The Effect of Boiling on Seismic Properties of Water-Saturated Fractured Rock

NASA Astrophysics Data System (ADS)

Grab, Melchior; Quintal, Beatriz; Caspari, Eva; Deuber, Claudia; Maurer, Hansruedi; Greenhalgh, Stewart

2017-11-01

Seismic campaigns for exploring geothermal systems aim at detecting permeable formations in the subsurface and evaluating the energy state of the pore fluids. High-enthalpy geothermal resources are known to contain fluids ranging from liquid water up to liquid-vapor mixtures in regions where boiling occurs and, ultimately, to vapor-dominated fluids, for instance, if hot parts of the reservoir get depressurized during production. In this study, we implement the properties of single- and two-phase fluids into a numerical poroelastic model to compute frequency-dependent seismic velocities and attenuation factors of a fractured rock as a function of fluid state. Fluid properties are computed while considering that thermodynamic interaction between the fluid phases takes place. This leads to frequency-dependent fluid properties and fluid internal attenuation. As shown in a first example, if the fluid contains very small amounts of vapor, fluid internal attenuation is of similar magnitude as attenuation in fractured rock due to other mechanisms. In a second example, seismic properties of a fractured geothermal reservoir with spatially varying fluid properties are calculated. Using the resulting seismic properties as an input model, the seismic response of the reservoir is then computed while the hydrothermal structure is assumed to vary over time. The resulting seismograms demonstrate that anomalies in the seismic response due to fluid state variability are small compared to variations caused by geological background heterogeneity. However, the hydrothermal structure in the reservoir can be delineated from amplitude anomalies when the variations due to geology can be ruled out such as in time-lapse experiments.

Characterizing the variability in chemical composition of flowback and produced waters - results from lab and field studies

NASA Astrophysics Data System (ADS)

Vieth-Hillebrand, Andrea; Wilke, Franziska D. H.; Schmid, Franziska E.; Zhu, Yaling; Lipińska, Olga; Konieczyńska, Monika

2017-04-01

The huge volumes and unknown composition of flowback and produced waters cause major public concerns about the environmental and social compatibility of hydraulic fracturing and the exploitation of gas from unconventional reservoirs. Flowback and produced waters contain not only residues of fracking additives but also chemical species that are dissolved from the target shales themselves. Shales are a heterogeneous mixture of minerals, organic matter, and formation water and little is actually understood about the fluid-rock interactions occurring during hydraulic fracturing of the shales and their effects on the chemical composition of flowback and produced water. To overcome this knowledge gap, interactions of different shales with different artificial stimulation fluids were studied in lab experiments under ambient and elevated temperature and pressure conditions. These lab experiments showed clearly that fluid-rock interactions change the chemical composition of the initial stimulation fluid and that geochemistry of the fractured shale is relevant for understanding flowback water composition. In addition, flowback water samples were taken after hydraulic fracturing of one horizontal well in Pomeranian region, Poland and investigated for their chemical composition. With this presentation, results from lab and field studies will be presented and compared to decipher possible controls on chemical compositions of flowback and produced water.

Syntectonic Fluid-Rock Interactions Involving Surficial Waters in the Sevier Thrust Belt, Tendoy Mountains, Southwest Montana

NASA Astrophysics Data System (ADS)

Johnson, A. C.; Anastasio, D. J.; Bebout, G. E.

2002-05-01

Calcite veins and Mississippian carbonates from the Sevier thrust front record syntectonic meteoric fluid infiltration and hydrocarbon migration. The Tendoy and Four Eyes Canyon thrust sheets were emplaced onto the western margin of the Late Cretaceous Western Interior Seaway \\{WIS\\}. Low salinity \\{Tice = -0.6° C to +3.6° C\\} and low temperature \\{110° C +/- 10\\} fluids interacted with hanging-wall carbonates at a depth of 5km. Most veins have single or multiple generations of varying apertures, composed predominately of large euhedral crystals with some finer grained layers and protolith inclusions. Orientation analysis of mutually cross-cutting, high-angle vein sets suggest development concurrent with Four Eyes Canyon thrusting but prior to Tendoy thrusting. These vein sets are generally cut by later synfolding bed-parallel shear veins. Reactivation of both the bed-parallel and bed-perpendicular vein sets \\{strike parallel and strike perpendicular\\} in the Four Eyes Canyon thrust sheet occurred subsequent to Sevier compression, creating wide, coarse crystalline veins that often transect Sevier structures. Oxygen and Carbon isotope analyses of veins allow for reconstruction of fluid-rock interactions during thrust sheet emplacement and later reactivation. All veins and variably deformed host-rocks were microsampled and analyzed for δ 18OV-SMOW and δ 13CV-PDB. Small Tendoy veins \\{1mm-1cm wide\\} have calcite δ 18O values of +8.9 to +28.8‰ and calculated fluid \\{as H2O\\} of -8.3 to +11.6‰ \\{100° C\\}, -7.3 to +12.6‰ \\{110° C\\}, and -6.3 to +13.6‰ \\{120° C\\}. Four Eyes Canyon veins \\{1cm-3m wide\\} have calcite δ 18O values of +5.9 to +17.0‰ and calculated fluid of -11.3 to -0.2‰ \\{100° C\\}, -10.3 to +0.8‰ \\{110° C\\}, and -9.3 to +1.8‰ \\{120° C\\}. While there is significant variation in δ 18O there is relatively little systematic variation seen in δ 13C. Protolith carbonate has δ 18O values of +22.2‰ +/- 3.2; and some multi-layered veins are more depleted in δ 18O in earlier-formed generations. For three sites in the Lost River Range \\{LRR\\}, Idaho, the calculated minimum fluid δ 18O is -7.5‰ \\{+150 to +250° C\\} \\{Bebout et al., 2001; GRL\\}. Although the uncertainty of the regional temperature is large, when assuming a temperature of 110° C +/- 10 the Tendoy has a minimum calculated δ 18O H2O value of -8.3 to -6.3‰ and the Four Eyes Canyon has a minimum calculated δ 18O H2O value of -11.3 to -9.3‰ . These fluid O-isotope compositions are similar to the minimum H2O δ 18O calculated for the LRR sites - all pointing to infiltration of the thrust sheets by meteoric waters, possibly relatively nearshore meteoric waters with isotopic compositions strongly influenced by the nearby WIS. Surficial fluids possibly infiltrated into the thrust sheets by topographic recharge and migrated updip towards the foreland, mixing to varying degrees with more deeply roused fluids. Smaller veins and longer travel times and distances favored more extensive fluid-rock interaction and thus more rock-controlled fluid compositions. Microfractures in veins healed by hydrocarbons indicate that hydrocarbons migrated with freshwater fluids. Calcite veins record a dynamic history of fluid pathways and fluid flow as permeability evolved during thrust emplacement.

B, Sr and Pb isotope geochemistry of high-pressure Alpine metaperidotites monitors fluid-mediated element recycling during serpentinite dehydration in subduction mélange (Cima di Gagnone, Swiss Central Alps)

NASA Astrophysics Data System (ADS)

Cannaò, E.; Agostini, S.; Scambelluri, M.; Tonarini, S.; Godard, M.

2015-08-01

Tectonic mixing of slab- and mantle-derived materials at the interface between converging plates highly enhances fluid-mediated mass transfer from the slab to the overlying mantle. Subduction mélanges can provide information about the interaction among different slices accreted at plate interface domains, with implications on the tectonic and geochemical evolution of the plate-interface itself. At Cima di Gagnone, pelitic schists and gneiss enclose chlorite harzburgite and garnet peridotite lenses, like in subduction mélanges located in-between downgoing slabs and overlying mantle. These peridotites host MORB-type eclogite and metarodingite, and derive from dehydration of serpentinized mantle protoliths. Their enrichment in fluid-mobile B, As, Sb, U, Th is the result of an early-stage oceanic serpentinization, followed by interaction with host metasediments during subduction burial. Here we define the element exchange process in the Gagnone mélange by means of the B, Sr and Pb isotope analysis of its main lithologies (ultramafic, mafic rocks and paragneiss). The 87Sr/86Sr and 206Pb/204Pb ratios of ultramafic rocks (0.7090-0.7124 and 18.292-18.837, respectively) show enrichments in radiogenic Sr and Pb after exchange with the host paraschist (up to 0.7287 87Sr/86Sr; 18.751 206Pb/204Pb). The δ11B values of peridotites (down to -10‰) point to a combined effect of (1) 11B release to deserpentinization fluids (serpentinized protoliths likely had positive δ11B and lower radiogenic Sr, Pb), and of (2) exchange with fluids from the surrounding metasediments. The whole Gagnone rock-suite is finally overprinted by retrograde fluids that essentially bring to an increase in radiogenic Pb (about 19.0 206Pb/204Pb) and to values of 0.710 87Sr/86Sr and of -10‰ δ11B. The recognition of different stages of interaction between mantle rocks and sedimentary/crustal reservoirs allows us to define the geochemical effects related to the early coupling of such rocks along the plate-interface. Our study shows that ultramafic rocks involved in subduction-zone metamorphism and serpentinization uptake radiogenic Pb and Sr released by associated sedimentary reservoirs. The exchange process envisioned here is not only representative of subduction mélanges: it can also be a proxy of mass transfer between slab and serpentinized supra-subduction mantle, as occurs in forearcs. Dehydration of the Gagnone-type serpentinized mantle releases crust-derived components to arcs, without direct involvement of metasediment dehydration and/or melting in subarc environments. The retention of appreciable amounts of fluid-mobile elements, radiogenic Pb and Sr in dehydrated Gagnone peridotites has implications on element recycling in the deep Earth's mantle.

Rb-Sr, K-Ar, and stable isotope evidence for the ages and sources of fluid components of gold-bearing quartz veins in the northern Sierra Nevada foothills metamorphic belt, California

USGS Publications Warehouse

Böhlke, John Karl; Kistler, R. W.

1986-01-01

Gold-bearing quartz veins occur in and near major fault zones in deformed oceanic and island-arc rocks west of the main outcrop of the Sierra Nevada composite batholith. Veins typically occupy minor reverse faults that crosscut blueschist to amphibolite-grade metamorphic rocks whose metamorphic ages range from early Paleozoic to Jurassic. Vein micas and carbonate-quartz-mica assemblages that formed by hydrothermal metasomatism of ultramafic wall rocks in the Alleghany, Grass Valley, Washington, and Mother Lode districts yield concordant K-Ar and Rb-Sr ages. The dated veins are significantly younger than prograde metamorphism, penetrative deformation, and accretion of their host rocks to the continental margin. New and previously published mineralization ages from 13 localities in the Sierra foothills range from about 140 to 110 m.y. ago, with mean and median between 120 and 115 m.y. The age relations suggest that mineralizing fluids were set in motion by deep magmatic activity related to the resumption of east-dipping subduction along the western margin of North America following the Late Jurassic Nevadan collision event.CO 2 -bearing fluids responsible for metasomatism and much of the vein mica, carbonate, albite, and quartz deposition in several northern mines were isotopically heavy (delta 18 O [asymp] 8-14ppm; delta D between about -10 and -50ppm) and do not resemble seawater, magmatic, or meteoric waters. Metasomatic and vein-filling mica, dolomite, magnesite, and quartz in altered ultramafic rocks generally formed from fluids with similar Sr and O isotope ratios at a given locality. Consistent quartz-mica delta 18 O fractionations (delta 18 O (sub Q-M) = 4.5-4.9ppm) from various localities imply uniform equilibration temperatures, probably between 300 degrees and 350 degrees C. On a local (mine) scale, fluids responsible for both carbonate alteration of mafic and ultramafic wall rocks and albitic alteration of felsic and pelitic rocks had similar Sr isotope ratios.Samples from three veins in the central Alleghany district fit a 115.7 + or - 3-m.y. Rb-Sr isochron with a ( 87 Sr/ 86 Sr) i value of approximately 0.7119. Inferred 87 Sr/ 86 Sr ratios of metasomatic fluids from mines in different parts of the foothills region vary considerably (0.704-0.718), suggesting that Sr was derived from sources ranging from "western assemblage" Mesozoic ophiolitic or arc volcanic rocks to early Paleozoic continent-derived clastic rocks of the Shoo Fly Complex. Systematic geographic variations in both Sr and O isotopes can be rationalized by assuming extensive fluid interaction with rocks similar to the ones that are exposed within a few kilometers of the veins, but the ultimate sources of the fluids, and of Au and other constituents, may be independent of these. Isotopically lighter (meteoric?) fluids deposited some late quartz overgrowths and occupied secondary fluid inclusions in earlier vein quartz.

Metamorphism and gold mineralization in the Blue Ridge, Southernmost Appalachians

USGS Publications Warehouse

Stowell, H.H.; Lesher, C.M.; Green, N.L.; Sha, P.; Guthrie, G.M.; Sinha, A.K.

1996-01-01

Lode gold mineralization in the Blue Ridge of the southernmost Appalachians is hosted by metavolcanic rocks (e.g., Anna Howe mine, AL; Royal Vindicator mine, GA), metaplutonic rocks (e.g., Hog Mountain mine, AL), and metasedimentary rocks (e.g., Lowe, Tallapoosa, and Jones Vein mines, AL). Most gold occurs in synkinematic quartz ?? plagioclase ?? pyrite ?? pyrrhotite ?? chlorite veins localized along polydeformational faults that juxtapose rocks with significantly different peak metamorphic mineral assemblages. Mineralogy, chemistry, and O and H isotope studies suggest that the three types of host rocks have undergone differing amounts and types of alteration during mineralization. Limited wall-rock alteration in metavolcanic- and metasediment-hosted deposits, and relatively extensive wall-rock alteration in granitoid-hosted deposits, suggests that most deposits formed from fluids that were close to equilibrium with metavolcanic and metasedimentary rocks. Stable isotope compositions of the fluids calculated from vein minerals and vein selvages are consistent with a predominantly metasedimentary fluid source, but vary from deposit to deposit (-22 to -47??? ??D, 4-5??? ??18O, and 5-7??? ??34S at Anna Howe and Royal Vindicator; -48 to -50??? ??D, 9-13??? ??18O, and ca. 19??? ??34S at Lowe and Jones Vein; and -22 to -23??? ??D, 8-11??? ??18O, 9-10??? ??34S, and -6 ??13C at Hog Mountain). Silicate mineral thermobarometry of vein, vein selvage, and wall-rock mineral assemblages indicate that mineralization and regional metamorphism occured at greenschist to amphibolite facies (480?? ?? 75??C at Anna Howe, 535?? ?? 50??C at 6.4 ?? 1 kbars at Lowe, 530?? ?? 50??C at 6.9 ?? 1 kbars at Tallapoosa, and 460?? ?? 50??C at 5.5 ?? 1 kbars at Hog Mountain). Oxygen isotope fractionation between vein minerals and selvage minerals consistently records equilibration temperatures that are similar to or slightly lower than those estimated from silicate thermometry. Auriferous veins contain numerous fluid inclusions that were emplaced in several stages and can be subdivided into five compositional types based on salt and CO2 concentrations. Fluid inclusion isochores for early formed inclusions from these veins intercept the pressure and temperature conditions estimated from silicate mineral thermobarometry and stable isotope thermometry, and are compatible with entrapment at those conditions. These fluids exhibit significant variation in salinity (XNaClequiv = 0.0-0.2) and CO2 (XCO2 = 0.0-0.2), suggesting variation in fluid-wall-rock interaction that accompanied gold deposition during declining temperatures. Less abundant and later fluids within the veins are dominantly CO2. The association of gold mineralization with structurally controlled concordant and discordant quartz sulfide veins, and the temperatures and pressures of wall-rock alteration and regional metamorphism indicate that the present distribution of gold is a result of metamorphism during progressive D2-D3 deformation. Isotopic data for alteration envelopes date this event as Alleghanian: 279 ?? 14 Ma (K-Ar whole rock) and 343 ?? 18 Ma (K-Ar biotite) at Lowe; and 315 ?? 18 Ma (Rb-Sr whole-rock isochron; 87Sr/86Sr, = 0.7061 ?? 0.0008) and 294 ?? 16 Ma (K-Ar whole-rock) at Hog Mountain. Available data are compatible with development of the lodes during early Alleghanian overthrusting of allochthons over sedimentary rocks of the autochthonous North American margin. The implication is that the fluids were derived from metasedimentary and/or metavolcanic formations in the lower parts of the crystalline thrust stack (or possibly from underlying autochthonous sedimentary formations), ascended along permeable fault zones, and were emplaced as veins into dilatent areas in and adjacent to the fault zones.

Tourmaline orbicules in peraluminous monzogranites of Argentina: A study case of fluid-rock interaction between leucogranite and country-rock metasediments

NASA Astrophysics Data System (ADS)

Lira, Raúl; Poklepovic, María F.

2017-12-01

Tourmaline orbicules hosted in peraluminous granites are documented worldwide. Seven occurrences were identified in Argentina. Petrography, mineral chemistry, whole-rock geochemistry mass balance and microthermometric studies were performed in orbicules formed at the cupola of a peraluminous A-type leucogranite (Los Riojanos pluton), as well as complementary investigation was achieved in other orbicules of similar geological setting. Mass balance computations in zoned orbicules consistently confirmed immobility of Si both in core and halo, immobility of K and little loss of Al during halo reactions. Elements gained and lost in the schorl-rich core are Fe, Al, Mg, Ti, Ba, Sr, Y and Zr, and Na, K, Rb and Nb, respectively; in the halo, K, Ba, Sr, Y, Zr and locally CaO, were gained, and Fe, Mg, Na, Al, Rb and Nb were lost. The schorl-rich core is enriched in LREE relative to the leucogranite host. A temperature-salinity plot from fluid inclusion data delineates a magmatic-meteoric mixing trend of diluting salinity with descending temperature. Computed δDH20 values from Los Riojanos orbicule schorl suggest magmatic and magmatic-meteoric mixed origins. In Los Riojanos, mass balance constraints suggest that Fe, Mg, Ba, Sr and metallic traces like Zn and V (±Pb) were most likely derived from country-rock schists and gneisses through fluid-rock exchange reactions. A late magmatic-, volatile-rich- fluid exsolution scenario for the formation of orbicules is envisaged. Schorl crystallization was likely delayed to the latest stages of leucogranite consolidation, not only favored by the high diffusivity of B2O3 preferentially partitioned into the exsolved aqueous-rich fluid, but also likely limited to the low availability of Fe and Mg from the scarce granitic biotite, and to the high F- content of the melt. The spatial confination of orbicules to the contact zone granite-metasediments suggests that orbicules were not formed until exsolved fluids reached the boundary with the biotite-rich country-rock.

Fluid-mediated mass transfer from a paleosubduction channel to its mantle wedge: Evidence from jadeitite and related rocks from the Guatemala Suture Zone

NASA Astrophysics Data System (ADS)

Harlow, George E.; Flores, Kennet E.; Marschall, Horst R.

2016-08-01

Jadeitites in serpentinite mélanges are the product of crystallization from and/or metasomatism by aqueous fluids that transfer components from and within a subduction channel-the slab-mantle interaction volume-into discrete rock units, most commonly found within the serpentinized or serpentinizing portion of the channel or the overlying mantle rocks at high pressure (1 to > 2 GPa). Two serpentinite mélanges on either side of the Motagua fault system (MFS) of the Guatemala Suture Zone contain evidence of this process. Whole rock compositional analyses are reported here from 86 samples including jadeitites and the related rocks: omphacitites, albitites and mica rocks. The predominance of a single phase in most of these rocks is reflected in the major element compositions and aspects of the trace elements, such as REE abundances tracking Ca in clinopyroxene. Relative to N-MORB all samples show relative enrichments in the high field strength elements (HFSE) Hf, Zr, U, Th, and the LILE Ba and Cs, contrasted by depletions in K and in some cases Pb or Sr. Most jadeitites are also depleted in the highly compatible elements Cr, Sc and Ni despite their occurrence in serpentinite mélange; however, some omphacitite samples show the opposite. Trace elements in these jadeitite samples show a strong similarity with GLOSS (globally subducted oceanic sediment) and other terrigenous sediments in terms of their trace-element patterns, but are offset to lower abundances. Jadeitites thus incorporate a strong trace-element signature derived from sediments mixed with that from fluid derived from altered oceanic crust. Enrichment in the HFSE argues for mobility of these elements in aqueous fluids at high P/T conditions in the subduction channel and a remarkable lack of fractionation that might otherwise be expected from dissolution and fluid transport.

External micro-PIXE analysis of fluid inclusions: Test of the LABEC facility on samples of quartz veins from Apuan Alps (Italy)

NASA Astrophysics Data System (ADS)

Massi, M.; Calusi, S.; Giuntini, L.; Ruggieri, G.; Dini, A.

2008-05-01

Fluid inclusions are small portions, usually smaller than 100 μm, of fluid trapped within minerals during or after growth. Their characteristics provide therefore fundamental information on nature and evolution of fluids present in the past in different geological environments. At the LABEC laboratory in Firenze, high-salinity fluid inclusions in quartz crystals, coming from the Apuan Alps metamorphic complex, were analysed at the external scanning microbeam. Results, although still preliminary, have already provided us with hints on fluid-rock interaction processes during the metamorphism of the Apuan Alps.

