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Governing processes of fluid mediated rock transformation, from experimental studies to characterization in nature

Fluid-mediated rock transformation, also called mineralogical replacement, are ubiquitous instances of fluid-rock interaction in the crust. With recent developments in measurement techniques, the characterization and understanding of replacement has potential to unravel fluid dynamics and migration pathways, the volume of reactive fluids involved, the deformation associated to the reaction, along with the thermodynamical properties of the reaction. The ambition of the proposed session is to draw a picture of the current state of knowledge about the driving processes of fluid-mediated transformation in the diagenetic domain and in the low metamorphic conditions, with or without associated deformation. We welcome any contribution focusing on methodological, experimental, analytical or nature-related studies of mineralogical replacements and associated phenomenon.

Co-organized by TS10
Convener: Nicolas Beaudoin | Co-conveners: Daniel Koehn, Sandra Piazolo, Christine V. Putnis, Renaud Toussaint
Presentations
| Wed, 25 May, 13:20–14:50 (CEST)
 
Room -2.47/48

Wed, 25 May, 13:20–14:50

Chairpersons: Christine V. Putnis, Daniel Koehn, Nicolas Beaudoin

13:20–13:22
Introduction to session

13:22–13:32
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EGU22-8313
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solicited
Helen E. King et al.

Isotopic doping is a powerful tool to identify newly formed mineral phases during fluid-mediated mineral transformation reactions. In particular, Raman spectroscopy of isotopically doped minerals can reveal incorporation of the isotopes into the structure of the minerals themselves, rather than enrichment of a fluid within a pore (1). In fluid mediated mineral transformations, dissolution of the reactant mineral enables O isotope exchange between water and dissolved oxyanions (e.g., CO3). Incorporation of the isotopically enriched oxyanions can result in crystals with different isotopic enrichments if the rate of the exchange in the fluid occurs on a similar timescale to the duration of the experiment and the crystals form at different times. This means that the amount of isotopic enrichment can be used as an internal stop clock and demonstrates the relative timings of precipitation in ex-situ analysis (2). In this presentation we will use previous examples to explore how fluid-mediated mineral transformation reactions can be followed using isotopic enrichment traced with Raman spectroscopy, including new data after deformation experiments. Using new data obtained from in-situ analysis of 18O exchange into dissolved carbonate species we will also show the importance of the solution chemistry on exchange kinetics in the fluid. In addition, we will use density functional theory calculations to explore how the mineral structure may influence the isotopic signature obtained from the Raman spectra. 

(1) King H.E. & Geisler T. (2018) Minerals, 8. 158.

(2) King H.E., Mattner D.C., Plümper O., Geisler T., Putnis A., (2014) Crystal Growth & Design, 14, 3910.

How to cite: King, H. E., Živković, A., Ohl, M., and Plümper, O.: Using Raman spectra of isotopically enriched transformation products to trace mineral reactions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8313, https://doi.org/10.5194/egusphere-egu22-8313, 2022.

13:32–13:38
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EGU22-2307
Andrew Putnis et al.

It is well-established that the mechanism of re-equilibration of a mineral assemblage at temperatures where the spatial scale of solid-state diffusion is restricted to intra-crystalline processes, is by dissolution-transport-precipitation. When the dissolution and precipitation steps are spatially coupled, pseudomorphic mineral replacement, in the absence of deformation, is a common observation in both nature and experiment. External stress appears to uncouple the dissolution and precipitation steps, inevitably leading to mass transport and dissolution-precipitation creep as the dominant deformation mechanism. The precipitation process involves nucleation and, in deforming rocks, the minimisation of surface energy leads towards textural equilibration and metamorphic differentiation. The overall process can be considered as a sequence of recrystallisation steps that lead to minimisation of chemical and textural components of the overall free energy. Examples will be given from metamorphic reactions, diagenesis and sub-solidus texture formation in igneous rocks.

