Compositional variations of olivine in shonkinite and its associated ultrabasic rock from the carbonatite complex of Tiruppattur, Tamil Nadu

The compositional variations of olivine from shonkinite (shon) and associated ultrabasic rock (ubr) are analysed and an attempt is made to trace their magmatic evolution. The analysed olivine in shon is subjected to a prolonged period of magmatic crystallization with the development of zoning of augite, aegirine-augite and jadeite at its peripheral portions by reaction with residual magma. On the other hand, the composition of olivine from ubr represents intermediate position in the course of magmatic evolution of olivine occurring in shon. The high concentration of Ca-Na-K-Al in olivine from ubr indicates its kimberlitic affinity. These features indicate that shon magma is the parent magma for ubr. The shon occurs in the form of nodules/xenoliths in ubr, which is a member of the ultrabasic complex in this area. Further study is required to isolate ubr of kimberlitic affinities from the ultrabasic complex enclosing the potash-rich alkali syenites at the inner portion of Jogipatti basin, which is a part of the Tiruppattur carbonatite complex, Tamil Nadu.