Monazite Th-U-total Pb geochronology and P-T thermodynamic modelling in a revision of the HP-HT metamorphic record in granulites from Stary Gierałtów (NE Orlica-Śnieżnik Dome, SW Poland)

Thermodynamic modelling and monazite Th-U-total Pb dating via electron microprobe were used to improve the pressure, temperature and timing constraints of the HP-HT metamorphic record in granulites from Stary Gieraltow (NE Orlica-Śnieznik Dome (OSD), SW Poland). The thermodynamic calculations constrained the P-T conditions to 20-22 kbar and ca. 920oC in the felsic to intermediate granulites and 20-22 kbar and ca. 970oC in the mafic granulite. These conditions are considered to closely represent the peak temperatures experienced by these rocks. In the intermediate granulite, the matrix monazite and monazite inclusions in garnet and allanite yielded an age of 349±2.5 Ma. An HP-HT metamorphic event with temperature conditions exceeding 900oC, which are greater than the closure temperatures of most geochronometers, must have disturbed and completely reset the isotopic systems, including the Th-U-Pb system in the monazite. Consequently, this resetting prevented us from constraining the age of potential earlier metamorphic events or the igneous protolith. The 349±2.5 Ma age reflects the timing of the late-stage HP-HT event and cooling below 900oC related to the initial exhumation of the granulites. A comparison of the new P-T-t constraints with previous data from the NE Orlica-Śnieznik Dome indicates that the activation of the channels that exhumed the HP rocks to mid-crustal depths most likely initiated at ca. 350 Ma, and all the metamorphic rocks in the OSD likely shared a common Variscan evolution after ca. 340 Ma.

[1]  W. Stawikowski,et al.  Structural, metamorphic and geochronological record in the Goszów quartzites of the Orlica–Śnieżnik Dome (SW Poland): implications for the polyphase Variscan tectonometamorphism of the Saxothuringian terrane , 2016 .

[2]  M. Hand,et al.  On ultrahigh temperature crustal metamorphism: phase equilibria, trace element thermometry, bulk composition, heat sources, timescales and tectonic settings , 2015 .

[3]  K. Walczak,et al.  Preserved near ultrahigh-pressure melt from continental crust subducted to mantle depths , 2015 .

[4]  A. Larionov,et al.  The Moldanubian Thrust Zone — A terrane boundary in the Central European Variscides refined based on lithostratigraphy and U–Pb zircon geochronology , 2015 .

[5]  R. Orłowski,et al.  Migmatization and large-scale folding in the Orlica–Śnieżnik Dome, NE Bohemian Massif: Pressure–temperature–time–deformation constraints on Variscan terrane assembly , 2014 .

[6]  J. Vozár,et al.  Ordovician and Cretaceous tectonothermal history of the Southern Gemericum Unit from microprobe monazite geochronology (Western Carpathians, Slovakia) , 2014, International Journal of Earth Sciences.

[7]  E. Oliot,et al.  Variscan thermal overprints exemplified by U-Th-Pb monazite and K-Ar muscovite and biotite dating at the eastern margin of the Bohemian Massif (East Sudetes, Czech Republic) , 2014 .

[8]  J. Majka,et al.  Constraints on the Devonian–Carboniferous closure of the Rheic Ocean from a multi-method geochronology study of the Staré Město Belt in the Sudetes (Poland and the Czech Republic) , 2013 .

[9]  K. Nejbert,et al.  Paleomagnetism and magnetic mineralogy of metabasites and granulites from Orlica-Śnieżnik Dome (Central Sudetes) , 2013, Acta Geophysica.

[10]  M. Corsini,et al.  Crustal influx, indentation, ductile thinning and gravity redistribution in a continental wedge: Building a Moldanubian mantled gneiss dome with underthrust Saxothuringian material (European Variscan belt) , 2012 .

[11]  A. Żelaźniewicz,et al.  Gneisses in the Orlica-Śnieżnik Dome, West Sudetes : a single batholitic protolith or a more complex origin? , 2011 .

[12]  K. Schulmann,et al.  Prograde and retrograde metamorphic fabrics – a key for understanding burial and exhumation in orogens (Bohemian Massif) , 2011 .

[13]  D. Harlov,et al.  Resetting monazite ages during fluid-related alteration , 2011 .

[14]  A. Larionov,et al.  Zircon geochronology and trace element characteristics of eclogites and granulites from the Orlica-Śnieżnik complex, Bohemian Massif , 2009, Geological Magazine.

[15]  D. Nakamura,et al.  A new formulation of garnet–clinopyroxene geothermometer based on accumulation and statistical analysis of a large experimental data set , 2009 .

[16]  I. Petrik,et al.  Metasomatic replacement of inherited metamorphic monazite in a biotite-garnet granite from the Nízke Tatry Mountains, Western Carpathians, Slovakia: Chemical dating and evidence for disequilibrium melting , 2009 .

[17]  J. Lekki,et al.  EPMA and PIXE dating of monazite in granulites from Stary Gierałtów, NE Bohemian Massif, Poland , 2008 .

[18]  D. Cherniak,et al.  Th diffusion in monazite , 2008 .

