Origin of salt giants in abyssal serpentinite systems

Scribano, Vittorio; Carbone, Serafina; Manuella, Fabio Carmelo; Hovland, Martin; Rueslåtten, Håkon; Johnsen, Hans-K.

doi:10.1007/s00531-017-1448-y

Cited by 32 publications

(38 citation statements)

References 88 publications

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“…13 Geofluids ones ( [39,52,54,55,58,80]; Hovland et al, 2018). Carrying this idea a step further, Scribano et al [81] suggested that the formation of a certain subseafloor giant salt deposit in deep marine basins may be genetically related to the serpentinization of ultramafic rocks. In the present context of passive margin hyperextension, mantle exhumation, and subsequent fluid circulation, several authors have already proposed that seawater-driven serpentinization may contribute to the transport of dissolved elements (Mg, Cr, and V; [82]).…”

Section: What About the Regional Circulation Of Primary Brines?mentioning

confidence: 99%

Nature and Origin of Mineralizing Fluids in Hyperextensional Systems: The Case of Cretaceous Mg Metasomatism in the Pyrenees

et al. 2019

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During the Albian, the hyperextension of the Pyrenean passive margin led to a hyperthinning of the continental crust and the subsequent subcontinental mantle exhumation. The giant Trimouns talc-chlorite deposit represents the most prominent occurrence of Albian metasomatism in the Pyrenees, with the occurrence of the largest talc deposit worldwide. Consequently, this deposit, which is located on a fault zone and a lithological contact, represents one of the major drains at the scale of the Pyrenees and one of the best geological targets in order to determine the origin(s) of the fluid(s) that circulated during this period. Talc-chlorite ore is characterized by the presence of brines trapped in dolomite, quartz, and calcite fluid inclusions in the vicinity of the talc-rich zone. Considered as being responsible for the formation of talc, these fluids may be interpreted in several ways: (i) primary brines expelled from Triassic evaporites, (ii) secondary brines produced through halite leaching by diagenetic/metamorphic fluids, and (iii) brines derived from seawater serpentinization of mantle rocks. Stable isotope analyses (δ13C, δ18O, δD, and δ37Cl) and Cl/Br ratio measurements in fluid inclusions and their host minerals were carried out in order to determine the origin of the fluid(s) involved in the formation of the ore deposit. The data are consistent with a primary brine origin for the mineralizing fluid, which could have been expelled from the Triassic levels. Other hypotheses have been tested, for example, the production of brines via the seawater concentration during serpentinization. The geochemical proxies used in this study provide equivocal results. The first hypothesis is by far the most realistic one considering the numerous occurrences of Trias formations nearby, their deformation during the extension, and the drainage of the expulsed brines as evidenced by the high-salinity fluid inclusions found all around the deposit. Alternatively, the exhumation of the mantle is considered as a major source of heat and stress that favored brine migration along the major shear zones. Our results fit well with brine circulation in a hyperextensional geodynamic context, which is related to the formation of the talc-chlorite ore, the thinning of the continental crust, and the exhumation of the subcontinental mantle, in accordance with recent works.

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Section: What About the Regional Circulation Of Primary Brines?mentioning

confidence: 99%

Nature and Origin of Mineralizing Fluids in Hyperextensional Systems: The Case of Cretaceous Mg Metasomatism in the Pyrenees

et al. 2019

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“…For example, Hovland et al [7,8] suggested that salt deposits may be related to submarine hydrothermal activity, especially when the solution attains supercritical conditions. Similarly, Scribano et al [9], approaching the problem from a petrologic perspective, suggested the salt giant origin in abyssal serpentinite systems. This paper is aimed at evaluating whether these challenging viewpoints are applicable to the Mediterranean salt deposits.…”

Section: Introductionmentioning

confidence: 94%

“…Most salts separated from the reactant seawater, being deeply incorporated in the fractured host rock, will hardly be re-dissolved in the ocean (such a fate would have been inevitable, on the contrary, in case of exfoliation-type processes moving along flat reaction fronts). Salts and brines remain, therefore, indefinitely trapped in pores and fractures in the newly formed serpentinite as long as no perturbation events will occur [9]. Reasonable inference in such "hidden salts" [8] derives from the interpretation of geophysical data as, for instance, from electromagnetic records acquired in convergent geodynamic settings [69].…”

