THE LESZCZYNIEC META-IGNEOUS COMPLEX IN THE EASTERN PART OF THE KARKONOSZE-IZERA BLOCK, WESTERN SUDETES - TRACE-ELEMENT AND ND ISOTOPE STUDY

Major, trace and Nd isotope data on twelve samples of meta-igneous roc ks of the eastern part of the Karkonosze-Izera Block, mostly from its uppermost tectonic unit, the Leszczyniec meta-igneous complex, are dis cussed. 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 maf ic rocks have smooth incompatible element patterns, with a strong depl etion of Th, Nb and LREE, and with high epsilon Nd-500 values, between +7 and +8. These characteristics support affinities with basaltic mel ts extracted from strongly depleted mantle sources, such as N-type MOR Bs. Some of these rocks display anomalies indicating probable accumula tion and/or crustal contamination processes. The felsic rocks are all characterized by flat HREE patterns, with deep negative anomalies of N b, Ti, Eu and Sr, and with also high positive epsilon Nd-500, from +6. 2 to +6.8. Most likely, these felsic rocks represent fractionational p roducts of parent magmas similar to those of the mafic rocks. The two analyzed samples of hornblende-rich metadiorites are markedly differen t. They are enriched in Th and LREE, with negative Nb anomalies, and t hey have low epsilon Nd-500 (+2-8 and +1.6). The metadiorites are remi niscent of island-arc lavas, but may also have formed by crustal conta mination of rift-related magmas. In contrast to most previous interpre tations, which regarded the Leszczyniec complex as a subduction-relate d igneous suite, it is suggested that the complex was emplaced in an e xtensional setting which contained continental-crust components and wa s, subsequently, incorporated into a sort of accretionary prism.