LOW-PRESSURE GRANULITES OF THE LIšOV MASSIF, SOUTHERN BOHEMIA: VISÉAN METAMORPHISM OF LATE DEVONIAN PLUTONIC ARC ROCKS

Abstract

The Lišov Granulite Massif differs from neighbouring granulite bodies in the Moldanubian Zone of southern Bohemia (Czech Republic) in including a higher proportion of intermediate-mafic and orthopyroxene-bearing rocks, associated with spinel peridotites but lacking eclogites. In addition to dominantly felsic garnet granulites, other major rock types include quartz dioritic two-pyroxene granulites, tonalitic granulites and charnockites. Minor bodies of high-pressure layered gabbroic garnet granulites and spinel peridotites represent tectonically incorporated foreign elements. The protoliths of the mafic-intermediate granulites (quartz-dioritic and tonalitic) crystallized ~360-370 Ma ago, as indicated by laser ablation inductively coupled plasma mass spectrometry U-Pb ages of abundant zircons with well-preserved magmatic zoning. Strongly metamorphically recrystallized zircons give ages of 330-340 Ma, similar to those of other Moldanubian granulites. For the overwhelming majority of the Lišov granulites peak metamorphic conditions probably did not exceed 800-900°C at 4-5 kbar; the equilibration temperature of the pyroxene granulites was 670-770°C. This is in sharp contrast to conditions of adjacent contemporaneous Moldanubian granulites, which are characterized by a distinct HP - HT signature. The mafic-intermediate Lišov granulites are thought to have originated during Viséan metamorphic overprinting of metaluminous, medium-K calc-alkaline plutonic rocks that formed the mid-crustal root of a Late Devonian magmatic arc. The protolith resembled contemporaneous calc-alkaline intrusions in the European Variscan Belt. © 2006 Oxford University Press.