Diamonds in the Bohemian Massif – evidence for ultrahigh-pressure
Vol.18,No.1(2011)
Diamond and coesite were discovered in high-pressure granulites of the north Bohemian crystalline basement in the Eger Crystalline Complex and České středohoří Mts. Diamonds, confirmed by micro-Raman spectroscopy, occur as 5–10 μm-sized inclusions in kyanite and garnet as well as in accessory zircon. Coesite was identified within kyanite enclosed in garnet. Diamond and coesite form at pressures above 4 and 3 GPa, respectively, and the presence of these two minerals in the continental crust indicates ultrahighpressure metamorphic conditions reached only during a continental subduction deep into the mantle. Preservation of coesite in felsic-intermediate crustal rocks is a rather unique phenomenon due to its very limited metastable survival within exhumed terranes. Importantly, the north Bohemian crystalline basement represents only the fifth accepted location worldwide where diamond has been documented in situ in the continental crust rather than in mantle rocks such as peridotites. Our discovery also strongly supports the previously questioned Bohemian provenance of macroscopic diamonds, found in the České středohoří Mts. area in the 19th and 20th century.
diamond; ultrahigh-pressure metamorphism; high-pressure granulite; Bohemian Massif