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Partition of trace elements in co-existing biotite, muscovite and potassium feldspar of granitic rocks, northern Portugal

1975; Elsevier BV; Volume: 16; Issue: 2 Linguagem: Inglês

10.1016/0009-2541(75)90002-9

1872-6836

Carlos A.R. De Albuquerque,

Geological and Geochemical Analysis

Chemical analyses are given for Na, K, and trace elements of muscovite and potassium feldspar of granitic rocks. The distribution of trace elements in co-existing minerals suggests that equilibrium was attained and that muscovite is a primary mineral. These observations and the comparison of the trace-element chemistry of megacrysts and groundmass potassium feldspars of porphyritic rock types lead to the conclusion that the megacrysts are in face phenocrysts which crystallized in equilibrium with the other minerals of the rock. The ranges of values of the distribution coefficients KD(Rb/K) and KD(Cs/K) in mineral pairs confirm other observations on the equilibrium among various minerals. However, application of experimental data on the temperature effect on KD leads to results conflicting with the petrologic observations. The possible influence of other factors on KD is analyzed and among these factors the composition of the feldspar and the solidus-liquidus temperature interval may play a dominant role.