Abstract
The primary minerals of a partly serpentinized Alpine type ultrabasic mass, lying in a zone of low Alpine metamorphism, were analysed with an electron microprobe. The distribution coefficients of Mg and Fe in coexisting orthopyroxenes, clinopyroxenes and olivines indicates an equilibrium temperature of around 1400°C. The Ca/Ca+Mg ratios in the clinopyroxenes indicate temperatures between 800° and 1000°C. This discrepancy in temperature estimations can partly be explained by the high Al2O3-contents of the clinopyroxenes, since a good correlation between Al2O3-contents and Ca/Ca+Mg ratio was found. The Na2O-content of the clinopyroxenes decreases in the successive pyroxenites that differentiated from the main lherzolite. From the mineralogical composition of the different rock types and the chemical compositions of the minerals it is concluded that the Totalp peridotite originated in the Upper Mantle.
In the Malenco serpentinite, the clinopyroxenes formed during the rather strong Alpine metamorphism are much poorer in Al2O3 and Na2O than the primary clinopyroxenes. On the other hand, the olivines, grown postdeformationally during the Alpine metamorphism, are not much different in composition to the primary olivines.
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Peters, T. Distribution of Mg, Fe, Al, Ca and Na in coexisting olivine, orthopyroxene and clinopyroxene in the Totalp serpentinite (Davos, Switzerland) and in the Alpine metamorphosed Malenco serpentinite (N. Italy). Contr. Mineral. and Petrol. 18, 65–75 (1968). https://doi.org/10.1007/BF00371986
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DOI: https://doi.org/10.1007/BF00371986
