GEOLOGICAL AND GEOCHEMICAL STUDIES ON CARBONATITES AND ROCKS OF CARBONATITIC (QUESTIONABLE) AFFINITY FROM AREAS NORTH OF THE NARMADA LINEAMENT IN MADHYA-PRADESH AND GUJARAT

In the region covering some 400 km(2) immediately to the north of Narm ada lineament between Dharmrai, Dhar district, Madhya Pradesh; in the east and Nakhal and Panwad, Vadodara district, Gujarat, in the west, n umerous E-W to ENE-WSW trending linear fault zones (c.l km to 5 km lon g X 20 m to over 100 m wide) occur within the Deccan basalts and infra trappean rocks. Brownish, brecciated, calcareous rocks, often with poc kets and veins of calcite (carbonatites ?) are found within such fract ure zones, and many of them show intrusive-like features. These faults apparently have developed sympathetic to the major Narmada rift to th e south which provided structural avenues for the emplacement of carbo natites and associated basic alkaline rocks as found at Ambadongar, Pa nwad, Kawant and Saidiwasan, as part of the Deccan volcanic episode. C omparison of major and selected trace element data on these carbonatit ic (?) rocks with Woolley and Kempe's average trace elements in carbon atite indicates that they are significantly impoverised in Zr, Nb, Y, La and U compared to the carbonatites and phonolites and phonolitic ne phelinites of Panwad, Saidiwasan and Nakhal which are enriched in thes e elements. Carbonate-rich racks of Bakhatgarh and Katarkheda in the e ast are rich in CaO and P2O5 compared to those of Panwad and Kawant. B ased on available data it is suggested that the carbonatitic (?) types found in the east may represent an early phase of carbonatite (?) imp overished in Zr, Nh, Y, La, U and Th compared to the late residual (?) phase found in the Panwad-Saidiwasan-Nakal area which records signifi cant radioactivity (upto 0.04% eU(3)O(8)) and higher abundances of Zr (0.06%) and Nb (upto 0.1%).