TEMPORAL ASSOCIATION OF DUCTILE DEFORMATION AND GRANITIC PLUTONISM - RB-SR AND AR-40-AR-39 ISOTOPIC EVIDENCE FROM ROOF PENDANTS ABOVE THE CENTRAL BOHEMIAN PLUTON, CZECH-REPUBLIC

The Stare Sedlo gneiss complex occurs as a roof pendant in the early C arboniferous Central Bohemian Pluton. Mylonitic tonalitic gneiss and a mpkibolite in the complex share a common foliation, which is discordan t to the margins of the granitoid masses of the enclosing pluton. Homb lende Ar-40-Ar-39 and biotite-whole-rock, biotite-plagioclase Rb-Sr is otopic data give closely corresponding early Carboniferous cooling age s for hornblende (500 degrees C) and biotite (300 degrees C) in amphib olite and mylonitic tonalitic gneiss, respectively. Ages of 338 +/- 2. 5, 335 +/- 2, and 331 +/- 2.5 Ma (biotite-whole-rock and biotite-plagi oclase Rb-Sr) and 332.3 +/- 3.0, 332.2 +/- 3.1, and 331.7 +/- 3.0 Ma ( hornblende Ar-40-Ar-39) are interpreted as representing times of closu re of isotopic systems associated with rapid cooling during the final stages of ductile deformation and metamorphism in a thrust regime. The y overlap the time of emplacement of at least early intrusions that sh ow some foliation, and possibly much of the Central Bohemian Pluton (i ncluding the 331 +/- 4 Ma old Blatna granodiorite) whose gross shape a nd emplacement are interpreted to have been controlled by a steeply di sposed ramp(s) in a major listric thrust zone.