Chondritic Features in a Diamondiferous Rock, Majhgawan, Central India: Implications for Diamond Genesis

Majhgawan, on the southeastern margin of the arc shaped Bundelkhand craton and within the Mesoproterozoic Vindhyan basin in Central India hosts the only diamond producing mine in India. Variously classifieds ultramafite, agglomeratic tuff, kimberlite, lamproite, orangeite, serpentine rock, a transitional rock etc the host rock for diamond, comprising mainly ultramafic breccia, and exposed in an elliptical outcrop pattern, shows significant differences in bulk chemistry and mineral compositions with other known kimberlites and related rocks of India. It shows textural features suggestive of crater facies volcanic eruption.

Several distinctive and hitherto unreported features of shock metamorphism in olivine such as parallel fractures, planar deformational features (PDFs), shock mosaicism, arrested mineral melts, veinlets of rock melts, mixed melts, spherules and darkened silicates have been documented, recording up to S6 stage of shock metamorphism and shock pressures > 45 Gpa. These shock metamorphic imprints as well as the presence of variety of features bearing starting resemblance to the chondrites suggest that the Majhgawan ultramafic breccia contains traces of chondritic components in it. Though it is Interpreted here that the Majhgawan body is a result of a billion year old, impact triggered eruption of mantle material, which has incorporated the surface remains of the chondritic matter, clearly much more study is called for on these lines to understand the textural and mineralogical complexities exhibited by the Majhgawan rocks. It is argued that the difficulty in providing a descriptive classification for this rock within the framework of the IUGS schemes for terrestrial rocks is attributed mainly to its identifications simple rock akin to the known diamondiferous primary sources. Some new thoughts on the genesis of the diamonds In the light of these findings are also touched upon.