Inferences from Microfractures and Geochemistry in Dynamic Shale-CO2 Packed Bed Experiments

NASA Astrophysics Data System (ADS)

Radonjic, M.; Olabode, A.

2016-12-01

Subsurface storage of large volumes of carbondioxide (CO2) is expected to have long term rock-fluid interactions impact on reservoir and seal rocks properties. Caprocks, particularly sedimentary types, are the ultimate hydraulic barrier in carbon sequestration. The mineralogical components of sedimentary rocks are geochemically active under enormous earth stresses, which generate high pressure and temperature conditions. It has been postulated that in-situ mineralization can lead to flow impedance in natural fractures in the presence of favorable geochemical and thermodynamic conditions. This experimental modelling research investigated the impact of in-situ geochemical precipitation on conductivity of fractures. Geochemical analyses were performed on four different samples of shale rocks, effluent fluids and recovered precipitates both before and after CO2-brine flooding of crushed shale rocks at moderately high temperature and pressure conditions. The results showed that most significant diagenetic changes in shale rocks after flooding with CO2-brine, reflected in the effluent fluid with predominantly calcium based minerals dissolving and precipitating under experimental conditions. Major and trace elements in the effluent (using ICP-OES analysis) indicated that multiple geochemical reactions are occurring with almost all of the constituent minerals participating. The geochemical composition of precipitates recovered after the experiments showed diagenetic carbonates and opal as the main constituents. The bulk rock showed little changes in composition except for sharper and more refined peaks on XRD analysis, suggesting that a significant portion of the amorphous content of the rocks have been removed via dissolution by the slightly acid CO2-brine fluid that was injected. Micro-indentation results captured slight reduction in the hardness of the shale rocks and this reduction appeared dependent on diagenetic quartz content. It can be inferred that convective reactive transport of dissolved minerals are involved in nanoscale precipitation-dissolution processes in shale. This reactive transport of dissolved minerals can occlude micro-fracture flow paths, thereby improving shale caprock seal integrity with respect to leakage risk under CO2 sequestration conditions.

Extraordinary phase separation and segregation in vent fluids from the southern East Pacific Rise

USGS Publications Warehouse

Von Damm, Karen L.; Lilley, M.D.; Shanks, Wayne C.; Brockington, M.; Bray, A.M.; O'Grady, K. M.; Olson, E.; Graham, A.; Proskurowski, G.

2003-01-01

The discovery of Brandon vent on the southern East Pacific Rise is providing new insights into the controls on midocean ridge hydrothermal vent fluid chemistry. The physical conditions at the time ofsampling (287 bar and 405??C) place the Brandon fluids very close to the critical point of seawater (298 bar and 407??C). This permits in situ study of the effects of near criticalphenomena, which are interpreted to be the primary cause of enhanced transition metal transport in these fluids. Of the five orifices on Brandon sampled, three were venting fluids with less than seawater chlorinity, and two were venting fluids with greater than seawater chlorinity. The liquid phase orifices contain 1.6-1.9 times the chloride content of the vapors. Most other elements, excluding the gases, have this same ratio demonstrating the conservative nature of phase separation and the lack of subsequent water-rock interaction. The vapor and liquid phases vent at the same time from orifices within meters of each other on the Brandon structure. Variations in fluid compositions occur on a time scale of minutes. Our interpretation is that phase separation and segregation must be occurring 'real time' within the sulfide structure itself. Fluids from Brandon therefore provide an unique opportunity to understand in situ phase separation without the overprinting of continued water-rock interaction with the oceanic crust, as well as critical phenomena. ?? 2002 Elsevier Science B.V. All rights reserved.

Stable isotope geochemistry of ultrahigh pressure metamorphic rocks from the Dabie-Sulu orogen in China: implications for geodynamics and fluid regime

NASA Astrophysics Data System (ADS)

Zheng, Yong-Fei; Fu, Bin; Gong, Bing; Li, Long

2003-07-01

Discovery of coesite, diamond, and extreme 18O-depletion in eclogites from the Dabie-Sulu orogen in central-east China has contributed much to our understanding of subduction of continental crust to mantle depths and its subsequent exhumation. Hydrogen, oxygen, and carbon isotope distributions were systematically investigated in the past 8 years for ultrahigh pressure (UHP) eclogites, gneisses, granulites, marbles, and peridotites from this exciting region. The available data show the following characteristic features: (1) variable δ18O values of -11‰ to +10‰ for the eclogites and gneisses, with both equilibrium and disequilibrium fractionations of oxygen isotopes among minerals; (2) disequilibrium fractionation of hydrogen isotopes between mica and epidote from both eclogites and gneisses, with low δD values up to -127‰ to -100‰ for phengite; (3) negative δ13C values of -28‰ to -21‰ for apatite as well as host-eclogites and gneisses; (4) positive δ13C values of +1‰ to +6‰ for coesite-bearing marble associated with eclogites; (5) zircons from metamorphic rocks of different grades show a large variation in δ18O from -11‰ to +9‰, with U-Pb ages of 700 to 800 Ma for the timing of low- δ18O magma crystallization. It appears that the UHP metamorphic rocks exhibit ranges of δ18O values that are typical of potential precursor protolith rocks. Preservation of the oxygen isotope equilibrium fractionations among the minerals of the UHP eclogites and gneisses suggests that these rocks acquired the low δ18O values by meteoric-hydrothermal alteration before the UHP metamorphism. Thus, the UHP metamorphic rocks largely reflect the δ18O values of their premetamorphic igneous or sedimentary precursors. The stable isotope data demonstrate that basaltic, granitic, and sedimentary protoliths of the eclogites, orthogneiss, and paragneiss in the orogen were at or near the earth's surface, and subjected to varying degrees of water-rock interaction at some time before plate subduction. The low- δ18O rocks were isolated from water-rock interactions during their descent to and return from mantle depths. It appears that the oxygen, hydrogen, and carbon on the earth's surface were recycled into the mantle at depths of >200 km by the continental subduction. A fried ice cream model is advanced as an analogy to the rapid processes of both plate subduction and exhumation, with a short residence time of the UHP slab at mantle depths. The entire cycle of subduction, UHP metamorphism, and exhumation is estimated to take place in about 10 to 20 Ma. The 18O-depleted zircons and other minerals acquired their oxygen isotope compositions from low- δ18O magmas that incorporated the isotopic signatures of meteoric water in rifting tectonic zones prior to solidification. The U-Pb discordia dating for the 18O-depleted zircons revealed that the meteoric water-rock interaction occurred at Neoproterozoic, a time being much earlier than the UHP metamorphism at Triassic, but correlated with the Rodinian breakup, positive carbon isotope anomaly in carbonates, and the snowball earth event. The unusually low δ18O values can be acquired from either the meteoric water of cold paleoclimates or the melt water of glacial ice or snow. Neoproterozoic rift magmatism along the northern margin of the Yangtze craton may have provided sufficient heat source to trigger the meteoric-hydrothermal circulation. It is possible that the unusual 18O-depletion in the meta-igneous rocks occurs at some time prior to the snowball earth event, when there is a transition from a very cold earth with continental glaciers to a widely glaciated earth where bulk of the earth is covered by sea ice as defined for the snowball earth. The heterogeneity of oxygen isotope compositions at outcrop scales demonstrates the absence of pervasive fluid infiltration during prograde, peak UHP, and retrograde metamorphism; most rocks appear to have recrystallized under virtually closed system conditions characterized by widespread lack of an aqueous fluid phase. Volatiles may not escape from the rock series during the rapid subduction of the continental crust, resulting in a general lack of syn-collisional arc-magmatism in this orogen. Big differences in pressure and time from the peak UHP stage to the retrograde HP eclogite-facies stage cause significant release of aqueous fluid by dehydration from decompressing slabs during exhumation. As a result, fluid flow occurred in a channellized way on small scales subsequent to the UHP metamorphism, with very limited mobility of fluid at peak UHP conditions. The fluid for retrograde reactions was internally buffered in stable isotope compositions. While some fluids were locally derived from the surrounding gneisses, more fluid was probably derived from internal dehydration of the rock units in question. In addition to the breakdown of hydroxyl-bearing minerals, exsolution of structural hydroxyl dissolved in nominally anhydrous minerals due to abrupt decrease in pressure may have been an important source for the retrograde fluid.

Stable-isotope studies of rocks and secondary minerals in a vapor-dominated hydrothermal system at The Geysers, Sonoma County, California

NASA Astrophysics Data System (ADS)

Lambert, Steven J.; Epstein, Samuel

1992-11-01

The Geysers, a vapor-dominated hydrothermal system, is developed in host rock of the Franciscan Formation, which contains veins of quartz and calcite whose δ 18O values record the temperatures and isotopic compositions of fluids prevailing during at least two different episodes of rock-fluid interaction. The first episode took place at about 200°C, during which marine silica and carbonate apparently interacted with ocean water entrapped in the sediments to form veins of quartz and calcite whose δ 18O values were around +19 and +16%, respectively. The calculated water/mineral ratios were less than unity. The water may have profoundly influenced the δ 18O values of spilitic basalts during their metamorphism to greenstones. Serpentinization and structural emplacement of ophiolite slabs were isotopically unrelated to this episode, which was essentially a low-grade (post-Cretaceous?) burial metamorphism. D/H ratios of actinolite, chlorite, and micas in host rocks were more profoundly altered during this episode than were 18O/ 16O ratios. A paleogeothermal gradient of about 53°C/km has been inferred for this episode, from δ 18O-depth distributions of vein minerals. The second episode, in part recorded by cogenetic vein quartz and calcite δ 18O values of +4 to +6% and +1 to +3%, respectively, began with large quantities of meteoric water circulating in fractures in the rock at temperatures of 160-180°C in response to the initiation of the Pliocene-Pleistocene Clear Lake magmatism. The temperature rose, and with the restricted circulation of fluids the ancestral hot-water system evolved into the presently active vapor-dominated system, which according to the cogenetic vein quartz and calcite δ 18O values involved temperatures as high as 320°C and fluid/mineral ratios near unity. The change in the oxygen-isotopic composition of the serpentinite within the host rock during this later activity was negligible. The δ 13C values of vein calcite at The Geysers reflect both a marine carbonate and organic component of carbon, but carbon-isotope exchange has been facilitated by the vapor-dominated hydrothermal fluid to a greater degree than in any other episode or in other hot-water systems.

A review of wave celerity in frictionless and axisymmetrical steel-lined pressure tunnels

NASA Astrophysics Data System (ADS)

Hachem, F. E.; Schleiss, A. J.

2011-02-01

Generally applicable approaches for estimating the “quasi-static”, which means without fluid-structure interaction and frequency-dependent water-hammer wave speed in steel-lined pressure tunnels are analyzed. The external constraints and assumptions of these approaches are discussed in detail. The reformulated formulas are then compared to commonly used expressions. Some special cases of wave speed calculation such as unlined pressure tunnels and open-air penstocks are investigated. The quasi-static wave speed is significantly influenced by the state of the backfill concrete and the near-field rock zone (cracked or uncracked). In the case when these two layers are cracked, the quasi-static wave speed is overestimated in between 1% and 8% compared to uncracked concrete and near-field rock layers. Depending on the stiffness of steel liner and penstock, the fluid-structure interaction leads to significant difference in wave speeds values. Compared to the quasi-static case, the fluid-structure interaction approach, applied to steel-lined tunnels, results up to 13% higher wave speed values in the high-frequency range (higher than 600 Hz) and up to 150% lower values for frequencies between 150 and 300 Hz in the considered test case.

Deep Boreholes Seals Subjected to High P,T conditions - Proposed Experimental Studies

NASA Astrophysics Data System (ADS)

Caporuscio, F.

2015-12-01

Deep borehole experimental work will constrain the P,T conditions which "seal" material will experience in deep borehole crystalline rock repositories. The rocks of interest to this study include mafic (amphibolites) and silicic (granitic gneiss) end members. The experiments will systematically add components to capture discrete changes in both water and EBS component chemistries. Experiments in the system wall rock-clay-concrete-groundwater will evaluate interactions among components, including: mineral phase stability, metal corrosion rates and thermal limits. Based on engineered barrier studies, experimental investigations will move forward with three focusses. First, evaluation of interaction between "seal" materials and repository wall rock (crystalline) under fluid-saturated conditions over long-term (i.e., six-month) experiments; which reproduces the thermal pulse event of a repository. Second, perform experiments to determine the stability of zeolite minerals (analcime-wairakitess) under repository conditions. Both sets of experiments are critically important for understanding mineral paragenesis (zeolites and/or clay transformations) associated with "seals" in contact with wall rock at elevated temperatures. Third, mineral growth at the metal interface is a principal control on the survivability (i.e. corrosion) of waste canisters in a repository. The objective of this planned experimental work is to evaluate physio-chemical processes for 'seal' components and materials relevant to deep borehole disposal. These evaluations will encompass multi-laboratory efforts for the development of seals concepts and application of Thermal-Mechanical-Chemical (TMC) modeling work to assess barrier material interactions with subsurface fluids and other barrier materials, their stability at high temperatures, and the implications of these processes to the evaluation of thermal limits.

The Impact of Mineralogy on the Geochemical Alteration of Shales During Hydraulic Fracturing Operations

NASA Astrophysics Data System (ADS)

Maher, K.; Harrison, A. L.; Jew, A. D.; Dustin, M. K.; Kiss, A. M.; Kohli, A. H.; Thomas, D.; Joe-Wong, C. M.; Brown, G. E.; Bargar, J.

2016-12-01

The extraction of oil and gas resources from low permeability shale reservoirs using hydraulic fracturing techniques has increased significantly in recent years. During hydraulic fracturing, large volumes of fluid are injected into subsurface shale formations, which drives substantial fluid-rock interaction that can release contaminants and alter rock permeability. Here, a combined experimental, imaging, and modeling approach was employed to systematically evaluate the impact of shale mineralogy on its physical and chemical alteration when exposed to fracturing fluids of different composition. Batch reactor experiments contained different shales with unique mineralogical compositions that were exposed to simulated hydraulic fracturing fluid. Experiments revealed that the balance between fluid acidity and acid neutralizing capacity of the rock was the strongest control on the evolution of fluid and rock chemistry. Carbonate mineral-rich shales rapidly recovered solution pH to circum-neutral conditions, whereas fluids in contact with carbonate mineral-poor shales remained acidic. The dissolution of shale minerals released metal contaminants, yet the precipitation of Fe(III)-bearing secondary phases helped to attenuate their release via co-precipitation or sorption. Post-reaction imaging illustrated that selective dissolution of carbonate minerals generated secondary porosity, the connectivity of which was dictated by initial carbonate distribution. Conversely, the precipitation of secondary Al- and Fe-bearing phases may occlude porosity, potentially inhibiting transport of water, contaminants, and hydrocarbons. The maturation of secondary Fe-bearing phases from amorphous to crystalline over time suggests that porosity will continue to evolve even after oxidation reactions have effectively ceased. These experiments reveal that the relative abundance and distribution of carbonate minerals is the master variable dictating both porosity alteration and contaminant release from shale formations, implying that the response of a reservoir to hydraulic fracturing can be better assessed using robust mineralogical data.

Field and petrological study of metasomatism and high-pressure carbonation from lawsonite eclogite-facies terrains, Alpine Corsica

NASA Astrophysics Data System (ADS)

Piccoli, Francesca; Vitale Brovarone, Alberto; Ague, Jay J.

2018-04-01

This study presents new field and petrological data on carbonated metasomatic rocks from the lawsonite-eclogite units of Alpine Corsica. These rocks form along major, slab-scale lithological boundaries of the subducted Alpine Tethys plate. Our results indicate that a large variety of rocks ranging from metamafic/ultramafic to metafelsic can react with carbon-bearing fluids, leading to carbon sequestration at high-pressure conditions. The process of carbonation includes both replacement of silicates by high-pressure carbonate, and carbonate veining. The field, microstructural and mineralogical data strongly suggest that the metasomatism was mediated by the infiltration of external fluids of mixed origin, including both mafic/ultramafic and metasedimentary sources. Our results support the following three-step evolution: (i) Release of aqueous fluids by lawsonite and/or antigorite breakdown at depth; (ii) Fluid channelization along the base of the metasedimentary pile of the subducted lithospheric plate and related reactive fluid flow leading to carbonate mineral dissolution; (iii) Further interactions of the resulting carbon-bearing fluids with slab-forming rocks at depths of ca. 70 km and carbonation of pre-existing silicate-rich lithologies. This study highlights the importance of carbonate-bearing fluids evolving along down-T, down-P paths, such as along slab-parallel lithological boundaries, for the sequestration of carbon in subduction zones, and suggests that similar processes may also operate in collisional settings. Fig. S2: Petrogenetic grid in the CaFMASH+CO2 system for the antigorite and clinopyroxene carbonation reactions, together with grossular forming reaction during decarbonation. Reactions are written with the high T assemblage to the right of the = sign.

Calcium-Mediated Adhesion of Nanomaterials in Reservoir Fluids.

PubMed

Eichmann, Shannon L; Burnham, Nancy A

2017-09-14

Globally, a small percentage of oil is recovered from reservoirs using primary and secondary recovery mechanisms, and thus a major focus of the oil industry is toward developing new technologies to increase recovery. Many new technologies utilize surfactants, macromolecules, and even nanoparticles, which are difficult to deploy in harsh reservoir conditions and where failures cause material aggregation and sticking to rock surfaces. To combat these issues, typically material properties are adjusted, but recent studies show that adjusting the dispersing fluid chemistry could have significant impact on material survivability. Herein, the effect of injection fluid salinity and composition on nanomaterial fate is explored using atomic force microscopy (AFM). The results show that the calcium content in reservoir fluids affects the interactions of an AFM tip with a calcite surface, as surrogates for nanomaterials interacting with carbonate reservoir rock. The extreme force sensitivity of AFM provides the ability to elucidate small differences in adhesion at the pico-Newton (pN) level and provides direct information about material survivability. Increasing the calcium content mitigates adhesion at the pN-scale, a possible means to increase nanomaterial survivability in oil reservoirs or to control nanomaterial fate in other aqueous environments.

Effects of Contaminated Fluids on Complex Moduli in Porous Rocks; Lab and Field.

NASA Astrophysics Data System (ADS)

Spetzler, H.; Snieder, R.; Zhang, J.

2006-12-01

The interaction between fluids and porous rocks has been measured in the laboratory and in a controlled field experiment. In the laboratory we measured the static and dynamic effect of various contaminated fluids on the wettability, capillary pressure and other flow properties on geometrically simple surfaces. The characteristics of the menisci were quantified by measuring the forces required to deform and move them. Rate dependent surface tension and contact angles describe the hysteresis of the contact line motion. Finally we used geometrically complex surfaces, i.e. real rocks, and observed similar behavior. Then we did a field experiment where we could controllably irrigate a test volume and observe changes in deformation. At low deformation rates, where viscous deformation of the fluid is negligible, the dynamic hystereses of menisci deformation become the dominant mechanism for changes in complex moduli of partially fluid saturated rocks. In the laboratory for contaminated samples we observe attenuation increasing from below 1 Hz to 1 mHz, the limit of our patience in making these measurements. In the field we used microseisms and solid Earth tides as low frequency deformation sources. In the case of the tides we compare changes in observed tilt with theoretical site specific tidal tilts. Preliminary theoretical modeling suggests that indeed small changes in the moduli should be observable in changes in tilt response. In this paper we present our laboratory results and the field data and analysis to date.

Alteration of fault rocks by CO2-bearing fluids with implications for sequestration

NASA Astrophysics Data System (ADS)

Luetkemeyer, P. B.; Kirschner, D. L.; Solum, J. G.; Naruk, S.

2011-12-01

Carbonates and sulfates commonly occur as primary (diagenetic) pore cements and secondary fluid-mobilized veins within fault zones. Stable isotope analyses of calcite, formation fluid, and fault zone fluids can help elucidate the carbon sources and the extent of fluid-rock interaction within a particular reservoir. Introduction of CO2 bearing fluids into a reservoir/fault system can profoundly affect the overall fluid chemistry of the reservoir/fault system and may lead to the enhancement or degradation of porosity within the fault zone. The extent of precipitation and/or dissolution of minerals within a fault zone can ultimately influence the sealing properties of a fault. The Colorado Plateau contains a number of large carbon dioxide reservoirs some of which leak and some of which do not. Several normal faults within the Paradox Basin (SE Utah) dissect the Green River anticline giving rise to a series of footwall reservoirs with fault-dependent columns. Numerous CO2-charged springs and geysers are associated with these faults. This study seeks to identify regional sources and subsurface migration of CO2 to these reservoirs and the effect(s) faults have on trap performance. Data provided in this study include mineralogical, elemental, and stable isotope data for fault rocks, host rocks, and carbonate veins that come from two localities along one fault that locally sealed CO2. This fault is just tens of meters away from another normal fault that has leaked CO2-charged waters to the land surface for thousands of years. These analyses have been used to determine the source of carbon isotopes from sedimentary derived carbon and deeply sourced CO2. XRF and XRD data taken from several transects across the normal faults are consistent with mechanical mixing and fluid-assisted mass transfer processes within the fault zone. δ13C range from -6% to +10% (PDB); δ18O values range from +15% to +24% (VSMOW). Geochemical modeling software is used to model the alteration productions of fault rocks from fluids of various chemistries coming from several different reservoirs within an active CO2-charged fault system. These results are compared to data obtained in the field.