[19]  K. Schulmann,et al.  Vertical extrusion and horizontal channel flow of orogenic lower crust: key exhumation mechanisms in large hot orogens? , 2008 .

[20]  R. Powell,et al.  An order-disorder model for omphacitic pyroxenes in the system jadeite-diopsidehedenbergite- acmite, with applications to eclogitic rocks , 2007 .

[21]  R. Powell,et al.  Progress relating to calculation of partial melting equilibria for metapelites , 2007 .

[22]  M. Thirlwall,et al.  Lu–Hf geochronology and trace element distribution in garnet: Implications for uplift and exhumation of ultra-high pressure granulites in the Sudetes, SW Poland , 2007 .

[23]  Michael J. Jercinovic,et al.  Geochronology: Understanding Geologic Processes by Integrating Composition and Chronology , 2007 .

[24]  R. Wirth,et al.  Pb diffusion in monazite: An experimental study of Pb+Th2Nd interdiffusion , 2006 .

[25]  Dumicz Marian The history of eclogites in the geological evolution of the Śnieżnik crystalline complex based on mesostructural analysis , 2006 .

[26]  D. Schneider,et al.  Exhumation and metamorphism of an ultrahigh-grade terrane: geochronometric investigations of the Sudete Mountains (Bohemia), Poland and Czech Republic , 2005, Journal of the Geological Society.

[27]  R. Armstrong,et al.  Sm–Nd and U–Pb dating of high‐pressure granulites from the Złote and Rychleby Mts (Bohemian Massif, Poland and Czech Republic) , 2005 .

[28]  K. Schulmann,et al.  Vertical extrusion and middle crustal spreading of omphacite granulite: a model of syn‐convergent exhumation (Bohemian Massif, Czech Republic) , 2004 .

[29]  E. Watson,et al.  Pb diffusion in monazite: a combined RBS/SIMS study , 2004 .

[30]  R. Powell,et al.  Activity–composition relations for phases in petrological calculations: an asymmetric multicomponent formulation , 2003 .

[31]  T. Holland,et al.  Mixing properties of phengitic micas and revised garnet‐phengite thermobarometers , 2002 .

[32]  M. Jercinovic,et al.  Microprobe monazite geochronology: putting absolute time into microstructural analysis , 2002 .

[33]  D. Cherniak,et al.  Pb diffusion in zircon , 2001 .

[34]  J. Blichert‐Toft,et al.  Lu–hf garnet geochronology: closure temperature relative to the Sm–Nd system and the effects of trace mineral inclusions , 2000 .

[35]  Worley,et al.  The effect of TiO2 and Fe2O3 on metapelitic assemblages at greenschist and amphibolite facies conditions: mineral equilibria calculations in the system K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3 , 2000 .

[36]  R. Gayer,et al.  A model for a continental accretionary wedge developed by oblique collision: the NE Bohemian Massif , 2000, Journal of the Geological Society.

[37]  M. Bröcker,et al.  Fluid influence on mineral reactions in ultrahigh-pressure granulites: a case study in the Śnieżnik Mts. (West Sudetes, Poland) , 1999 .

[38]  Ganguly,et al.  Diffusion kinetics of samarium and neodymium in garnet, and a method for determining cooling rates of rocks , 1998, Science.

[39]  Roger Powell,et al.  An internally consistent thermodynamic data set for phases of petrological interest , 1998 .

[40]  Ian S. Williams,et al.  Pb, U and Th diffusion in natural zircon , 1997, Nature.

[41]  Z. Cymerman,et al.  Terranes and terrane boundaries in the Sudetes, northeast Bohemian Massif , 1997, Geological Magazine.

[42]  A. Provost,et al.  Electron microprobe dating of monazite , 1996 .

[43]  R. Kryza,et al.  High‐pressure granulites from the Sudetes (south‐west Poland): evidence of crustal subduction and collisional thickening in the Variscan Belt , 1996 .

[44]  W. McDonough,et al.  The composition of the Earth , 1995 .

[45]  H. Maluski,et al.  Terrane boundaries in the Bohemian Massif: Result of large-scale Variscan shearing , 1990 .

[46]  A. Tindle,et al.  Trace Element Discrimination Diagrams for the Tectonic Interpretation of Granitic Rocks , 1984 .

[47]  B. Budzyń,et al.  Stability of monazite and disturbance of the Th-U-Pb system under experimental conditions of 250–350 °C and 200–400 MPa , 2015 .

[48]  Donna L. Whitney,et al.  Abbreviations for names of rock-forming minerals , 2010 .

[49]  R. Gotowała,et al.  The boundary zone of the East and West Sudetes on the 1:50 000 scale geological map of the Velké Vrbno, Staré Město and Śnieżnik Metamorphic Units , 2003 .

[50]  W. Franke,et al.  The eastern termination of the Variscides: terrane correlation and kinematic evolution , 2000, Geological Society, London, Special Publications.

[51]  N. Bakun-czubarow Ilmenite-bearing ecologites of the West Sudetes -their geochemistry and mineral chemistry , 1998 .

[52]  N. Bakun-czubarow Geodynamic significance of the variscan HP eclogite-granulite series of the Złote Mountains in the Sudetes , 1991 .