Correlation and distinction between similar metapelite units: a geochemical approach in a case study from the Eastern Alps (Italy)

Major and trace element geochemistry can be used in correlating or discrimi nating different sedimentary and volcanic rock units and their metamorphic equivalents. A geochemical study has been done on metapelites coming from f our different lithostratigraphic units, showing similar petrographic featur es and identical metamorphic characters. They come from the boundary betwee n the Merano-Mules and Monteneve complexes, belonging to the Austroalpine c rystalline basement of the Alps. In this area, the passage from one complex to the other is not sharp and the lithostratigraphic setting is still ambi guous. Whole rock analyses (XRF and ICP-MS) were carried out on rocks sampled from four areas (B, T, M and R), along a cross-section through the boundary bet ween the two complexes, in order to detect geochemical similarities or diff erences among the metapelite levels. Considering both major and trace elements as variables, chemical data have been treated by statistical analysis. Cluster analysis pointed out that roc ks from the sampling area B form a well defined group with respect to the s amples from the other areas. The contents of several major and trace elements, or combinations thereof, have been plotted in binary and ternary diagrams. Some of them confirm the common pelitic character of the protoliths and others clearly show systemat ic differences between the B group and the other samples. Chemical data have been plotted in the A-CN-K diagram to obtain information on the nature of the protoliths and on processes which may have occurred p rior to metamorphism. Samples from the B group and samples from the other g roups plot along two different alignments. They should represent a short pa rt of trends corresponding to an intermediate stage of weathering of rocks derived from two different sources, and could have been affected by slight K-metasomatism.