Publication details
UHP-UHT peak conditions and near-adiabatic exhumation path of diamond-bearing garnet-clinopyroxene rocks from the Eger Crystalline Complex, North Bohemian Massif
| Authors | |
|---|---|
| Year of publication | 2016 |
| Type | Article in Periodical |
| Magazine / Source | Lithos |
| MU Faculty or unit | |
| Citation | |
| web | http://www.sciencedirect.com/science/article/pii/S0024493716000621 |
| Doi | http://dx.doi.org/10.1016/j.lithos.2016.02.001 |
| Field | Geology and mineralogy |
| Keywords | Ultrahigh-pressure; Diamond; Ti-in-zircon; Granulite; Thermobarometry; Bohemian Massif |
| Description | Intermediate garnet-clinopyroxene rocks from the Eger Crystalline Complex, North Bohemian Massif, contain microdiamonds enclosed in garnet and zircon. P-T evolution of the rocks is evaluated using using univariant equilibria and thermodynamic modelling, and ternary feldspar solvus, Ti-in-garnet, Zr-in-rutile and Ti-in-zircon thermometry. Zircon mantle domains with diamond inclusions contain 111-189 ppm Ti, reflecting temperatures of 1037-1117 degrees C at c. 4.5-5.0 GPa. Ti-in-garnet thermometry using the Ti content of diamond-bearing garnet core yielded temperatures of 993-1039 degrees C at c. 5.0 GPa. An omphacite inclusion in garnet (reflecting c. 2.3-2.4 GPa at c. 1050 degrees C) and metastably preserved kyanite represent relics of eclogite-facies conditions. The dominant high-pressure granulite-facies mineral assemblage of low-Ca garnet, diopsidic clinopyroxene, antiperthitic feldspar and quartz equilibrated at 1.8-2.1 GPa and c. 1050 degrees C. Thermodynamic modelling shows that a steep rimward decrease of XGrs and increase of X-Mg in garnet reflect omphacite and kyanite breakdown reactions producing garnet and plagioclase during decompression without heating. The Ti content in the rim zone of zircon (13-42 ppm), exsolved plagioclase and K-feldspar associated with matrix diopside and garnet rim, matrix rutile grains containing 2028-4390 ppm Zr and late biotite reflect temperatures of c. 830-900 degrees C at c. 1.4 GPa. Our results show that the garnet-clinopyroxene rocks from North Bohemia are UHP-UHT rocks which were extensively overprinted under HP granulite-facies conditions during rapid exhumation along a near-adiabatic P-T path. The UHT peak and UHT-HT exhumation distinguish this area from the other UHP terrains worldwide. The calculated UHP-UHT conditions are similar to those determined for the associated garnet peridotites, providing evidence for juxtaposition of these crustal and mantle rocks during deep Variscan subduction. |
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