Nanoscale surface properties and interaction with fundamental biomolecules of chlorite and phlogopite

The surface properties of minerals have important implications in geology, environment, industry and biotechnology and for certain aspects in the research on the origin of life. This research project aims to widen the knowledge on the nanoscale surface properties of chlorite and phlogopite by means of advanced methodologies, and also to investigate the interaction of fundamental biomolecules, such as nucleotides, RNA, DNA and amino acid glycine with the surface of the selected phyllosilicates. Multiple advanced and complex experimental approaches based on scanning probe microscopy and spatially resolved spectroscopy were used and in some cases specifically developed. The results demonstrate that chlorite exposes at the surface atomically flat terraces with 0.5 nm steps typically generated by the fragmentation of the octahedral sheet of the interlayer (brucitic-type). This fragmentation at the nanoscale generates a high anisotropy and inhomogeneity with surface type and isomorphous cationic substitutions determining variations of the effective surface potential difference, ranging between 50-100 mV and 400-500 mV, when measured in air, between the TOT surface and the interlayer brucitic sheet. The surface potential was ascribed to be the driving force of the observed high affinity of the surface with the fundamental biomolecules, like single molecules of nucleotides, DNA, RNA and amino acids. Phlogopite was also observed to present an extended atomically flat surface, featuring negative surface potential values of some hundreds of millivolts and no significant local variations. Phlogopite surface was sometimes observed to present curvature features that may be ascribed to local substitutions of the interlayer cations or the presence of a crystal lattice mismatch or structural defects, such as stacking faults or dislocation loops. Surface chemistry was found similar to the bulk. The study of the interaction with nucleotides and glycine revealed a lower affinity with respect to the brucite-like surface of chlorite.

Long-term fluid circulation in extensional faults in the central Catalan Coastal Ranges: P-T constraints from neoformed chlorite and K-white mica

The neoformation of chlorite and K-white mica in fault rocks from two main faults of the central Catalan Coastal Ranges, the Vallès and the Hospital faults, has allowed us to constrain the P–T conditions during fault evolution using thermodynamic modeling. Crystallization of M1 and M2 muscovite and microcline occured as result of deuteric alteration during the exhumation of the pluton (290 °C > T > 370 °C) in the Permian. After that, three tectonic events have been distinguished. The first tectonic event, attributed to the Mesozoic rifting, is characterized by precipitation of M3 and M4 phengite together with chlorite and calcite C1 at temperatures between 190 and 310 °C. The second tectonic event attributed to the Paleogene compression has only been identified in the Hospital fault with precipitation of low-temperature calcite C2. The shortcut produced during inversion of the Vallès fault was probably the responsible for the lack of neoformed minerals within this fault. Finally, the third tectonic event, which is related to the Neogene extension, is characterized in the Vallès fault by a new generation of chlorite, associated with calcite C4 and laumontite, formed at temperatures between 125 and 190 °C in the absence of K-white mica. Differently, the Hospital fault is characterized by the precipitation of calcite C3 during the syn-rift stage at temperatures around 150 °C and by low-temperature fluids precipitating calcites C5, C6 and PC1 during the post-rift stage. During the two extensional events (Mesozoic and Neogene), faults acted as conduits for hot fluids producing anomalous high geothermal gradients (50 °C/km minimum).

A thermodynamic model for di-trioctahedral chlorite from experimental and natural data in the system MgO-FeO-Al2O3-SiO2-H2O. Applications to P-T sections and geothermometry

We present a new thermodynamic activity-composition model for di-trioctahedral chlorite in the system FeO–MgO–Al2O3–SiO2–H2O that is based on the Holland–Powell internally consistent thermodynamic data set. The model is formulated in terms of four linearly independent end-members, which are amesite, clinochlore, daphnite and sudoite. These account for the most important crystal-chemical substitutions in chlorite, the Fe–Mg, Tschermak and di-trioctahedral substitution. The ideal part of end-member activities is modeled with a mixing-on-site formalism, and non-ideality is described by a macroscopic symmetric (regular) formalism. The symmetric interaction parameters were calibrated using a set of 271 published chlorite analyses for which robust independent temperature estimates are available. In addition, adjustment of the standard state thermodynamic properties of sudoite was required to accurately reproduce experimental brackets involving sudoite. This new model was tested by calculating representative P–T sections for metasediments at low temperatures (<400 °C), in particular sudoite and chlorite bearing metapelites from Crete. Comparison between the calculated mineral assemblages and field data shows that the new model is able to predict the coexistence of chlorite and sudoite at low metamorphic temperatures. The predicted lower limit of the chloritoid stability field is also in better agreement with petrological observations. For practical applications to metamorphic and hydrothermal environments, two new semi-empirical chlorite geothermometers named Chl(1) and Chl(2) were calibrated based on the chlorite + quartz + water equilibrium (2 clinochlore + 3 sudoite = 4 amesite + 4 H2O + 7 quartz). The Chl(1) thermometer requires knowledge of the (Fe3+/ΣFe) ratio in chlorite and predicts correct temperatures for a range of redox conditions. The Chl(2) geothermometer which assumes that all iron in chlorite is ferrous has been applied to partially recrystallized detrital chlorite from the Zone houillère in the French Western Alps.

