The Leszczyniec meta-igneous complex in the eastern part of the Karkonosze-Izera Block, Western Sudetes: trace element and Nd isotope study
Kryza, Ryszard; Mazur, Stanisław; Pin, Christian
published: Dec 1, 1995
ArtNo. ESP154017001003, Price: 29.00 €
Major, trace and Nd isotope data on twelve samples of meta-igneous rocks of the eastern part of the Karkonosze-Izera Block, mostly from its uppermost tectonic unit, the Leszczyniec meta-igneous complex, are discussed. The complex is composed of both plutonic and volcanic members of basic, intermediate and acidic compositions, recently dated at ca. 500 Ma using the U-Pb zircon method. Typically, the fine-grained mafic rocks have smooth incompatible element patterns, with a strong depletion of Th, Nb and LREE, and with high ∈ Nd500 values, between +7 and +8. These characteristics support affinities with basaltic melts extracted from strongly depleted mantle sources, such as N-type MORBs. Some of these rocks display anomalies indicating probable accumulation and/or crustal contamination processes. The felsic rocks are all characterized by flat HREE patterns, with deep negative anomalies of Nb, Ti, Eu and Sr, and with also high positive ∈ Nd500>/sub>, from +6.2 to +6.8. Most likely, these felsic rocks represent fractionational products of parent magmas similar to those of the mafic rocks. The two analyzed samples of hornblende-rich metadiorites are markedly different. They are enriched in Th and LREE, with negative Nb anomalies, and they have low ∈ Nd500 (+2.8 and +1.6). The metadiorites are reminiscent of island-arc lavas, but may also have formed by crustal contamination of rift-related magmas. In contrast to most previous interpretations, which regarded the Leszczyniec complex as a subduction related igneous suite, it is suggested that the complex was emplaced in an extensional setting which contained continental-crust components and was, subsequently, incorporated into a sort of accretionary prism.