How to cite: Putnis, A., Moore, J., and Austrheim, H.: Fluid-rock reaction mechanisms and the inevitable consequences for mass transport and texture formation., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2307, https://doi.org/10.5194/egusphere-egu22-2307, 2022.

13:38–13:44
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EGU22-10527
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ECS
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Virtual presentation
Benjamin Lefeuvre et al.

Hydrothermal dolomitization of limestones, i.e. fluid-mediated stoichiometric substitution Casolid ↔ Mgfluid replacing CaCO3 with dolomite CaMg(CO3)2, plays a key role in the structural integrity and permeability of the rock that can have dramatic consequences for earthquake hazards, reservoir quality, civil engineering. This particular reaction creates km-scale geobodies usually related to ore deposits or hydrocarbons, and being very efficient bodies for carbon sequestration. As for numerous hydrothermal reactions, various chemo-physical models built from chemical analysis and experiments in analogous replacement compete to explain this mineralogical transformation. Yet, relevant comparison to natural systems remains limited, and the way to explain the creation of large dolomite geobodies remains unexplained. Only recently dolomitization has been successfully recreated in laboratory under a reasonable timescale [1, 2], a few hours to a week according to the fluid reactivity.

This project proposes to use non-destructive imagery methods (xCT) coupled with hydrothermal reactors to reproduce dolomitization in-situ. We choose to study two natural samples representing two end-members: (1) Carrara marble which contains homogeneous polymineralic calcite grains; (2) Layens limestones (French Pyrenees) which is a marble already dolomitized naturally. These two samples were incubated in hydrothermal Teflon reactors in a Mg-enriched aqueous solution [3] at 200°C for different time steps. Microtomography have been acquired at various stages of the reaction, allowing us to track the propagation of the dolomitization front within the samples. This approach allows us to mimic natural dolomitization over time and provides a detailed study of the morphology of the reaction front between calcite and dolomite. Quantifying and describing the microstructures related to replacements (pores, fractures, grains orientation and size) help unravelling how dolomitization can propagate in nature.

 

 

References

[1] L. Jonas, T. Müller, R. Dohmen, L. Baumgartner, B. Pultlitz, Geology (2015)

[2] J. Weber, M. Cheshire, M. Bleuel, D. Mildner, Y-J. Chang, A. Ievlev, K. Littrell, J. Ilavsky, A. Stack, L. Anovitz, Geochimica et Cosmochimica Acta 303 (2021)

[3] V. Vandeginste, O. Snell, M. Hall, E. Steer, A. Vandeginste, Nature communications (2019)

How to cite: Lefeuvre, B., Beaudoin, N., Centrella, S., and Callot, J.-P.: What control hydrothermal dolomitization? Experimental replacement with time-step monitoring by X-ray microtomography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10527, https://doi.org/10.5194/egusphere-egu22-10527, 2022.

13:44–13:50
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EGU22-2331
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ECS
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On-site presentation
Lorena Hernández-Filiberto et al.

The presence of aqueous fluids is ubiquitous in the Earth’s crust. Grain boundaries play an important role in enabling fluids to penetrate through the rock system. Their influence in fluid-rock reactions that might lead to relevant processes such as mineral replacements, the formation of new minerals and dissolution of others, element mobilization, variations in rock density, changes in stress distribution, mass transfer, etc., are commonly observed in many rock samples as well as generated and observed in laboratory experiments. As a product of these reactions, porosity and fractures might also be generated and potentially allow the fluid to penetrate even further.

Here we present our first analyses on different rock samples where the fluid-rock interaction has been induced through hydrothermal laboratory experiments using either Carrara Marble or plagioclase samples. The evidence for such interactions having previously occurred in natural rocks has been investigated in a sequence of a granulite rock samples from the Bergen Arcs in Norway. Using light microscopy as well as SEM, EDX and Electron Microprobe analysis we have investigated possible fluid pathways and evidence of fluid-mineral reactions as well as the mechanisms that could explain such processes.