Section: Beyond the Evaporite Model: The Serpentinite Feet Of Salt Gimentioning

confidence: 99%

“…Moreover, clayey submarine ridges, sometimes exceeding hundreds km in length, can form in those cases where closely juxtaposed mud volcanoes were aligned along major fracture systems, as, for example, an extinct slow-spreading ridge [31]. Mud volcanoes often emit saline brines and hydrocarbons, possibly originating from buried serpentinites [9,32], and such fluids may be associated with other hydrothermal components [33,34]. Normal sediments (e.g., pelagic oozes, chalk) [35,36] and fragments of the wall rocks (likewise xenoliths in volcanic rocks) [37] are usually intercalated with the effusive hydrothermal clays which therefore may resemble a tectonic mélange.…”

Section: Introductionmentioning

confidence: 99%

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Tracking the Serpentinite Feet of the Mediterranean Salt Giant

2018

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Interpretation of seismic profiles and results of scientific drillings in the Mediterranean subseafloor provided indication of gigantic salt deposits which rarely crop out on land, such as in Sicily. The salt giants were ascribed to the desiccation, driven by the solar energy, of the entire basin. Nevertheless, the evaporite model hardly explains deep-sea salt deposits. This paper considers a different hypothesis suggesting that seawater reached NaCl saturation during serpentinization of ultramafic rocks. Solid salts and brine pockets were buried within the serpentinite bodies being later (e.g., in the Messinian) released, due to serpentinite breakdown, and discharged at seafloor as hydrothermal heavy brines. Therefore, sea-bottom layers of brine at gypsum and halite saturation were formed. The model is applicable to the Mediterranean area since geophysical data revealed relicts of an aged (hence serpentinized) oceanic lithosphere, of Tethyan affinity, both in its western “Atlantic” extension (Gulf of Cádiz) and in eastern basins, and xenoliths from Hyblean diatremes (Sicily) provided evidence of buried serpentinites in the central area. In addition, the buoyant behavior of muddled serpentinite and salts (and hydrocarbons) gave rise to many composite diapirs throughout the Mediterranean area. Thus, the Mediterranean “salt giant” consists of several independent geobodies of serpentinite and salts.

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“…Only higher salt concentrations within the pore fluids would reduce heat flow for identical subseafloor depths of the reflections. One potential source for such excess salt could be found associated with the serpentinization reactions at depth as described, for example, by Scribano et al (2017), which could be leached and brought to the surface by hydrothermal venting. Active faulting can reach into the upper mantle as shown from the seismicity study by Hutchinson et al (2019) and is likely to partake in, if not, facilitate hydrothermal circulation.…”

Section: Bsr-like Events and Faulting On The Abyssal Plainmentioning

confidence: 99%

Focused Fluid Flow Along the Nootka Fault Zone and Continental Slope, Explorer‐Juan de Fuca Plate Boundary

Riedel

Rohr

Spence

et al. 2020

Geochem Geophys Geosyst

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Geophysical and geochemical data indicate there is abundant fluid expulsion in the Nootka fault zone (NFZ) between the Juan de Fuca and Explorer plates and the Nootka continental slope. Here we combine observations from >20 years of investigations to demonstrate the nature of fluid‐flow along the NFZ, which is the seismically most active region off Vancouver Island. Seismicity reaching down to the upper mantle is linked to near‐seafloor manifestation of fluid flow through a network of faults. Along the two main fault traces, seismic reflection data imaged bright spots 100–300 m below seafloor that lie above changes in basement topography. The bright spots are conformable to sediment layering, show opposite‐to‐seafloor reflection polarity, and are associated with frequency reduction and velocity push‐down indicating the presence of gas in the sediments. Two seafloor mounds ~15 km seaward of the Nootka slope are underlain by deep, nonconformable high‐amplitude reflective zones. Measurements in the water column above one mound revealed a plume of warm water, and bottom‐video observations imaged hydrothermal vent system biota. Pore fluids from a core at this mound contain predominately microbial methane (C1) with a high proportion of ethane (C2) yielding C1/C2 ratios <500 indicating a possible slight contribution from a deep source. We infer the reflective zones beneath the two mounds are basaltic intrusions that create hydrothermal circulation within the overlying sediments. Across the Nootka continental slope, gas hydrate‐related bottom‐simulating reflectors are widespread and occur at depths indicating heat flow values of 80–90 mW/m2.

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Origin of salt giants in abyssal serpentinite systems

Cited by 32 publications

References 88 publications

Nature and Origin of Mineralizing Fluids in Hyperextensional Systems: The Case of Cretaceous Mg Metasomatism in the Pyrenees

Nature and Origin of Mineralizing Fluids in Hyperextensional Systems: The Case of Cretaceous Mg Metasomatism in the Pyrenees

Tracking the Serpentinite Feet of the Mediterranean Salt Giant

Focused Fluid Flow Along the Nootka Fault Zone and Continental Slope, Explorer‐Juan de Fuca Plate Boundary

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