Sequential granite emplacement: a structural study of the late Variscan Strzelin intrusion, SW Poland

Teresa Oberc-Dziedzic,Ryszard Kryza,Stanisław Madej,Christian Pin

doi:10.1007/s00531-013-0863-y

Abstract

The Strzelin Massif in SW Poland (Central European Variscides) records a protracted igneous evolution, with three main magmatic stages: (1) tonalitic I, (2) granodioritic and (3) tonalitic II/granitic. In the northern part of this Massif, the Strzelin intrusion proper comprises three successively emplaced rock types: a medium-grained biotite granite (303 ± 2 Ma), a fine-grained biotite granite (283 ± 8 Ma) and a fine-grained biotite-muscovite granite; based on field evidence, the third variety postdates both types of the biotite granites. The structural data from the three granites, including their parallel, approximately E–W striking and steeply dipping lithological contacts and ENE–WSW trending subhorizontal magmatic lineations, suggest that the emplacement of all three successive granite varieties was controlled by an active, long-lived strike-slip fault, striking ESE–WNW, with a dextral sense of movement. After the emplacement of the youngest biotite-muscovite granite, the intrusion underwent brittle extension which produced “Q joints” striking NNW–SSE to N–S and dipping at 55–70° WSW to W, and showing evidence of broadly N–S directed sinistral displacements. The structural observations, supported by new geochronological data, indicate that the internal structure of the composite granitoid intrusion, including the faint magmatic foliation and lineation, formed in a long-lived strike-slip setting, different from the subsequent, post-emplacement extensional tectonics that controlled the development of brittle structures.

Highlights

Extensive granitoid plutonism is a distinct feature of the European Variscides (Fig. 1a)
In the Bohemian Massif in the eastern part of the Variscan belt (Fig. 1b), the igneous activity continued from the late Devonian to early Permian and produced granitoid magmas generated from various sources and, differing in their petrographic and geochemical characteristics (Finger et al 1997)
The internal structures of the Strzelin intrusion, including the lineation, were formed earlier and in a different tectonic environment (WNW–ESE oriented dextral strike-slip zone) than the Q fractures that originated during ENE–WSW to E–W extension and minor N–S directed sinistral shearing (Fig. 11)

Summary

Introduction

Extensive granitoid plutonism is a distinct feature of the European Variscides (Fig. 1a). Both the medium- and fine-grained biotite granites are cut by steep, several meters to tens of centimeters sized, Fig. 6 Internal structures of the Strzelin intrusion. The youngest fine-grained biotite-muscovite granite, that forms steep E–W, ESE–WNW striking dykes, usually shows a foliation and lineation which are oblique to the walls of the dykes (Fig. 7d).

Results

Conclusion