Geological position, mineral assemblages and contamination of granitic pegmatites in the Moldanubian Zone, Czech Republic; examples from the Vlastějovice region
| Authors | |
|---|---|
| Year of publication | 2013 |
| Type | Article in Periodical |
| Magazine / Source | Journal of Geological Sciences |
| MU Faculty or unit | |
| Citation | |
| Doi | http://dx.doi.org/10.3190/jgeosci.132 |
| Field | Geology and mineralogy |
| Keywords | tourmaline amphibole granitic pegmatites Fe-skarn fractionation contamination Vlastějovice Moldanubian Zone |
| Description | Three groups of pegmatites distinct in their geological position, age, internal structure, mineral assemblages and chemical composition of minerals (tourmaline, amphibole, garnet, biotite) were distinguished in the Vlastějovice region, Moldanubian Zone: a) tourmaline-bearing pegmatites (Qz+Kfs+Pl+Bt+Ms+Tur) enclosed in pre-Variscan orthogneiss, b) contaminated amphibole-bearing pegmatites (Pl+Qz+Amp+Kfs+Fl) cutting Fe-skarn, and c) tourmaline-bearing pegmatites cutting gneisses (Qz+Kfs+Pl+Bt+Ms+Ab+Tur+Grt) and Fe-skarn (Qz+Kfs+Pl+Bt+TurAb,Amp,Grt,Elb). The pegmatites enclosed in orthogneiss show simple internal structure and mineral assemblages, low tectonic and metamorphic overprint, and represent the earliest generation of granitic pegmatites in the Moldanubian Zone. The amphibole-bearing pegmatites, likely anatectic and related to the Variscan regional metamorphism, are spatially restricted to Fe-skarn body and highly variable in shape, size, in-situ Ca,Fe(F,REE)-contamination from host Fe-skarn and degree of hydrothermal overprint. The tourmaline-bearing pegmatites related to the Variscan magmatic event cut different rocks (gneisses, Fe-skarn) and belong to the Moldanubian rare-element pegmatite province. Tourmaline-bearing pegmatites were evidently generated from the granite-pegmatite body in the footwall contact of the Fe-skarn body. Degrees of the textural differentiation and geochemical fractionation of the individual tourmaline-bearing pegmatites are comparable to those of the respective parts of the parental footwall granite-pegmatite body. This observation seems consistent with the model of sequential derivation of pegmatite melts from evolving parental granite. Primitive to highly evolved and usually B-rich pegmatites originated during the Variscan orogeny from the MP conditions of ~6-7 kbars to the LP conditions of P ~2 kbars, and manifest that formation of various granitic pegmatites is an integral part of the tectono-magmatic evolution of the region. |
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