Geochemistry and Petrogenesis of the Malani Igneous Suite, North Peninsular India

Major and trace element data have been obtained for the ca. 730 Ma granites of the Siwana and Jalor complexes, Rajasthan and the Tosham complex, Haryana. On the basis of geologic, geochronologic and chemical data these granites are classified as anorogenic, and are believed to have been formed during a wide-spread thermal event centered around 800 Ma. All of the complexes show evidence of differentiation at high levels through fractionation of alkali feldspar, plagioclase, and amphibole. The granite from the Siwana complex is peralkaline and Shows high rare-earth (REE) contents with little fractionation between LREE and HREE. This granite may have been derived as a high temperature melt from an anhydrous granulitic source region from which a previous melt had been extracted or by melting of a metasomatized lower crustal source. The Jalor quartz syenites and granites are more primitive, metaluminous and have more fractionated REE patterns. These rocks are most likely differentiates of a mantle-derived magma. The Tosham granites are metaluminous to peraluminous and show isotopic and chemical characteristics typical of magmas derived from a high-grade metasedimentary source, These observations indicate that a variety of granite types can be formed during a period of anorogenic magmatism.