Magmatic fabrics and emplacement of the cone-sheet-bearing Knížecí Stolec durbachitic pluton (Moldanubian Unit, Bohemian Massif): implications for mid-crustal reworking of granulitic lower crust in the Central European Variscides

Abstract

The~340 Ma Knížecí Stolec durbachitic pluton was emplaced as a deep-seated cone-sheetbearing ring complex into the Křišt'anov granulite body (Moldanubian Unit, Bohemian Massif). Prior to the emplacement of the durbachitic magma, the steep sub-concentric metamorphic foliation in the granulite formed due to intense ductile folding during highgrade retrograde metamorphism. Subsequently, the durbachitic pluton intruded discordantly into the granulite at around~340 Ma. The steep margin-parallel magmatic fabric in the durbachitic rocks may have recorded intrusive strain during emplacement. After the emplacement, but prior to the final solidification, the pluton was overprinted by the regional flat-lying fabric under lower pressure-temperature conditions (T = 765 ± 53°C; P = 0.76 ± 0.15 GPa). Based on this study and comparison with other ultrapotassic plutons, we suggest that the flat-lying fabrics, widespread throughout the exhumed lower to middle crust (Moldanubian Unit), exhibit major variations in character, intensity, kinematics, and shape of the fabric ellipsoid. These fabrics may have formed at different structural levels and in different parts of the root prior to~337Ma. Therefore, we suggest that this apparently ''single'' orogenic fabric recorded multiple deformation events and heterogenous finite deformation rather than reflecting a single displacement field within the orogenic root.

Magmatic history and geophysical signature of a post-collisional intrusive center emplaced near a crustal-scale shear zone: the Plechý granite pluton (Moldanubian batholith, Bohemian Massif)

“…(2) To the east, the pluton discordantly intrudes partly retrogressed granulites (Verner et al 2007). No ductile structural aureole with preserved evidence for emplacement-related strain or deflection or faulting of host rock markers (even on a meter scale) was observed near the intrusive contacts.…”

“…(3) To the north, the pluton is in intrusive contact with finegrained, equigranular muscovite-biotite granite; however, the relative ages of the two granites are uncertain. (4) To the northeast, the pluton is juxtaposed against the older, *340 Ma melasyenite to melagranite of the Knížecí Stolec pluton (Verner et al 2007) along a *NNW-SSE fault. (5) The southwestern margin of the pluton is crosscut by the *NW-SE Pfahl shear zone.…”

“…Elsewhere we attempted to address the emplacement of syn-collisional upper-crustal plutons (Ž ák et al 2005a, b) and syn-exhumation mid-crustal ultrapotassic plutons (Verner et al , 2007Ž ák et al 2005a) in the Bohemian Massif. In the present paper, we concentrate on the fabrics and emplacement of the post-collisional S-type granites that intruded the high-grade Moldanubian Unit during and after the LP-HT regional metamorphism.…”

“…(1) The syn-collisional Late Devonian-Early Carboniferous (*370-340 Ma) crustal thickening broadly overlaps with the emplacement of metaluminous, calc-alkaline and high-K, I-type plutons. (2) Rapid exhumation of the lower-to middle-crust at around *340 Ma (e.g., Willner et al 2002 and references therein) is associated with the intrusion of ultrapotassic, magnesium-rich plutons (e.g., Holub 1997;Janoušek and Holub 2007;Verner et al 2006Verner et al , 2007. (3) During and after the subsequent LP-HT regional metamorphism and anatexis in the innermost part of the orogenic belt (variously referred to as the Moldanubian Unit, Moldanubian Zone, or Moldanubicum) dated at *337-321 Ma (e.g., Kalt et al 1999Kalt et al , 2000Tropper et al 2006;Vrána et al 1995;Willner et al 2002), the Moldanubian Unit was intruded by large volumes of peraluminous, S-type and high-K I-type granitoids.…”

Model of syn‐convergent extrusion of orogenic lower crust in the core of the Variscan belt: implications for exhumation of high‐pressure rocks in large hot orogens

“…(2004); 8, Štípská & Powell (2005); 9, Tajčmanová et al. (2006); 10, Verner et al. (2008); 11, Rötzler & Romer (2001)– Saxonian Granulites.…”