Ocean floor basalt, not continental gabbro: a reinterpretation of the Hoher Bogen amphibolites, Teplá-Barrandian, Bohemian massif

Abstract

At its southern margin along the Hoher Bogen mountain, the Teplá-Barrandian (Bohemian massif, Central Europe) is made up of a 1-to 4-km wide belt of amphibolites. An upper amphibolite/lower granulite facies Variscan metamorphism has brought forth coarse-grained, weakly foliated rocks with hbl+pl±cpx±opx±grt parageneses. Since the beginning of this century, these rocks, together with fine-grained or mylonitized amphibolites, have been regarded as metamorphic gabbros (gabbro amphibolites) of the Neukirchen-Kdyne igneous complex. Relics of magmatic textures, however, cannot be found anywhere. The amphibolites are therefore reinterpreted as metamorphic basalts. The Hoher Bogen amphibolites (HBA) derive from N-type MORB. The most primitive samples have Mg#s between 60 and 65. Locally occurring (garnet-)hornblendites and leucodioritic mobilisates are the products of partial melting of amphibolites during the Variscan metamorphism and do not belong to the primary magmatic rock association. Ultramafic rocks are tectonically emplaced between the HBA belt and the metapelitic rocks of the Moldanubian. At the very least, the metapyroxenites among them seem to have a cumulus origin. Together with the ultramafic rocks, the HBA belt may be regarded as a metaophiolite, comparable to the Mariánské Lazne complex. The reinterpretation of the former "gabbro amphibolites" as a metaophiolite has consequences for the geology of the Teplá-Barrandian: the size of the Neukirchen-Kdyne igneous complex is reduced. The HBA belt is a piece of oceanic crust which is possibly younger than the Precambrian metasedimentary/metavolcanic country rock of the Neukirchen-Kdyne igneous complex.

Geogene and anthropogenic controls on the mineralogy and geochemistry of modern alluvial–(fluvial) gold placer deposits in man-made landscapes in France, Switzerland and Germany

“…Low to medium grade regionally metamorphosed rocks and late Variscan granites in the crystalline basement were uplifted along this boundary fault, providing a prominent source rock area for the Danube drainage system. About 50 km NNE of the sampling site metabasic and ultrabasic rocks of the Teplá Barrandian unit are exposed (Propach and Pfeiffer, 1998).…”

“…These minerals place this type of deposit into a special position, because a dual source-model has to be designed for this mineral assemblage. The presence of PGM in the heavy mineral suite can plausibly be explained by erosion of the head waters of the rivers into the (ultra)basic igneous rocks of the Teplá-Barrandiam Zone which were interpreted as part of metaophiolite sequence sensu lato by Propach and Pfeiffer (1998) and that host so-called Cyprus-type VMS deposits beyond the border in the Czech part of the Bohemian Massif (Mrázek and Pouba, 1995) (Fig. 1f).…”

Morphology and mineral chemistry of monazite–zircon-bearing stream sediments of continental placer deposits (SE Germany): Ore guide and provenance marker

“…Primary PGE mineralization in the Bohemian Massif is sporadic and bound to small intercalations of (ultra)basic magmatic rocks Johan, 1989;Pašava et al, 2003). There are no large basic complexes at the western edge of the Bohemian Massif which might contribute to the buildup of a heavy mineral spectrum typical of these igneous rocks and, on the other hand, monazite is an uncommon accessory mineral in this kind of magmatic rocks (Propach and Pfeiffer, 1998). The situation faced with in the Naab River drainage system may be refound downstream in the Donau as well.…”

Heavy mineral-based provenance analysis of Mesozoic continental-marine sediments at the western edge of the Bohemian Massif, SE Germany: with special reference to Fe–Ti minerals and the crystal morphology of heavy minerals

“…On the basis of their chromium contents, the lherzolitic spinels and the harzburgite magnesiochromites are held to be analogous to those from abyssal peridotites and oceanic (including back-arc basins) ophiolites, whereas the chromites in the dunite resemble those from arc-related ophiolitic sequences. About 80 km east of the sampling site at Wackersdorf, metabasic and ultrabasic rocks of the Tepla-Barrandian unit are exposed within the Bayerischer Wald (Propach and Pfeiffer 1998) (Fig. 1b).…”