Terrestrial plagioclase

Figure 5. Correlation of 27AT/uMg secondary ion intensity ratios vs. 27Al/MMg elemental ratio measured with the electron probe for Allende anorthite (0) and terrestrial plagioclase W-...

The data plot along a line of dope 0.5, reflecting instrumental mass fractionation of 7%famu. The proper correction for is indicated by the terrestrial plagioclase... 

Onuma et al. 1970). By comparison with other terrestrial rocks, the range of observed 8 0-valnes is very narrow. For instance, terrestrial plagioclase exhibits an O-isotope variation which is at least ten times greater than that for all lunar rocks (Taylor 1968). This difference may be attributed to the much greater role of low-temperature processes in the evolution of the Earth s crust and to the presence of water on the Earth. 

Bell, P. M. Mao, H.-K. (1973a) Measurements of the polarized crystal-field spectra of ferrous and ferric iron in seven terrestrial plagioclases. Ann. Rept. Geophys. Lab., Yearb. 72, 574-6. 

Among the minerals mentioned above calcite and kaolinite may be important for controlling /CO2 of terrestrial geothermal waters. It was cited by Giggenbach (1981) that /CO2 (or Xco2> mole fraction of CO2) of terrestrial geothermal waters is controlled by plagioclase -1- CO2 = calcite -H kaolinite . 

In addition to the hydrothermal controls, the elemental cycles of Ca and Mg are also linked to those of CO2 and Si02 because the mobilization of Ca and Mg during terrestrial weathering from silicates, such as plagioclase, involves consumption of CO2. In the case of calcium, the net chemical reaction is... 

The experiments crystallized plagioclase in the composition range Ango-An4o, which covers most terrestrial magmatic plagioclases. In the case of lanthanides, Bindeman et al. (1998) find a positive correlation between RT In and Xad-For lanthanum the relationship is... 

Since the REE are not readily fractionated in sedimentary processes (except that Ce3+ may be oxidized to Ce4+ and separated as the insoluble phosphate in marine environments, or less frequently as the hydroxide in terrestrial environments), this pattern is recording a previous signature of igneous events involving partial melting (or crystal fractionation) and removal of Eu by plagioclase as a residual phase. 

The primary rock-forming silicate minerals in terrestrial rocks can react with liqnid water to form various two-layer and three-layer clays (Faure 1998). For example, Na-plagioclase (i.e., albite) is transformed into kaoUnte by the reaction ... 

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