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Author: |
Zbigniew CYMERMAN
Państwowy Instytut Geologiczny Oddział Dolno¶l±ski, al. Jaworowa 19, 53-122 Wrocław
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Title: |
STRUCTURAL AND KINEMATIC ANALYSIS AND THE VARISCAN TECTONIC EVOLUTION OF THE KACZAWA COMPLEX (THE SUDETES)
(with 96 Figures and 15 Plates)
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Abstract.
The Kaczawa complex is the largest geological unit of the Sudetes, and is built of the Palaeozoic
volcano-sedimentary rocks metamorphosed during the Variscan orogeny in greenschist facies conditions.
Detailed structural and kinematic analysis of the whole Kaczawa complex revealed two principal deformational
events (D1 and D2). The first, main deformation event (D1) was marked by localised variable ductile shearing,
causing a pervasive bed-parallel (locally pressure-solution) S1 foliation, associated with a W–E to NW–SE
trending L1 stretching mineral lineation. In the localised, heterogeneous shear zones the kinematic indicators
(e.g. S–C mylonitic structures and s-type porphyroclasts) generally indicate tectonic transport to the west and
northwest. The D1 deformation took place in a transpressional tectonic regime, where the overriding thrust
sheets moved, in general, to the west and northwest. During the localised D2 deformation, tectonic movements
became extensional and more brittle, which mainly formed brittle-ductile C' type extensional shear-bands,
sometimes regarded as S2 crenulation cleavage, crosscut S1 foliation. The C' type extensional asymmetric shear-
bands document normal-type displacement towards the east, except for local minor top-to-the-west movements.
As a result of combined structural and kinematic analysis, a new structural model for the Variscan evolution of
the Kaczawa complex is proposed. Crustal shortening by the nappe stacking during the D1 transpressional
deformation resulted in the development of thrust slices. Five tectonic units (Jakuszowa, Dobromierz, Cieszów,
Pyszczyńska Góra and ¦roda ¦l±ska thrust sheets) which are built from metabasic rocks of oceanic crust has
been overthrusted more or less toward the west along the Kaczawa zone on the allochthoneous units: Chełmiec,
Rzeszówek, Wleń, Radzimowice, Bolków, Sady Górne and Domanice. On the other hand, these units forming
also imbricated thrust sheets, were thrusted westwards on less deformed and metamorphosed parautochthoneous
units (Lubań ¦l±ski, Pilchowice, ¦wierzawa, Luboradz and an unnamed unit from the vicinity of Bolesławiec).
The important role of the Kaczawa Zone has been underlined here as a regional-scale décollement with high-
strain zones, which incorporate lower-strain domains, formed during the D1 sinistral transpressional regime. In
the tectonic model of the evolution of the Kaczawa complex which is presented here, the western part (lower
structural units) of the Kaczawa complex belongs to the Saxothuringian Terrane, and those structural units
overriding the Kaczawa zone, mainly the Dobromierz and Jakuszowa units, belong to the Central Sudetic
Terrane. This model is supported by the geochemical data. There is a clear division between alkali metabasalt-
dominated volcanic rocks and metasediments in the western part of the Kaczawa and MORB-like metabasalts
found in the eastern part of the complex. The main tectonic structures of the Kaczawa complex formed by the
sinistral transpressional processes (D1 deformation) and later was modified by local development of extensional
structures during the late-Variscan orogeny (D2 deformation) and then followed by the brittle Alpine
deformations.
Key words:
foliations, lineations, folds, shear zones, transpression, thrust sheets, kinematics, Variscides,
Kaczawa complex, Sudetes.
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Geological Map
Mineral
