Geochemical variability and origin of gabbroid to dioritoid rocks of the Železné hory Plutonic Complex

Geoscience Research Reports 49, 2016, pages 233–238

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Published online: 30 September 2016

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Abstract

The Železné hory Plutonic Complex consists of Variscan gabbroic to dioritic and granitoid rocks in its northern part (the Nasavrky Plutonic Complex between Seč in W and Skuteč in E) as well as of largely pre-Variscan rocks in various stages of deformation and metamorphic recrystallization in the southern parts. The Variscan mafic rocks, according to field relations (chilled margins, hybridization) roughly contemporaneous with biotite granites of the Žumberk (Křižanovice) type, are hornblende gabbros and gabbrodiorites corresponding to the calc-alkaline group. They have increased contents of Ba and some other mantle incompatible elements. Some geochemical parameters, namely the high Th/Ta ratios, are typical for magmas originated in supra-subduction environment. Pre-Variscan gabbros from the SW part of the area, namely the body near Horní Bradlo, are predominantly cumulitic rocks extremely poor in incompatible elements and were probably derived from tholeiitic magma type. Their composition does not suggest any link to the subduction processes. Gabbros and diorites from the SE to S part of the area are variable; most of samples display some affinity to the tholeiitic gabbro cumulates but some rocks associated to granitoids (e.g., from Petrkov W of Hlinsko) are geochemically similar to the northern, subduction-related gabbroic rocks.