A low-δ18O intrusive breccia from Koegel Fontein, South Africa: Remobilisation of basement that was hydrothermally altered during global glaciation?

NASA Astrophysics Data System (ADS)

Olianti, Camille A. E.; Harris, Chris

2018-02-01

The Cretaceous Koegel Fontein igneous complex is situated on the west coast of South Africa, and has a high proportion of rocks with abnormally low δ18O values. The rocks with the lowest δ18O values (- 5.2‰) belong to intrusive matrix-supported breccia pipes and dykes, containing a variety of clast types. The breccia rocks range in SiO2 from 44 to 68 wt% and their whole-rock δ18O values vary between - 5.2‰ and + 1.8‰. The major and trace element composition of the breccia rocks is consistent with them containing variable proportions of clasts of Cretaceous intrusive rocks and basement gneiss and the matrix being fluidized material derived from the same source as the clasts. Based on the nature of the clasts contained in the breccia, it was emplaced just prior to intrusion of the main Rietpoort Granite at 134 Ma. All components of the breccia have low δ18O value and, at least in the case of the gneiss clasts, this predates incorporation in the fluidized material. Although the early Cretaceous appears to have been a period of cold climate, it is unlikely that the δ18O values of ambient precipitation ( - 10‰) would have been low enough to have generated the required 18O-depletion. The basement gneiss was probably 2-3 km below the Cretaceous surface, minimizing the possibility of interaction with isotopically unmodified meteoric water, and there is no evidence for foundered blocks of cover rocks in the breccia. There is, therefore, no evidence for downwards movement of material. We favour a model where basement gneiss interacted with extremely 18O-depleted fluid during crustal reworking at 547 Ma, a time of global glaciation. Low-δ18O metamorphic fluids produced by dehydration melting of 18O-depleted gneiss became trapped and, as the fluid pressure increased, failure of the seal resulted in explosive upwards movement of fluidized breccia. Migration was along pre-existing dykes, incorporating fragments of these dykes, as well as the country rock gneiss.

Origin of CaCl2 brines by basalt-seawater interaction: Insights provided by some simple mass balance calculations

NASA Astrophysics Data System (ADS)

Hardie, Lawrence A.

1983-06-01

Modern rift zone hydrothermal brines are typically CaCl2-bearing brines, an unusual chemical signature they share with certain oil field brines, fluid inclusions in ore minerals and a few uncommon saline lakes. Many origins have been suggested for such CaCl2 brines but in the Reykjanes, Iceland, geothermal system a strong empirical case can be made for a basalt-seawater interaction origin. To examine this mechanism of CaCl2 brine evolution some simple mass balance calculations were carried out. Average Reykjanes olivine tholeiite was “reacted” with average North Atlantic seawater to make an albite-chlorite-epidotesphene rock using Al2O3 as the conservative rock component and Cl as the conservative fluid component. The excess components released by the basalt to the fluid were “precipitated” at 275° C as quartz, calcite, anhydrite, magnetite and pyrite to complete the conversion to greenstone. The resulting fluid was a CaCl2 brine of seawater chlorinity with a composition remarkably similar to the actual Reykjanes brine at 1750 m depth. Thus, the calculations strongly support the idea that the Reykjanes CaCl2 brines result from “closed system” oceanic basalt-seawater interaction (albitization — chloritization mechanism) at greenschist facies temperatures. The calculation gives a seawater: basalt mass ratio of 3∶1 to 4∶1 (vol. ratio of 9∶1 to 12∶1), in keeping with experimental results, submarine vent data and with ocean crust cooling calculations. The brine becomes anoxic because there is insufficient dissolved or combined oxygen to balance all the Fe released from the basalt during alteration. Large excesses of Ca are released to the fluid and precipitate out in the form of anhydrite which essentially sweeps the brine free of sulfate leaving an elevated Ca concentration. The calculated rock-water interaction basically involves Na + Mg + SO4 ⇌ Ca + K, simulating chemical differences observed between oceanic basalts and greenstones from many mid-ocean ridges.

The Role of Halogens in High-Grade Metamorphism and Anatexis

NASA Astrophysics Data System (ADS)

Aranovich, L.; Safonov, O.

2016-12-01

We review factors controlling the distribution of the two major halogens, F and Cl, in high-grade metamorphic rocks; their compositional correlations and partitioning between minerals; experimental data on stability and phase equilibria of the halogen-bearing minerals; the influence of halogens on Fe-Mg exchange reactions; and the means of estimating concentrations/activity of halogen species concentration/ activity in the fluid phase ("chlorimetry and fluorimetry") via calculation of equilibrium conditions for mineral assemblages containing halogen-bearing phases. Clear negative correlation between the F content and XFe=Fe/(Fe+Mg) suggests that natural biotite and amphibole obey the Fe-F avoidance rule. A strong positive correlation exists between K and Cl in amphibole. A scattering of points on the XFe -Cl and TiO2- Cl diagrams indicate the possible involvement of an exotic Cl-rich phase (fluid or melt) during the formation of Cl-bearing biotite and amphibole. Fluorine and Cl substituting for OH-groups substantially stabilize minerals relative to dehydration and melting. They should also strongly affect partitioning of Fe and Mg between biotite, amphibole and anhydrous minerals. This effect is quantified for Fe-Mg exchange reactions involving biotite (Zhu and Sverjensky, 1992), but remains to be evaluated for amphibole. Calculations based on recent thermodynamic systematics show that the relatively Mg-rich, Cl-poor biotite (for example, XFe = 0.4 and about 0.2 wt.% Cl) may coexist with a fairly Cl-rich fluid, i.e. total Cl/(Cl+H2O) from 0.1-0.3, depending on the assemblage, under granulite facies P-T conditions. Alkali (and Ca) metasomatism caused by interaction of high grade rocks with halogen-bearing fluids has major impact on the subsolidus phase transformations and melting processes during high-grade metamorphism and anatexis. For example, an increase in sodium content in plagioclase (Pl) by 20 mol% due to infiltration of Na- fluid into the quartz (Qtz)-bearing rocks decreases melting temperature by about 50o. Similar effect may occur in the originally Qtz-absent rocks due to interaction with Ca-rich fluids. Acknowledgements: This work was supported by RFBR grant 15-05-01053.

Experimental multi-phase CO2-brine-rock interactions at elevated temperature and pressure: Implications for CO2 sequestration in deep-saline aquifers

USGS Publications Warehouse

Rosenbauer, R.J.; Koksalan, T.

2004-01-01

Long-term CO2 saturated brine-rock experiments were conducted to evaluate the effects of multiphase H2O-CO2 fluids on mineral equilibria and the potential for CO2 sequestration mineral phases within deep-saline aquifers. Experimental results were consistent with theoretical thermodynamic calculations when CO2-saturated brines were reacted with limestone rocks. The CO2-saturated brine-limestone reactions were characterized by compositional and mineralogical-changes in the aquifer fluid and formation rocks that were dependent on initial brine composition as were the changes in formation porosity, especially dissolved sulfate. The solubility of CO2 was enhanced in brines in the presence of both limestone and sandstone rocks relative to brines alone. Reactions between CO2 saturated brines and arkosic sandstones were characterized by desiccation of the brine and changes in the chemical composition of the brine suggesting fixation of CO2 in mineral phases. These reactions occured on a measurable but kinetically slow time scale at 120??C.

Deeply subducted continental fragments - Part 1: Fracturing, dissolution-precipitation, and diffusion processes recorded by garnet textures of the central Sesia Zone (western Italian Alps)

NASA Astrophysics Data System (ADS)

Giuntoli, Francesco; Lanari, Pierre; Engi, Martin

2018-02-01

Contiguous continental high-pressure terranes in orogens offer insight into deep recycling and transformation processes that occur in subduction zones. These remain poorly understood, and currently debated ideas need testing. The approach we chose is to investigate, in detail, the record in suitable rock samples that preserve textures and robust mineral assemblages that withstood overprinting during exhumation. We document complex garnet zoning in eclogitic mica schists from the Sesia Zone (western Italian Alps). These retain evidence of two orogenic cycles and provide detailed insight into resorption, growth, and diffusion processes induced by fluid pulses in high-pressure conditions. We analysed local textures and garnet compositional patterns, which turned out remarkably complex. By combining these with thermodynamic modelling, we could unravel and quantify repeated fluid-rock interaction processes. Garnet shows low-Ca porphyroclastic cores that were stable under (Permian) granulite facies conditions. The series of rims that surround these cores provide insight into the subsequent evolution: the first garnet rim that surrounds the pre-Alpine granulite facies core in one sample indicates that pre-Alpine amphibolite facies metamorphism followed the granulite facies event. In all samples documented, cores show lobate edges and preserve inner fractures, which are sealed by high-Ca garnet that reflects high-pressure Alpine conditions. These observations suggest that during early stages of subduction, before hydration of the granulites, brittle failure of garnet occurred, indicating high strain rates that may be due to seismic failure. Several Alpine rims show conspicuous textures indicative of interaction with hydrous fluid: (a) resorption-dominated textures produced lobate edges, at the expense of the outer part of the granulite core; (b) peninsulas and atoll garnet are the result of replacement reactions; and (c) spatially limited resorption and enhanced transport of elements due to the fluid phase are evident along brittle fractures and in their immediate proximity. Thermodynamic modelling shows that all of these Alpine rims formed under eclogite facies conditions. Structurally controlled samples allow these fluid-garnet interaction phenomena to be traced across a portion of the Sesia Zone, with a general decrease in fluid-garnet interaction observed towards the external, structurally lower parts of the terrane. Replacement of the Permian HT assemblages by hydrate-rich Alpine assemblages can reach nearly 100 % of the rock volume. Since we found no clear relationship between discrete deformation structures (e.g. shear zones) observed in the field and the fluid pulses that triggered the transformation to eclogite facies assemblages, we conclude that disperse fluid flow was responsible for the hydration.

Intra-slab COH fluid fluxes evidenced by fluid-mediated decarbonation of lawsonite eclogite-facies altered oceanic metabasalts

NASA Astrophysics Data System (ADS)

Vitale Brovarone, Alberto; Chu, Xu; Martin, Laure; Ague, Jay J.; Monié, Patrick; Groppo, Chiara; Martinez, Isabelle; Chaduteau, Carine

2018-04-01

The interplay between the processes controlling the mobility of H2O and C-bearing species during subduction zone metamorphism exerts a critical control on plate tectonics and global volatile recycling. Here we present the first study on fresh, carbonate-bearing, lawsonite eclogite-facies metabasalts from Alpine Corsica, France, which reached the critical depths at which important devolatilization reactions occur in subducting slabs. The studied samples indicate that the evolution of oceanic crustal sequences subducted under present-day thermal regimes is dominated by localized fluid-rock interactions that are strongly controlled by the nature and extent of inherited (sub)seafloor hydrothermal processes, and by the possibility of deep fluids to be channelized along inherited or newly-formed discontinuities. Fluid channelization along inherited discontinuities controlled local rehydration and dehydration/decarbonation reactions and the stability of carbonate and silicate minerals at the blueschist-eclogite transition. Fluid-mediated decarbonation was driven by upward, up-temperature fluid flow in the inverted geothermal gradient of a subducting oceanic slab, a process that has not been documented in natural samples to date. We estimate that the observed fluid-rock reactions released 20-60 kg CO2 per m3 of rock (i.e. 0.7-2.1 wt% CO2), which is in line with the values predicted from decarbonation of metabasalts in open systems at these depths. Conversely, the estimated time-integrated fluid fluxes (20-50 t/m2) indicate that the amount of carbon transported by channelized fluid flow within the volcanic part of subducting oceanic plates is potentially much higher than previous numerical estimates, testifying to the percolation of C-bearing fluids resulting from devolatilization/dissolution processes operative in large reservoirs.

FLUID EVOLUTION AND MINERAL REACTIONS DURING SHEAR ZONE FORMATION AT NUSFJORD, LOFOTEN, NORWAY (Invited)

NASA Astrophysics Data System (ADS)

Kullerud, K.

2009-12-01

At Nusfjord in Lofoten, Norway, three 0.3 - 3 m thick shear zones occur in a gabbro-anorthosite. During deformation, the shear zones were infiltrated by a hydrous fluid enriched in Cl. In the central parts of the shear zones, fluid-rock interaction resulted in complete break-down of the primary mafic silicates. Complete hydration of these minerals to Cl-free amphibole and biotite suggests that the hydrous fluid was present in excess during deformation in these parts of the shear zones. Along the margins of the shear zones, however, the igneous mafic silicates (Cpx, Bt, Opx) were only partly overgrown by hydrous minerals. Here, Cl-enriched minerals (Amph, Bt, Scp, Ap) can be observed. Amphibole shows compositions covering the range 0.1 - 4.0 wt % Cl within single thin sections. Mineral textures and extreme compositional variations of the Cl-bearing minerals indicate large chemical gradients of the fluid phase. Relics of primary mafic silicates and compositionally zoned reaction coronas around primary mafic silicates suggest that the free fluid was totally consumed before the alteration of the primary phases were completed. The extreme variations in the Cl-content of amphibole are inferred to monitor a gradual desiccation of the Cl-bearing grain-boundary fluid during fluid-mineral reactions accordingly: 1) The first amphibole that formed during the reactions principally extracted water from the fluid, resulting in a slight increase in the Cl content of the fluid. 2) Continued amphibole-forming reactions resulted in gradual consumption of the free fluid phase, principally by extracting water from the fluid, resulting in an increase in its Cl-content. Higher Cl-content of the fluid resulted in higher Cl-content of the equilibrium amphibole. 3) The most Cl-enriched amphibole (4 wt % Cl) formed in equilibrium with the last volumes of the grain-boundary fluid, which had evolved to a highly saline solution. Mineral reactions within a 1-2 thick zone of the host rock along the contact to the shear zones indicate a more complicated involvement of fluids during shear zone formation than described above. Apparently, fluids have been transported laterally from the outer parts of the shear zones into the gabbro-anorthosite along thin recrystallized zones of plagioclase. The fluid that infiltrated the undeformed host rock of the shear zones resulted in formation of Cl-free amphibole and garnet between the primary mafic minerals and plagioclase. A working hypothesis is that narrow fractures formed within the host rock, outside the sheared rock during shear zone formation. During shear zone formation, the central parts of the shear zones were completely hydrated by an externally derived Cl-bearing hydrous fluid. Some of the fluid migrated to the marginal parts of the shear zones and evolved to a highly saline solution. However, during desiccation of the fluid along the marginal parts of the shear zones, some of the fluid escaped along narrow fractures into the host rock of the shear zones. The Cl-free amphibole that formed from this fluid suggests that the narrow pathways of the fluid provided a path for water transport, but acted as a filter for the much larger ions of Cl.

Stable isotopic constraints on fluid-rock interaction and Cu-PGE-S redistribution in the Sonju Lake intrusion, Minnesota

USGS Publications Warehouse

Park, Y.-R.; Ripley, E.M.; Miller, J.D.; Li, C.; Mariga, J.; Shafer, P.

2004-01-01

The Sonju Lake intrusion, part of the 1.1 Ga Midcontinent rift-related Beaver Bay Complex, is a 1,200-m-thick, strongly differentiated, layered sequence of mafic cumulates located in northeastern Minnesota. Basal melatroctolite and dunite layers are overlain by troctolite, gabbro, Fe-Ti oxide-rich gabbro, apatite diorite, and monzodiorite. Stratigraphic intervals rich in Pt + Pd, Cu, and S occur over ???500 m in the Fe-Ti oxide-rich gabbro and apatite diorite units. Peak concentrations show offsets that are similar to those found in other tholeiitic layered intrusions. Concentrations of Pd in excess of 100 ppb are confined to the lowermost 25 m of the interval. Copper shows a sharp increase to 630 ppm above the Pd-rich interval. Sulfur contents are low (<375 ppm) in the Cu-rich interval, but they increase to values as high as 3,150 ppm above in the apatite diorite. Disseminated sulfides in the intrusion have ??34S values that range from -2.2 to 3 per mil Vienna-Canyon Diablo Troilite (V-CDT) and suggest that contamination by country rock sulfur was not an important process in the formation of the metal-rich interval. ??18O values of plagioclase from the intrusion range from 5.6 to 12.0 per mil (V-SMOW) and indicate that a relatively low-18O fluid (??18O ???3-5 ???) interacted with the rocks of the intrusion at temperatures less than ???275??C. Clinopyroxene and Fe-Ti oxides (ilmenite with minor amounts of titanomagnetite) show much more restricted ranges in ??18O values (4.6-5.7 and 5.5-6.7 per mil, respectively) and attest to the kinetic control of the oxygen isotope exchange process. The externally derived fluid that interacted with rocks now enriched in platinum group elements (PGE) + Cu- and Fe-sulfide minerals locally liberated sulfur and replaced chalcopyrite and pyrite with goethite. In the Cu-rich zone, goethite that replaces chalcopyrite may contain up to 8.5 weight percent Cu. It is evident that hydrothermal alteration resulted in a decoupling of copper and sulfur, with sulfur being transferred out of the Cu-rich interval. Interaction between rocks in the PGE-Cu-S interval of the Sonju Lake intrusion and an externally derived fluid at low temperatures modified what appears to have been a primary stratigraphic metal-sulfur zonation. The effects of hydrothermal alteration on PGE and base-metal sulfide mobility and redistribution must be understood before models of primary zonation processes can be meaningfully applied. ?? 2004 by Economic Geology.

Porosity and permeability development in compacting chalks during flooding of nonequilibrium brines: Insights from long-term experiment

NASA Astrophysics Data System (ADS)

Nermoen, Anders; Korsnes, Reidar I.; Hiorth, Aksel; Madland, Merete V.

2015-05-01

We report the complete chemical alteration of a Liège outcrop chalk core resulting from a 1072 flow-through experiment performed during mechanical compaction at 130°C. Chemical rock-fluid interactions alter the volumetric strain, porosity, and permeability in a nontrivial way. The porosity reduced only from 41.32% to 40.14%, even though the plug compacted more than 25%. We present a novel analysis of the experimental data, which demonstrates that the geochemical alteration does not conserve the volume of the solids, and therefore, the strain is partitioned additively into a pore volume and solid volume component. At stresses beyond yield, the observed deformation can be explained by grain reorganization reducing the pore space between grains and solid volume changes from the rock-fluid interactions. The mechanical and chemical effects are discussed in relation to the observed permeability development.

Aquifer storage and recovery: recent hydrogeological advances and system performance.

PubMed

Maliva, Robert G; Guo, Weixing; Missimer, Thomas M

2006-12-01

Aquifer storage and recovery (ASR) is part of the solution to the global problem of managing water resources to meet existing and future freshwater demands. However, the metaphoric "ASR bubble" has been burst with the realization that ASR systems are more physically and chemically complex than the general conceptualization. Aquifer heterogeneity and fluid-rock interactions can greatly affect ASR system performance. The results of modeling studies and field experiences indicate that more sophisticated data collection and solute-transport modeling are required to predict how stored water will migrate in heterogeneous aquifers and how fluid-rock interactions will affect the quality of stored water. It has been well-demonstrated, by historic experience, that ASR systems can provide very large volumes of storage at a lesser cost than other options. The challenges moving forward are to improve the success rate of ASR systems, optimize system performance, and set expectations appropriately.

Experimentally determined rock-fluid interactions applicable to a natural hot dry rock geothermal system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Charles, R.W.; Holley, C.E. Jr.; Tester, J.W.

1980-02-01

The Los Alamos Scientific Laboratory is pursuing laboratory and field experiments in the development of the Hot Dry Rock concept of geothermal energy. The field program consists of experiments in a hydraulically fractured region of low permeability in which hot rock is intercepted by two wellbores. These experiments are designed to test reservoir engineering parameters such as: heat extraction rates, water loss rates, flow characteristics including impedance and buoyancy, seismic activity and fluid chemistry. Laboratory experiments have been designed to provide information on the mineral reactivity which may be encountered in the field program. Two experimental circulation systems have beenmore » built to study the rates of dissolution and alteration in dynamic flow. Solubility studies have been done in agitated systems. To date, pure minerals, samples of the granodiorite from the actual reservoir and Tijeras Canyon granite have been reacted with distilled water and various solutions of NaCl, NaOH, and Na/sub 2/CO/sub 3/. The results of these experimental systems are compared to observations made in field experiments done in a hot dry rock reservoir at a depth of approximately 3 km with initial rock temperatures of 150 to 200/sup 0/C.« less

The seismogenic Gole Larghe Fault Zone (Italian Southern Alps): quantitative 3D characterization of the fault/fracture network, mapping of evidences of fluid-rock interaction, and modelling of the hydraulic structure through the seismic cycle

NASA Astrophysics Data System (ADS)

Bistacchi, A.; Mittempergher, S.; Di Toro, G.; Smith, S. A. F.; Garofalo, P. S.

