Rare eclogite‐mafic granulite in felsic granulite in Blanský les: precursor of intermediate granulite in the Bohemian Massif?

Abstract

International audienc

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

“…The sequence from eclogite to intermediate granulite studied here involves the same samples as presented in Štípská et al . (,b) and their petrology is summarized here (Fig. ).…”

“…Štípská et al . (,b) described the eclogite – mafic granulite to intermediate granulite transition from a low‐strain domain of felsic granulite in the core of the Blanský les massif on Kleť mountain (Franěk et al ., , ). There, the dark, fine‐grained eclogite occurs as up to metre‐scale oval bodies that progressively grade into intermediate granulite with the appearance of macroscopically visible ternary feldspar (Fig.…”

“…At Kleť in the Blanský les rare eclogite – mafic granulite boudins occur (referred to here as eclogite) in felsic granulite that may be used to better understand the rock evolution in the orogenic root of the Bohemian massif and the timing of the evolution of the orogenic lower crust. Ternary‐feldspar‐bearing intermediate‐composition granulites (referred to here as intermediate granulite), occurring as several metre‐thick layers in strongly deformed felsic granulite, were produced by metasomatic transformation of eclogite, primarily by the diffusive addition of K 2 O, H 2 O and at a larger scale by addition of melt (Štípská et al ., ,b). This study extends that work by examining the REE geochemistry of garnet and zircon and the geochronology of zircon.…”

Tracking the prograde P–T path of Precambrian eclogite using Ti-in-quartz and Zr-in-rutile geothermobarometry

“…Calibrations The calibration and pressure dependence of Zr-in-rutile presented in Tomkins et al (2007) has proven reliable in a number of studies (e.g., Racek et al 2008;Kooijman et al 2012;Ewing et al 2013;Štípská et al 2014). The Ti-in-quartz calibration (Thomas et al 2010) has, however, been discussed by Huang and Audétat (2012) who inferred that quartz which grew at slow rates and relatively "low" temperatures (600-800 °C) might result in an underestimation of T, and presented a recalibration of the Ti-inquartz geothermometer.…”

“…Besides equilibrium phase diagrams, trace element geothermometers such as 1 3 56 Page 2 of 15 zirconium-in-rutile and titanium-in-quartz (hereinafter referred to as Zr-in-rutile and Ti-in-quartz, respectively; Zack et al 2004;Watson et al 2006;Wark and Watson 2006;Ferry and Watson 2007;Thomas et al 2010) have proven independent means of P-T estimation for metamorphic terranes (e.g., Kooijman et al 2012;Ewing et al 2013;Ashley et al 2013). The Zr-in-rutile geothermometer is particularly useful for determination of equilibration temperatures of high-grade metamorphic rocks such as granulite, for which Fe-Mg exchange geothermometry is problematic (e.g., Zack et al 2004;Baldwin and Brown 2008;Zhang et al 2009;Jiao et al 2011;Kooijman et al 2012;Ewing et al 2013;Štípská et al 2014;Korhonen et al 2014;Liu et al 2015). Ti incorporation in quartz is more dependent on pressure than Zr in rutile (e.g., Thomas et al 2010).…”