Reappraisal of the petrologic status of Newania ‘carbonatite’ of Rajasthan, western India

Abstract

Considerable data exist on the geology, petrochemistry and isotopic compositions of the Newania carbonatite body (NCB) of Rajasthan in western India. The NCB consists of dolomitic carbonatite and ankeritic carbonatite while the ‘sovite’ is present only as late stage fine veins intruding the dolomitic and ferroan phases. The absence of any associated alkaline activity, low Sr, Ba and Σ REE contents, wide variations in δ 13C and δ 18O values and an unusual sequence of ‘carbonatite emplacement’ represented by dolomitic→ankeritic→calcitic carbonatite characterize the body. None of these criteria, whether considered individually or collectively, provide incontrovertible evidence in favour of an exclusive magmatic origin for these carbonatitic rocks. We present a critical review of the Newania ‘carbonatite’, including the metasomatic aureole, and put forward the possibility that the body may not represent only magmatic carbonates. Instead, it probably appears to be an example of post-magmatic selective metasomatism of magnesio carbonatite affected by ferruginous solutions. Our inferences are based upon critical evaluation of existing database, C and O isotopic data, and observations at NCB.