2016-12-01

The Gole Larghe Fault Zone (GLFZ) was exhumed from 8 km depth, where it was characterized by seismic activity (pseudotachylytes) and hydrous fluid flow (alteration halos and precipitation of hydrothermal minerals in veins and cataclasites). Thanks to glacier-polished outcrops exposing the 400 m-thick fault zone over a continuous area > 1.5 km2, the fault zone architecture has been quantitatively described with an unprecedented detail, providing a rich dataset to generate 3D Discrete Fracture Network (DFN) models and simulate the fault zone hydraulic properties. The fault and fracture network has been characterized combining > 2 km of scanlines and semi-automatic mapping of faults and fractures on several photogrammetric 3D Digital Outcrop Models (3D DOMs). This allowed obtaining robust probability density functions for parameters of fault and fracture sets: orientation, fracture intensity and density, spacing, persistency, length, thickness/aperture, termination. The spatial distribution of fractures (random, clustered, anticlustered…) has been characterized with geostatistics. Evidences of fluid/rock interaction (alteration halos, hydrothermal veins, etc.) have been mapped on the same outcrops, revealing sectors of the fault zone strongly impacted, vs. completely unaffected, by fluid/rock interaction, separated by convolute infiltration fronts. Field and microstructural evidence revealed that higher permeability was obtained in the syn- to early post-seismic period, when fractures were (re)opened by off-fault deformation. We have developed a parametric hydraulic model of the GLFZ and calibrated it, varying the fraction of faults/fractures that were open in the post-seismic, with the goal of obtaining realistic fluid flow and permeability values, and a flow pattern consistent with the observed alteration/mineralization pattern. The fraction of open fractures is very close to the percolation threshold of the DFN, and the permeability tensor is strongly anisotropic, resulting in a marked channelling of fluid flow in the inner part of the fault zone. Amongst possible seismological applications of our study, we will discuss the possibility to evaluate the coseismic fracture intensity due to off-fault damage, a fundamental mechanical parameter in the energy balance of earthquakes.

Petrophysical laboratory invertigations of carbon dioxide storage in a subsurface saline aquifer in Ketzin/Germany within the scope of CO2SINK

NASA Astrophysics Data System (ADS)

Zemke, K.; Kummmerow, J.; Wandrey, M.; Co2SINK Group

2009-04-01

Since June of 2008 carbon dioxide has been injected into a saline aquifer at the Ketzin test site [Würdemann et al., this volume]. The food grade CO2 is injected into a sandstone zone of the Stuttgart formation at ca. 650 m depth at 35°C reservoir temperature and 62 bar reservoir pressure. With the injection of CO2 into the geological formation, chemical and physical reservoir characteristics are changed depending on pressure, temperature, fluid chemistry and rock composition. Fluid-rock interaction could comprise dissolution of non-resistant minerals in CO2-bearing pore fluids, cementing of the pore space by precipitating substances from the pore fluid, drying and disintegration of clay minerals and thus influence of the composition and activities of the deep biosphere. To testing the injection behaviour of CO2 in water saturated rock and to evaluate the geophysical signature depending on the thermodynamic conditions, flow experiments with water and CO2 have been performed on cores of the Stuttgart formation from different locations including new wells of ketzin test site. The studied core material is an unconsolidated fine-grained sandstone with porosity values from 15 to 32 %. Permeability, electrical resistivity, and sonic wave velocities and their changes with pressure, saturation and time have been studied under simulated in situ conditions. The flow experiments conducted over several weeks with brine and CO2 showed no significant changes of resistivity and velocity and a slightly decreasing permeability. Pore fluid analysis showed mobilization of clay and some other components. A main objective of the CO2Sink laboratory program is the assessment of the effect of long-term CO2 exposure on reservoir rocks to predict the long-term behaviour of geological CO2 storage. For this CO2 exposure experiments reservoir rock samples were exposed to CO2 saturated reservoir fluid in corrosion-resistant high pressure vessels under in situ temperature and pressure conditions over a period of several months. Before and after the CO2 exposure experiment cyclic measurements of physical properties were carried out on these cores in a mechanical testing system. After experimental runs of up to 3 months no significant changes in flow and petrophysical data were observed. [For the microbilogical studies see Wandrey et al., this volume.] To study the impact of fluid-rock interactions on petrophysical parameters, porosity and pore radii distribution have been investigated before and after the experiment by NMR relaxation and mercury-injection. NMR measurements on rock core plugs saturated with brine may return valuable information on the porous structure of the rock core. The distribution of NMR-T2 values (CPMG) reflects the pore sizes within the rock core. NMR pore size is a derivative of the ratio pore surface/volume. The mercury injection pore size is an area-equivalent diameter of the throats connecting the pore system. Most of the tested samples show in the NMR measurements a slightly increasing porosity and a higher part of large pores. The mercury measurements and thin- section for microstructural characterisation after the CO2 exposure will be done at a later date.

U-Pb dating of large zircons in low-temperature jadeitite from the Osayama serpentinite melange, southwest Japan: insights into the timing of serpentinization

USGS Publications Warehouse

Tsujimori, T.; Liou, J.G.; Wooden, J.; Miyamoto, T.

2005-01-01

Crystals of zircon up to 3 mm in length occur in jadeitite veins in the Osayama serpentinite mélange, Southwest Japan. The zircon porphyroblasts show pronounced zoning, and are characterized by both low Th/U ratios (0.2-0.8) and low Th and U abundances (Th = 1-81 ppm; U = 6-149 ppm). They contain inclusions of high-pressure minerals, including jadeite and rutile; such an occurrence indicates that the zircon crystallized during subduction-zone metamorphism. Phase equilibria and the existing fluid-inclusion data constrain P-T conditions to P > 1.2 GPa at T > 350°C for formation of the jadeitite. Most U/Pb ages obtained by SHRIMP-RG are concordant, with a weighted mean 206Pb/238U age of 472 ± 8.5 Ma (MSWD = 2.7, n = 25). Because zircon porphyroblasts contain inclusions of high-pressure minerals, the SHRIMP U-Pb age represents the timing of jadeitite formation, i.e., the timing of interaction between alkaline fluid and ultramafic rocks in a subduction zone. Although this dating does not provide a direct time constraint for serpentinization, U-Pb ages of zircon in jadeitite associated with serpentinite result in new insights into the timing of fluid-rock interaction of ultramafic rocks at a subduction zone and the minimum age for serpentinization.

Simulation of geochemical processes responsible for the formation of the Zhezqazghan deposit

NASA Astrophysics Data System (ADS)

Ryzhenko, B. N.; Cherkasova, E. V.

2014-05-01

Physicochemical computer simulation of water-rock systems at a temperature of 25-150°C and under a pressure of up to 600 bar has been carried out for quantitative description of the mineralization formation conditions at sandstone- and shale-hosted copper deposits. The simulation is based on geological and geochemical information concerning the Zhezqazghan deposit and considers (i) a source of ore matter, (ii) composition of the fluid that transfers ore matter to the ore formation zone, and (iii) factors of ore concentration. It has been shown that extraction of copper from minerals of rocks and its accumulation in aqueous solution are optimal at a high mass ratio of rock to water (R/W > 10), Eh of +200 to -100 mV, and an obligatory content of chloride ions in the aqueous phase. The averaged ore-bearing fluid Cl95SO44//Ca50(Na + K)30Mg19 (eq %), pH ˜ 4, mineralization of up to 400 g/L, is formed by the interaction of red sandstone beds with a sedimentogenic brine (a product of metamorphism of seawater in carbonate rocks enriched in organic matter). The ore concentration proceeds in the course of cooling from 150 to 50°C during filtration of ore-bearing fluid through red sandstone beds in the rock-water system thermodynamically opened with respect to the reductive components.

Ancient Aqueous Environments at Endeavour Crater, Mars

NASA Technical Reports Server (NTRS)

Arvidson, R. E.; Squyres, S. W.; Bell, J. F.; Catalano, J. G.; Clark, B. C.; Crumpler, L. S.; de Souza, P. A.; Fairen, A. G.; Farrand, W. H.; Fox, V. K.;

Ancient aqueous environments at Endeavour crater, Mars

USGS Publications Warehouse

Arvidson, R. E.; Squyres, S. W.; Bell, J.F.; Catalano, J.G.; Clark, B. C.; Crumpler, L.S.; de Souza, P.A.; Fairén, A.G.; Farrand, W. H.; Fox, V.K.; Gellert, Ralf; Ghosh, A.; Golombeck, M.P.; Grotzinger, J.P.; Guinness, E.A.; Herkenhoff, Kenneth E.; Jolliff, B.L.; Knoll, A.H.; Li, R.; McLennan, S.M.; Ming, D. W.; Mittlefehldt, D. W.; Moore, Johnnie N.; Morris, R.V.; Murchie, S.L.; Parker, T.J.; Paulsen, G.; Rice, J.W.; Ruff, S.W.; Smith, M.D.; Wolff, M.J.

2014-01-01

Opportunity has investigated in detail rocks on the rim of the Noachian age Endeavour crater, where orbital spectral reflectance signatures indicate the presence of Fe+3-rich smectites. The signatures are associated with fine-grained, layered rocks containing spherules of diagenetic or impact origin. The layered rocks are overlain by breccias, and both units are cut by calcium sulfate veins precipitated from fluids that circulated after the Endeavour impact. Compositional data for fractures in the layered rocks suggest formation of Al-rich smectites by aqueous leaching. Evidence is thus preserved for water-rock interactions before and after the impact, with aqueous environments of slightly acidic to circum-neutral pH that would have been more favorable for prebiotic chemistry and microorganisms than those recorded by younger sulfate-rich rocks at Meridiani Planum.

Arsenic in rocks and stream sediments of the central Appalachian Basin, Kentucky

USGS Publications Warehouse

Tuttle, Michele L.W.; Goldhaber, Martin B.; Ruppert, Leslie F.; Hower, James C.

2002-01-01

Arsenic (As) enrichment in coal and stream sediments has been documented in the southern Appalachian basin (see Goldhaber and others, submitted) and is attributed to interaction of rocks and coal with metamorphic fluids generated during the Allegheny Orogeny (late Paleozoic). Similarly derived fluids are expected to affect the coal and in the Kentucky Appalachian Basin to the north as well. In addition, similar processes may have influenced the Devonian oil shale on the western margin of the basin. The major goals of this study are to determine the effect such fluids had on rocks in the Kentucky Appalachian basin (fig. 1), and to understand the geochemical processes that control trace-metal source, residence, and mobility within the basin. This report includes data presented in a poster at the USGS workshop on arsenic (February 21 and 22, 2001), new NURE stream sediment data3 , and field data from a trip in April 2001. Although data for major and minor elements and all detectable trace metals are reported in the Appendices, the narrative of this report primarily focuses on arsenic.

Massive production of abiotic methane during subduction evidenced in metamorphosed ophicarbonates from the Italian Alps

PubMed Central

Vitale Brovarone, Alberto; Martinez, Isabelle; Elmaleh, Agnès; Compagnoni, Roberto; Chaduteau, Carine; Ferraris, Cristiano; Esteve, Imène

2017-01-01

Alteration of ultramafic rocks plays a major role in the production of hydrocarbons and organic compounds via abiotic processes on Earth and beyond and contributes to the redistribution of C between solid and fluid reservoirs over geological cycles. Abiotic methanogenesis in ultramafic rocks is well documented at shallow conditions, whereas natural evidence at greater depths is scarce. Here we provide evidence for intense high-pressure abiotic methanogenesis by reduction of subducted ophicarbonates. Protracted (≥0.5–1 Ma), probably episodic infiltration of reduced fluids in the ophicarbonates and methanogenesis occurred from at least ∼40 km depth to ∼15–20 km depth. Textural, petrological and isotopic data indicate that methane reached saturation triggering the precipitation of graphitic C accompanied by dissolution of the precursor antigorite. Continuous infiltration of external reducing fluids caused additional methane production by interaction with the newly formed graphite. Alteration of high-pressure carbonate-bearing ultramafic rocks may represent an important source of abiotic methane, with strong implications for the mobility of deep C reservoirs. PMID:28223715

Geological and Geochemical Controls on Subsurface Microbial Life in the Samail Ophiolite, Oman.

PubMed

Rempfert, Kaitlin R; Miller, Hannah M; Bompard, Nicolas; Nothaft, Daniel; Matter, Juerg M; Kelemen, Peter; Fierer, Noah; Templeton, Alexis S

2017-01-01

Microbial abundance and diversity in deep subsurface environments is dependent upon the availability of energy and carbon. However, supplies of oxidants and reductants capable of sustaining life within mafic and ultramafic continental aquifers undergoing low-temperature water-rock reaction are relatively unknown. We conducted an extensive analysis of the geochemistry and microbial communities recovered from fluids sampled from boreholes hosted in peridotite and gabbro in the Tayin block of the Samail Ophiolite in the Sultanate of Oman. The geochemical compositions of subsurface fluids in the ophiolite are highly variable, reflecting differences in host rock composition and the extent of fluid-rock interaction. Principal component analysis of fluid geochemistry and geologic context indicate the presence of at least four fluid types in the Samail Ophiolite ("gabbro," "alkaline peridotite," "hyperalkaline peridotite," and "gabbro/peridotite contact") that vary strongly in pH and the concentrations of H 2 , CH 4 , Ca 2+ , Mg 2+ , [Formula: see text], [Formula: see text], trace metals, and DIC. Geochemistry of fluids is strongly correlated with microbial community composition; similar microbial assemblages group according to fluid type. Hyperalkaline fluids exhibit low diversity and are dominated by taxa related to the Deinococcus-Thermus genus Meiothermus , candidate phyla OP1, and the family Thermodesulfovibrionaceae. Gabbro- and alkaline peridotite- aquifers harbor more diverse communities and contain abundant microbial taxa affiliated with Nitrospira , Nitrosospharaceae, OP3, Parvarcheota, and OP1 order Acetothermales. Wells that sit at the contact between gabbro and peridotite host microbial communities distinct from all other fluid types, with an enrichment in betaproteobacterial taxa. Together the taxonomic information and geochemical data suggest that several metabolisms may be operative in subsurface fluids, including methanogenesis, acetogenesis, and fermentation, as well as the oxidation of methane, hydrogen and small molecular weight organic acids utilizing nitrate and sulfate as electron acceptors. Dynamic nitrogen cycling may be especially prevalent in gabbro and alkaline peridotite fluids. These data suggest water-rock reaction, as controlled by lithology and hydrogeology, constrains the distribution of life in terrestrial ophiolites.

Geological and geochemical controls on subsurface microbial life in the Samail Ophiolite, Oman

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rempfert, Kaitlin R.; Miller, Hannah M.; Bompard, Nicolas

Microbial abundance and diversity in deep subsurface environments is dependent upon the availability of energy and carbon. However, supplies of oxidants and reductants capable of sustaining life within mafic and ultramafic continental aquifers undergoing low-temperature water-rock reaction are relatively unknown. We conducted an extensive analysis of the geochemistry and microbial communities recovered from fluids sampled from boreholes hosted in peridotite and gabbro in the Tayin block of the Samail Ophiolite in the Sultanate of Oman. The geochemical compositions of subsurface fluids in the ophiolite are highly variable, reflecting differences in host rock composition and the extent of fluid-rock interaction. Principal component analysis of fluid geochemistry and geologic context indicate the presence of at least four fluid types in the Samail Ophiolite (“gabbro,” “alkaline peridotite,” “hyperalkaline peridotite,” and “gabbro/peridotite contact”) that vary strongly in pH and the concentrations of H 2, CH 4, Ca 2+, Mg 2+, NO 3 more » $-$, SO$$2-\\atop{4}$$, trace metals, and DIC. Geochemistry of fluids is strongly correlated with microbial community composition; similar microbial assemblages group according to fluid type. Hyperalkaline fluids exhibit low diversity and are dominated by taxa related to the Deinococcus-Thermus genus Meiothermus, candidate phyla OP1, and the family Thermodesulfovibrionaceae. Gabbro- and alkaline peridotite- aquifers harbor more diverse communities and contain abundant microbial taxa affiliated with Nitrospira, Nitrosospharaceae, OP3, Parvarcheota, and OP1 order Acetothermales. Wells that sit at the contact between gabbro and peridotite host microbial communities distinct from all other fluid types, with an enrichment in betaproteobacterial taxa. Together the taxonomic information and geochemical data suggest that several metabolisms may be operative in subsurface fluids, including methanogenesis, acetogenesis, and fermentation, as well as the oxidation of methane, hydrogen and small molecular weight organic acids utilizing nitrate and sulfate as electron acceptors. Dynamic nitrogen cycling may be especially prevalent in gabbro and alkaline peridotite fluids. As a result, these data suggest water-rock reaction, as controlled by lithology and hydrogeology, constrains the distribution of life in terrestrial ophiolites.« less

Geological and Geochemical Controls on Subsurface Microbial Life in the Samail Ophiolite, Oman

PubMed Central

Rempfert, Kaitlin R.; Miller, Hannah M.; Bompard, Nicolas; Nothaft, Daniel; Matter, Juerg M.; Kelemen, Peter; Fierer, Noah; Templeton, Alexis S.

2017-01-01

Microbial abundance and diversity in deep subsurface environments is dependent upon the availability of energy and carbon. However, supplies of oxidants and reductants capable of sustaining life within mafic and ultramafic continental aquifers undergoing low-temperature water-rock reaction are relatively unknown. We conducted an extensive analysis of the geochemistry and microbial communities recovered from fluids sampled from boreholes hosted in peridotite and gabbro in the Tayin block of the Samail Ophiolite in the Sultanate of Oman. The geochemical compositions of subsurface fluids in the ophiolite are highly variable, reflecting differences in host rock composition and the extent of fluid-rock interaction. Principal component analysis of fluid geochemistry and geologic context indicate the presence of at least four fluid types in the Samail Ophiolite (“gabbro,” “alkaline peridotite,” “hyperalkaline peridotite,” and “gabbro/peridotite contact”) that vary strongly in pH and the concentrations of H2, CH4, Ca2+, Mg2+, NO3-, SO42-, trace metals, and DIC. Geochemistry of fluids is strongly correlated with microbial community composition; similar microbial assemblages group according to fluid type. Hyperalkaline fluids exhibit low diversity and are dominated by taxa related to the Deinococcus-Thermus genus Meiothermus, candidate phyla OP1, and the family Thermodesulfovibrionaceae. Gabbro- and alkaline peridotite- aquifers harbor more diverse communities and contain abundant microbial taxa affiliated with Nitrospira, Nitrosospharaceae, OP3, Parvarcheota, and OP1 order Acetothermales. Wells that sit at the contact between gabbro and peridotite host microbial communities distinct from all other fluid types, with an enrichment in betaproteobacterial taxa. Together the taxonomic information and geochemical data suggest that several metabolisms may be operative in subsurface fluids, including methanogenesis, acetogenesis, and fermentation, as well as the oxidation of methane, hydrogen and small molecular weight organic acids utilizing nitrate and sulfate as electron acceptors. Dynamic nitrogen cycling may be especially prevalent in gabbro and alkaline peridotite fluids. These data suggest water-rock reaction, as controlled by lithology and hydrogeology, constrains the distribution of life in terrestrial ophiolites. PMID:28223966

Geological and geochemical controls on subsurface microbial life in the Samail Ophiolite, Oman

DOE PAGES

Rempfert, Kaitlin R.; Miller, Hannah M.; Bompard, Nicolas; ...

