@article{561fdb03ac364e52b64b19f179dd2765,
title = "Mineralogical heterogeneity of UHP garnet peridotite in the Moldanubian Zone of the Bohemian Massif (Nov{\'e} Dvory, Czech Republic)",
abstract = "Previous reports on Nov{\'e} Dvory garnet peridotites indicated that they lacked primary spinel, and prograde metamorphism evidence was uncommon. This study revealed the presence of Al- and Cr-rich spinels, clinopyroxenes with a lower content of Na and Fe than what has been previously reported, and chemical heterogeneity in garnet in Nov{\'e} Dvory garnet peridotites. Cr-poor (0.06-0.12 a.p.f.u.) and Cr-rich (0.10-0.27 a.p.f.u.) garnet populations were identified, and they had contrasting coronas around garnet. The garnet peridotite samples were classified into three types on the basis of the chemical composition of garnet and constituent minerals: type A that includes Cr-rich spinel and Cr-rich garnet; type B that includes Cr-poor garnet and no spinel; and type C that includes both Al- and Cr-rich spinel and both Cr-rich and Cr-poor garnet. The finding of spinel relics (Cr# = [100 Cr/ (Cr + Al)] ~ 60-70) in garnet from type A peridotite suggests that the Nov{\'e} Dvory peridotite body may have been located at relatively shallow depths prior to the ultrahigh-pressure metamorphic stage of >4 GPa. Suitable geothermobarometers were used to establish the P-T history of the rocks. The core compositions of clinopyroxene inclusions in garnet and host garnet yielded 978-1002 °C, 4.87-5.12 GPa (type B) and 1034 °C, 4.93 GPa (type C); stage I. Garnet porphyroblasts in type A peridotite lack clinopyroxene inclusions. The core compositions of garnet and pyroxenes yielded 1005-1072 °C, 4.42-4.46 GPa (type A); stage II. The innermost garnet rims and cores of matrix pyroxenes surrounding garnet yielded 1222-1325 °C, 5.03-5.67 GPa (type B) and 1189-1267 °C, 5.59-6.97 GPa (type C); stage II. Thus, Nov{\'e} Dvory peridotite has experienced an increase in the P-T conditions, and its chemical heterogeneity (especially in the Cr content of garnet) in type C peridotites may have been created by the mechanical mixing of different rock types (i.e., Cr-rich and Cr-poor types) during the compression and/or decompression stage(s).",
keywords = "Bohemian Massif, Garnet peridotite, Phlogopite, Primary spinel, Ultrahigh-Pressure",
author = "Juliah Muriuki and Daisuke Nakamura and Takao Hirajima and Martin Svojtka",
note = "Funding Information: The garnet peridotite samples studied here were mainly collected as part of a cooperative project between Kyoto University and the Czech Academy of Sciences. We would like to thank members of the project, T. Kobayashi, K. Naemura, T. Usuki, and K. Yoshida and also thank A. Yasumoto for his analyses of X-ray mapping at Okayama University of Science. We specially thank K. Naemura for his support with Raman spectroscopy analyses at Kyoto University. We also acknowledge K. Fukui and T. Baba for their early works on these peridotite samples, T. Nozaka and T. Fujise for providing comments on this study in Okayama University and T. Fujiwara for making thin sections. We are particularly grateful to M. Obata and an anonymous reviewer for their constructive comments which helped improve this paper. We also deeply thank M. Enami for his careful editorial work. This work was supported by JSPS KAKENHI Grant Numbers JP16K05610 to DN and JP25257208 to TH and by the Institute of Geology of the Czech Academy of Sciences institutional support RVO67985831 to MS. Funding Information: The garnet peridotite samples studied here were mainly collected as part of a cooperative project between Kyoto University and the Czech Academy of Sciences. We would like to thank members of the project, T. Ko-bayashi, K. Naemura, T. Usuki, and K. Yoshida and also thank A. Yasumoto for his analyses of X–ray mapping at Okayama University of Science. We specially thank K. Naemura for his support with Raman spectroscopy analyses at Kyoto University. We also acknowledge K. Fukui and T. Baba for their early works on these peridotite samples, T. Nozaka and T. Fujise for providing comments on this study in Okayama University and T. Fujiwara for making thin sections. We are particularly grateful to M. Obata and an anonymous reviewer for their constructive comments which helped improve this paper. We also deeply thank M. Enami for his careful editorial work. This work was supported by JSPS KAKENHI Grant Numbers JP16K05610 to DN and JP25257208 to TH and by the Institute of Geology of the Czech Academy of Sciences institutional support RVO67985831 to MS. Publisher Copyright: {\textcopyright} 2020 Tohoku University.",
year = "2020",
doi = "10.2465/JMPS.190126",
language = "English",
volume = "115",
pages = "1--20",
journal = "Journal of Mineralogical and Petrological Sciences",
issn = "1345-6296",
publisher = "Tohoku University",
number = "1",
}