No abstract

We present, major element geochemical data for ilmenite grains obtained from heavy mineral concentrate of diamondiferous Majhgawan kimberlite clan diatreme in Central Indian Diamond Province (CIDP) in Panna District of Madhya Pradesh, India. The chemical composition of 148 ilmenite grains suggests different compositional trends when plotted over “Haggerty's parabola” and as seen in MgO-Cr2O3 bivariant plots. The study indicates that the ilmenite crystallized in three stages: the first stage where Cr - poor ilmenite is crystallized from protokimberlitic or kimberlitic melt and forms the base of Haggerty's parabola on MgO-Cr2O3 plots; the second stage ilmenite is rich in MgO and Cr2O3 -represented by left branch of Haggerty’s parabola-might have formed by interaction between melt and lithosphere; the third stage ilmenite is formed by sub-solidus recrystallization in an evolved kimberlite melt due to oxidation and is reflected in the right branch of Haggerty’s parabola in MgO-Cr2O3 plots. The various trends in the ilmenite composition from Majhgawan pipe are attributed to conditions prevailing during ilmenite crystallization in a kimberlite melt ascending through the lithospheric mantle. These geochemical features indicate a genetic link between ilmenite and the host kimberlite melt.

In kimberlite, olivine is an important constituent and it is found as mineral grains of different sizes, which can be of xenocrystic and magmatic origin. To know the processes, that are involved and controls the compositional variations of olivine, can provide distinct understanding into the genesis and evolution of kimberlites. In addition to this the textural features of kimberlitic olivine, which are recorded as textural events during magma assent constrains the ascent of kimberlite and the processes involved. Unambiguous identification of kimberlitic olivine and its textural features require careful petrographic examination combined with mineral compositional analysis and use of high magnification images (BSE-SEM), all this is integrated to know the origin of olivine grain which in turn constrain the process involved in ascent of kimberlite and its petrogenesis. In this study we review the use of kimberlitic olivine in deducing the upper mantle conditions and process for kimberlite petrogenesis.

Occurrences of the small, elongated, irregular shape of charnockite patches along the foliation planes of the leptynites in Digapahandi area, Ganjam district, Odisha of Eastern Ghats Belt (EGB) are reported. Petrography and mineral chemistry of charnockite patches and host leptynites suggest that both the rocks have analogues mineral assemblages, except the presence of ortho-pyroxene in charnockite patches. The mineral chemistry studies revealed that mineral phases common in both rocks are chemically identical. Based on whole rocks geochemistry it is evident that both charnockite patches and host leptynites are iso-chemical. The adamellite composition, per-aluminous nature with positive Europium anomaly of host leptynite and charnockite patches suggests their co-genetic relation. Higher values of (La/Yb)N and (Gd/Lu)N of leptynites indicate the highly fractionated HREE pattern of leptynites. High concentrations of HREE in charnockite patches are due to the influence of fluid phase in granulite facies metamorphism. The charnockite patches are characterized by higher K2O content, higher HREE concentration, and less abundance of biotite indicating the in-situ growth of patchy charnockites.