How to cite: Hernández-Filiberto, L., Putnis, C. V., Putnis, A., and Austrheim, H.: Grain boundaries as reactive fluid pathways in rocks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2331, https://doi.org/10.5194/egusphere-egu22-2331, 2022.

13:50–13:56
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EGU22-1987
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ECS
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Highlight
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Virtual presentation
Xiongjie Zhou and Regina Katsman

Methane (CH4) bubbles in muddy aquatic sediments threaten climate sustainability and sediment mechanical stability. Mechanical response of muddy sediment to bubble growth is described by Linear Elastic Fracture Mechanics (LEFM). Minor roles of mechanical sediment characteristics in CH4 bubble solute supply and growth rates were quantified compared to biogeochemical controls. We investigate them using a coupled single-bubble mechanical/reaction-transport numerical and analytical models. We demonstrate that inner pressure of the growing bubble at fracturing, concentration at its surface, bubble size and spatial location, are uniquely defined by Fracture Toughness. However, a temporal evolution of the bubble inner pressure at expansion between the fracturing events depends on Young’s modulus. Fracture Toughness and Young’s modulus thus play complementary, spatial and temporal, roles in bubble growth. Their proportionality suggested by LEFM manages the bubble growth rates.  Fracture Toughness controls development of longer flatter bubbles in the deeper sediments. A substantial role of mechanical muddy sediment characteristics in the CH4 bubble growth dynamics and solute exchange is demonstrated, comparable to the role of the biogeochemical controls. Their contribution to emergence of “no-growth” and competitive bubble growth conditions, affecting a macro-scale gas dynamics are discussed that encourages a proper experimental evaluation of muddy sediment mechanical characteristics.

How to cite: Zhou, X. and Katsman, R.: Mechanical controls on methane bubble solute exchange within muddy aquatic sediments and its growth characteristics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1987, https://doi.org/10.5194/egusphere-egu22-1987, 2022.

13:56–14:02
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EGU22-2361
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ECS
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On-site presentation
Maude Julia et al.

Calcium carbonates are ubiquitous minerals in nature and have been recently studied for potential environmental remediation as a toxic element retainer following reaction with contaminated water. This work aims to study the effect of cadmium ions, a major pollutant in soil and waterways, on calcium carbonate dissolution and growth using different experimental and analytical methods. Firstly, calcite growth and dissolution in the presence of varied Cd2+ concentrations have been observed with in situ atomic force microscopy (AFM). Then hydrothermal experiments have been conducted to compare calcite and Carrara marble samples to study the effect of grain boundaries on calcium carbonate dissolution in the presence of solutions containing Cd2+. Results indicate that a new (Ca,Cd)CO3 phase is formed on the calcite surfaces that become increasingly covered and possibly passivated by the presence of this new layer. This is observed in both the AFM experiments as well as hydrothermal experiments using calcite crystals. However, the grain boundaries within Carrara marble act as fluid pathways within the rock allowing access for the Cd – rich solutions to penetrate within the sample. Surface passivation compared with coupled dissolution-precipitation replacement reactions are investigated in terms of molar volume changes and solubility differences between parent (CaCO3) and product ((Ca,Cd)CO3) phases as well as reaction kinetic considerations.

How to cite: Julia, M., V.Putnis, C., E.King, H., and Renard, F.: The effect of cadmium on calcium carbonate growth and dissolution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2361, https://doi.org/10.5194/egusphere-egu22-2361, 2022.

14:02–14:08
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EGU22-8827
Chen Zhu et al.

We carried out 137Ba and 34S-spiked experiments and measured barium attachment and detachment fluxes from and to barite crystal surfaces in solutions at solubility equilibrium with barite. The [Ba]/[SO4] ratios in solutions varied from 0.06 to 52. Both attachment and detachment fluxes increase with [Ba]/[SO4] ratios. As expected, since the solutions were near solubility equilibrium ( ), the attachment and detachment fluxes were nearly equal and net fluxes or reaction rates were zero.