2017-02-07

Microbial abundance and diversity in deep subsurface environments is dependent upon the availability of energy and carbon. However, supplies of oxidants and reductants capable of sustaining life within mafic and ultramafic continental aquifers undergoing low-temperature water-rock reaction are relatively unknown. We conducted an extensive analysis of the geochemistry and microbial communities recovered from fluids sampled from boreholes hosted in peridotite and gabbro in the Tayin block of the Samail Ophiolite in the Sultanate of Oman. The geochemical compositions of subsurface fluids in the ophiolite are highly variable, reflecting differences in host rock composition and the extent of fluid-rock interaction. Principal component analysis of fluid geochemistry and geologic context indicate the presence of at least four fluid types in the Samail Ophiolite (“gabbro,” “alkaline peridotite,” “hyperalkaline peridotite,” and “gabbro/peridotite contact”) that vary strongly in pH and the concentrations of H 2, CH 4, Ca 2+, Mg 2+, NO 3 more » $-$, SO$$2-\\atop{4}$$, trace metals, and DIC. Geochemistry of fluids is strongly correlated with microbial community composition; similar microbial assemblages group according to fluid type. Hyperalkaline fluids exhibit low diversity and are dominated by taxa related to the Deinococcus-Thermus genus Meiothermus, candidate phyla OP1, and the family Thermodesulfovibrionaceae. Gabbro- and alkaline peridotite- aquifers harbor more diverse communities and contain abundant microbial taxa affiliated with Nitrospira, Nitrosospharaceae, OP3, Parvarcheota, and OP1 order Acetothermales. Wells that sit at the contact between gabbro and peridotite host microbial communities distinct from all other fluid types, with an enrichment in betaproteobacterial taxa. Together the taxonomic information and geochemical data suggest that several metabolisms may be operative in subsurface fluids, including methanogenesis, acetogenesis, and fermentation, as well as the oxidation of methane, hydrogen and small molecular weight organic acids utilizing nitrate and sulfate as electron acceptors. Dynamic nitrogen cycling may be especially prevalent in gabbro and alkaline peridotite fluids. As a result, these data suggest water-rock reaction, as controlled by lithology and hydrogeology, constrains the distribution of life in terrestrial ophiolites.« less

Os and S isotope studies of ultramafic rocks in the Duke Island Complex, Alaska: variable degrees of crustal contamination of magmas in an arc setting and implications for Ni-Cu-PGE sulfide mineralization

NASA Astrophysics Data System (ADS)

Stifter, Eric C.; Ripley, Edward M.; Li, Chusi

2016-10-01

The Duke Island Complex is one of the several "Ural-Alaskan" intrusions of Cretaceous age that occur along the coast of SE Alaska. Significant quantities of magmatic Ni-Cu-PGE sulfide mineralization are locally found in the complex, primarily within olivine clinopyroxenites. Sulfide mineralization is Ni-poor, consistent with petrologic evidence which indicates that sulfide saturation was reached after extensive olivine crystallization. Olivine clinopyroxenites were intruded by magmas that produced sulfide-poor, adcumulate dunites. As part of a study to investigate the potential for Ni-rich sulfide mineralization in association with the dunites, a Re-Os and S isotope study of the dunites, as well as sulfide mineralization in the olivine clinopyroxenites, was initiated. Importantly, recent drilling in the complex identified the presence of sulfidic and carbonaceous country rocks that may have been involved in the contamination of magmas and generation of sulfide mineralization. γOs (110 Ma) values of two sulfidic country rocks are 1022 and 2011. δ34S values of the country rocks range from -2.6 to -16.1 ‰. 187Os/188Os ratios of sulfide minerals in the mineralization hosted by olivine clinopyroxenites are variable and high, with γOs (110 Ma) values between 151 and 2059. Extensive interaction with Re-rich sedimentary country rocks is indicated. In contrast, γOs (110 Ma) values of the dunites are significantly lower, ranging between 2 and 16. 187Os/188Os ratios increase with decreasing Os concentration. This inverse relation is similar to that shown by ultramafic rocks from several arc settings, as well as altered abyssal dunites and peridotites. The relation may be indicative of magma derivation from a sub-arc mantle that had experienced metasomatism via slab-derived fluids. Alternatively, the relation may be indicative of minor contamination of magma by crustal rocks with low Os concentrations but high 187Os/188Os ratios. A third alternative is that the low Os concentrations and elevated 187Os/188Os ratios denote subsolidus interaction with seawater or meteoric water. δ34S values of the dunites range between -6.4 and 6.6 ‰, and are consistent with the addition of S during fluid-rock interaction and serpentinization. The sharp contrast between the Os isotope ratios of the dunites and those of the sulfide mineralization illustrate that magmas that were spatially part of the same intrusive system may have experienced very different histories of interaction with country rocks. An important corollary is that because of the concentrations of Os and S, elevated Os isotope ratios (a function of high Re concentrations) and variable sulfur isotope ratios of sulfidic and carbonaceous country rocks, both S and Os isotope data from the olivine clinopyroxenite-hosted sulfide mineralization, are consistent with less than ˜2 % of bulk rock contamination. Even lower fractional abundance values may be indicated if the contaminant was a S-C-Os-rich fluid or partial melt derived from the sulfidic-carbonaceous metasedimentary country rocks. Despite the low degrees of contamination, the amounts of Os and S in the sulfide mineralization that may have been derived from country rocks often exceed 50 %.

Magmas near the critical degassing pressure drive volcanic unrest towards a critical state.

PubMed

Chiodini, Giovanni; Paonita, Antonio; Aiuppa, Alessandro; Costa, Antonio; Caliro, Stefano; De Martino, Prospero; Acocella, Valerio; Vandemeulebrouck, Jean

2016-12-20

During the reawaking of a volcano, magmas migrating through the shallow crust have to pass through hydrothermal fluids and rocks. The resulting magma-hydrothermal interactions are still poorly understood, which impairs the ability to interpret volcano monitoring signals and perform hazard assessments. Here we use the results of physical and volatile saturation models to demonstrate that magmatic volatiles released by decompressing magmas at a critical degassing pressure (CDP) can drive volcanic unrest towards a critical state. We show that, at the CDP, the abrupt and voluminous release of H 2 O-rich magmatic gases can heat hydrothermal fluids and rocks, triggering an accelerating deformation that can ultimately culminate in rock failure and eruption. We propose that magma could be approaching the CDP at Campi Flegrei, a volcano in the metropolitan area of Naples, one of the most densely inhabited areas in the world, and where accelerating deformation and heating are currently being observed.

Geochemical Specific Characters of the Oil and the Origin of the Oil and Gas Fields

NASA Astrophysics Data System (ADS)

Gottikh, Rimma; Pisotskiy, Bogdan; Plotnikova, Irina

2010-05-01

It is generally assumed that the fluid regime of the basement of ancient platforms is not associated with that of the sedimentary cover. This assumption is mainly due to the substantial time gap between the formation of the crystalline and sedimentary rocks as well as the evolutionary differences between the thermal regime of the interior and the redox potentials of fluid systems. The presence of loosely aggregated zones filled with salt-water solutions, oil or gas in the upper basement is explained by downward fluid flows from sedimentary rocks through tectonic faults into the disintegrated crystalline rocks. The formation of such zones is believed to be due to the crustal stratification due to Earth's pulsation, periodic variations of its rotational rate, hydrogenic deconsolidation, burial of the post-Early Proterozoic disintegration zones, etc. This pattern suggests that the matter and energy exchange between the Earth's spheres in the late stages of the platform development could only take place with the help of magmatic melts and the associated fluids during the tectonomagmatic cycles of the Earth's crust transformation. Gas and liquid hydrocarbon components mainly occur in crystalline basement rocks of ancient platforms penetrated to a depth of more than 3000 m due to deep degassing processes. The traces of the upward migration of fluids are sealed in the geological sequence, including the sedimentary cover, within secondary inclusions of rocks and minerals. The fluids are complex, reduced, multicomponent systems that transport lithophilous, chalcophilous and siderophilous elements. The presence of microelements in the bituminous phase of inclusions indicates that metals mainly occur in the complexes containing organic ligands. During the evolution of the fluid systems under new pressure and temperature conditions, low-solubility substances were separated out of the fluid to form hard bitumen, and the lighter components migrated into the overlying fractured and porous rocks. The high metal content of carbonaceous substances and their compositional variations governed by homogenisation temperatures of the inclusions suggest that they are not the products of the decomposition of oil fields. The constant presence of uranium in the fluid and its differentiation products allows the tracing of the systems' migration ways from the crystalline basement to oil-saturated reservoir zones of the sedimentary cover The known geochemical properties of bitumen and oil - high platinum content, specific distributions of rare earth elements, that are not characteristic of the upper crust formations, as well as 143Nd/144Nd and 87Sr/86Sr isotopic compounds, which are out of balance with the organic matter of sedimentary rocks - suggest that hydrocarbons are accumulated in the presence of cooling high-alkalinity mafite-ultramafite intrusions. This logically corresponds to the distribution of seismic anomalies and magnetic and gravity fields in the consolidated crust below the various petroleum fields (for example, South Tatarstan and Nepsky arches of the Romashkino and Verkhne-Chonskoye oil fields). The acquired geochemical and thermodynamic characteristics of the reduced fluids and their differentiation products from the crystalline basement and the sedimentary cover of the southern Siberian and eastern East European platforms indicate that these were formed outside of the sedimentary cover and that the migration was directed upwards. The analysis of the magmatic evolution on platforms reveals its alkaline trend due to the impeded degassing of magmatic sources at depth and the inflow of new doses of alkaline fluids or melts into them. Further evolution of the zones of partial melting of the substratum led, in the authors' view, to the generation of oil-forming fluids and their transportation into the Earth's upper crust. Their interaction with the surrounding rocks in turn led to the formation of oil accumulations. Thus, oil is the product of the interaction of deep, reduced fluids. Oil, graphite of the Archaean crystalline complexes and hard bitumens are interrelated elements of the evolution of deep, high-enthalpy systems. These large-scale reduced palaeofluid phenomena are obviously related to geodynamic and tectonomagmatic processes. The source of these fluid systems, their impact on the geological environment and its consequences can be determined through additional integrated geochemical studies using the isotopes of heavy elements and through the correlation of the observed potential fields with the structure of the consolidated crust and the sedimentary cover for the identification of geodynamic processes in geophysically inhomogeneous zones of the geological medium.

Release of Particulate Iron Sulfide during Shale-Fluid Interaction.

PubMed

Kreisserman, Yevgeny; Emmanuel, Simon

2018-01-16

During hydraulic fracturing, a technique often used to extract hydrocarbons from shales, large volumes of water are injected into the subsurface. Although the injected fluid typically contains various reagents, it can become further contaminated by interaction with minerals present in the rocks. Pyrite, which is common in organic-rich shales, is a potential source of toxic elements, including arsenic and lead, and it is generally thought that for these elements to become mobilized, pyrite must first dissolve. Here, we use atomic force microscopy and environmental scanning electron microscopy to show that during fluid-rock interaction, the dissolution of carbonate minerals in Eagle Ford shale leads to the physical detachment, and mobilization, of embedded pyrite grains. In experiments carried out over a range of pH, salinity, and temperature we found that in all cases pyrite particles became detached from the shale surfaces. On average, the amount of pyrite detached was equivalent to 6.5 × 10 -11 mol m -2 s -1 , which is over an order of magnitude greater than the rate of pyrite oxidation expected under similar conditions. This result suggests that mechanical detachment of pyrite grains could be an important pathway for the mobilization of arsenic in hydraulic fracturing operations and in groundwater systems containing shales.

Fluid-related inclusions in Alpine high-pressure peridotite reveal trace element recycling during subduction-zone dehydration of serpentinized mantle (Cima di Gagnone, Swiss Alps)

NASA Astrophysics Data System (ADS)

Scambelluri, Marco; Pettke, Thomas; Cannaò, Enrico

2015-11-01

Serpentinites release at sub-arc depths volatiles and several fluid-mobile trace elements found in arc magmas. Constraining element uptake in these rocks and defining the trace element composition of fluids released upon serpentinite dehydration can improve our understanding of mass transfer across subduction zones and to volcanic arcs. The eclogite-facies garnet metaperidotite and chlorite harzburgite bodies embedded in paragneiss of the subduction melange from Cima di Gagnone derive from serpentinized peridotite protoliths and are unique examples of ultramafic rocks that experienced subduction metasomatism and devolatilization. In these rocks, metamorphic olivine and garnet trap polyphase inclusions representing the fluid released during high-pressure breakdown of antigorite and chlorite. Combining major element mapping and laser-ablation ICP-MS bulk inclusion analysis, we characterize the mineral content of polyphase inclusions and quantify the fluid composition. Silicates, Cl-bearing phases, sulphides, carbonates, and oxides document post-entrapment mineral growth in the inclusions starting immediately after fluid entrapment. Compositional data reveal the presence of two different fluid types. The first (type A) records a fluid prominently enriched in fluid-mobile elements, with Cl, Cs, Pb, As, Sb concentrations up to 103 PM (primitive mantle), ∼102 PM Tl, Ba, while Rb, B, Sr, Li, U concentrations are of the order of 101 PM, and alkalis are ∼2 PM. The second fluid (type B) has considerably lower fluid-mobile element enrichments, but its enrichment patterns are comparable to type A fluid. Our data reveal multistage fluid uptake in these peridotite bodies, including selective element enrichment during seafloor alteration, followed by fluid-rock interaction along with subduction metamorphism in the plate interface melange. Here, infiltration of sediment-equilibrated fluid produced significant enrichment of the serpentinites in As, Sb, B, Pb, an enriched trace element pattern that was then transferred to the fluid released at greater depth upon serpentine dehydration (type A fluid). The type B fluid hosted by garnet may record the composition of the chlorite breakdown fluid released at even greater depth. The Gagnone study-case demonstrates that serpentinized peridotites acquire water and fluid-mobile elements during ocean floor hydration and through exchange with sediment-equilibrated fluids in the early subduction stages. Subsequent antigorite devolatilization at subarc depths delivers aqueous fluids to the mantle wedge that can be prominently enriched in sediment-derived components, potentially triggering arc magmatism without the need of concomitant dehydration/melting of metasediments or altered oceanic crust.

The main factors controlling petrophysical alteration in hydrothermal systems of the Kuril-Kamchatka island arch

NASA Astrophysics Data System (ADS)

Frolova, J.; Ladygin, V.; Rychagov, S.; Shanina, V.; Blyumkina, M.

2009-04-01

This report is based on the results of petrophysical studies obtained on a number of hydrothermal systems in the Kuril-Kamchatka island arc (Pauzhetsky, Mutnovsky, Koshelevsky, Essovsky, a volcano of Ebeko, Oceansky). Mineral composition and pore-space structure of primary rocks change intensively during hydrothermal process, results in alteration of petrophysical properties - porosity, density, permeability, hygroscopy, sonic velocity, elastic modulus, mechanical properties, thermal and magnetic characteristics. Petrophysical alterations gradually lead to the change of the structure of hydrothermal system, and its hydrodynamic and temperature regime. The tendency of petrophysical alteration can be different. In some cases rocks "improvement" is observed i.e. consolidation, hardening, decrease of porosity and permeability, removal of hygroscopy. In other cases rocks "deterioration" occurs, i.e. formation of secondary porosity and permeability, a decrease of density, strength, and elastic modulus, and occurrence of hygroscopic moisture. The classical example of cardinal petrophysical alteration is the transformation of hard basalts to plastic clays. The opposite example is the transformation of only slightly consolidates porous tuffs to hard and dense secondary quartzite. The character of petrophysical alteration depends on a number of factors including peculiarities of primary rocks, temperature, pressure and composition of thermal fluids, duration of fluid-rock interaction, and condition of fluid (steam, water, boiling water). The contribution of each factor to change of volcanic rocks properties is considered and analyzed in details. In particular, primary rocks controls speed, intensity and character of petrophysical alterations. Factors favorable for alteration are high porosity and permeability, micro crakes, weak cementation, glassy structure, basaltic composition. Kuril-Kamchatka region represents the volcanic island arch so host rocks in hydrothermal systems are mainly volcanic or volcaniclastic types of Neogene-Quaternary age. Volcanic rocks (lava rocks) are dense with high strength and elastic modulus and low porosity and permeability. The speed of their alteration is low. Basically volcanic rocks form impermeable horizons in the structure of hydrothermal system. But sometimes they form fracture-type reservoir. The origin of fracturing can be various. Volcanoclastic rocks are characterized by lower physical and mechanical properties, higher porosity and permeability. Due to high porosity and permeability they are greatly exposed to thermal fluids so they are altered intensively. Volcaniclastic rocks are the most common host rocks of geothermal reservoirs. Typically they form porous or fracture-porous aquifers. But in some cases they form water confining layers. The well-studied example is Pauzhetskaya hydrothermal system. The main reservoir is composed of highly porous (30-40%) and permeable medium-grained tuffs. The caprock is composed of fine-grained argillized tuffs. They are highly porous but due to small pore size porosity is un-effective for fluid and permeability is low. The temperature and pressure in a hydrothermal system cardinally influence on rocks properties. High-temperature deep fluids (Т>200C) cause the perfect tendency of petrophysical alteration - consolidation, hardening, a decrease of porosity and permeability, and removal of a hygroscopic moisture. This petrophysical tendency is observed independently of composition of fluids. This is the result of the development of high-temperature secondary minerals, which fill pores and cracks, and substitute matrix and phenocrystals. The contacts between grains become strong and dense, intergranular porosity is disappeared that reinforces cementation of rock. The petrophysical alteration caused by low-temperature subsurface fluids (Т<150C) are more difficult and diverse. Depending on what process prevails - rocks leaching, sedimentation of secondary minerals in pores and cracks or replacement of primary minerals by secondary minerals, it can lead to both: an increase or a decrease in petrophysical properties. Financial support from RFBR (project 05-07-00118-a)

Geochemical constraints on the genesis of the Scheelite dome intrusion-related gold deposit, Tombstone gold belt, Yukon, Canada

USGS Publications Warehouse

Mair, J.L.; Goldfarb, R.J.; Johnson, C.A.; Hart, C.J.R.; Marsh, E.E.

2006-01-01

The Scheelite dome intrusion-related gold deposit, western Selwyn basin, Yukon, is hosted in hornfelsed metasedimentary strata that lie adjacent to the exposed apices of a monzogranite to quartz monzonite plutonic complex of the mid-Cretaceous Tombstone-Tungsten magmatic belt, Tintina gold province, Alaska and Yukon. A variety of mineralization styles occur throughout a 10- ?? 3-km east-trending corridor and include reduced Au- and W-rich skarns, Au, W- and Ag-Pb-Zn-Sb-rich quartz tension-vein arrays, and multiphase fault veins and isolated zones of Au-rich sericite-carbonate altered rock. Integrated U-Pb SHRIMP data for magmatic zircon and Ar-Ar data for magmatic and hydrotbermal biotite indicate that gold mineralization occurred within 1 to 2 m.y. of magma emplacement. Fluid inclusion, oxygen isotope, and arsenopyrite geothermometry data indicate that hydrothermal minerals formed at depths of 6 to 9 km over a temperature range from 550??C. High-temperature Au-rich skarns formed at >400??C, whereas vein-hosted mineralization formed at 280?? to 380??C. In skarns, Au is strongly associated with enrichments of Bi, Te, W, and As, whereas a variety of Au-rich veins occur, with Asrich (type 1), and Te- and W-rich (type 2) end members. Silver-Pb-Zn-Sb veins are typically Au poor and represent the latest and lowest temperature phase in the hydrothermal paragenesis. The fluid inclusion data indicate that all mineralization styles were formed from low-salinity (???4 wt % NaCl equiv) aqueous-carbonic fluids, consistent with the composition of fluid inclusions within infilled miarolitic cavities in the intrusive rocks. However, the nonaqueous fluid was predominantly CH4 in skarn, CO2 in Au-Te and Au-W veins, and a fluid with roughly equal amounts Of CO2, CH4, and N2 in Au-As and Ag-Pb-Zn-Sb veins. Oxygen isotope data are consistent with a mineralizing fluid of predominantly magmatic origin that was variably modified to more positive ??18O values during interaction with 18O-enriched metasedimentary strata. Sulfur isotope data suggest two possible sources of sulfur, a magmatic source characterized by ??34S values of approximately -5 to 0 per mil and sulfur from the metasedimentary country rocks characterized by more negative ??34S values of approximately -15 to -10 per mil. Collectively the data indicate that gold at Scheelite Dome was deposited from a magmatic-hydrothermal system. Interaction of magmatic fluids with graphitic hornfels rocks resulted in reduction of the ore fluids, higher CH4/CO2 ratios, and modification of the oxygen and sulfur isotope values of the ore fluids toward those of the metasedimentary hornfels. Progressive reduction and cooling of hydrotbermal fluids, in addition to phase separation in vein-hosted mineralization, were the mechanisms for gold deposition. Compared to other intrusion-related gold deposits associated with the Tombstone-Tungsten magmatic belt magmatism, exposed mineralization at Scheelite Dome is predominantly hosted by hornfelsed metasedimentary rocks. This results in more diverse mineralization styles and a greater spread of isotope and fluid inclusion data. ?? 2006 Society of Economic Geologists, Inc.

Comparison of hydrothermal activity between the Adriatic and the Red Sea rift margins

NASA Astrophysics Data System (ADS)

Ball, Philip; Incerpi, Nicolò; Birkle, Peter; Lacsamana, Elizabeth; Manatschal, Gianreto; Agar, Susan; Zhang, Shuo; Borsato, Ron

2017-04-01

Detailed field studies, and access to high-quality seismic reflection and refraction data have led to an improved understanding of the architecture and evolution of magma poor and magma rich margins. Associated with the spatial-temporal evolution of the rift, it is evident that there are evolving, extensive, fluid-rock interactions due to the infiltration of fluids within the sediment, basement and lithospheric mantle. Key questions therefore arise: What are the different fluid-rock reactions that can be typed to different geodynamic stages of the rift evolution? What are their compositions and how do they interact with their environment (basement, sediments, evaporites, hydrosphere, and magmatism)? What are the implications for the evolution of the margin rheology, thermal structure, depositional environments/organic matter maturity, and reservoir quality? The Adriatic paleo-rifted margin is preserved in both SE Switzerland and northern Italy. The field exposures provide a unique opportunity to study the fluid flow history of a hyperextended magma poor extensional margin. Analysis of breccias, cement veins and replacement minerals reveal that the margin records a complex, long-lasting history of dolomitization, calcification and silicification during the Jurassic rifting. The Red Sea by contrast is a young rifted margin. It differs from the paleo-Adriatic margin by several characteristics: volcanism is more evident, and syn-tectonic sediments, including evaporites (halite and anhydrite) are thicker. Several core and fluid samples are available from both onshore and offshore wells, which reveal rift-related hydrothermal alteration. In addition, we find evidence for the presence of an extreme dynamic hydraulic system with infiltration of surface water into sub-salt units during Late Pleistocene. In this study we present results from petrographic and geochemical analysis of basement and sedimentary rocks from Adriatic field-derived samples and core/subsurface fluid samples for the Eastern Red Sea margin. The results are presented using rift domain interpretations, thereby enabling the simple comparison of the observed hydrothermal alteration within a first-order (spatial temporal) rift geodynamic framework.

