Geochemical zoning

Thermobarometry, or the calculation oi P-T conditions from mineral compositions, is not based on mineral zoning, nor does it directly inform processes that cause geochemical zoning. Nonetheless, P-T calculations in metamorphic rocks usually require selecting compositions from minerals that are compositionally heterogeneous. How one selects compositions from a zoned mineral can strongly influence retrieved P and T, and that issue is worth discussion. 

Fig. 3. Variations in relative importance of the different geochemical zones of diagenesis (see text) and the diagenetic minerals formed in a profile covering proximal to distal continental arid to semi-arid environments, as well as subaquatic marine environments. Mn- and Fe-oxides should be encountered in the oxic zone of these different settings.

Figure 10.5. Concentration profiles showing downgradient propagation of the reaction fronts and pH-buffered geochemical zones during tailings fluid intrusion. Groundwater flows from left to right. DIC denotes total dissolved inorganic carbon. All concentration units are in molL-1, except for pH. Solid, dashed, and dotted lines represent concentration profiles at 0 (initial conditions), 2.5, and 5 years from the start of the simulation, respectively.

Ad models cannot predict the sharp fronts and distinct geochemical zones (cf. Figure 10.5) ... 

Figure 2.87 Geochemical zoning of pollution halo from dumping organic waste...

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