The isotope flux data together with step velocity data from AFM studies by Kowacz et al. (2007) were simultaneously fit into the Zhang and Nancollas (1998) process-based AB crystal growth model, which describes crystal growth and dissolution through nucleation and propagation of kink sites. The Newton Conjugate Gradient Trust Region algorithm was used for simultaneously and optimally regressing both attachment and detachment rate coefficients. Simultaneous fitting step velocity data of Kowacz et al. (2007) significantly reduced the number of non-unique solutions. The excellent agreement indicates that attachment and detachment fluxes and step velocity are consistent and complement each other.

The results of this study demonstrate significant isotopic changes in solutions and solids from mineral-fluid interactions at solubility equilibrium. The Zhang and Nancollas (1998) model has been used as a foundation for interpreting isotopes and trace element data. Our results therefore have significant implications for extending it to the understanding in diagenetic and low temperature metamorphic processes.

How to cite: Zhu, C., kang, J., Bracco, J., and gong, L.: Barite reactivity at solubility equilibrium as a function of [Ba2+]/[SO42-] ratios, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8827, https://doi.org/10.5194/egusphere-egu22-8827, 2022.

14:08–14:14
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EGU22-12060
Encarnacion Ruiz-Agudo et al.

Hydration of anhydrous minerals such as periclase (MgO) is a common process during retrograde metamorphism (mainly serpentinization) and, generally, during fluid-rock interactions. Changes in mineralogy due to hydration reactions may have an impact on rock properties (Kuleci et al. 2016) and implications for the rheology of the crustal rocks (Yardley et al., 2014). Also, the hydration of periclase is an important industrial reaction, particularly in the field of cement and lime mortars. Dolomitic lime used for building purposes contains significant amounts of periclase, which hydrates at a slower rate than lime (CaO), and commonly delayed MgO hydration and swelling occurs in hardened mortar eventually resulting in fracture formation (Jug et al. 2007). It also negatively impacts the durability of MgO-based refractory ceramics (Amaral et al., 2011). Hydration of periclase involves a volume increase of ~110%, resulting in very high stresses if the process occurs in a confined space, which can lead to reaction-induced fracturing of crustal rocks (Zheng et al., 2018). Hence, understanding the mechanisms of periclase hydration is crucial for technical applications, such as avoiding dolomitic lime mortars fracturing due to swelling, and for understanding the feedback between hydration and rock properties in nature.

 

The hydration of periclase to brucite was investigated experimentally. Here we show, using in situ atomic force microscopy (AFM) and complementary techniques, that upon the reaction of periclase cleavage surfaces with deionized water, spherical nanoparticles form initially oriented along the periclase step edges, subsequently covering the whole periclase surface. With increasing reaction time, nanoparticles develop straight facets and acquire hexagonal features consistent with the structure of brucite. Additionally, differences in adhesion between the outer part and the centre of the nanoparticles were observed, suggesting the initial formation of a precursor (possibly amorphous) that subsequently transforms into crystalline brucite. These results reveal a nonclassical particle-mediated reaction mechanism for the hydration of periclase into brucite.

 

Amaral, L. F., Oliveira, I. R., Bonadia, P., Salomão, R., & Pandolfelli, V. C. (2011). Chelants to inhibit magnesia (MgO) hydration. Ceramics International, 37(5), 1537-1542.

Jug K, Heidberg B, Bredow T (2007) Cyclic cluster study on the formation of brucite from periclase and water. J Phys Chem C 111(35):13,103–13,108

Kuleci, H., Schmidt, C., Rybacki, E., Petrishcheva, E., & Abart, R. (2016). Hydration of periclase at 350 °C to 620 °C and 200 MPa: Experimental calibration of reaction rate. Mineralogy and Petrology, 110(1), 1–10.

