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

Abstract

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 Granite. The amphibolites occur in both the upper and lower metamorphic complexes, which are separated by a major subhorizontal shear zone in the Western Tatra Mountains. The amphibolites can be divided into three types: massive, striped and garnetiferous. The striped and massive amphibolites, concordant with a dominant S1 foliation, and the garnet amphibolites, which cross‐cut the S1 banding in the gneisses, were all originally intrusive dolerites. The striped amphibolites (consisting primarily of hornblende, andesine and quartz), and later, cross‐cutting garnet‐hornblende‐andesine‐quartz‐bearing amphibolites, predominate in the lower part of the dominantly migmatitic upper complex, and are exposed mainly on the ridges. The massive amphibolites, which contain a similar mineral assemblage, mainly occur in the usual unmigmatized lower structural unit. Chemical studies indicate that three amphibolite suites are present, which probably originated as a series of enriched tholeiites, similar to more recent plume‐influenced magmas, which were derived by partial melting of a spinel lherzolite with primitive mantle composition and compositionally slightly modified by crustal contamination. The amphibolites were intruded as dolerites into clastic sediments which had accumulated in an extensional basin floored by attenuated continental crust, a situation similar to that of amphibolites found in metamorphic complexes within the Variscan belt, e.g. in the Orlica–Snieznik area of the Sudetes, where amphibolites chemically similar to those in the Western Tatra also occur. Copyright © 2000 John Wiley & Sons, Ltd.

Variscan post-collisional cooling and uplift of the Tatra Mountains crystalline block constrained by integrated zircon, apatite and titanite LA-(MC)-ICP-MS U-Pb dating and rare earth element analyses

“…1b). The metamorphic complex is composed of metapelitic-metapsammitic rocks (paragneisses and mica schists), intercalated with amphibolites, with three groups of amphibolites (Gawęda et al, 2000). Two amphibolite units have been dated by U-Pb zircon geochronology and likely represent two distinct oceanic domains that formed at c. 560 and c. 500 Ma (Gawęda et al, 2016b;Gawęda et al, 2017).…”

“…Two amphibolite units have been dated by U-Pb zircon geochronology and likely represent two distinct oceanic domains that formed at c. 560 and c. 500 Ma (Gawęda et al, 2016b;Gawęda et al, 2017). A third amphibolite unit is garnet-bearing (Gawęda et al, 2000) and likely represents retrograde eclogites (Burda et al, 2015). Based on its trace element geochemistry and Sr-Nd isotope compositions, the protolith of the c. 560 Ma amphibolites was interpreted as MORB-type basalt (Gawęda et al, 2017), while the c. 500 Ma amphibolites likely represent tholeiitic basalts that intruded a basin floored by attenuated continental crust, as they exhibit varying degrees of lower crustal contamination (Gawęda et al, 2000;Gawęda et al, 2016b).…”

“…Crystalline nappes within the metamorphic envelope are comprised of different lithologies and metamorphic grade (e.g. Gawęda et al, 2000;Gawęda and Burda, 2004;Burda and Gawęda, 2009). The nappes are bounded by local ductile and brittle-ductile shear zones, dated by the K-Ar method on syn-tectonic muscovite crystals at c. 343-298 Ma (Deditius, 2004).…”

“…The chemical composition of this amphibolite corresponds to the suite 1 amphibolites defined by Gawęda et al (2000), with Zr/Y~4, ΣREE = 102.87, flat chondrite (C1)-normalized REE patterns with Ce N / Yb N = 2.17 and Eu/Eu* = 0.8 (Supplementary Table 1). The protolith of these amphibolites are interpreted as mantle plume-related tholeiites.…”

Pre-Variscan evolution of the Western Tatra Mountains: new insights from U-Pb zircon dating

“…The Upper Unit is composed of migmatitic rocks: gneisses and amphibolites, graphite quartzites and subordinate intercalations of mica schists (Burda and Gawęda 1997 , 1999 ; Gawęda et al 2000 ). The peak of metamorphism in this unit was under upper amphibolite facies conditions ( T = 690–780°C, P = 7.5–10 kbar; Kohút and Janak 1994 ; Gawęda et al 1998 ).…”