The Spa?ice eclogite: constraints on the P–T–t history of the Gföhl granulite terrane, Moldanubian Zone, Bohemian Massif |
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| Authors: | L G Medaris Jr E D Ghent H F Wang J H Fournelle E Jelínek |
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| Institution: | (1) Department of Geology and Geophysics, University of Wisconsin-Madison, Madison, WI, USA;(2) Department of Geology and Geophysics, University of Calgary, Calgary, Alberta, Canada;(3) Institute of Geochemistry, Mineralogy and Mineral Resources, Charles University, Praha, Czech Republic |
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| Abstract: | Summary In the Kutná Hora Complex, the Běstvina Formation, which is similar to Gf?hl granulite, contains eclogite that has escaped
widespread retrograde recrystallization. The eclogite assemblage, garnet + omphacite + quartz + rutile ± plagioclase, yields
an estimate for peak metamorphic conditions of 18–20 kbar and 835–935 °C, which is comparable to that determined from felsic
granulite, 14–20 kbar and 900–1000 °C. Garnet in eclogite exhibits both prograde and retrograde compositional zoning, from
which constraints on thermal history of the Gf?hl terrane can be derived by diffusion modelling. At 900 °C, a garnet grain
of 800–1000 μm radius would homogenize in 7.5–11.7 million years, but the existence of compositional gradients on a length
scale of 100–200 μm suggests that the duration of peak metamorphism may have been limited to ∼500,000 years. Diffusion modelling
of retrograde zoning in garnet yields a cooling rate of 150–100 °C/m.y. for a radius of 800–1000 μm and initial temperature
of 900 °C. The relatively brief duration of high-pressure/high-temperature metamorphism and rapid cooling and exhumation of
the Gf?hl terrane may be a consequence of lithospheric delamination during Early Carboniferous collision of Bohemia (Teplá-Barrandia)
and Moldanubia (Franke, 2000). |
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