Reaction of seawater with fresh mid-ocean ridge gabbro creates ';atypical' REE pattern and high REE fluid fluxes: Experiments at 425 and 475 °C, 400 and 1000 bar

NASA Astrophysics Data System (ADS)

Beermann, O.; Garbe-Schönberg, D.; Holzheid, A. D.

2013-12-01

High-temperature MOR hydrothermalism significantly affects ocean chemistry. The Sisters Peak (SP) hydrothermal field at 5°S on the slow-spreading Mid-Atlantic Ridge (MAR) emanates fluids >400°C [1] that have high concentrations of H2, transition metals, and rare earth elements (REE) exhibiting ';atypical' REE pattern characterized by depletions of LREE and HREE relative to MREE and no Eu anomaly [2]. This is in contrast to the ';typical' LREE enrichment and strong positive Eu anomaly known from many MOR vent fluids observed world-wide [e.g., 3]. Besides temperature, the seawater-to-rock ratio (w/r ratio) has significant control on the fluid chemistry [e.g., 4, 5]. To understand how vent fluid REE-signatures are generated during water-rock interaction processes we reacted unaltered gabbro with natural bottom seawater at 425 °C and 400 bar and at 425 and 475 °C at 1000 bar at variable w/r (mass) ratios ranging from 0.5-10 by using cold seal pressure vessels (CSPV). The run durations varied from 3-72 h. Reacted fluids were analysed for major and trace elements by ICP-OES and ICP-MS. In our experiments, ';atypical' REE fluid pattern similar to those of SP fluids were obtained at high w/r ratio (5 and 10) that might be characteristic for focused fluid-flow along e.g., detachment faults at slow-spreading MOR [6]. In contrast, more ';typical'-like REE pattern with elevated LREE and slightly positive Eu anomalies have been reproduced at low w/r ratio (0.5-1). Results of numerical simulations imply that strong positive Eu anomalies of fluids and altered gabbro from high temperature MOR hydrothermal systems can be created by intense rock leaching processes at high w/r ratio (5-10). This suggests that hydrothermal circulation through the ocean crust creates ';typical' REE fluid pattern with strong positive Eu anomalies if seawater reacts with gabbroic host rock that has been already leached in REE at high fluid fluxes. Simulations of the temporal chemical evolution of high temperature MOR hydrothermal systems reveal that rock and fluid REE contents can rapidly decrease within several months particularly at high fluid fluxes. In contrast, the reaction with ';fresh', unaltered rock is evident from the high REE concentration of SP fluids. Both, fluid access to fresh rock and the fluid flux should therefore significantly control chemical fluxes to the ocean. Thus, high chemical fluxes can be expected in particular from early stage high-temperature MOR hydrothermal systems that are assumed to be not uncommon along the slow-spreading MAR. [1] Koschinsky A., Garbe-Schönberg D., Sander S., Schmidt K., Gennerich H.-H., and Strauss H. (2008) Geology 36, 615-618. [2] Schmidt K., Garbe-Schönberg D., Bau M., and Koschinsky A. (2010) Geochim. Cosmochim. Acta 74, 4058-4077. [3] Douville E., Bienvenu P., Charlou J. L., Donval J. P., Fouquet Y., Appriou P., and Gamo T. (1999). Geochim. Cosmochim. Acta 63, 627-643. [4] Seyfried [Jr.] W. E. and Bischoff J. L. (1977) Earth. Planet. Sci. Lett. 34, 71-77. [5] Hajash A. and Chandler G. W. (1981) Contrib. Mineral. Petrol. 78, 240-254. [6] McCaig A.M. and Harris M. (2012) Geology 40, 367-370.

Geochemical and tectonic implications on plate-interface evolution achieved from high-pressure ultramafic rocks in mélange settings

NASA Astrophysics Data System (ADS)

Cannaò, E.; Agostini, S.; Scambelluri, M.; Tonarini, S.

2014-12-01

Geochemical studies of fluid-mobile elements (FME) joined with B, Sr and Pb isotopic analyses of high-pressure mélanges terranes help constraining tectonic processes and mass transfer during accretion of slab and suprasubduction mantle in plate-interface domains. Here we focus on ultramafic rocks from two plate interface settings: (I) metasediment-dominated mélange (Cima di Gagnone, CdG, Adula Unit), where eclogite-facies de-serpentinized garnet peridotite and chlorite harzburgite lenses are embedded in paraschist; (II) dominated by high-pressure serpentinite (Erro-Tobbio, ET, and Voltri Units, VU, Ligurian Alps). CdG metaperidotite shows low [B], negative δ 11B and high Sr and Pb isotopic ratios. As, Sb loss from metasediment and gain by garnet and chlorite metaperidotite points to exchange between the two systems. Presence of As and Sb in eclogite-facies peridotite minerals and preferential low-T mobility of such elements suggest that exchange was during early subduction burial and prior to eclogitization. Based on high [B], positive δ11B, oxygen and hydrogen isotope, the ET serpentinties were recently interpreted as supra-subduction mantle flushed by slab fluids (Scambelluri & Tonarini, 2012, Geology, 40, 907-910). Their 206Pb/204Pb and 87Sr/86Sr isotope ratios range between 18.300-18.514 and 0.7048-0.7060, respectively. Compared with ET rocks, VU serpentinites have higher As, Sb (up to 1.3 and 0.39 ppm, respectively) and are enriched in radiogenic Sr (up to 0.7105 87Sr/86Sr). This signature reflects interaction with fluids that exchanged with sedimentary rocks, either in outer rise environments or during accretion atop the slab. In the above cases, the serpentinized mantle rocks fingerprint interaction with fluids from different sources, indicating a timing of accretion to plate interface domains. We provide evidence that serpentinized mantle slices of different size and provenance (slab or wedge) accreted to plate interface domains since early subduction stages. They also represent FME and radiogenic isotope sources for arcs and for deep mantle refertilization.

Oxygen isotope evidence for submarine hydrothermal alteration of the Del Puerto ophiolite, California

USGS Publications Warehouse

Schiffman, P.; Williams, A.E.; Evarts, R.C.

1984-01-01

The oxygen isotope compositions and metamorphic mineral assemblages of hydrothermally altered rocks from the Del Puerto ophiolite and overlying volcaniclastic sedimentary rocks at the base of the Great Valley sequence indicate that their alteration occurred in a submarine hydrothermal system. Whole rock ??18O compositions decrease progressively down section (with increasing metamorphic grade): +22.4??? (SMOW) to +13.8 for zeolite-bearing volcaniclastic sedimentary rocks overlying the ophiolite; +19.6 to +11.6 for pumpellyite-bearing metavolcanic rocks in the upper part of the ophiolite's volcanic member; +12.3 to +8.1 for epidote-bearing metavolcanic rocks in the lower part of the volcanic member; +8.5 to +5.7 for greenschist facies rocks from the ophiolite's plutonic member; +7.6 to +5.8 for amphibolite facies or unmetamorphosed rocks from the plutonic member. Modelling of fluid-rock interaction in the Del Puerto ophiolite indicates that the observed pattern of upward enrichment in whole rock ??18O can be best explained by isotopic exchange with discharging 18O-shifted seawater at fluid/rock mass ratios near 2 and temperatures below 500??C. 18O-depleted plutonic rocks necessarily produced during hydrothermal circulation were later removed as a result of tectonism. Submarine weathering and later burial metamorphism at the base of the Great Valley sequence cannot by itself have produced the zonation of hydrothermal minerals and the corresponding variations in oxygen isotope compositions. The pervasive zeolite and prehnite-pumpellyite facies mineral assemblages found in the Del Puerto ophiolite may reflect its origin near an island arc rather than deep ocean spreading center. ?? 1984.

Oxygen isotopes in garnet and accessory minerals to constrain fluids in subducted crust

NASA Astrophysics Data System (ADS)

Rubatto, Daniela; Gauthiez-Putallaz, Laure; Regis, Daniele; Rosa Scicchitano, Maria; Vho, Alice; Williams, Morgan

2017-04-01

Fluids are considered a fundamental agent for chemical exchanges between different rock types in the subduction system. Constraints on the sources and pathways of subduction fluids thus provide crucial information to reconstruct subduction processes. Garnet and U-Pb accessory minerals constitute some of the most robust and ubiquitous minerals in subducted crust and can preserve multiple growth zones that track the metamorphic evolution of the sample they are hosted in. Microbeam investigation of the chemical (major and trace elements) and isotopic composition (oxygen and U-Pb) of garnet and accessory minerals is used to track significant fluid-rock interaction at different stages of the subduction system. This approach requires consideration of the diffusivity of oxygen isotopes particularly in garnet, which has been investigated experimentally. The nature of the protolith and ocean floor alteration is preserved in relict accessory phases within eclogites that have been fully modified at HP conditions (e.g. Monviso and Dora Maira units in the Western Alps). Minerals in the lawsonite-blueschists of the Tavsanli zone in Turkey record pervasive fluid exchange between mafic and sedimentary blocks at the early stage of subduction. High pressure shear zones and lithological boundaries show evidence of intense fluid metasomatism at depth along discontinuities in Monviso and Corsica. In the UHP oceanic crust of the Zermatt-Saas Zone, garnet oxygen isotopes and tourmaline boron isotopes indicate multistage fluid infiltration during prograde metamorphism. Localized exchanges of aqueous fluids are also observed in the subducted continental crust of the Sesia-Lanzo Zone. In most cases analyses of distinct mineral zones enable identification of multiple pulses of fluids during the rock evolution.

The source and significance of argon isotopes in fluid inclusions from areas of mineralization

NASA Astrophysics Data System (ADS)

Kelley, S.; Turner, G.; Butterfield, A. W.; Shepherd, T. J.

1986-09-01

Argon isotopes in fluid inclusions in quartz veins associated with granite-hosted tungsten mineralization in the southwest and north of England have been investigated in detail by the 40Ar- 39Ar technique. The natural argon is present as a number of discrete components which can be identified through correlations with 39Ar, 38Ar and 37Ar induced by neutron bombardment of potassium, chlorine and calcium. The potassium-correlated component arises principally from in situ decay of potassium in solid phases in the inclusions. In the case of the Hemerdon tungsten deposit of southwest England the phases responsible are small (≈ 25 μm) captive authigenic micas which are shown to have been deposited from a fluid 268 ± 20 Ma ago, shortly after the emplacement of the host granite. The chlorine-correlated component is present in the brines which constitute the fluid phase of the inclusions. The argon in these hydrothermal fluids is made up in part of "parentless" or "excess" 40Ar leached from surrounding crustal rocks, and in part of dissolved ancient atmospheric argon. Absolute concentrations of both atmospheric and excess components in the brine can be estimated from ( 40ArCl ) ratios and independent determinations of the salinity of the inclusions. The absolute concentrations of the atmospheric argon are close to those found in modern meteoric water, while those of the excess component can be interpreted in terms of the degree of interaction betwen the circulating fluids and country rock. A calcium-correlated component, with a much higher ratio of excess to atmospheric argon than that in the brine, was found to be a dominant phase in one sample from the Hemerdon deposit, indicating the presence of a solid phase (probably a CaSO 4 daughter mineral). Inclusions of this composition represent fluids which have had a more prolonged interaction- with crustal rocks. The results obtained from this study provide a systematization and a framework for future multi-component argon studies of fluid inclusions, together with an indication of the wide range of information which can be inferred.

Geochemistry of serpentinites in subduction zones: A review

NASA Astrophysics Data System (ADS)

Deschamps, Fabien; Godard, Marguerite; Guillot, Stéphane; Hattori, Kéiko

2013-04-01

Over the last decades, numerous studies have emphasized the role of serpentinites in the subduction zones geodynamics. Their presence and effective role in this environment is acknowledged notably by geophysical, geochemical and field observations of (paleo-) subduction zones. In this context, with the increasing amount of studies concerning serpentinites in subduction environments, a huge geochemical database was created. Here, we present a review of the geochemistry of serpentinites, based on the compilation of ~ 900 geochemical analyses of abyssal, mantle wedge and subducted serpentinites. The aim was to better understand the geochemical evolution of these rocks during their subduction history as well as their impact in the global geochemical cycle. When studying serpentinites, it is often a challenge to determine the nature of the protolith and their geological history before serpentinisation. The present-day (increasing) geochemical database for serpentinites indicates little to no mobility of incompatible elements at the scale of the hand-sample in most serpentinized peridotites. Thus, Rare Earth Elements (REE) distribution can be used to identify the initial protolith for abyssal and mantle wedge serpentinites, as well as magmatic processes such as melt/rock interactions taking place before serpentinisation. In the case of subducted serpentinites, the interpretation of trace element data is more difficult due to secondary enrichments independent of the nature of the protolith, notably in (L)REE. We propose that these enrichments reflect complex interactions probably not related to serpentinisation itself, but mostly to fluid/rock or sediment/rock interactions within the subduction channel, as well as intrinsic feature of the mantle protolith which could derive from the continental lithosphere exhumed at the ocean-continent transition. Additionally, during the last ten years, numerous studies have been carried out, notably using in situ approaches, to better constrain the geochemical budget of fluid-mobile elements (FME; e.g. B, Li, Cl, As, Sb, U, Th, Sr) stored in serpentinites and serpentine phases. These elements are good markers of the fluid/rock interactions taking place during serpentinisation. Today, the control of serpentinites on the behaviour of these elements, from their incorporation to their gradually release during subduction, is better understood. Serpentinites must be considered as a component of the FME budget in subduction zones and their role, notably on arc magmas composition, is undoubtedly underestimated presently in the global geochemical cycle.

Orientation, composition, and entrapment conditions of fluid inclusions in the footwall of the northern Snake Range detachment, Nevada

NASA Astrophysics Data System (ADS)

Carter, Matthew J.; Siebenaller, Luc; Teyssier, Christian

2015-12-01

Footwall rocks of the northern Snake Range detachment fault (Hampton and Hendry's Creeks) offer exposures of quartzite mylonites (sub-horizontal foliation) that were permeated by surface fluids. An S-C-C‧ mylonitic fabric is defined by dynamically recrystallized quartz and mica. Electron backscatter diffraction analyses indicate a strong preferred orientation of quartz that is overprinted by two sets of sub-vertical, ESE and NNE striking fractures. Analyses of sets of three perpendicular thin sections indicate that fluid inclusions (FIs) are arranged according to macroscopic fracture patterns. FIs associated with NNE and ESE-striking fractures coevally trapped unmixed CO2 and H2O-rich fluids at conditions near the critical CO2-H2O solvus, giving minimum trapping conditions of T = 175-200 °C and ∼100 MPa H2O-rich FIs trapped along ESE-trending microcracks in single crystals of quartz may have been trapped at conditions as low as 150 °C and 50 MPa indicating the latest microfracturing and annealing of quartz in an overall extensional system. Results suggest that the upper crust was thin (4-8 km) during FI trapping and had an elevated geotherm (>50 °C/km). Footwall rocks that have been exhumed through the brittle-ductile transition in such extensional systems experience both brittle and crystal-plastic deformation that may allow for circulation of meteoric fluids and grain-scale fluid-rock interactions.

Geology and geochemistry of Carlin-type gold deposits in China

USGS Publications Warehouse

Rui-Zhong, H.; Wen-Chao, S.; Xian-Wu, B.; Guang-Zhi, T.; Hofstra, A.H.

2002-01-01

The Carlin-type gold deposits in China lie mostly near the margins of the Proterozoic Yangtze and Aba cratons. Submicron-sized gold in micron-sized arsenian pyrite is disseminated in fractured Cambrian through Triassic carbonaceous shale and carbonate rocks, and is associated with anomalous Hg, Sb, As, U, and Tl. Alteration typically includes silicification, argilization, and sulfidation. Aqueous fluid inclusions contain CO2, have relatively low temperatures of homogenization (250-150 ??C), and salinities (8-2 wt% equiv. NaCl) that typically decrease from early to later stages. The indicated pressures of 105-330x105 Pa correspond to depths in excess of 1.0 to 3.0 km, assuming hydrostatic conditions. The ??D values of fluid inclusions (-87 to -47%) and the calculated ??18 values for water in ore fluids (-2.1 to 16.2%) reflect interactions between meteoric water and sedimentary rocks. The ??13C values of calcite (-9 to 2%) and ??34S values of sulfides (-24 to 17%) suggest that C and S were derived from marine carbonate (and organic carbon) and diagenetic sulfides (and organic sulfur) in the vicinity of the deposits. Geologic relationships and geochronologic evidence indicate the deposits formed during a late phase of the Yanshanian orogeny (140-75 Ma). These gold deposits share much in common with the Carlin-type gold deposits in Nevada, USA. Both occur in carbonaceous, pyritic, sedimentary rocks deposited on extended margins of Precambrian cratons. The smaller Chinese deposits are generally in more siliceous rocks and the larger Nevada deposits in more calcareous rocks. In both countries, the host rocks prior to mineralization were affected by contractional deformation that produced many of the ore-controlling structures and the deposits do not show consistent spatial or genetic relationships with epizonal plutons. However, the Nevada deposits show broad spatial and temporal relationships with shifting patterns of calc-alkaline magmatism. The ore and alteration mineral assemblages, residence of gold, geochemical signatures, paragenetic sequence, and fluid inclusions are remarkably similar, which indicates that the deposits formed from low salinity, moderately acidic, CO2 and H2S-rich in the crust similar processes at relatively shallow levels in the crust (<5 km). However, the deposits in China are associated with large Hg, Sb, As, U, and Tl deposits, which may reflect higher background abundances of these elements. Stable isotopic data suggest meteoric water evolved to become ore fluids through interactions with sedimentary rocks, although contributions of volatiles or metals from deeper levels are present in some deposits in Nevada. In both countries, the deposits appear to have formed in an area of high paleothermal gradients after a change in stress regime during the later phases of orogenic activity.

Carbonation of Subduction Interface Ultramafic Rocks and Implications for Deep Carbon Cycling: Evidence from Hybrid Serpentinite-Marble in the Voltri Massif, Italy

NASA Astrophysics Data System (ADS)

Scambelluri, M.; Bebout, G. E.; Gilio, M.; Belmonte, D.; Campomenosi, N.; Crispini, L.

