@article{63,
  keywords = {Eclogite-facies metamorphism, exhumation, Lu-Hf and Sm-Nd garnet geochronology, Phase-equilibria modelling, Variscan orogeny},
  author = {Stephen Collett and Pavla {\v S}t{\'\i}psk{\'a} and Karel Schulmann and Vit Pe{\v r}est{\'y} and J{\'e}r{\'e}mie Soldner and Robert Anczkiewicz and Ondrej Lexa and Andrew Kylander-Clark},
  title = {Combined Lu-Hf and Sm-Nd geochronology of the Mari{\'a}nsk{\'e} L{\'a}zn{\v e} Complex: New constraints on the timing of eclogite- and granulite-facies metamorphism},
  abstract = {Abstract Lu-Hf and Sm-Nd garnet-whole rock geochronology combined with petrographic observations, minero-chemical variations, thermodynamic modelling and structural data was used to constrain the P{\textendash}T{\textendash}t{\textendash}d evolution of eclogites from the Mari{\'a}nsk{\'e} L{\'a}zn{\v e} Complex (Bohemian Massif). Boudins of mostly isotropic eclogite with relict steep eclogite-facies fabric are affected by steep migmatitic foliation, which is followed on a regional scale by the development of almost pervasive, predominantly SE-dipping, extensional foliation. The structural succession shows continuous transition from eclogite to garnetiferous migmatitic amphibolite and to amphibolite migmatite. A least retrogressed sample of eclogite shows clusters of fine-grained inclusion-poor garnet, omphacite relicts surrounded by a fine-grained clinopyroxene-plagioclase symplectite with minor amphibole, biotite-plagioclase intergrowths after white mica, kyanite with plagioclase-spinel coronas and accessory rutile. Rare potassic white mica occurs as inclusions in omphacite. A more retrogressed eclogite, with no omphacite or kyanite relicts, contains inclusion-poor garnet surrounded by amphibole-plagioclase corona in a matrix dominated by plagioclase-amphibole symplectite with minor clinopyroxene. In places, the symplectite is overgrown by coarse-grained amphibole. Peak P{\textendash}T conditions, inferred from combined conventional thermobarometry and phase-equilibria modelling and based on inclusions of white mica (up to 3.33 Si p.f.u.), matrix omphacite (Jd33{\textendash}36) and garnet core (Alm33{\textendash}38Prp38{\textendash}42Grs22{\textendash}25Sps1) compositions are  25 kbar at 650{\textendash}750 {\textdegree}C. A \HT\ overprint occurred at  14{\textendash}18 kbar and \>800 {\textdegree}C based on coexisting clinopyroxene (Jd18{\textendash}24), plagioclase (An18{\textendash}35), and amphibole (Na(B) \<0.20; Al(C) = 0.60{\textendash}1.15) in symplectite after original omphacite and phase-equilibria modelling of garnet mantle compositions. Lu-Hf and Sm-Nd garnet geochronology has been applied to both samples, an older age (c. 390 Ma) obtained by the Lu-Hf method is interpreted as the timing of \HP\ metamorphism, while c. 15 Ma younger ages were obtained by the Sm-Nd method. As temperatures for the \HT\ overprint exceed the empirically and experimentally determined closure temperature of the Sm-Nd system the Sm-Nd ages are interpreted to date cooling following the \HT\ overprint. Combined together, contrasting eclogite and amphibolite-facies migmatite fabrics, the mineral textures, calculated P{\textendash}T conditions, and distinct Lu-Hf and Sm-Nd ages, provide a complete P{\textendash}T{\textendash}t{\textendash}D path characterised by rapid ( 15 Ma) transition from \HP\ subduction, crustal thickening to extensional \HT\ shearing. This unconventional exhumation path does not fit to models of monocyclic exhumation in a subduction channel proposed for the M{\"u}nchberg and {\.Z}EV\ Devonian \HP\ units to the west. In contrast, the post-peak extensional low angle shearing shortly after subduction and collision resembles more the geodynamic model typical for the Iberian subduction system both in time scales and sequence of tectonic events.},
  year = {2018},
  booktitle = {Lithos},
  journal = {Lithos},
  series = {Lithos},
  volume = {304{\textendash}307},
  pages = {74-94},
  issn = {0024-4937},
  url = {https://www.sciencedirect.com/science/article/pii/S0024493718300495},
  doi = {https://doi.org/10.1016/j.lithos.2018.02.007},
}