AG Petrology of the Ocean Crust

Room 5320

Department of Geosciences
University of Bremen
Klagenfurter Straße 2
28359 Bremen
Germany

Phone: +49 421 218 65405
Fax: +49 421 218 65429
Email: c.hansen@uni-bremen.de

Christian Hansen


Dissertation

Experimental investigations on Lithium and Boron isotope fractionation during serpentinization

An essential part of the important geochemical exchange between seawater, oceanic crust and the earths’ mantle is controlled by the process of serpentinization. In oceanic core complexes, serpentine minerals form in the course of hydration of exposed mantle peridotites. Subsequently these mineral phases break down during plate subduction, releasing their water fraction into the mantle wedge, where partial melting is induced. Associated mass transfer can potentially be traced via fluid mobile elements Lithium and Boron. However, a precise determination of isotope fractionation coefficients is a mandatory premise for the isotope tracer deployment.

I use an experimental Batch reactor setup, in which the process of serpentinization is simulated in order to derive basic fractionation coefficients between fluid and reaction products. Thereby reaction educts olivine (powder) and fluid are reacted within a flexible gold cell in a controlled P-T environment. Concomitant monitoring of P, T, S, pH, X, δ11B, δ7Li, will help to put precise constraints on the intrinsic fractionation process.


Experimental investigations on the fundamental feedback mechanisms between permeability and reaction turnover in fluid rock interactions

Fluid rock interactions play a key role in geoscientific research. For instance, the related processes govern the climate critical mass transfer between seawater and oceanic crust, as well as they are of major importance to applied geosciences by influencing hydraulic and rock mechanical properties. In an attempt for understanding these processes multiple factors have to be considered, including changes in porosity distribution, permeability and their feedback relationship with decisive dissolution and precipitation rates. To date, the knowledge about these interdependencies is very limited, which results in an inability to make precise predictions on natural systems behaviour.
As part of a DFG funded Koselleck project we will use a new systematic experimental approach to investigate versatile feedback mechanisms during fluid-rock interactions. In a setup for carrying out percolation experiments corrosive or oversaturated fluids can be forced through rock core (∅ 10 mm) or powder samples under precisely defined pressure (≤ 200 bar) and temperature (≤ 250 °C) conditions. Evolution of pore space geometry is monitored by concomitant µ-CT imaging, while sequential analysis of fluid composition will provide information on thermodynamic and kinetic characteristics. Construction of this setup will be followed by exemplary investigation of Anhydrite precipitation and replacement, which will eventually give new insight into the formation of polymetallic sulfide deposits. Moreover the comprehensive nature of this study will help to significantly improve the parameterization of numerical models used to make predictions on a variety of natural systems (e.g. serpentinization, steatitization, carbonatization, gypsum formation).



Scientific career

  • 2007 - 2010: Studies in Geosciences (B.Sc.), Bremen University
    • 2010: Bachelor thesis: "Petrologische Untersuchungen an Mantel-Xenolithen aus unterkarbonischen Bombenschalsteinen der Dill-Mulde: Rekonstruktion des Alterationsprozesses anhand der Mineralchemie sekundärer Bildungen"
  • 2010 - 2012: Studies in Geosciences (M.Sc.), Göttingen University
    • 2012 Master thesis: "Dating Mesozoic and Cenozoic methane-seep carbonates using 87Sr/86Sr-isotope ratios"
  • 2012 - 2016: Ph.D. student at the research group "Petrology of the ocean crust" at Bremen University
    • March 2016: Dr. rer. nat. in Geosciences



Publications

  • Hansen CT, Meixner A, Kasemann SA, Bach W (2017): New insight on Li and B isotope fractionation during serpentinization derived from batch reaction investigations. Geochimica et Cosmochimica Acta 217, 51-79.
    doi:10.1016/j.gca.2017.08.014 |
  • Hawkes JA, Hansen CT, Goldhammer T, Bach W, Dittmar T (2016): Molecular alteration of marine dissolved organic matter under experimental hydrothermal conditions. Geochimica et Cosmochimica Acta 175, 68-85.
    doi:10.1016/j.gca.2015.11.025 |
  • Kahl W-A, Hansen CT, Bach W (2016): A new X-ray-transparent flow-through reaction cell for a μ-CT-based concomitant surveillance of the reaction progress of hydrothermal mineral–fluid interactions. Solid Earth 7, 651-658.
    doi:10.5194/se-7-651-2016 |
  • Hawkes JA, Rossel PE, Stubbins A, Butterfield D, Connely DP, Achterberg EP, Koschinsky A, Chavagnac V, Hansen CT, Bach W, Dittmer T (2015): Efficient removal of recalcitrant deep-ocean dissolved organic matter during hydrothermal circulation. Nature Geoscience 8(11), 856-860.
    doi:10.1038/ngeo2543 |
  • Kiel S, Hansen C, Nitzsche KN, Hansen BT (2014): Using 87Sr/86Sr ratios to date fossil methane seep deposits: Methodological requirements and an example from the Great Valley Group, California. J. Geol., 122(4), 353-366.
    doi:10.1086/676594 |
  • Brandmeier M, Erasmi S, Hansen C, Höweling A, Nitzsche K, Ohlendorf T, Mamani M, Wörner G (2013): Mapping patterns of mineral alteration in volcanic terrains using ASTER data and field spectrometry in Southern Peru. J. South Am. Earth Sci., 48, 296-314.
    doi:10.1016/j.jsames.2013.09.011 |



Conference Abstracts

  • Los CL, Hansen C, Bach W (2017): Sulphidation of the oceanic lithosphere: an experimental approach. European Geosciences Union General Assembly 2017, Vienna, Austria.
  • Hansen C, Meixner A, Kasemann S, Bach W (2015): New insight on lithium and boron isotope fractionation during serpentinization derived from batch reaction investigations. Goldschmidt Conference 2015, Prague, Czech Republic.
  • Hansen C, Meixner A, Kasemann S, Bach W (2014): New insight on lithium and boron isotope fractionation during serpentinization derived from batch reaction investigations. DMG Meeting 2014, Jena, Germany.