Informace o publikaci
Petrography and mineralogy of metabasite-artefacts from the Neolithic settlement at Brno-Holásky and comparison with rocks from source region near Želešice, South Moravian Region, Czech Republic
| Autoři | |
|---|---|
| Rok publikování | 2018 |
| Druh | Konferenční abstrakty |
| Fakulta / Pracoviště MU | |
| Citace | |
| Popis | Rocks from two different sources were studied petrographically and mineralogically using optical microscopy and electron microprobe analyses – metabasites used for manufacturing of polished stone artefacts found in the Neolithic settlement at Brno-Holásky (Trnová, 2017) and rocks from Želešice- metabasite body (Veverka, 2016). The comparison of these two different rock collections could be helpful to determine the source area of Neolithic mining within the Želešice source region and specify the rock variety preferred for production of polished stone industry during the Neolithic period. Želešice area is situated in the metabasite zone of the Brno batholith south of Brno and approximately 8 km WSW of the Brno-Holásky Neolithic settlement. Metabasites from the Brno-Holásky settlement are characteristic by gray-green color, distinctive metamorphic foliation and common presence of tiny veinlets. Fine-grained amphibole predominates in the rocks along with plagioclase. Magnetite is common accesory mineral compared to somewhat rarer ilmenite, apatite and chlorite and secondary titanite. All the studied rocks were described as amphibole-rich greenschists to amphibolites (Trnová, 2017). Most of the rocks from the Želešice-metabasite body were described by Veverka (2016). Amphibole and plagioclase predominate but common epidote, chlorite, biotite and quartz occur in some rock-varieties along with titanite, ilmenite, magnetite, apatite and rare tourmaline and sericite. The rocks from the Želešice-metabasite body were described as chloritic greenschist, metadiorites and epidote-rich amphibolites with rare occurrence of biotite - gneiss with tourmaline. Amphiboles from the artefacts have composition of actinolite to magnesiohornblende with some transitions to tschermakite, ferrotschermakite, ferrohornblend and ferropargasite. In the rocks from Želešice actinolite to magnesiohornblende prevail and pargasite to edenite were determined exceptionally. Plagioclases from the artefacts are more basic, show wider range of basicity and have elevated contents of Fe3+ (up to 0.018 apfu) compared to plagioclases from Želešice–rocks (up to 0.009 apfu). Magnetite shows the composition of the end-member only with traces of Al and Mg in the both rocks from Brno-Holásky and Želešice area, while ilmenite is enriched significantly in Mn in the rocks from Želešice area. Chlorite is Mg-rich in both collections as well as biotite in the rocks from Želešice. Tourmaline from the biotite gneiss in Želešice corresponds to Fe-rich dravite. Amphibolites to greenschists from the source area near Želešice are very close in their petrography and mineral-composition to the raw material used for production of polished stone artefacts at the Neolithic settlement near Brno-Holásky. However, the rocks from Želešice area differ from the raw material in higher contents of epidote especially. The sample determined as chloritic greenschist, which was considered as the most similar rock to the raw material of the stone artefacts comes from the vicinity of the contact of the metabasite body with granitoides of the Brno batholith where the metabasites were influenced by contact metamorphism and rheological properties of metabasites have improved therefore. |