Origin of metabasites from upper tectonic unit of the Lavrion area (SE Attica, Greece): Geochemical implications for dual origin with distinct provenance of blueschist and greenschist's protoliths

摘要

The Lavrion area forms the westernmost part of the Attic-Cycladic crystalline belt (ACCB) and is built up by two tectonic units metamorphosed at HP/LT conditions. In the Upper Tectonic Unit metabasic rocks occur as greenschists and blueschists. Major and trace elements plotted against Mg# show a systematic increase in TiO2, Fe2O3~*, Na2O, Zr, Y, V, La and Yb and a decrease in Al2O3, Ni and Cr with decreasing Mg#. Typically, the blueschists always exhibit a more evolved basaltic composition. The greenschists are characterized by LREE-depleted chondrite-normalized REE patterns and Zr/Nb values that range from 15 to 24. The blueschists are characterized by slightly LREE-enriched chondrite-normalized REE patterns and lower Zr/Nb ratios (6.6-11.3). Both rock types share common geochemical features like flat HFSE patterns or slight positive Nb anomalies with La/Nb