2015-12-01

Release of COH fluids from hydrous minerals and carbonates influences element recycling and magmatism at subduction zones. Contradictory interpretations exist regarding the retention/storage of C in subducting plates and in the forearc to subarc mantle. Multiple lines of evidence indicate mobility of C in forearcs; however, the magnitude of this loss is highly uncertain[1-5]. A poorly constrained fraction of the 40-115 Mt/y of C initially subducted is released into fluids (e.g., by decarbonation, carbonate dissolution), and 18-43 Mt/y is returned at arc volcanoes[2-5, refs. therein]. The imbalance could reflect subduction into the deeper mantle or forearc/subarc storage[4-7]. We examine the fate of C in slab/interface ultramafic rocks, and by analogy serpentinized mantle wedge, via study of fluid-rock evolution of marble and variably carbonated serpentinite (Ligurian Alps). Based on petrography, and major/trace element and C and O isotope compositions, we demonstrate that serpentinite dehydration at 2-2.5 GPa, 550°C released aqueous fluids triggering breakdown of dolomite in nearby marbles, thus releasing C into fluids. Carbonate + olivine veins document flow of COH fluids; interaction of these COH fluids with serpentinite led to formation of high-pressure carbonated ultramafic-rock domains, thus resulting in retention of C in some rocks at an ancient subduction interface. We stress that lithologically complex interfaces could contain sites of both C release and C addition, further confounding estimates of net C loss at forearc and subarc depths [cf 4,5]. Sites of C retention, also including carbonate veins and graphite as reduced carbonate[7], could influence the transfer of slab C to at least the depths beneath volcanic fronts. 1. Poli S et al. 2009 EPSL; 2. Ague and Nicolescu 2014 Nat Geosci; 3. Cook-Collars et al. 2014 Chem Geol; 4. Collins et al. 2015 Chem Geol; 5. Kelemen and Manning 2015 PNAS; 6. Sapienza et al. 2009 CMP; 7 Galvez et al. 2013 Nat Geosci

Orebody geometry, fluid and metal sources of the Omitiomire Cu deposit in the Ekuja Dome of the Damara Belt in Namibia

NASA Astrophysics Data System (ADS)

Kitt, Shawn; Kisters, Alexander; Vennemann, Torsten; Steven, Nick

2018-02-01

The Omitiomire Cu deposit (resource of 137 Mt at 0.54% Cu) in the Ekuja Dome of the Damara Belt in Namibia is hosted by an anastomosing, low-angle Pan-African (ca. 520 Ma) shear zone system developed around an older (ca. 1100-1060 Ma), late Mesoproterozoic intrusive breccia between a suite of mafic rocks (originally lava flows) and later tonalitic gneisses. High-grade ore shoots preferentially formed along contacts between tectonically interleaved biotite-epidote-quartz-chalcocite schists and felsic gneisses, and are directly related to an increase in the number and cumulative thickness of thin, contact-parallel mineralized shear zones. Alteration and mineralization are associated with elevated concentrations of K2O, Cr, Rb, S, and Cu and a loss of Na2O, CaO, and MgO. Oxygen isotope fractionation for quartz-biotite, quartz-feldspar, and quartz-amphibole mineral pairs support equilibrium temperatures of between 500 and 650 °C during the fluid/rock interaction. Mineral separates from amphibole-biotite gneisses and mineralized schists have similar ranges in δ18O values of about 1.2 to 2 ‰ relative to VSMOW. Coexisting minerals are arranged in an order of increasing δ18O values from biotite, to epidote, amphibole, and quartz, suggesting that the Omitiomire Shear Zone was a rock-dominated system. Similarly, H-isotope results for mineral separates from biotite-epidote schists and amphibole gneisses do not show any reversals for D/H fractionations, with δD values of between -48 and -82 ‰, typical of metamorphic-magmatic rocks. The homogeneous and low δ34S values (-6.1 to -4.7 ‰ CDT) are compatible with a local redistribution of sulfur from magmatic rocks and interaction with sulfur derived from metamorphic fluids of metasedimentary origin. The relatively low fluid/rock ratios and elevated Cu values (>1500 ppm) from unaltered amphibolite point to a local redistribution of an earlier (late Mesoproterozoic) Keweenaw-type Cu mineralization into later Pan-African shear zones during the exhumation of the Ekuja Dome. The timing, polyphase evolution, and tectonic setting of the Omitiomire deposit show remarkable similarities with the large Cu deposits of the Domes Region in the adjoining Lufilian Arc of northern Zambia. This suggests the presence of a much larger, regionally significant Cu province extending from central Namibia, through northern Botswana, and into Zambia.

Continental Subduction: Mass Fluxes and Interactions with the Wider Earth System

NASA Astrophysics Data System (ADS)

Cuthbert, S. J.

2011-12-01

Substantial parts of ultra-high pressure (UHP) terrains probably represent subducted passive continental margins (PCM). This contribution reviews and synthesises research on processes operating in such systems and their implication for the wider Earth system. PCM sediments are large repositories of volatiles including hydrates, nitrogen species, carbonates and hydrocarbons. Sediments and upper/ mid-crustal basement are rich in incompatible elements and are fertile for melting. Lower crust may be more mafic and refractory. Juvenile rift-related mafic rocks also have the potential to generate substantial volumes of granitoid melts, especially if they have been hydrated. Exposed UHP terrains demonstrate the return of continental crust from mantle depths, show evidence for substantial fluxes of aqueous fluid, anatexis and, in entrained orogenic peridotites, metasomatism of mantle rocks by crust- derived C-O-H fluids. However, substantial bodies of continental material may never return to the surface as coherent masses of rock, but remain sequestered in the mantle where they melt or become entrained in the deeper mantle circulation. Hence during subduction, PCM's become partitioned by a range of mechanisms. Mechanical partitioning strips away weaker sediment and middle/upper crust, which circulate back up the subduction channel, while denser, stronger transitional pro-crust and lower crust may "stall" near the base of the lithosphere or be irreversibly subducted to join the global mantle circulation. Under certain conditions sediment and upper crustal basement may reach depths for UHPM. Further partitioning takes place by anatexis, which either aids stripping and exhumation of the more melt-prone rock-masses through mechanical softening, or separates melt from residuum so that melt escapes and is accreted to the upper plate leading to "undercrusting", late-orogenic magmatism and further refinement of the crust. Melt that traverses sections of mantle will interact with it causing metasomatism and refertilisation. Partitioning also takes place by solid-fluid and melt-fluid partitioning. Dehydration may take place both during subduction and exhumation, and fluxes between dehydrating and hydrating rock masses influence the internal fluid budget of the orogen (essential for eclogitisation and densification of mafic lithologies). Ascending granitic melts advect dissolved water to shallow levels, or even the atmosphere. Irreversible subduction of PCM sediment carries water plus nitrogen species to the deeper mantle. Decarbonation of voluminous PCM carbonates depends on thermal regime and may release a pulse of CO2 to the atmosphere, but is limited in colder subduction zones hence transferring large volumes of carbon to the deep mantle. This may ultimately be mobilised by melting or dissolution to form fluid media for diamond formation.

Unravelling the structural control of mississippi valley-type deposits and prospects in carbonate sequences of the Western Canada Sedimentary Basin

USGS Publications Warehouse

Pana, D.

2006-01-01

Re-examination of selected MVT outcrops and cores in the Interior Plains and Rocky Moun-tains of Alberta, corroborated with previous paragenetic, isotopic and structural data, suggests Laramide structural channelling of dolomitizing and mineralizing fluids into strained carbonate rocks. At Pine Point, extensional faults underlying the trends of MVT ore bodies and brittle faults overprinting the Great Slave Lake Shear Zone define apinnate fault geometry and appear to be kinematically linked. Chemical and isotopic characteristics of MVT parental fluids are consistent with seawater and brine convection within fault-confined verticalaquifers, strong water-basement rock interaction, metalleaching from the basement, and focused release of hydrothermal fluids within linear zones of strained carbonate caprocks. Zones of recurrent strain in the basement and a cap of carbonate strata constitute the critical criteria for MVTexploration target selection in the WCSB.

Complex fragmentation and silicification structures in fault zones: quartz crystallization and repeated fragmentation in the Rusey fault zone (Cornwall/UK)

NASA Astrophysics Data System (ADS)

Yilmaz, Tim I.; Blenkinsop, Tom; Duschl, Florian; Kruhl, Jörn H.

2015-04-01

Silicified fault rocks typically show structures resulting from various stages of fragmentation and quartz crystallization. Both processes interact episodically and result in complex structures on various scales, which require a wide spectrum of analysis tools. Based on field and microstructural data, the spatial-temporal connection between deformation, quartz crystallization and fluid and material flow along the Rusey fault zone was investigated. The fault can be examined in detail in three dimensions on the north Cornwall coast, UK. It occurs within Carboniferous sandstones, siltstones, mudstones and slates of the Culm basin, and is likely to have had a long history. The fault rocks described here formed during the younger events, possibly due to Tertiary strike-slip reactivation. Frequent fragmentation, flow and crystallization events and their interaction led to various generations of complex-structured quartz units, among them quartz-mantled and partly silicified wall-rock fragments, microcrystalline quartz masses of different compositions and structures, and quartz vein patterns of various ages. Lobate boundaries of quartz masses indicate viscous flow. Fragments are separated by quartz infill, which contains cm-sized open pores, in which quartz crystals have pyramidal terminations. Based on frequent occurrence of feathery textures and the infill geometry, quartz crystallization from chalcedony appears likely, and an origin from silica gel is discussed. Fragmentation structures are generally fractal. This allows differentiation between various processes, such as corrosive wear, wear abrasion and hydraulic brecciation. Material transport along the brittle shear zone, and displacement of the wall-rocks, were at least partly governed by flow of mobile fluid-quartz-particle suspensions. The complex meso- to microstructures were generated by repeated processes of fragmentation, quartz precipitation and grain growth. In general, the brittle Rusey fault zone represents a zone of multiple fragmentation, fluid flow, crystallization and quartz dissolution and precipitation, and is regarded as key example of large-scale cyclic interaction of these processes. The geological evidence of interactions between processes implies that feedbacks and highly non-linear mechanical behaviour generated the complex meso- and microstructures. The fault zone rheology may also therefore have been complex.

Monitoring Fluid Flow in Fractured Carbonate Rocks Using Seismic Measurements

NASA Astrophysics Data System (ADS)

Li, W.; Pyrak-Nolte, L. J.

2008-12-01

The physical properties of carbonate rock are strongly influenced by the rock fabric which depends on the depositional environment, diagenetic and tectonic processes. The most common form of heterogeneity is layering caused by a variation in porosity among layers and within layers. The variation in porosity among layers leads to anisotropic behavior in the hydraulic, mechanical and seismic properties of carbonate rocks. We present the results of a laboratory study to examine the effect of fabric-controlled layering on fluid flow and seismic wave propagation through intact and fractured carbonate rock. Experiments were performed on cubic samples of Austin Chalk Cordova Cream. Samples AC1, AC5 and AC6 are cubic samples that measure 100 mm on edge. The samples were sealed and contained three inlet and three outlet ports for fluid invasion experiments. Two orthogonal seismic arrays were used to record both compressional and shear wave transmission through intact and fractured samples. The arrays used piezoelectric contact transducers with a central frequency 1.0 MHz. Between the two arrays, sixteen sources and sixteen receivers were used. Seismic measurements were made on the samples as a function of stress and during fluid saturation. The location of the invading fluid front as a function of time was monitored by using the peak-to-peak amplitude of the transmitted signals. The front was assumed to be between a source-receiver pair when the signal amplitude decreased by 50% over the initial value. The hydraulic gradient was parallel and perpendicular to the layers for AC5 and AC6, respectively. Sample AC1 was fractured and flow ports were established on the edges of the fracture plane. The weakly directed fabric controlled the rate at which fluid flowed through the samples. From the seismic data on AC6, the fluid first spread vertically along a layer before flowing across the layers. For AC6, it took the fluid two and half hours to flow between the inlet and the outlet across the layers. However, for AC5, the water flowed quickly along the layers and crossed the entire sample in one and a half hours. From the seismic data on fractured sample AC1, the water initially took more than 15 hours to transverse the sample though portions of the fracture were invaded after two hours. No water was produced at the outlet over a 15 hour period. Upon inspection, chemical precipitation was observed along the fracture plane and fracture- matrix interaction controlled the saturation of the matrix. Seismic monitoring of the fluid-front during saturation indicates that fine bedding affects the hydraulic properties of the sample while geochemical interactions in fractures affect fracture-matrix communication. Acknowledgments: The authors wish to acknowledge support of this work by the Geosciences Research Program, Office of Basic Energy Sciences US Department of Energy (DEFG02-97ER14785 08) and by Exxon Mobil Upstream Research Company.

Hydro-Mechanical Modelling of Slow Slip Phenomena at the Subduction Interface.

NASA Astrophysics Data System (ADS)

Petrini, C.; Gerya, T.; Madonna, C.; van Dinther, Y.

2016-12-01

Subduction zones experience a spectrum of slip phenomena, ranging from large devastating megathrust earthquakes to aseismic slow slip events. Slow slip events, lasting hours to years and being perceptible only by instruments, are believed to have the capability to induce large earthquakes. It is also repeatedly proposed that such slow events are controlled by fluid-rock interactions along the subduction interface, thus calling for development of fully coupled seismo-hydro-mechanical modeling approaches to identify their physics and controlling parameters. We present a newly developed finite difference visco-elasto-plastic numerical code with marker-in-cell technique, which fully couples mechanical deformation and fluid flow. We use this to investigate how the presence of fluids in the pore space of a (de)compacting rock matrix affects elastic stress accumulation and release along a fluid-bearing subduction interface. The model simulates the spontaneous occurrence of quasi-periodic slow slip phenomena along self-consistently forming highly localized shearbands, which accommodate shear displacement between two plates. The produced elastic rebound events show a slip velocity on the order of cm/yr, which is in good agreement with measured data. The governing gradual strength decrease along the slowly propagating shear bands is related to a drop in total pressure caused by shear localization at nearly constant (slightly decreasing) fluid pressure. Gradual reduction of the difference between the total and fluid pressure decreases brittle/plastic strength of fluid-bearing rocks along the shear bands, thus providing a dynamic feedback mechanism for the accumulated elastic stress release at the subduction interface.

Carbon Dioxide - rock interaction: from molecular observations to theorised interactions in fluid-rock systems

NASA Astrophysics Data System (ADS)

Calcara, Massimo; Borgia, Andrea

2013-04-01

Current global warming theories have produced some benefits: among them, detailed studies on CO2 and its properties, possible applications and perspectives. Starting from its use as a "green solvent" (for instance in decaffeination process), to enhance system in oil recovery, to capture and storage enough amount of CO2 in geological horizon. So, a great debate is centred around this molecule. One More useful research in natural horizon studies is its theorised use in Enhanced Geothermal Systems with CO2 as the only working fluid. In any case, the CO2 characteristics should be deeply understood, before injecting a molecule prone to change easily its aggregation state at relatively shallow depth. CO2 Rock interaction becomes therefore a focal point in approaching research sectors linked in some manner to natural or induced presence of carbon dioxide in geological horizons. Possible chemical interactions between fluids and solids have always been a central topic in defining evolution of the system as a whole in terms of dissolutions, reactions, secondary mineral formation and, in case of whichever plant, scaling. Questions arise in case of presence of CO2 with host rocks. Chemical and molecular properties are strategic. CO2 Rock interactions are based on eventual solubility capability of pure liquid and supercritical CO2 seeking and eventually quantifying its polar and/or ionic solvent capabilities. Single molecule at STP condition is linear, with central carbon atom and oxygen atoms at opposite site on a straight line with a planar angle. It has a quadrupolar moment due to the electronegativity difference between carbon and oxygen. As soon as CO2 forms bond with water, it deforms even at atmospheric pressure, assuming an induced dipole moment with a value around 0.02 Debye. Hydrated CO2 forms a hydrophilic bond; it deforms with an angle of 178 degrees. Pure CO2 forms self aggregates. In the simplest case a dimer, with two molecules of CO2 exerting mutual attraction and forming at a first impact a structure defined parallel or slipped parallel or a more stable T shaped. As soon as pressure is applied, density changes and appears a stable (induced) dipole moment 0.22 Debye: phase changes and CO2 dipole moment reaches 0.85 Debye dipole moment. Pure CO2, here the only liquid phase, assumes Lewis acid/base properties. Polar solvent properties seem to be real, and some experiments have observed this characteristics. This stated, present work try to show computer aided simulation in chemical and physical evolution of a portion of rock with liquid and supercritical CO2, with and without water, in granite and oceanic basalt formations.

Sulfur isotopes in Icelandic thermal fluids

NASA Astrophysics Data System (ADS)

Gunnarsson-Robin, Jóhann; Stefánsson, Andri; Ono, Shuhei; Torssander, Peter

2017-10-01

Multiple sulfur isotope compositions of thermal fluids from Iceland were measured in order to evaluate the sources and reactions of sulfur and sulfur isotope fractionation in geothermal systems at Icelandic divergent plate boundaries, characterized by MORB-like basalts. The geothermal systems studied had a wide range of reservoir temperatures of 56-296 °C and Cl concentrations of 18-21,000 ppm. Dissolved sulfide (∑ S- II) and SO4 concentrations in liquid water measured < 0.01-165 ppm and 1.3-300 ppm, respectively, and H2S(g) concentrations in the vapor 4.9-2000 ppm. The δ34S and Δ33S values for different phases and oxidation states were highly variable: δ34S∑ S- II = - 11.6 to 10.5‰ (n = 99), Δ33S∑ S- II = - 0.12 to 0.00‰ (n = 45), δ34SSO4 = - 1.0 to 24.9‰ (n = 125), Δ33SSO4 = - 0.04 to 0.02‰ (n = 50), δ34SH2S(g) = - 2.6 to 5.9‰ (n = 112) and Δ33SH2S(g) = - 0.03 to 0.00‰ (n = 56). The multiple sulfur isotope values of the thermal fluids are interpreted to reflect various sources of sulfur in the fluids, as well as isotope fractionation occurring within the geothermal systems associated with fluid-rock interaction, boiling and oxidation and reduction reactions. The results of isotope geochemical modeling demonstrate that the sources of S- II in the thermal fluid are leaching of basalt (MORB) and seawater SO4 reduction for saline systems with insignificant magma gas input, and that the observed ranges of δ34S and Δ33S for ∑ S- II and H2S(g) reflect isotope fractionation between minerals and aqueous and gaseous species upon fluid-rock interaction and boiling. The sources of SO4 are taken to be multiple, including oxidation of S- II originating from basalt, leaching of SVI from the basalts and the seawater itself in the case of saline systems. In low-temperature fluids, the δ34S and Δ33S values reflect the various sources of sulfur. For high-temperature fluids, fluid-rock interaction, ∑ S- II oxidation and SO4 reduction and sulfide and sulfate mineral formation result in a large range of δ34S and Δ33S values for ∑ S- II and SO4 in the fluids, highlighting the importance and effects of chemical reactions on the isotope systematics of reactive elements like sulfur. Such effects needed to be quantified in order to reveal the various sources of an element.

Zinc and germanium in the sedimentary rocks of Gale Crater on Mars indicate hydrothermal enrichment followed by diagenetic fractionation

NASA Astrophysics Data System (ADS)

Berger, Jeff A.; Schmidt, Mariek E.; Gellert, Ralf; Boyd, Nicholas I.; Desouza, Elstan D.; Flemming, Roberta L.; Izawa, Matthew R. M.; Ming, Douglas W.; Perrett, Glynis M.; Rampe, Elizabeth B.; Thompson, Lucy M.; VanBommel, Scott J. V.; Yen, Albert S.

2017-08-01

Zinc and germanium enrichments have been discovered in sedimentary rocks in Gale Crater, Mars, by the Alpha Particle X-ray Spectrometer on the rover Curiosity. Concentrations of Zn (910 ± 840 ppm) and Ge (65 ± 58 ppm) are tens to hundreds of times greater than in Martian meteorites and estimates for average silicate Mars. Enrichments occur in diverse rocks including minimally to extensively altered basaltic and alkalic sedimentary rocks. The magnitude of the enrichments indicates hydrothermal fluids, but Curiosity has not discovered unambiguous hydrothermal mineral assemblages. We propose that Zn- and Ge-rich hydrothermal deposits in the source region were dispersed in siliciclastic sediments during transport into the crater. Subsequent diagenetic mobilization and fractionation of Zn and Ge is evident in a Zn-rich sandstone (Windjana; Zn 4000 ppm, Ge 85 ppm) and associated Cl-rich vein (Stephen; Zn 8000 ppm, Ge 60 ppm), in Ge-rich veins (Garden City; Zn 2200 ppm, Ge 650 ppm), and in silica-rich alteration haloes leached of Zn (30-200 ppm). In moderately to highly altered silica-rich rocks, Ge remained immobile relative to leached elements (Fe, Mn, Mg, and Ca), consistent with fluid interaction at pH ≪ 7. In contrast, crosscutting Ge-rich veins at Garden City suggest aqueous mobilization as Ge-F complexes at pH < 2.5. Multiple jarosite detections by the CheMin X-ray diffractometer and variable Zn concentrations indicate diagenesis of lower Mount Sharp bedrock under acidic conditions. The enrichment and fractionation of Zn and Ge constrains fluid events affecting Gale sediments and can aid in unraveling fluid histories as Curiosity's traverse continues.

Aqueous fluid composition in CI chondritic materials: Chemical equilibrium assessments in closed systems

NASA Astrophysics Data System (ADS)

Zolotov, Mikhail Yu.

2012-08-01

Solids of nearly solar composition have interacted with aqueous fluids on carbonaceous asteroids, icy moons, and trans-neptunian objects. These processes altered mineralogy of accreted materials together with compositions of aqueous and gaseous phases. We evaluated chemistry of aqueous solutions coexisted with CI-type chondritic solids through calculations of chemical equilibria in closed water-rock-gas systems at different compositions of initial fluids, water/rock mass ratios (0.1-1000), temperatures (<350 °C), and pressures (<2 kbars). The calculations show that fluid compositions are mainly affected by solubilities of solids, the speciation of chlorine in initial water-rock mixtures, and the occurrence of Na-bearing secondary minerals such as saponite. The major species in modeled alkaline solutions are Na+, Cl-, CO32-,HCO3-, K+, OH-, H2, and CO2. Aqueous species of Mg, Fe, Ca, Mn, Al, Ni, Cr, S, and P are not abundant in these fluids owing to low solubility of corresponding solids. Typical NaCl type alkaline fluids coexist with saponite-bearing mineralogy that usually present in aqueously altered chondrites. A common occurrence of these fluids is consistent with the composition of grains emitted from Enceladus. Na-rich fluids with abundant CO32-,HCO3-, and OH- anions coexist with secondary mineralogy depleted in Na. The Na2CO3 and NaHCO3 type fluids could form via accretion of cometary ices. NaOH type fluids form in reduced environments and may locally occur on parent bodies of CR carbonaceous chondrites. Supposed melting of accreted HCl-bearing ices leads to early acidic fluids enriched in Mg, Fe and other metals, consistent with signs of low-pH alteration in chondrites. Neutralization of these solutions leads to alkaline Na-rich fluids. Sulfate species have negligible concentrations in closed systems, which remain reduced, especially at elevated pressures created by forming H2 gas. Hydrogen, CO2, and H2O dominate in the gaseous phase, though the abundance of methane cannot be fairly estimated.

