Garnet pyroxenite in the Biskupice peridotite, Bohemian Massif: anatomy of a Variscan high-pressure cumulate

Abstract

A strongly layered garnet pyroxenite, consisting of cm-scale layers of garnetite, garnet orthopyroxenite, garnet clinopyroxenite, and websterite, occurs in the Biskupice garnet peridotite, which is located in migmatitic gneiss of the Gföhl Assemblage in the Vysočina District, western Moravia. Major-and trace-element compositions and REE patterns of minerals and layers in the pyroxenite are consistent with origin of the layers by HT-HP crystallization and accumulation of variable proportions of garnet, orthopyroxene, and clinopyroxene. The present compositions of the minerals (pyroperich garnet, low-Al, low-Ca enstatite and low-Al, high-Ca diopside) are the result of extensive subsolidus re-equilibration at ~900 ºC and ~37 kbar, during the Variscan (332 Ma) Orogeny. Neodymium and strontium isotopic values (ε

Chromium-rich illite/smectite in the basal Balinka Conglomerate of the Upper Carboniferous-Permian Boskovice Basin (Bohemian Massif)

“…Cr-rich spinelides (Cr-spinel, magnesiochromite, chromite) are common accessory minerals in altered ultrabasic and basic rocks of Gföhl Unit of the Moldanubian zone adjacent to the Boskovice Basin (Fig. 8; Weiss, 1966;Medaris et al, 2005Medaris et al, , 2013Hršelová et al, 2018)…”

“…On the basis of textural position, the chromium-rich I/S in the Balinka Conglomerate can be considered mostly A. Serpentinite occurrences in Gföhl Unit surrounding the Boskovice Basin. Serpentinized spinel (±garnet) type is defined modified after Weiss (1966) and Medaris et al (2013). B. Compositions of the chromium-bearing spinels in the heavy mineral assemblage of conglomerates in the Boskovice Basin and peridotites from the adjacent Gföhl Unit including two subtypes of spinel (±garnet) Mohelno type peridotites (see Medaris et al, 2005;Hršelová et al, 2018, for explanations).It can be seen that, while magnesiochromite is common in peridotites, it is almost absent in the Balinka Conglomerate.…”

Mantle Zn Isotopic Heterogeneity Caused by Melt‐Rock Reaction: Evidence From Fe‐Rich Peridotites and Pyroxenites From the Bohemian Massif, Central Europe

“…In the elemental plots, light gray solid circles denote Fe‐rich peridotites from Tok (Siberia) and the North China Craton (Ionov et al, ; Xiao et al, ; Zhao et al, ). Empty circles denote garnet pyroxenites from the Bohemian Massif and the North China Craton (Hu et al, ; Medaris et al, , ; Svojtka et al, ; Zhao, Zhang, et al, ). The black stars denote the composition of the primitive mantle (McDonough & Sun, ).…”