Informatics Publishing Limited

Fareeduddin ¹, N. C. Pant ², S. Neogi ¹

Affiliations
1 Geological Survey of India, PPOD Division, A M S E Wing, Bangalore - 560 078, IN
2 Geological Survey of India, EPMA Lab , Op P, H & HP, Faridabad - 12 1 001, IN

Abstract

Thc Kodomali body is one among the six pipes, reportedly of kimberlitic composition in Mainpur area, district Raipur, Chhattisgarh. It occurs within the Bundelt granitoid that is emplaced in the lower part of the Khariar/Pairi group of rocks. Recent age determinations have indicated that the Kodomali has intruded into Bundeli granitoids at about 500 Ma. The Kodomali diatreme exhibits a distinct macro crystal texture with coarse olivine occurring in a very fine grained groundmass made of diopside, phlogopite, spinel and secondary serpentine. Two generations of olivine occur in the rock. Macrocrystal olivine is distinctly xenocrystic whereas microphenocrystic olivine, which is zoned with more forsteritic cores than their margins, show chemical parameters suggestive of crystallization from a melt Fe-poor diopside and T₁-rich, Al and Cr-Poor phlogopite constitute the bulk of the groundmass. Phlogopite cores are I richer in T₁ and Al compared to rims and show crystallisation trends typical of orangaeites. Spinel group minerals (Magnesio-Chromite) occur as (1) coarse xenocrystic zoned grains with T₁ poor, Al and Mg rich cores relative to the rims and (11) as line size grains in groundmass. Some coarse spinel group mineral grains are enveloped by corona of sphene against macrocrystic perovskite, inferred to result from low temperature hydrothermal alteration through interaction with Si-Bearing fluids. Groundmass spinel, also represented by magnesian chromite, is sparse, has no perceptible zoning and exhibits T₁- magnetite crystallization trend that is charactenstic of orangeites. The petro-Mineralogical attributes of the Kodomali diatreme show close affinities with the South African orangeites. Recent studies on another diatreme in the area is also suggestive of an orangeitic affinity for the rock. These studies imply that the Mainpur area represents an orangeitc field of Palaeozoic age.

Keywords

Kimberlite, Orangeite, Petrography, Mineral Chemistry, Khariar, Pairi, Kodomali, Mainpur, Chhatisgarh.

Full Text

     

A. Joshi ¹, N. C. Pant ², S. Neogi ³, J. K. Nanda ⁴

Affiliations
1 A-2, Pushpa Bhavan, Geological Survey of India, New Delhi - 110 049, IN
2 EPMA Laboratory, Geological Survey of India, Faridabad - 121 001, IN
3 PPOD, A M S E Wing, Geological Survey of India, Bangalore - 560 078, IN
4 OP Orissa, Geological Survey of India, Bhubaneshwar - 75 1 012, IN

Abstract

High-Al gabbro is reported here for the first time from three anorthosite complexes of Orissa sector of Eastern Ghats Granulite Belt (EGGB). It has distinctly different textural, mineralogical and chemical characters from the anorthosite within which it occurs, and also from the spatially associated Fe, Ti and REE enriched ferrodiorite suite.

The high-Al gabbro of EGGB is comparable to similar rocks from other anorthosite complexes in major, trace element compositions and Mg# range (50-58). However, in contrast to the high-Al gabbro of the Laramie Anorthosite Complex (LAC), it does not form the most primitive rock of this association and exhibits negative Eu anomaly (Eu/EU^* 0 2 0 6). The Mg enriched composition of the silicates of the high-Al gabbro and higher MgO contents of the associated anorthosite and ferrodiorite of the LAC are other critical differences.

Variable composition of the parental melts for these rocks at EGGB and LAC is interpreted Derivation of these aluminous melts by partial melting of basalt under high pressure i s suggested.

Keywords

Petiogenesis, High-Al Gabbio, Anorthosite, Ferrodiorite, Eastern Ghats Granulite Belt, Orissa.

Full Text