Petrographic and geochemical comparison between the Copper Age “Ljubljana type” axes and similar lithotypes from Eisenkappler Diabaszug complex (southern Austria)
Introduction
In the Caput Adriae area (north eastern Italy, Slovenia, north western Croatia) most of the Copper Age polished stone axes are made from selected types of metamorphic rocks (Bernardini et al., 2009, Bernardini et al., 2011a, Bernardini et al., 2011b, Bernardini et al., 2012, Bernardini et al., 2013). In a recent study we have characterized a large group of artefacts particularly abundant in the Ljubljansko barje pile dwellings (Slovenia; Fig. 1 and Table 1), in order to try defining the most probable raw material source (Bernardini et al., 2013). These Copper Age axes, made from magmatic and variably metamorphosed igneous rock types, are characterized by homogeneous typology and a common OIB-like signature. Their typology, distribution, petrographic and geochemical features suggested a possible provenance from the presumed Palaeozoic diabase/shale complex (Eisenkappler Diabaszug) intruded by the northern Karawanken plutonic belt in southern Austria (Bernardini et al., 2013). However, accurate petrographic description, mineral chemistry and geochemical analyses of trace elements were unavailable for the ultramafic rocks, diabase and pillow lavas outcropping in that area (Exner, 1956, Exner, 1972, Loeschke and Rolser, 1971). In this paper petrography and geochemistry of various rock types sampled from the Eisenkappler Diabaszug complex (hereafter EDC; Fig. 2) are presented and compared with the data already available for the “Ljubljana type” axes (hereafter Lt).
Section snippets
Materials and methods
The group of Lt axes includes 42 artefacts: most of them (29) were found in the pile dwelling settlements near Ljubljana, 6 are from archaeological caves of Trieste Karst, the other few artefacts were discovered in the Friuli plain, Vipava valley and Istrian peninsula (Fig. 1 and Table 1).
The archaeological data indicate that most of them date back to the second half of the fourth millennium BC, when these metamorphosed rock types are the most common raw materials used for the production of
Optical microscopy
Petrographic features of the Lt axes have been already described by Bernardini et al. (2013) and are summarized as follows. The prehistoric artefacts have been divided in three groups according to their metamorphic overprint (green schist facies), from magmatic (Lt1) to “weakly” (significant presence of magmatic relics; Lt2) and “strongly” metamorphosed rocks (very rare magmatic relics; Lt3). The axes belonging to Lt1 group are made of sub-volcanic basic rocks showing intersertal to subophitic
Discussion and conclusion
Petrography and geochemistry of magmatic and metamorphosed igneous rock types sampled from the EDC have been studied and compared with the data available for the “Ljubljana type” axes (Bernardini et al., 2013). From a petrographic point of view, only two of the outcrops sampled in EDC (localities B and E) can be compared to magmatic Lt1 and strongly metamorphosed L3 axe groups respectively. The metamorphic artefacts and rocks from area E are characterized by very fine aggregates of amphibole
Acknowledgements
The authors are grateful to the National Museum of Slovenia for permission to analyse part of the studied artefacts. Thanks are also due to M. Di Giovannantonio for the review of the draft, to L. Furlan, Department of Mathematics and Geosciences, Trieste University, and L. Tauro at the Department of Geosciences in Padova for sample preparation. We are grateful to R. Carampin (CNR–IGG Padova) for his assistance during microprobe analysis. This research was supported by the European Charisma 2011
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