Replacive formation of sulphides in the oceanic lithosphere and the effect on rock porosity evolution

This thesis describes the replacive formation of sulfides in the oceanic lithosphere through the interplay of discharging hydrothermal fluids and seawater. Chemical and 3D analyses on sulfate chimneys showed that anhydrite precipitation and corrosion likely control porosity and sulfide formation in the chimney conduit. Batch experiments using several oceanic lithologies and a synthetic, H2S-bearing vent fluid showed that sulfide root zones were more easily formed in less reducing rock types where sulfur activity was highest. The onset of anhydrite growth in fractured basalt in a flow-through experiment was found to be only possible at temperatures above 120 degrees C and was accompanied by many Fe-bearing phases in the basalt core. The results of this thesis stress the importance of porosity for sulfide formation in hydrothermal processes

On the controls of mineral assemblages and textures in alkaline springs, Samail Ophiolite, Oman

Interactions between meteoric water and ultramafic rocks in the Oman Ophiolite generate waters of variable physicochemical characteristics. The discharge of these waters forms complex alkaline pool networks, in which mineral precipitation is triggered by mixing, evaporation, and uptake of atmospheric CO2. A systematic and colocalized sampling of waters and solids in two individual spring sites allowed us to determine the saturation state of a range of minerals and correlate them to the different water and precipitate types. We subdivided the waters of the spring sites into three distinctive types: i) Mg-type; moderately alkaline (7.9<pH<9.5), Mg2+–HCO3 −- rich waters, ii) Ca-type; hyperalkaline (pH>11.6), Ca2+–OH−-rich waters, and iii) Mix-type; alkaline to hyperalkaline (9.6 < pH < 11.5) waters with intermediate chemical composition. We first report the occurrence of hydrated magnesium (hydroxy-) carbonate phases in Mg-type waters. Nesquehonite forms in these waters via evaporation and transforms into dypingite and hydromagnesite under CO2-rich conditions. In Ca-type waters, the coupling of atmospheric CO2 uptake with evaporation leads to the formation of a calcitic crystalline crust on the air-water interface. The crusts are aragonite- and brucite-bearing, where Mg-type and Ca-type waters discharge and vigorously mix at the same pool. Unlike the Mg-type and Ca-type waters, the pools of Mix-type waters host massive aragonite-dominated deposits due to high Mg/Ca ratio that favors the growth of aragonite over calcite. The hydrodynamics during mixing spatially control brucite precipitation and restrict its formation and accumulation around specific mixing zones, where a continuous supply of Mg of inflowing Mg-type waters takes place. Crystal morphologies record the effect on the values of supersaturation and supersaturation rates in the pools due to mixing processes, evaporation and CO2 uptake. In Ca-type waters, CO2 uptake and evaporation dictate the textural characteristics of calcite both in crystalline crusts and rock coatings. Textural evolution of aragonite from crystalline sheaves to spheroidal shapes underlines the different supersaturation rates of calcium carbonate crystallization in flocculent material of Mix-type waters. Geochemical models of mixing between Mgtype and Ca-type waters revealed the evolution of mineral saturation indices under various mixing proportions, and their relation to the observed mineralogy and geochemistry of the pool waters. The thorough documentation of mineral assemblages and crystal morphologies enabled us to provide a more detailed account of how water composition, mixing, and mineral precipitation co-evolve in the alkaline spring systems, where CO2 is sequestered.The present research has been funded by the European Union Seventh Framework Programme FP7/2007-2013 under the FP7 People Program (Marie Curie Action– ITN “Abyss”) under REA grant agreement no. 608001, and the F7 Ideas: European Research Council grant PROMETHEUS under grant agreement no. 340863

Sulfidbildung durch Verdrängungsreaktionen in der Ozeanische Lithosphere und deren Auswirkung auf die Gesteinsporosität