Acidic Fluids Across Mars: Detections of Magnesium-Nickel Sulfates

NASA Technical Reports Server (NTRS)

Yen, A. S.; Ming, D. W.; Gellert, R.; Mittlefehldt, D. W.; Rampe, E. B.; Vaniman, D. T.; Thompson, L. M.; Morris, R. V.; Clark, B. C.; VanBommel, S. J.

2017-01-01

Calcium, magnesium and ferric iron sulfates have been detected by the instrument suites on the Mars rovers. A subset of the magnesium sulfates show clear associations with nickel. These associations indicate Ni(2+) co-precipitation with or substitution for Mg(2+) from sulfate-saturated solutions. Nickel is ex-tracted from primary rocks almost exclusively at pH values less than 6, constraining the formation of these Mg-Ni sulfates to mildly to strongly acidic conditions. There is clear evidence for aqueous alteration at the rim of Endeavour Crater (Meridiani Planum), in the Murray formation mudstone (Gale Crater), and near Home Plate (Gusev Crater). The discovery of Mg-Ni sulfates at these locations indicates a history of fluid-rock interactions at low pH.

Estimation of reactive surface area using a combined method of laboratory analyses and digital image processing

NASA Astrophysics Data System (ADS)

Ma, Jin; Kong, Xiang-Zhao; Saar, Martin O.

2017-04-01

Fluid-rock interactions play an important role in the engineering processes such as chemical stimulation of enhanced geothermal systems and carbon capture, utilization, and storage. However, these interactions highly depend on the accessible reactive surface area of the minerals that are generally poorly constrained for natural geologic samples. In particular, quantifying surface area of each reacting mineral within whole rock samples is challenging due to the heterogeneous distribution of minerals and pore space. In this study, detailed laboratory analyses were performed on sandstone samples from deep geothermal sites in Lithuania. We measure specific surface area of whole rock samples using a gas adsorption method (so-called B.E.T.) with N2 at a temperature of 77.3K. We also quantify their porosity and pore size distribution by a Helium gas pycnometer and a Hg porosimetry, respectively. Rock compositions are determined by a combination of X-ray fluorescence (XRF) and quantitative scanning electron microscopy (SEM) - Energy-dispersive X-ray spectroscopy (EDS), which are later geometrically mapped on images of two-dimensional SEM- Backscattered electrons (BSE) with a resolution of 1.2 μm and three-dimensional micro-CT with a resolution of 10.3 μm to produce a digital mineral map for further constraining the accessibility of reactive minerals. Moreover, we attempt to link the whole rock porosity, pore size distribution, and B.E.T. specific surface area with the digital mineral maps. We anticipate these necessary analyses to provide in-depth understanding of fluid sample chemistry from later hydrothermal reactive flow-through experiments on whole rock samples at elevated pressure and temperature.

A review of porosity-generating mechanisms in crustal shear zones

NASA Astrophysics Data System (ADS)

Fusseis, F.; Regenauer-Lieb, K.; Revets, S.

2009-04-01

Knowledge of the spatiotemporal characteristics of permeability is critical for the understanding of fluid migration in rocks. In diagenetic and metamorphic rocks different porosity-generating mechanisms contribute to permeability and so influence fluid migration and fluid/rock interaction. However, little is known about their relative contributions to the porosity architecture of a rock in a tectono-metamorphic environment. This presentation reviews porosity-generating mechanisms that affect fluid migration in shear zones, the most important crustal fluid conduits, in the context of the tectonometamorphic evolution of rocks. Mechanisms that generate porosity can be classified in a) those that involve the direct action of a fluid, b) processes in which a fluid partakes or that are supported by a fluid or c) mechanism that do not involve a fluid. a) Hydraulic fracturing, where it happens through the formation of tensile fractures, occurs where pore fluid pressures equalize the combined lithostatic pressure and strength of the rock (Etheridge et al., 1984, Cox & Etheridge, 1989, Oliver, 1996). Here an internally released (devolatilisation reactions, e.g., Rumble, 1994, Hacker, 1997, Yardley, 1997 and references therein) or externally derived (infiltrating from metamorphic, magmatic or meteoric sources, Baumgartner et al., 1997, Jamtveit et al., 1997, Thompson, 1997, Gleeson et al., 2003) fluid directly causes the mechanical failure of a rock. Where a fluid is in chemical disequilibrium with a rock (undersaturated with regard to a chemical species) minerals will be dissolved, generating dissolution porosity. Rocks ‘leached' by the removal of chemical components by vast amounts of fluid are reported to lose up to 60% of their original volume (e.g., Kerrich et al., 1984, McCaig 1988). Dissolution porosity is probably an underrated porosity-generating mechanism. It can be expected along the entire metamorphic evolution, including diagenesis (Higgs et al., 2007) and weathering (e.g., Holdren & Berner, 1979, Berner & Holdren, 1979). b) Fluids contribute to replacement porosity by acting as agents providing chemical components for replacement reactions (e.g. cation exchange in feldspars). Porosity results from changes in molar volume between reactants and products and dissolution (Walker et al., 1995, Putnis, 2002, Putnis et al., 2007). Porosity generated this way is restricted to individual mineral grains, however, these may make up significant proportions of a rock. Where a fluid is involved in metamorphic reactions volume changes arise (Hacker et al., 1997). During devolatilisation reactions these are negative; porosity is generated directly as the reaction progresses (Rumble et al., 1982, Oliver et al., 1990, Rumble 1994). During rehydration or recarbonation the volume changes are positive, which creates stresses on the grain scale which potentially cause fracturing of individual grains (Jamtveit et al., 2007). A mechanical process generating porosity is creep cavitation, which is associated with viscous grain boundary sliding. Cavities form at stress concentrations in crystals and along their boundaries as well as at triple junctions in grain aggregates essentially by diffusion, which is supported by the presence of a fluid (Dyson et al., 1976, Kassner & Hayes, 2003, Rybacki et al., 2008, Fusseis et al., in review). c) Where rocks are subjected to temperature changes (e.g., during burial, contact metamorphism or exhumation) individual minerals expand or contract heterogeneously (e.g., Fei, 1995). Anisotropic thermal expansion creates stresses on the grain scale resulting in cracks, which form porosity without the evolvement of a fluid (e.g., Sprunt & Brace, 1974, Kranz, 1983). Despite these mechanisms have been described in the literature, they were rarely discussed in the context of their potential to affect permeability (with the exception of hydraulic fracturing). However, all of them commonly occur in crustal shear zones. It seems reasonable to assume that the total porosity in shear zones is the sum of porosities generated by all of these mechanisms, and that the individual porosities have different effects on permeability. We propose that a fundamental understanding of the porosity evolution in a shear zone can be derived from an assessment of the stress-temperature-fluid/rock chemistry-time path during the tectonometamorphic history of a rock. In this contribution we present a first evaluation of typical porosity-permeability evolutions. We furthermore present a new generation of numerical experiments that allows the quantitative assessment of the roles of the thermal, chemical and mechanical generation of porosity and their feedbacks on the evolution of shear zones. References: Baumgartner et al., 1997, in Jamtveit & Yardley, eds. Fluid flow and transport in rocks, 83-98, Berner & Holdren, 1979, Geochim Cosmochim Acta 43, 1173-1186, Cox & Etheridge, 1989, JSG 11/1-2, 147-162, Etheridge et al., 1984, JGR 89/B6, 4344-4358, Fei, 1995, in Ahrens, ed. Mineral Physics and Crystallography, AGU, 29-44, Fusseis et al., in review, Nature, Gleeson et al., 2003, Geofluids 3, 33-48, Hacker, 1997, JGR 102/B11, 24459-24467, Higgs et al., 2007, J Sed Res 77, 1003-1025, Holdren & Berner, 1979, Geochim Cosmochim Acta 43, 1161-1171, Jamtveit et al., 1997, in Jamtveit & Yardley, eds. Fluid flow and transport in rocks, 57-82, Jamtveit et al., 2007, EPSL 267, 620-627, Dyson et al., 1976, Proc Roy Soc London A, 349/1657, 245-259, Kassner & Hayes, 2003, Int J Plasticity 19, 1715-1748, Kerrich et al., 1984, JGR 89/B6, 4331-4343, Kranz, 1983, Tectonophysics 100, 449-480, McCaig 1988, Geology 16, 867-870, Oliver, 1996, JMG 14, 477-492, Oliver et al., 1990, JMG 8, 311-331, Putnis, 2002, Min Magaz 66/5, 689-708, Putnis et al., 2007, Lithos 2007, 10-18, Rumble et al., 1982, Amer J Sci 282, 886-919, Rumble, 1994, JGR 99/B8, 15499-15502, Rybacki et al., 2008, GRL 35, L04304, Sprunt & Brace, 1974, Int J Rock Mech Min Sci & Geomech Abstr 11, 139-150, Thompson, 1997, in Jamtveit & Yardley, eds. Fluid flow and transport in rocks, 297-314, Walker et al., 1995, Min Magaz 95, 505-534, Yardley, 1997, in Jamtveit & Yardley, eds. Fluid flow and transport in rocks, 99-121.

Modelling Earthquakes Using a Poro-Elastic Two-Phase Flow Formulation

NASA Astrophysics Data System (ADS)

Petrini, C.; Gerya, T.; van Dinther, Y.; Connolly, J. A.; Madonna, C.

2017-12-01

Seismicity along subduction zones ranges from large devastating megathrust earthquakes to aseismic slow slip events. These different slip phenomena are widely believed to be influenced by fluids and interactions of fluids with the host rock. To understand the slip or strain mode along the megathrust interface, it is thus crucial to understand the role of fluids. Considering the spatiotemporal limitations of observations, a promising approach is to develop a numerical model that couples the deformation of both fluids and solids in a single framework. The objective of this study is the development of such a seismo-hydro-mechanical approach and the subsequent identification of parameters that control the mode of slip. We present a newly developed finite difference visco-elasto-plastic numerical code with marker-in-cell technique, which fully couples inertial mechanical deformation and fluid flow. It allows for the accurate treatment of localised brittle/plastic deformation through global iterations. To accurately simulate both long- and short-term deformation an adaptive time step is introduced. This makes it possible to resolve seismic event with time steps on the order of milliseconds. We use this new tool to investigate how the presence of fluids in the pore space of an visco-elasto-brittle/plastic (de)compacting rock matrix affects elastic stress accumulation and release along a fluid-bearing subduction interface. The model is able to simulate spontaneous quasi-periodic seismic events, nucleating near the brittle-ductile transition zone, along self-consistently forming highly localized ruptures, which accommodate shear displacement between two plates. The generated elastic rebound events show slip velocities on the order of m/s. The governing gradual strength decrease along the propagating fracture is related to a drop in total pressure due to shear localization in combination with an increase in fluid pressure due to elastic compaction of the pore space in a rock with low permeability (6e-19 m2). Reduction of the differential pressure decreases brittle/plastic strength of fluid-bearing rocks along the rupture, thus providing a dynamic feedback mechanism for the accumulated elastic stress release at the subduction interface.

Effects of CO2-rich fluids on a redbed reservoir: outcrop analogue study from the Buntsandstein (Germany)

NASA Astrophysics Data System (ADS)

Kasch, N.; Kley, J.; Koester, J.; van Geldern, R.; Wehrer, M.; Wendler, J.

2010-12-01

Carbon capture and storage (CCS) in saline aquifers will induce fluid-rock interactions, with effects on the mineralogy and physical properties of the reservoir. These effects are difficult to study in real reservoirs. Outcrop analogues provide access to relatively large rock volumes, but it may be difficult to prove that CO2 was involved in the mineral reactions observed. We present circumstantial evidence for the presence of CO2-rich fluids during the alteration of Triassic Buntsandstein redbeds from Germany. Fluid-rock interaction there is evidenced by localized bleaching of the red sandstones in fringes of a few mm to a few cm width along joints and fine cracks. The fringes can be traced along individual joints for a few dm to m. 3D geometric analysis on a cm scale shows that the bleached cracks form a complex interconnected network. On the outcrop scale, bleaching is essentially restricted to one north-trending joint set which is parallel to Miocene basalt dikes in the area. In underground salt mines, the dikes have caused bleaching of potassium salt minerals along their contacts. In the same mines CO2 is found trapped within rock salt along north-trending fractures, sometimes causing violent gas eruptions during mining operations. Together, these observations suggest that bleaching along north-trending joints in the Buntsandstein is causally related to the migration of CO2-rich fluids associated with the basalt volcanism. Today, CO2 ascends in CO2-enriched waters. We analyzed 12 samples of such waters. Their δ18O values correspond to meteoric waters. The δ13C (DIC) values of four water samples show signatures typical of volcanogenic CO2. Five samples contain mixed signals of volcanogenic and carbonatic CO2 or biogenic CO2 from soil. Volcanogenic and carbonatic CO2 are restricted to waters interpreted to rise along NW-SE striking basement faults. The switch of preferential fluid channeling from N-trending fractures in Tertiary time to NW-trending fractures today is compatible with a coeval rotation of the largest horizontal stress from N to NW, corroborating the control of fluid pathways by the contemporary stress field. Geochemical analyses of the bleached fringes show that bleaching causes a decrease in Fe and Mn due to hematite dissolution. Using cathodoluminescence microscopy and -spectroscopy combined with electron microprobe analysis and stable carbon isotopes, we detected two major fluid-mineral interactions probably involving CO2: (1) precipitation of zoned, joint-filling calcites and pore-filling calcite cements, the latter replacing an earlier dolomite, and (2) alkali feldspar alteration. We interpret Fe-rich calcite crystal cores to reflect incorporation of iron released by coeval bleaching during the dolomite-calcite transformation. This recrystallisation was associated with a volume increase, possibly suggesting some degree of sealing and enhanced retention of CO2. On the other hand, feldspar alteration has a destructing effect on the feldspar grains, implying that bleaching creates pore space.

Meteoric water in metamorphic core complexes

NASA Astrophysics Data System (ADS)

Teyssier, Christian; Mulch, Andreas

2015-04-01

The trace of surface water has been found in all detachment shear zones that bound the Cordilleran metamorphic core complexes of North America. DeltaD values of mica fish in detachment mylonites demonstrate that these synkinematic minerals grew in the presence of meteoric water. Typically deltaD values are very negative (-120 to -160 per mil) corresponding to deltaD values of water that are < -100 per mil given the temperature of water-mica isotopic equilibration (300-500C). From British Columbia (Canada) to Nevada (USA) detachment systems bound a series of core complexes: the Thor-Odin, Valhalla, Kettle-Okanogan, Bitterroot -Anaconda, Pioneer, Raft River, Ruby Mountain, and Snake Range. The bounding shear zones range in thickness from ~100 m to ~1 km, and within the shear zones, meteoric water signature is recognized over 10s to 100s of meters beneath the detachment fault. The age of shearing ranges generally from Eocene in the N (~50-45 Ma) to Oligo-Miocene in the S (25-15 Ma). DeltaD water values derived from mica fish in shear zones are consistent with supradetachment basin records of the same age brackets and can be used for paleoaltimetry if coeval isotopic records from near sea level are available. Results show that a wave of topography (typically 4000-5000 m) developed from N to S along the Cordillera belt from Eocene to Miocene, accompanied by the propagation of extensional deformation and volcanic activity. In addition, each detachment system informs a particular extensional detachment process. For example, the thick Thor-Odin detachment shear zone provides sufficient age resolution to indicate the downward propagation of shearing and the progressive incorporation of footwall rocks into the hanging wall. The Kettle detachment provides a clear illustration of the dependence of fluid circulation on dynamic recrystallization processes. The Raft River system consists of a thick Eocene shear zone that was overprinted by Miocene shearing; channels of meteoric paleofluids can be traced into a zone of pervasive flow (in the direction of extension from W to E) in which a high transient geotherm is preserved. In the Snake Range the pattern of meteoric signature is consistent with the expected diachronous fluid-rock interaction that would be expected from a rolling-hinge detachment; in the arched section of the detachment meteoric fluid-rock interaction was cut-off early, while the long-lived portion of the E-dipping detachment continued to receive surface fluids. In summary, the hydrology of extending crust involves circulation of surface fluids through the upper crust to the ductile detachment shear zones in the root system of normal faults. Synkinematic hydrous phases encapsulate the signature of meteoric fluids and indicate high-elevation catchment areas for the Cordillera, with development of topography from N to S over Cenozoic time. Meteoric fluids leave a distinct stable isotopic signature that tracks the spatial and temporal interaction among fluid, rock, and structures/ microstructures, and provides useful fingerprints of the inter-relationship between tectonics and crustal hydrology.

Linking the optically monitored channel evolution with tremor like seismic activity during aero-fracturing in a very fine granular medium

NASA Astrophysics Data System (ADS)

Turkaya, Semih; Toussaint, Renaud; Kvalheim Eriksen, Fredrik; Zecevic, Megan; Daniel, Guillaume

2014-05-01

The characterization and comprehension of rock deformation processes due to fluid flow is a challenging problem with numerous applications in many fields. This phenomenon has received an ever-increasing attention in Earth Science, Physics, with many applications in natural hazard understanding, mitigation or forecast (e.g. earthquakes, landslides with hydrological control,volcanic eruptions), or in the industry, as CO2 sequestration. Even though the fluids and rocks are relatively easier to understand individually, the coupled behaviour of porous media with a dynamic fluid flow makes the system difficult to comprehend. The dynamic interaction between flow and the porous media, rapid changes in the local porosity due to the compaction and migration of the porous material, fracturing due to the momentum exchange in fast flow, make understanding of such a complex system a challenge. In this study, analogue models are developed to predict and control the mechanical stability of rock and soil formations during the injection or extraction of fluids. The models are constructed and calibrated based on the experimental data acquired. This experimental data obtained from solid-fluid interaction are monitored using a combination of techniques, both from geophysics and from experimental fluid mechanics. The experimental setup consists of a rectangular Hele-Shaw cell with three closed boundaries and one semi-permeable boundary which enables the flow of the fluid but not the solid particles. Non expanding polystyrene beads around 80μm size are used as solid particles and air is used as the intruding fluid. During the experiments, the fluid is injected steadily (or injected and suddenly stopped to see the pushback in a setup with four impermeable boundaries) into the system from the point opposite to the semi-permeable boundary so that the fluid penetrates into the solid and makes a way via creating channels, fractures or directly using the pore network to the semi-permeable boundary. The acoustic signals emitted during the mentioned solid-fluid interactions are recorded by various sensors - i.e. Piezoelectric Shock Accelerometer (Freq. range: 1Hz - 26kHz) and Piezoelectrical Sensors (Freq. range: 100kHz - 1MHz) with a sampling rate of 1MHz - on the Hele-Shaw cell. After the experiment, those signals are compared and investigated further in both time and frequency domains. Moreover, by using different techniques localization of the acoustic emissions are done and compared. Furthermore, during the experiments pictures of the Hele-Shaw cell are taken using a high speed camera. Thus, it is possible to visualize the solid-fluid interaction and to process images to gather information about the mechanical properties of the solid partition. The link between the visual and the mechanical wave signals is investigated. The spectrum of the signal is observed to be strongly affected by the size and shape of deforming channels created during the process. The power of the recorded signal is related to the integrated deformation rate in the process. Fast avalanches and rearrangements of grains at small scales are related to high frequency (above 10 kHz) acoustic emissions.

Modeling of viscoelastic properties of nonpermeable porous rocks saturated with highly viscous fluid at seismic frequencies at the core scale

NASA Astrophysics Data System (ADS)

Wang, Zizhen; Schmitt, Douglas R.; Wang, Ruihe

2017-08-01

A core scale modeling method for viscoelastic properties of rocks saturated with viscous fluid at low frequencies is developed based on the stress-strain method. The elastic moduli dispersion of viscous fluid is described by the Maxwell's spring-dash pot model. Based on this modeling method, we numerically test the effects of frequency, fluid viscosity, porosity, pore size, and pore aspect ratio on the storage moduli and the stress-strain phase lag of saturated rocks. And we also compared the modeling results to the Hashin-Shtrikman bounds and the coherent potential approximation (CPA). The dynamic moduli calculated from the modeling are lower than the predictions of CPA, and both of these fall between the Hashin-Shtrikman bounds. The modeling results indicate that the frequency and the fluid viscosity have similar effects on the dynamic moduli dispersion of fully saturated rocks. We observed the Debye peak in the phase lag variation with the change of frequency and viscosity. The pore structure parameters, such as porosity, pore size, and aspect ratio affect the rock frame stiffness and result in different viscoelastic behaviors of the saturated rocks. The stress-strain phase lags are larger with smaller stiffness contrasts between the rock frame and the pore fluid. The viscoelastic properties of saturated rocks are more sensitive to aspect ratio compared to other pore structure parameters. The results suggest that significant seismic dispersion (at about 50-200 Hz) might be expected for both compressional and shear waves passing through rocks saturated with highly viscous fluids.