Figure 5
From: Quaternary low-temperature serpentinization and carbonation in the New Caledonia ophiolite
Summary of the water–rock interaction events recorded by the GR2H sample. (a) Schematic diagram based on the SEM image displayed in Fig. 2c. Three steps can be distinguished based on mineralogical and textural features. Magnetite–dolomite–lizardite vein (Step 2, right panel) crosscut and thus postdate the mesh texture (Step 1, left panel) highlighted by the alignment of small magnetite grains (black). Pervasive olivine alteration in Step 2 occurs within an alteration front of a few hundreds of µm, and gradually increases towards the vein. Olivine embedded in the vein material displays pronounced alteration features (etch pits). Fe-poor lizardite and dolomite are also located in the vein as well as in the alteration front. A late alteration stage (Step 3) led to the formation of pyroaurite, which involved CO2-rich and oxygenated waters. (b) Main chemical reactions associated with each of the three steps described in (a), deduced from mineral textures, isotopic data and thermochemical modeling. Lizardite and brucite with the highest Fe content are named Lz(Fe) and Brc(Fe) respectively, whereas Brc(Mg) means Fe-poor brucite.
