Hot N Sour Mantle Soup on Indian Plate During Cretaceous- Evidence from Clumped Isotope and Geochemical Studies of Sung Valley Carbonatite, India

Abstract:

Geological processes involved in the formation of Carbonatite rocks are complex and so is the understanding about its formational temperature. Fluid inclusion studies (1) on Carbonatite and their associated Ijolites showed a homogenization temperature of 1000-1100°C for Ijoltes and a temperature (T) range of 200-600°C was assigned to the carbonatite melts. Liquid immiscibility process is held responsible for the origin of parental carbonated (ijolititic/ nephelinitic) magma. The homogenization T signifies about a time interval during which there must be a considerable amount of T dropdown soon after the formation of Ijolite and subsequent crystallization of the residual carbonatite magma. However the lack of information about the T of the primary carbonated melt remains as an important area of petrological research. Experimental studies suggest a T range of 950-1400°C for the primary carbonate melt (2). Advent of Clumped isotope thermometry (3) allowed independent method for estimation of the formational T and provide avenues to derive composition of CO₂ in equilibrium with carbonate melt. Earlier attempt involving carbonatites from several locations (4) captured range of T between 83°-416°C . Here we present our observation on calcite growth T in the carbonatites from the Cretaceous Sung valley ultramafic-alkaline-carbonatite complex. Based on stable C,O isotope study and Sr, Nd isotopic composition a mantle origin- genetically linked with the Kerguelen plume was proposed (5). Clumped isotope study on the same samples revealed consistent C and O isotope compositions, providing Δ47 values ranging from 0.32 to 0.48. δ¹³C and δ¹⁸O (in VPDB) values of the present study falls within the “Primary Igneous Carbonatite Field” (6). Using high T thermometry equation (7) we obtained a T range of 137-474 °C for the calcite present in the samples. The T recorded in our study is lower than that deduced experimental values of 960-625°C at 0.1 GPa (8) and fluid inclusion based data (1), suggesting involvement of water during calcite crystallization.

Ref: 1.Romanchev 1972, Geochem Intern; 2.Gaillard et al., 2008, Science; 3. Ghosh et al.,2006, GCA ; 4. Dennis and Schrag, 2010, GCA; 5. Srivastava et al., 2005. Lithos ; 6.Taylor et al.,1967, GCA; 7. Kluge et al.,2015, GCA, 8. Watkinson and Willey, 1971, Jour. Of Petrology