Yardley, B.W.D., Rhede, D., Heinrich, W.,  (2014). Rates of Retrograde Metamorphism and Their Implications for the Rheology of the Crust: An Experimental Study. Journal of Petrology, 55, (3), 623-641.

Zheng, X., Cordonnier, B., Zhu, W., Renard, F., & Jamtveit, B. (2018). Effects of confinement on reaction‐induced fracturing during hydration of periclase. Geochemistry, Geophysics, Geosystems., 19, 2661–2672.

 

How to cite: Ruiz-Agudo, E., Ruiz-Agudo, C., Lázaro-Calisalvo, C., Álvarez-Lloret, P., and Rodríguez-Navarro, C.: Nanoscale observations of periclase (MgO) hydration , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12060, https://doi.org/10.5194/egusphere-egu22-12060, 2022.

14:14–14:20
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EGU22-8368
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On-site presentation
Stephen Centrella et al.

Using the example of dolomitization where calcite is replaced by dolomite, estimation of the fluid composition in equilibrium with dolomite for major and trace elements was estimated based on EPMA and LA-ICP-MS data using a mass balance approach. The method consists in an analytical quantification of the mass transfer between the original calcite and the newly formed dolomite giving us which elements are coming in and out of the system. Chemical composition of the aqueous fluid in equilibrium with dolomite can be estimated such as the partition coefficient for each element involved in the reaction. This approach was tested using three existing datasets obtained from natural dolomite and original limestone in both Jurassic limestones of the Layens anticline in the Pyrenees (France), and two from the Middle Devonian Presqu’ile barrier from Pine Point (Canada). These are completed with data acquired in Cretaceous limestones of the Benicassim area of the Maestrat Basin (Spain). Using the result obtained with the mass balance calculation, the amount of fluid required to dolomitized a fixed amount of limestone can be obtained for different fluid source (brine and seawater). Results show that the four dolomitization reactions have similar solid volume variation (-14 to -10 vol.%) and the fluid in equilibrium with the dolomite have also similar concentration in trace element. Estimation of the partition coefficients for all trace elements for the three regions were determined and compared.

How to cite: Centrella, S., Hoareau, G., Beaudoin, N. E., Motte, G., Lanari, P., and Piccoli, F.: Estimation of the partial fluid composition after fluid-rock interaction: from mass balance calculations with an application to natural dolomitization, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8368, https://doi.org/10.5194/egusphere-egu22-8368, 2022.

14:20–14:26
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EGU22-10265
Daniel Koehn et al.

Fluid mixing is interpreted as one of the main drivers for the development of hydrothermal mineralization whereby the actual physical processes that lead to mineral precipitation, and thus ore localization, are poorly understood. In this contribution, we will shed light on the mechanisms that are active in a simple fluid-mixing scenario by simulating the infiltration of a metal-rich fluid into a rock saturated with seawater derived pore-fluid and study the developing mineral saturation patterns.

We combine an advection-diffusion code in the microstructural model Elle with the geochemical module iphreeqc to study the distribution of enhanced saturation indices during fluid mixing. In the simulations the hot highly saline metal rich fluid enters the small 5x5m system through two high-permeable faults from below and percolates into the pore space. For the fluid we solve transport of temperature and 12 chemical species, giving us a fluid composition at every node in the model. We then use iphreeqc to calculate the mineral saturation indices for minerals in every node and we use these values as a proxy for reaction localization. In order to better understand the effects of fluid mixing on mineralization we specifically look at the saturation index of Baryte, which is a mineral in the investigated system that only precipitates when elements of both fluids are present. Our simulations show that the saturation index of Baryte is at a maximum in a fluid comprising 90 to 80 percent of pore fluid and 10 to 20 percent of metal rich fluid. During the infiltration into the permeable faults, the metal rich fluid pushes the pore fluid away, and mixing is occurring at the interface between the two fluids and is driven mainly by diffusion. With temperature diffusion being three orders of magnitude faster than matter diffusion, the temperature is negligible for the mixing, which is only driven by matter diffusion at the model scale.

