U-Th-total Pb dating of monazite from orthogneisses and their ultra-high temperature metapelitic enclaves; implications for the multistage tectonic evolution of the Madurai Block, southern India

EPMA dating of monazite in enclaves of sapphirine-bearing granulites and their host granites from the SE part of the Madurai Block is reported. The granulites are strongly migmatitic and comprise quartzofeldspathic leucosome veins and restitic domains of sapphirine, garnet, orthopyroxene, sillimanite and cordierite. Inclusions of sapphirine-quartz intergrowths in garnet testify to an UHT stage of metamorphism; this was followed by decompression during which garnet was replaced by coronitic intergrowths of orthopyroxene and sillimanite. Monazite inclusions in garnet, orthopyroxene and quartz give a bimodal age distribution of mid- to early Neoproterozoic (1500-850 Ma) ages in the cores which are rimmed by late Neoproterozoic age domains (630-580 Ma). Monazites in the granite and the charnockite exclusively yield Pan-African values.