Geochemistry and palaeotectonic setting of amphibolites from the Western Tatra Mountains, southern Poland

Amphibolites from the crystalline basement of the Western Tatra Mountains, which are found as small lenses within migmatitic gneisses and mica schists , were formed during pre- or early Variscan amphibolite-facies metamorphic events, and subsequently intruded by the post-metamorphic Variscan Tatra Gr anite. The amphibolites occur in both the upper and lower metamorphic compl exes, which are separated by a major subhorizontal shear zone in the Wester n Tatra Mountains. The amphibolites can be divided into three types: massiv e, striped and garnetiferous. The striped and massive amphibolites, concord ant with a dominant S-1 foliation, and the garnet amphibolites, which cross -cut the S-1 banding in the gneisses,were all originally intrusive dolerite s. The striped amphibolites (consisting primarily of hornblende, andesine a nd quartz), and later, cross-cutting garnet-hornblende-andesine-quartz-bear ing amphibolites, predominate in the lower part of the dominantly migmatiti c upper complex, and are exposed mainly on the ridges. The massive amphibol ites, which contain a similar mineral assemblage, mainly occur in the usual ly unmigmatized lower structural unit. Chemical studies indicate that three amphibolite suites are present, which probably originated as a series of e nriched tholeiites, similar to more recent plume-influenced magmas, which w ere derived by partial melting of a spinel Iherzolite with primitive mantle composition and compositionally slightly modified by crustal contamination . The amphibolites were intruded as dolerites into elastic sediments which had accumulated in an extensional basin floored by attenuated continental c rust, a situation similar to that of amphibolites found in metamorphic comp lexes within the Variscan belt, e.g. in the Orlica-Snieznik area of the Sud etes, where amphibolites chemically similar to those in the Western Tetra a lso occur. Copyright (C) 2000 John Wiley & Sons, Ltd.