We will show that two types of reactive waves with high saturation indices of Baryte develop in the system: travelling and stable waves. Traveling waves progress during advection through the permeable faults and layers and are potentially too fast for minerals to precipitate. Therefore, these areas probably remain permeable in a natural system during advection dominated transport. In contrast, areas with low fluid velocities, and hence low advection, are diffusion dominated with reaction waves that are stable over a long time. These areas are prone for mineral reactions, because there is enough time for the reactions to take place. Stable reactive waves and thus areas of mineralization are fault walls, areas below seals, and areas between two faults where fluid velocities are diverging. We discuss the implications of our results in light of hydrothermal mineral systems.

How to cite: Koehn, D., Ulrich, K., Toussaint, R., Mullen, G., and Boyce, A.: The role of stable and traveling reactive waves in mineralization, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10265, https://doi.org/10.5194/egusphere-egu22-10265, 2022.

14:26–14:32
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EGU22-2293
Christine V. Putnis and Encarnación Ruiz-Agudo

Mineral-fluid replacement reactions occur ubiquitously throughout the crust of the Earth, often resulting in the formation of nanoparticles. Recent research highlights the formation of nanoparticles1, especially in the light of mineral/crystal growth by non-classical growth mechanisms, whereby solids form from prenucleation species or clusters within an aqueous solution from which solid nanoparticles precipitate. This is very often related to the dissolution of an existing mineral/solid phase that is coupled at the mineral-fluid interface with the precipitation of a new more stable phase2. This process will occur wherever aqueous fluids can penetrate and react with constituent minerals of a rock, that is, along fractures, grain boundaries and initial or reaction-induced interconnected porosity, all potential pathways for fluid-mediated reactions. Examples given here highlight fluid pathways and subsequent nanoparticle formation, an understanding of which can be useful for potential environmental remediation strategies, such as carbon mineralization and toxic element sequestration. Recent advances in analytical techniques, such as advances in atomic force microscopy, advanced scanning and transmission microscopies, are enabling the imaging of nanoparticles. Examples presented illustrate the conditions under which nanoparticles form during the coupling of dissolution and precipitation and enable a better understanding of the mechanisms that drive fluid-mineral reactions.

References

1Putnis C.V. and Ruiz-Agudo E. 2021. Nanoparticles formed during mineral-fluid interactions. Chem. Geol. 586, 120614.

2Ruiz-Agudo E., Putnis C.V., Putnis A. 2014. Coupled dissolution and precipitation at mineral-fluid interfaces. Chem. Geol., 383, 132-146.

How to cite: Putnis, C. V. and Ruiz-Agudo, E.: Nanoparticles formed during mineral-fluid interactions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2293, https://doi.org/10.5194/egusphere-egu22-2293, 2022.

14:32–14:38
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EGU22-11236
Renaud Toussaint et al.

We propose a subcritical fracture growth model, coupled with the elastic redistribution of the acting mechanical stress along rugous rupture fronts. We show the ability of this model to quantitatively reproduce the intermittent dynamics of cracks propagating along weak disordered interfaces [1]. We assume that the fracture energy of such interfaces (in the sense of a critical energy release rate) follows a spatially correlated normal distribution. We compare various statistical features from the obtained fracture dynamics to that from experimental cracks propagating in sintered polymethylmethacrylate (PMMA) interfaces. In previous works, it has been demonstrated that such approach could reproduce the mean advance of fractures and their local front velocity distribution. Here, we go further by showing that the proposed model also quantitatively accounts for the complex self-affine scaling morphology of crack fronts and their temporal evolution, for the spatial and temporal correlations of the local velocity fields and for the avalanches size distribution of the intermittent growth dynamics. We thus provide new evidence that Arrhenius-like subcritical growth laws are particularly suitable for the description of creeping cracks.

