Browsing by Author "Schwarzenbach, Esther M."
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- Effect of water activity on rates of serpentinization of olivineLamadrid, Hector M.; Rimstidt, J. Donald; Schwarzenbach, Esther M.; Klein, Frieder; Ulrich, Sarah; Dolocan, Andrei; Bodnar, Robert J. (Nature, 2017-07-14)The hydrothermal alteration of mantle rocks (referred to as serpentinization) occurs in submarine environments extending from mid-ocean ridges to subduction zones. Serpentinization affects the physical and chemical properties of oceanic lithosphere, represents one of the major mechanisms driving mass exchange between the mantle and the Earth’s surface, and is central to current origin of life hypotheses as well as the search for microbial life on the icy moons of Jupiter and Saturn. In spite of increasing interest in the serpentinization process by researchers in diverse fields, the rates of serpentinization and the controlling factors are poorly understood. Here we use a novel in situ experimental method involving olivine micro-reactors and show that the rate of serpentinization is strongly controlled by the salinity (water activity) of the reacting fluid and demonstrate that the rate of serpentinization of olivine slows down as salinity increases and H₂O activity decreases.
- Sulfur cycling within subduction zones: Insights from exhumed mafic and ultramafic slabSchwarzenbach, Esther M.; Li, J.; John, T.; Caddick, Mark J.; Petroff, Matthew; Gill, Benjamin C. (2019-04)Subduction zones significantly control the geochemical cycling and elemental transfer between the surficial andinternal reservoirs of the Earth. Amongst the most hydrophile elements sulfur is the fifth most abundant element on Earth. Subduction of oceanic lithosphere transports sulfur together with numerous other elements into Earth’s mantle and releases sulfur-bearing fluids modifying the redox state and the chemical budget of the mantle. Here, we present bulk rock sulfur geochemical data of exhumed mafic and ultramafic slab material to provide new insights into the sulfur cycle within subduction zones. Our data shows that small bodies of detached slab material are subject to metasomatic processes during exhumation (e.g., within a subduction zone channel), where fluids thatare circulating along the plate interface cause sulfur mobilization. Sulfur mobilization is thereby more pronounced within serpentinites compared to mafic rocks. In contrast, large sequences of obducted ophiolitic sections can retain their seafloor alteration signatures, particularly at moderate peak P-T conditions. Furthermore, dehydration-related vein systems in blue schists provide evidence for sulfur transfer within the subducted oceanic crust. These vein systems carry distinct sulfur isotopic signatures that reflect dehydration processes of underlying sequences suggesting a negative sulfur isotope signature of the dehydrating subducting slab. Our data provides new insights into the sulfur transfer between the slab and the mantle wedge, which may eventually control the formation of arc-related melts and porphyry deposits.
- Sulphur and carbon cycling in the subduction zone melangeSchwarzenbach, Esther M.; Caddick, Mark J.; Petroff, Matthew; Gill, Benjamin C.; Cooperdock, Emily H. G.; Barnes, Jaime D. (Springer Nature, 2018-10-19)Subduction zones impose an important control on the geochemical cycling between the surficial and internal reservoirs of the Earth. Sulphur and carbon are transferred into Earth's mantle by subduction of pelagic sediments and altered oceanic lithosphere. Release of oxidizing sulphate- and carbonate-bearing fluids modifies the redox state of the mantle and the chemical budget of subduction zones. Yet, the mechanisms of sulphur and carbon cycling within subduction zones are still unclear, in part because data are typically derived from arc volcanoes where fluid compositions are modified during transport through the mantle wedge. We determined the bulk rock elemental, and sulphur and carbon isotope compositions of exhumed ultramafic and metabasic rocks from Syros, Greece. Comparison of isotopic data with major and trace element compositions indicates seawater alteration and chemical exchange with sediment-derived fluids within the subduction zone channel. We show that small bodies of detached slab material are subject to metasomatic processes during exhumation, in contrast to large sequences of obducted ophiolitic sections that retain their seafloor alteration signatures. In particular, fluids circulating along the plate interface can cause sulphur mobilization during several stages of exhumation within high-pressure rocks. This takes place more pervasively in serpentinites compared to mafic rocks.