in particular the leached layer theory. Most importantly, our data provide critical evidence for 51 a single mechanism based on interfacial dissolution-reprecipitation. This concept not only 52 unifies weathering processes for the first time, but we also suggest that nanoscale-surface 53 processes can have a potentially negative impact on CO 2 uptake associated with chemical 54 weathering. The results in this study, when combined with recently published research on 55 fluid-assisted mineral replacement reactions, supports the idea that dissolution-reprecipitation 56 is a universal mechanism controlling fluid-mineral interactions . 57Based on this we propose the existence of a chemical weathering continuum based solely on 58 the interfacial dissolution-reprecipitation mechanism. 59 3

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The Focused Ion Beam (FIB) tool has been successfully used as both a means to prepare site-specific TEM foils for subsequent analysis by TEM, as well as a stand-alone instrument for micromachining of materials. TEM foil preparation with FIB technique has drastically changed traditional TEM specimen preparation because it allows site-specific foil preparation. FIB consists of cutting electron transparent foils through Ga-ion milling on a bulk sample. Optical microscopy together with a micromanipulator is used to transfer the foil from the specimen to a TEM grid coated with a holey carbon support film. No further carbon coating is required. This novel technology offers significant benefits in precision and speed of preparing site-specific TEM foils from inclusions in minerals, grain boundaries, microfossils, thin films on substrates and various coatings. FIB cut TEM foils can be investigated with modern TEM techniques such as various diffraction techniques, analytical electron microscopy (AEM) including line scan and elemental mapping, electron energy-loss spectroscopy (EELS) and high-resolution electron microscopy (HREM). With the FIB instrument (FEI FIB200) operated since fall 2002 at GFZ Potsdam we have prepared and investigated several hundreds of high quality TEM foils from silicates, carbonates, metals alloys, ceramic materials and diamond.

[1] To specify quantitatively the effect of pressure and water weakening on the flow strength of feldspar we performed triaxial creep experiments in a gas deformation apparatus at temperatures of 1000-1150°C, confining pressures of 100-450 MPa, and axial stresses of 10-400 MPa, resulting in strain rates of $6 Â 10 À7 to 3 Â 10 À3 s À1 . Dense samples with a grain size of $3 mm were prepared by hot-isostatic pressing of anorthite glass powder. Hydrous samples contain about 0.33 ± 0.14 wt % H 2 O and dry specimens 0.0005-0.02 wt % H 2 O. The estimated residual glass content of wet samples is <2 vol %. Samples deformed by grain boundary diffusion-controlled creep at low stresses and dislocation creep at stresses^150 MPa. We estimate an activation volume of V % 24 cm 3 mol À1 for anhydrous samples deforming in diffusion creep. For wet samples, deformed in hydrous conditions with varying buffers fixing oxygen fugacity, the activation volume is about 38 cm 3 mol À1 . Creep rate of hydrous anorthite aggregates depends on water fugacity raised to a power of r = 1.0 ± 0.3, suggesting hydrolysis of oxygen bonds. Considering the effect of activation volume and water fugacity on extrapolation of constitutive laws to conditions prevailing in the continental lower crust, viscosities of hydrous feldspar aggregates increase by a factor of <3.Citation: Rybacki, E., M. Gottschalk, R. Wirth, and G. Dresen (2006), Influence of water fugacity and activation volume on the flow properties of fine-grained anorthite aggregates,

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Here we examine Fe speciation within Fe-encrusted biofilms formed during 2-month seafloor incubations of sulfide mineral assemblages at the Main Endeavor Segment of the Juan de Fuca Ridge. The biofilms were distributed heterogeneously across the surface of the incubated sulfide and composed primarily of particles with a twisted stalk morphology resembling those produced by some aerobic Fe-oxidizing microorganisms. Our objectives were to determine the form of biofilm-associated Fe, and identify the sulfide minerals associated with microbial growth. We used micro-focused synchrotron-radiation X-ray fluorescence mapping (lXRF), X-ray absorption spectroscopy (lTXAFS), and X-ray diffraction (lXRD) in conjunction with focused ion beam (FIB) sectioning, and high resolution transmission electron microscopy (HRTEM). The chemical and mineralogical composition of an Fe-encrusted biofilm was queried at different spatial scales, and the spatial relationship between primary sulfide and secondary oxyhydroxide minerals was resolved. The Fe-encrusted biofilms formed preferentially at pyrrhotite-rich (Fe 1Àx S, 0 6 x 6 0.2) regions of the incubated chimney sulfide. At the nanometer spatial scale, particles within the biofilm exhibiting lattice fringing and diffraction patterns consistent with 2-line ferrihydrite were identified infrequently. At the micron spatial scale, Fe lEXAFS spectroscopy and lXRD measurements indicate that the dominant form of biofilm Fe is a short-range ordered Fe oxyhydroxide characterized by pervasive edge-sharing Fe-O 6 octahedral linkages. Double corner-sharing Fe-O 6 linkages, which are common to Fe oxyhydroxide mineral structures of 2-line ferrihydrite, 6-line ferrihydrite, and goethite, were not detected in the biogenic iron oxyhydroxide (BIO). The suspended development of the BIO mineral structure is consistent with Fe(III) hydrolysis and polymerization in the presence of high concentrations of Fe-complexing ligands. We hypothesize that microbiologically produced Fe-complexing ligands may play critical roles in both the delivery of Fe(II) to oxidases, and the limited Fe(III) oxyhydroxide crystallinity observed within the biofilm. Our research provides insight into the structure and formation of naturally occurring, microbiologically produced Fe oxyhydroxide minerals in the deep-sea. We describe the initiation of microbial seafloor weathering, and the morphological and mineralogical signals that result from that process. Our observations provide a starting point from which progressively older and more extensively weathered seafloor sulfide minerals may be examined, with the ultimate goal of improved interpretation of ancient microbial processes and associated biological signatures.