Geochemistry of Fe-rich peridotites and associated pyroxenites from Horní Bory, Bohemian Massif: insights into subduction-related melt-rock reactions
Abstract
Variscan, mantle-derived peridotites and associated pyroxenites occur as boudins in Moldanubian granulite near the town of Horní Bory in western Moravia. The peridotites consist of two compositionally distinct suites, one of Mg-lherzolite (Mg-number = 89-91, 87Sr/86Sr = 0.7046-0.7068, eNd = +4.1 to +5.3), and another of Fe-dunite/wehrlite (Mg-number = 83-88, 87Sr/86Sr = 0.7079-0.7087, eNd = –2.8 to –1.3).
Modelling of Mg-Fe exchange between peridotite and Fe-rich melts reveals that the modal and chemical composition of the Fe-dunite/wehrlite suite can be produced by melt-rock reactions between lherzolite and SiO2-undersaturated melts of basaltic composition at melt/rock ratios ranging from 0.3 to 2. In such a model, pyroxenites represent the crystalline product (+-trapped liquid) of melts migrating along conduits in peridotite.
The Fe-dunite/wehrlite suite and pyroxenites are enriched in the LILE and depleted in the HFSE. The trace element and Sr-Nd isotopic compositions of Horní Bory.