This thesis describes the replacive formation of sulfides in the oceanic lithosphere through the interplay of discharging hydrothermal fluids and seawater. Chemical and 3D analyses on sulfate chimneys showed that anhydrite precipitation and corrosion likely control porosity and sulfide formation in the chimney conduit. Batch experiments using several oceanic lithologies and a synthetic, H2S-bearing vent fluid showed that sulfide root zones were more easily formed in less reducing rock types where sulfur activity was highest. The onset of anhydrite growth in fractured basalt in a flow-through experiment was found to be only possible at temperatures above 120 degrees C and was accompanied by many Fe-bearing phases in the basalt core. The results of this thesis stress the importance of porosity for sulfide formation in hydrothermal processes

Fluid-driven metamorphism of the continental crust governed by nanoscale fluid flow

The transport of fluids through the Earth’s crust controls the redistribution of elements to form mineral and hydrocarbon deposits, the release and sequestration of greenhouse gases, and facilitates metamorphic reactions that influence lithospheric rheology. In permeable systems with a well-connected porosity, fluid transport is largely driven by fluid pressure gradients. In less permeable rocks, deformation may induce permeability by creating interconnected heterogeneities, but without these perturbations, mass transport is limited along grain boundaries or relies on transformation processes that self-generate transient fluid pathways. The latter can facilitate large-scale fluid and mass transport in nominally impermeable rocks without large-scale fluid transport pathways. Here, we show that pervasive, fluid-driven metamorphism of crustal igneous rocks is directly coupled to the production of nanoscale porosity. Using multi-dimensional nano-imaging and molecular dynamics simulations, we demonstrate that in feldspar, the most abundant mineral family in the Earth’s crust, electrokinetic transport through reaction-induced nanopores (<100 nm) can potentially be significant. This suggests that metamorphic fluid flow and fluid-mediated mineral transformation reactions can be considerably influenced by nanofluidic transport phenomena

Mineral assemblages and geochemical profiles in alkaline springs, Samail Ophiolite, Oman

The datasets include the analysis of the chemical profiles of the collected water samples (ICP-OES, IC for chemical compositions and on-site water parameter measurements) and the mineralogical analysis of the collected solid samples (Raman, XRD) from the serpentinite-hosted alkaline springs in Oman

Graphical Representations of Adolescents' Psychophysiological Reactivity to Social Stressor Tasks: Reliability and Validity of the Chernoff Face Approach and Person-Centered Profiles for Clinical Use

Low-cost methods exist for measuring physiology when clinically assessing adolescent social anxiety. Two barriers to widespread use involve lack of (a) physiological expertise among mental health professionals, and (b) techniques for modeling individual-level physiological profiles. We require a "bridge approach" for interpreting physiology that does not require users to have a physiological background to make judgments, and is amenable to developing individual-level physiological profiles. One method-Chernoff Faces-involves graphically representing data using human facial features (eyes, nose, mouth, face shape), thus capitalizing on humans' abilities to detect even subtle variations among facial features. We examined 327 adolescents from the Tracking Adolescents' Individual Lives Survey (TRAILS) study who completed baseline social anxiety self-reports and physiological assessments within the social scenarios of the Groningen Social Stressor Task (GSST). Using heart rate (HR) norms and Chernoff Faces, 2 naive coders made judgments about graphically represented HR data and HR norms. For each adolescent, coders made 4 judgments about the features of 2 Chernoff Faces: (a) HR within the GSST and (b) aged-matched HR norms. Coders' judgments reliably and accurately identified elevated HR relative to norms. Using latent class analyses, we identified 3 profiles of Chernoff Face judgments: (a) consistently below HR norms across scenarios (n = 193); (b) above HR norms mainly when speech making (n = 35); or (c) consistently above HR norms across scenarios (n = 99). Chernoff Face judgments displayed validity evidence in relation to self-reported social anxiety and resting HR variability. This study has important implications for implementing physiology within adolescent social anxiety assessments