In situ U-Th-Pbtotal dating of polychronous monazite in the Koraput anorthosite pluton, Eastern Ghats Granulite Belt (India), and implications

U-Th-Pb-total age determinations in monazite in a noritic anorthosite at the margin of the Koraput anorthosite pluton constrain the time of emplacement and sub-solidus chemical modifications in the Grenvillian-age anorthosite pluton in the Eastern Ghats Province (EGP), India. The monazites hosted within dynamically recrystallized orthopyroxene and plagioclase grains are large (50-500 m in diameter) and complexly zoned. Based on the textural-chemical heterogeneities, these monazites are classified into three groups. Group-I monazites exhibit a low-ThO2 core mantled by a high-ThO2 rim. By contrast, the group-II monazites exhibit high-ThO2 cores laced by ThO2-poor mantles, and outermost rims with still lower ThO2 contents. Skeletal group-III monazites at polygonized grain/phase boundaries exhibit patchy and concentric zones with decreasing ThO2 towards the margin. The U-Th-Pb-total chemical ages obtained using electron probe microanalyses exhibit four age clusters. The oldest age population (mean 939 +/- 4.5 Ma) obtained in cores in group-I, II and III monazites with patchy zones corresponds with the emplacement of the Koraput anorthosite, and this age population is consistent with 980-930 Ma emplacement ages reported in other EGP anorthosite massifs. Younger monazites mantling the cores in group-II monazites and in group-III monazites with mean ages of 877 +/- 5 Ma and 749 +/- 18 Ma possibly reflect episodic monazite growth by fluid-aided dissolution-precipitation culminating with the disintegration of Rodinia at similar to 750 Ma. The youngest age population (mean 574 +/- 19 Ma) in the outermost monazite rims and monazite veins represents renewed monazite growth during the Pan African assembly of the Grenvillian-age EGP domain with the proto-Indian cratons.