Reference:

[1] Vincent-Dospital, T., Cochard, A., Santucci, S., Måløy, K.J., Toussaint, R.,  Thermally activated intermittent dynamics of creeping crack fronts along disordered interfaces. Sci Rep 11, 20418 (2021). https://doi.org/10.1038/s41598-021-98556-x

How to cite: Toussaint, R., Vincent-Dospital, T., Cochard, A., Santucci, S., and Måløy, K. J.: Fracture, mechanics and chemistry: Intermittency and avalanche statistics in thermally activated creeping crack fronts along disordered interfaces, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11236, https://doi.org/10.5194/egusphere-egu22-11236, 2022.

14:38–14:44
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EGU22-10618
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Virtual presentation
Ana P. Jesus et al.

The Samail ophiolite in Oman was sampled by scientific drilling targeting crucial sections of the oceanic crust and mantle during the Oman Drilling Project- OmanDP [1]. Drillhole CM1A aimed at characterizing the transition from the lower crust to the mantle Moho Transition Zone (MTZ), where both magmatic and hydrothermal exchanges took place. Four magmatic sequences were defined: SI- Layered Gabbro, with thin wehrlite and dunite layers (1.5-160.2 m); SII- fully serpentinized Dunite (160.2-250.0 m); SIII- Dunite with rodingitized gabbro (250.0-311.0 m) and; SIV- Mantle, harzburgite with opx-dunite levels (311.0-404.2 m).

We present a sulfur and Sr isotope profile to characterize the sulfur cycling during hydrothermal alteration within the MTZ (SI-SIII). Acid Volatile Sulfides (AVS), Cr-Reducible Sulfur (CRS) and acid-soluble sulfate (SO4) were sequentially extracted and analyzed for δ34S on the same whole-rock powders analyzed for Sr isotopes.

The crust-mantle transition records extreme and often decoupled variations in sulfur (δ34S=-25.8 to +56.9‰) and 87Sr/86Sr (0.703088-0.711688) signatures. Total extracted sulfur from sulfide (TS=AVS+CRS) contents increase gradually from the top to the bottom of SI from ca ~65-2820 ppm, to maximum of 5043 ppm in a Cpx-Pl-dunite layer ca. 16 m above SII. Sulfide assemblages comprises magmatic pyrrhotite+pentlandite+chalcopyrite and secondary pyrrhotite (in Fe-serpentine pseudomorphs)+bornite+cubanite+millerite+sphalerite±haezlewoodite. Excluding one dunite layer with δ34SAVS=+11.4‰, the δ34SAVS,CRS (-0.6 to +3.3‰) for SI are close to slightly elevated relative to mantle values. Scarce sulfates have identical δ34S relative to coexisting sulfides implying formation via abiotic oxidation of precursor sulfides. Despite widespread background alteration, olivine gabbros preserve primitive 87Sr/86Sr ratios (0.703088-0.703332) whereas serpentinised ultramafic layers have significantly more radiogenic signatures (0.707817-0.711688), close to or above Cretaceous seawater (87Sr/86Sr=0.70745). Gradual enrichment in sulfides by magmatic processes in SI, towards the MTZ, was followed by hydrothermal alteration with minor incorporation of seawater sulfate, leading to highly decoupled Sr-34S enrichment in the ultramafic layers due to their Sr-depleted nature. Narrow pegmatoid dikelets (amphibole+zoisite+prehnite+titanite) within SI have low TS (<80 ppm), mildly radiogenic 87Sr/86Sr (<0.704923) and a fracture-hosted, higher fS2sulfide assemblage (pyrite+Co-pentlandite+siegenite) with δ34SCRS down to -25.8‰ implying low-T (<110 C), open-system bacterial sulfate reduction (BSR) processes.

