Multiple magmatic fabrics in the Sazava pluton (Bohemian Massif, Czech Republic): a result of superposition of wrench-dominated regional transpression on final emplacement

摘要

The Sazava pluton (～ 354 Ma) of the Central Bohemian Plutonic Complex was emplaced syntectonically into the upper crustal Neo-Proterozoic and Lower Paleozoic host rock along the SE margin of the Tepla-Barrandian Zone, Bohemian Massif (Czech Republic). The host rock is characterized by transpressional fabric dominated by steep SE-NW dipping foliations and subhorizontal NE-SW stretching lineations associated with flattening to a plane strain ellipsoid. The strain intensity, degree of oblateness and temperature conditions of deformation increase in the host rock towards the pluton margin. In the pluton, quartz microfabric indicates progressive cooling of the syntectonically emplaced magma. The AMS method revealed multiple magmatic fabrics and lateral variations in the shapes of the AMS ellipsoid and the magnetic fabric intensity in the pluton. The central part of the pluton yields prolate shapes of the AMS ellipsoid and a low degree of anisotropy with preserved steep magnetic lineations, whereas, along the pluton margins, oblate AMS ellipsoids are associated with a high degree of anisotropy. We interpret the multiple fabrics and the partially decoupled fabric pattern between the host rock and the pluton as being a result of superposition of regional tectonic strain during highly oblique transpression on emplacement-related intrusive strain, where outer solidified and more rigid edges of the pluton enabled preservation of older steep fabrics in its interior.