Emplacement depths and radiometric ages of Paleozoic plutons of the Neukirchen-Kdyne massif: differential uplift and exhumation of Cadomian basement due to Carboniferous orogenic collapse (Bohemian Massif)

摘要

The igneous complex of Neukirchen-Kdyne is located in the southwestern part of the Tepla-Barrandian unit (TBU) in the Bohemian Massif. The TBU forms the most extensive surface exposure of Cadomian basement in central Europe. Cambrian plutons show significant changes in composition, emplacement depth, isotopic cooling ages, and tectonometamorphic overprint from NE to SW. In the NE, the Vsepadly granodiorite and the Smrzovice diorite intruded at shallow crustal levels (20 km). The Teufelsberg (Certuv kamen) diorite, on the other hand, forms an unusual intrusion dated at 359 +/- 2 Ma (concordant U-Pb zircon age). K-Ar dating of biotite of the Teufelsberg diorite yields 342 +/- 4 Ma. These ages, together with published cooling ages of homblende and mica in adjacent plutons, are compatible with widespread medium to high-grade metamorphism and strong deformation fabrics, suggesting a strong Variscan impact under elevated temperatures at deeper structural levels. The plutons of the Neukirchen area are cut by the steeply NE dipping Hoher-Bogen shear zone (HBSZ), which forms the boundary with the adjacent Moldanubian unit. The HBSZ is characterized by top-to-the-NE normal movements, which were particularly active during the Lower Carboniferous, A geodynamic model is presented that explains the lateral gradients in Cambrian pluton composition and emplacement depth by differential uplift and exhumation, the latter being probably related to long-lasting movements along the HBSZ as a consequence of Lower Carboniferous orogenic collapse. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 56]