The Chimakurti, Errakonda, and Uppalapadu plutons, Eastern Ghats Belt, India: An unusual association of tholeiitic and alkaline magmatism

Mesoproterozoic tholeiitic and alkalic magmatism is widespread in the southern segment of the Eastern Ghats Belt, India, and is particularly well recorded in three cospatial plutons: Chimakurti, a pluton consisting of clinopyroxenite, anorthosite, and gabbro; Errakonda, a ferrosyenite pluton; and the Uppalapadu nepheline syenite. U-Pb zircon ages of ferrosyenite and nepheline syenite suggest that these cospatial plutons were intruded at approximately 1352 Ma, and Nd and Sr isotope compositions suggest that each pluton experienced varying degrees of crustal assimilation. Petrography, mineral chemistry, geochemistry and isotopic compositions suggest that the clinopyroxenite, anorthosite, and gabbro of the Chimakurti suite were derived from a high-Al tholeiitic parental magma. The ferrosyenite exhibits A-type characteristics and are interpreted as a differentiate or partial melt of a tholeiitic source. The Uppalapadu nepheline syenites were derived from an alkaline (basanitic) parental magma. These three plutons illustrate the spectrum of basaltic magmas that may be involved in producing intraplate intrusive complexes. Tholeiitic magmas emplaced at depth in the crust may differentiate to produce massif anorthosites and related A-type differentiates, represented in the Eastern Ghats Belt by the Chimakurti and Errakonda plutons. More alkalic basalts, such as basanites, will evolve to nepheline syenites like those of the Uppalapadu pluton. The 1352 Ma magmatism in the Eastern Ghats is unusual in that it documents a spatial and temporal association of both tholeiitic and alkaline endmembers of continental rift magmatism.