Chemistry of minerals from amphibole-chlorite veins of ODP Site 209-1270

We examined small-scale shear zones in drillcore samples of abyssal peridotites from the Mid-Atlantic Ridge. These shear zones are associated with veins consisting of chlorite + actinolite/tremolite assemblages, with accessory phases zircon and apatite, and they are interpreted as altered plagiogranite melt impregnations, which originate from hydrous partial melting of gabbroic intrusion in an oceanic detachment fault. Ti-in-zircon thermometry yields temperatures around 820°C for the crystallization of the evolved melt. Reaction path modeling indicates that the alteration assemblage includes serpentine of the adjacent altered peridotites. Based on the model results, we propose that formation of chlorite occurred at higher temperatures than serpentinization, thus leading to strain localization around former plagiogranites during alteration. The detachment fault represents a major pathway for fluids through the oceanic crust, as evidenced by extremely low d18O of altered plagiogranite veins (+3.0-4.2 per mil) and adjacent serpentinites (+ 2.6-3.7 per mil). The uniform oxygen isotope data indicate that fluid flow in the detachment fault system affected veins and adjacent host serpentinites likewise.

Geochemistry of the oceanic crust from ocean drilling samples

This book presents new data on chemical and mineral compositions and on density of altered and fresh igneous rocks from key DSDP and ODP holes drilled on the following main tectonomagmatic structures of the ocean floor: 1. Mid-ocean ridges and abyssal plains and basins (DSDP Legs 37, 61, 63, 64, 65, 69, 70, 83, and 91 and ODP Legs 106, 111, 123, 129, 137, 139, 140, 148, and 169); 2. Seamounts and guyots (DSDP Legs 19, 55, and 62 and ODP Legs 143 and 144); 3. Intraplate rises (DSDP Legs 26, 33, 51, 52, 53, 72, and 74 and ODP Legs 104, 115, 120, 121, and 183); and 4. Marginal seas (DSDP Legs 19, 59, and 60 and ODP Legs 124, 125, 126, 127, 128, and 135). Study results of altered gabbro from the Southwest Indian Ridge (ODP Leg 118) and serpentinized ultramafic rocks from the Galicia margin (ODP Leg 103) are also presented. Samples were collected by the authors from the DSDP/ODP repositories, as well as during some Glomar Challenger and JOIDES Resolution legs. The book also includes descriptions of thin sections, geochemical diagrams, data on secondary mineral assemblages, and recalculated results of chemical analyses with corrections for rock density. Atomic content of each element can be quantified in grams per standard volume (g/1000 cm**3). The suite of results can be used to estimate mass balance, but parts of the data need additional work, which depends on locating fresh analogs of altered rocks studied here. Results of quantitative estimation of element mobility in recovered sections of the upper oceanic crust as a whole are shown for certain cases: Hole 504B (Costa Rica Rift) and Holes 856H, 857C, and 857D (Middle Valley, Juan de Fuca Ridge).

Mineral, chemical and isotopic compositions of hydrothermally altered sediments from the Middle Valley (Juan de Fuca Ridge), ODP Site 139-858

Li and Li isotopes have been measured in the clay fraction of sediments recovered from the Middle Valley hydrothermal site on the Juan De Fuca Ridge. The Li content of pure detrital clays is 51 ppm while hydrothermal clays and carbonates have lower Li (22+/-11 ppm). However, there is no clear relationship between the mineralogy of the hydrothermal alteration products and their Li content. The d7Li value of the detrital clays is +5.8?. Hydrothermal clays and carbonates have d7Li in the range of -3.9? to +7.8?; these values do not seem to be dependent on the temperature at which they formed. Modelling of the Li and Li isotope systematics indicates that the fluid from which the alteration products form is significantly enriched in Li (higher than 10000 µmol/kg) relative to pore fluids recovered from within the sediments (up to 589 µmol/kg; [Wheat, C.G., M.J. Mottl, 1994. Data report: trace metal composition of pore water from Sites 855 through 858, Middle valley, Juan De Fuca Ridge. In Mottl, M.J., Davis, E.E., Fisher, A.T., Slack, J.F. (Eds.), Proc. ODP, Sci. Res. 139: 749-755; doi:10.2973/odp.proc.sr.139.269.1994]), and that this Li is derived from sediment. Thus, the alteration products are not in equilibrium with their conjugate pore fluids; rather, the alteration minerals formed at lower water/sediment ratios. This suggests that fluid flow pathways at Middle Valley were more diffuse in the past than they are today.