Petrology of the gabbro-diorite-syenite-granite complex of Chanduluru, Prakasam alkaline province, Andhra Pradesh, India

The calc-alkaline complex of Chanduluru (CL) in the Prakasam alkaline province of Andhra Pradesh is composed of two distinct petrographic suites viz. a gabbro-diorite suite and a melasyenite-granite suite. The chief rock forming minerals of the complex are clinopyroxene, amphibole, biotite, plagioclase, K-feldspar and quartz: the accessory minerals include apatite, sphene, zircon, opaque oxide and garnet. Major, trace and rare earth element variations in the two suites of rocks suggest two distinct petrogenetic series. The two suites are derived from two different parental magmas of varying composition and source. A mantle derived gabbroic magma has yielded gabbro-diorite suite by fractional crystallization. The underplating of the gabbroic magma has led to partial melting of the LREE-enriched amphibolite crust to yield a melasyenitic magma, which on fractional crystallization has yielded melasyenite-granite suite. The complex is emplaced in a within-plate-collision tectonic environment.