When minerals tell us about water-rock reactions deep in the ocean

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last modified 18-06-2008 10:22

A team from the universities of Montpellier, Marseille, Grenoble and the ESRF has just unveiled the structure of a newly-discovered mineral located in ocean ridges. This kind of mineral, called polyhedral serpentine, has provided valuable information about hydrothermal processes on the ocean floor. The results of this research are published in the European Journal of Mineralogy.

• unveiled = enthüllt
• ridges = Grate

Depending on their location, serpentines play different roles:

• they trigger earthquake and volcanoes in subduction zones,
  

• they are soft “aseismic” materials in continental active fault zones
  

• they are at the basis of alteration processes which help support primitive organisms at mid-ocean ridges (underwater volcanic ranges).

• serpetine = Schlange
• asmeic = erdbebensicher

[...]

• The water, heated by volcanic activity, modifies the rocks to form serpentine during reactions that take place at high temperature (100-400°C)

[...]

• Image of the polyhedral serpentine displaying its peculiar facetted morphology (Scanning electron microscopy)

• "fault area = aufgeworfene Bruchlinie

• ... "it is essential to describe these minerals in a fundamental way to search for past chemical and mechanical processes that are potentially recorded in their structure and chemistry” ...

µ-XANES mapping at the iron K-edge on a selected area of a thin section (Californian sample)

• containing a polyhedral serpentine vein (V2)

• an older fibrous serpentine vein: chrysotile + polygonal serpentine (V1).

• A) Total iron content distribution in the sample, proportional to the height of the edge -jump of the XANES spectra.

• B) Distribution of the energy-position of the FeK-edge. Note the electron-volt shift of the edge energy that can be attributed to changes in the oxidation state of iron and/or to structural changes (iron local geometry).

• C) Averaged XANES spectra for the V1 and V2 regions,as well as almandine and andradite standard compounds used for pre-edge calibration (the zoom inset shows the deconvolution of V1 and V2 pre-edges).

Credits: Eur. J. Mineral., www.schweizerbart.de