The Dunite Sequence-SII has decreasing TS towards its interior (2-1253 ppm), consistent with extensive desulfurization producing an assemblage (awaruite+pentlandite+Co-pentlandite+magnetite, coexisting with brucite), during extremely low oxygen and sulfur fugacities typical of early serpentinization stages. SIII is highly heterogenous and S-depleted (3-623 ppm), with a heazlewoodite-bearing assemblage and lower 87Sr/86Sr (0.703952) relative to SII dunites (0.707065). The MTZ upper limit (SII) marks the onset of large shifts in S-isotopic composition, tendentially increasing downward throughout SII (δ34SCRS=-2.5, +15.6‰; δ34SSO4=+19.2, +32.4‰) and SIII (δ34SCRS=+1.4, +56.9‰; δ34SSO4=+19.4, +36.5‰). The occurrence of both sulfides and sulfates with δ34S above Cretaceous seawater sulfate (~18‰) can be explained by input of fluids at the top of SII which composition progressed towards extreme heavy values via closed system BSR during multi-staged serpentinization events.

AJ acknowledges WWU International Visiting Scholars and EU-H2020 Marie Sklodowska-Curie #894599 Fellowships, FCT-project UIDB/GEO/50019/2020 

[1] Kelemen PB, Matter JM, Teagle DAH, Coggon JA, OmanDP Science Team (2020) Proceedings of the OmanDP: College Station, TX (IODP).

How to cite: Jesus, A. P., Strauss, H., Benoit, M., Rospabé, M., Ceuleneer, G., Gonçalves, M. A., and Bosch, D.: Sulfur and strontium isotopic geochemistry of the crust-mantle transition of the Oman Ophiolite: records of fluid circulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10618, https://doi.org/10.5194/egusphere-egu22-10618, 2022.

14:44–14:50
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EGU22-7619
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ECS
Irène Aubert et al.

Normal fault zones can have a significant role on fluid flows as they can form barriers or drains (Agosta et al., 2010; Bense et al., 2013; Brogi and Novellino, 2015). In carbonates rocks, which are very sensitive to fluid-rock interactions, these fault-related fluid flows can strongly enhance or alter carbonate reservoir properties (Deville de Periere et al., 2017; Fournier and Borgomano, 2009).

This work aims at determine fluid flow evolution in a carbonate reservoir affected by a normal fault. For this purpose, we studied structural and diagenetic properties of the Esperelles normal fault and the surrounding Barremian and Aptian formations located on the northern flank of Nerthe anticline (SE France). Esperelles fault developed during the Durancian uplift (Albian) and was weakly reactivated during the opening of Liguro-Provençal basin during Oligo-Miocene times.

We defined seven different cements under cathodoluminescence (C0 to C6), their distributions along the outcrop, their geochemical properties (18O and 13C stable isotopes, Δ47 thermometry), and their ages (U-Pb). Diagenetic properties have been correlated with petrophysical measurements. We determined the paragenetic sequence, as well as the nature and temperature of the fluids that led to the formation of C1 and C6 cements. Four U-Pb ages have been obtained using an ELEMENT XR (Thermo-Fisher) SF-ICP-MS coupled to a 193 nm Excimer Laser (ESI) at CEREGE (Aix-en-Provence, France).  These ages allowed to relate the C6 cementing phase with the opening of Liguro-Provençal basin. This study shows that fault zone development impacted reservoir fluid flows, leading to significant diagenetic events and development of heterogeneous reservoir properties.

 

References

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How to cite: Aubert, I., Léonide, P., Fournier, F., Bitault, H., Lamarche, J., Godeau, N., Deschamps, P., Correa, R., and Marié, L.: Effect of normal fault activity on carbonate reservoir diagenetic evolution (Urgonian facies, SE France), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7619, https://doi.org/10.5194/egusphere-egu22-7619, 2022.