High-Ti muscovite as a prograde relict in high pressure granulites with metamorphic Devonian zircon ages (Běstvina granulite body, Bohemian Massif): Consequences for the relamination model of subducted crust

Long-lived high-temperature granulite-facies metamorphism in the Eastern Himalayan orogen, south Tibet

“…Therefore it is possible that the garnet only experienced a limited diffusion modification during retrograde metamorphism. In fact, many studies demonstrated that garnets in HT (N 800°C and even up to 900°C) granulites have partially or completely preserved their prograde growth zoning, characterized by decreasing grossular and spessartine contents, accompanied by an increasing pyrope content, during late cooling and exhumation (e.g., Anczkiewicz et al, 2007;Kobayashi et al, 2011;Nahodilova et al, 2014).…”

Uncoupled U/Pb and REE response in zircon during the transformation of eclogite to mafic and intermediate granulite (Blanský les, Bohemian Massif)

“…340 Ma, but spread of ages goes from Cambrian to Carboniferous ( c . 500 – 335 Ma) (van Breemen et al ., ; Prince et al ., ; Schulmann et al ., ; Sláma et al ., , ; Friedl et al ., ; Nahodilová et al ., ).…”

“…The ascent was followed by subhorizontal reworking in a mid‐crustal migmatitic ‘channel’ (Schulmann et al ., ; Štípská et al ., ; Lexa et al ., ). At least part of the Gföhl unit is interpreted as originally deeply subducted Saxothuringian crust (O'Brien, ; Janoušek & Holub, ; Lexa et al ., ; Chopin et al ., ; Nahodilová et al ., ). This genetic link is supported by a similar rock association of kyanite – K‐feldspar granulite, garnetiferous peridotite, eclogite, together with diamond‐bearing quartzofeldspathic rocks that occur in both domains (e.g.…”

“…In HP rocks that show predominantly 340 Ma zircon ages, scarce garnet and zircon ages up to 380 Ma are also reported (e.g. Prince et al ., ; Nahodilová et al ., ). This led to the idea that at least some rocks from the Devonian and Carboniferous subduction zone were relaminated to the upper plate and stayed at depth until exhumation at 340 Ma (Willner et al ., , ; Lexa et al ., ).…”

“…Hoskin & Black, ): (i) It can grow from solid‐state breakdown of Zr‐bearing phases such as garnet, hornblende or ilmenite, but the amount of zircon produced by such reactions is not likely to be large (Sláma et al ., ). (ii) Zircon may grow from crystallizing melt (Roberts & Finger, ; Schaltegger et al ., ; Vavra et al ., ; Hermann et al ., ; Skrzypek et al ., ) natural studies combined with thermodynamic modelling show that, for example, up to 20 – 40% of the zircon present grew from melt in felsic granulite during cooling (Skrzypek et al ., ; Nahodilová et al ., ). (iii) Precipitation from fluid (Williams et al ., ; Rubatto & Hermann, ; Hay & Dempster, ) and (iv) Ostwald ripening (Ayers et al ., ) are other processes proposed for new zircon growth.…”