The Newania carbonatite complex of India is one of the few dolomite-dominated carbonatites of the... more The Newania carbonatite complex of India is one of the few dolomite-dominated carbonatites of the world. Intruding into Archean basement gneisses, the rocks of the complex have undergone limited diversification and are not associated with any alkaline silicate rock. Although the magmatic nature of the complex was generally accepted, its age of emplacement had remained equivocal because of the disturbed nature of radioisotope systems. Many questions about the nature of its mantle source and mode of origin had remained unanswered because of lack of geochemical and isotopic data. Here, we present results of our effort to date the complex using 147 Sm-143 Nd, 207 Pb-206 Pb and 40 Ar-39 Ar dating techniques. We also present mineral chemistry, major and trace element geochemistry and Sr-Nd isotopic ratio data for these carbonatites. Our age data reveal that the complex was emplaced at *1,473 Ma and parts of it were affected by a thermal event at *904 Ma. The older 207 Pb-206 Pb ages reported here (*2.4 Ga) and by one earlier study (*2.3 Ga; Schleicher et al. Chem Geol 140:261-273, 1997) are deemed to be a result of heterogeneous incorporation of crustal Pb during the post-emplacement thermal event. The thermal event had little effect on many magmatic signatures of these rocks, such as its dolomite-magnesiteankerite-Cr-rich magnetite-magnesio-arfvedsonite-pyrochlore assemblage, mantle like d 13 C and d 18 O and typical carbonatitic trace element patterns. Newania carbonatites show fractional crystallization trend from high-Mg to high-Fe through high-Ca compositions. The least fractionated dolomite carbonatites of the complex possess very high Mg# (C80) and have similar major element oxide contents as that of primary carbonatite melts experimentally produced from peridotitic sources. In addition, lower rare earth element (and higher Sr) contents than a typical calciocarbonatite and mantle like Nb/Ta ratios indicate that the primary magma for the complex was a magnesio-carbonatite melt and that it was derived from a carbonate bearing mantle. The Sr-Nd isotopic data suggest that the primary magma originated from a metasomatized lithospheric mantle. Trace element modelling confirms such an inference and suggests that the source was a phlogopite bearing mantle, located within the garnet stability zone. Keywords Carbonatites Á Geochronology Á Geochemistry Á Continental lithospheric mantle Á Newania Á India Communicated by C. Ballhaus.
Many tholeiitic dyke-sill intrusions of the Late Cretaceous Deccan Traps continental flood basalt... more Many tholeiitic dyke-sill intrusions of the Late Cretaceous Deccan Traps continental flood basalt province are exposed in the Satpura Gondwana Basin around Pachmarhi, central India. We present field, petrographic, major and trace element, and Sr-Nd-Pb isotope data on these intrusions and identify individual dykes and sills that chemically closely match several stratigraphically defined formations in the southwestern Deccan (Western Ghats). Some of these formations have also been identified more recently in the northern and northeastern Deccan. However, the Pachmarhi intrusions are significantly more evolved (lower Mg numbers and higher TiO 2 contents) than many Deccan basalts, with isotopic signatures generally different from those of the chemically similar lava formations, indicating that most are not feeders to previously characterized flows. They appear to be products of mixing between Deccan basalt magmas and partial melts of Precambrian Indian amphibolites, as proposed previously for several Deccan basalt lavas of the lower Western Ghats stratigraphy. Broad chemical and isotopic similarities of several Pachmarhi intrusions to the northern and northeastern Deccan lavas indicate petrogenetic relationships. Distances these lava flows would have had to cover, if they originated in the Pachmarhi area, range from 150 to 350 km. The Pachmarhi data enlarge the hitherto known chemical and isotopic range of the Deccan flood basalt magmas. This study highlights the problems and ambiguities in dyke-sill-flow correlations even with extensive geochemical fingerprinting.
The Newania carbonatite complex of India is one of the few dolomite-dominated carbonatites of the... more The Newania carbonatite complex of India is one of the few dolomite-dominated carbonatites of the world. Intruding into Archean basement gneisses, the rocks of the complex have undergone limited diversification and are not associated with any alkaline silicate rock. Although the magmatic nature of the complex was generally accepted, its age of emplacement had remained equivocal because of the disturbed nature of radioisotope systems. Many questions about the nature of its mantle source and mode of origin had remained unanswered because of lack of geochemical and isotopic data. Here, we present results of our effort to date the complex using 147 Sm-143 Nd, 207 Pb-206 Pb and 40 Ar-39 Ar dating techniques. We also present mineral chemistry, major and trace element geochemistry and Sr-Nd isotopic ratio data for these carbonatites. Our age data reveal that the complex was emplaced at *1,473 Ma and parts of it were affected by a thermal event at *904 Ma. The older 207 Pb-206 Pb ages reported here (*2.4 Ga) and by one earlier study (*2.3 Ga; Schleicher et al. Chem Geol 140:261-273, 1997) are deemed to be a result of heterogeneous incorporation of crustal Pb during the post-emplacement thermal event. The thermal event had little effect on many magmatic signatures of these rocks, such as its dolomite-magnesiteankerite-Cr-rich magnetite-magnesio-arfvedsonite-pyrochlore assemblage, mantle like d 13 C and d 18 O and typical carbonatitic trace element patterns. Newania carbonatites show fractional crystallization trend from high-Mg to high-Fe through high-Ca compositions. The least fractionated dolomite carbonatites of the complex possess very high Mg# (C80) and have similar major element oxide contents as that of primary carbonatite melts experimentally produced from peridotitic sources. In addition, lower rare earth element (and higher Sr) contents than a typical calciocarbonatite and mantle like Nb/Ta ratios indicate that the primary magma for the complex was a magnesio-carbonatite melt and that it was derived from a carbonate bearing mantle. The Sr-Nd isotopic data suggest that the primary magma originated from a metasomatized lithospheric mantle. Trace element modelling confirms such an inference and suggests that the source was a phlogopite bearing mantle, located within the garnet stability zone. Keywords Carbonatites Á Geochronology Á Geochemistry Á Continental lithospheric mantle Á Newania Á India Communicated by C. Ballhaus.
Many tholeiitic dyke-sill intrusions of the Late Cretaceous Deccan Traps continental flood basalt... more Many tholeiitic dyke-sill intrusions of the Late Cretaceous Deccan Traps continental flood basalt province are exposed in the Satpura Gondwana Basin around Pachmarhi, central India. We present field, petrographic, major and trace element, and Sr-Nd-Pb isotope data on these intrusions and identify individual dykes and sills that chemically closely match several stratigraphically defined formations in the southwestern Deccan (Western Ghats). Some of these formations have also been identified more recently in the northern and northeastern Deccan. However, the Pachmarhi intrusions are significantly more evolved (lower Mg numbers and higher TiO 2 contents) than many Deccan basalts, with isotopic signatures generally different from those of the chemically similar lava formations, indicating that most are not feeders to previously characterized flows. They appear to be products of mixing between Deccan basalt magmas and partial melts of Precambrian Indian amphibolites, as proposed previously for several Deccan basalt lavas of the lower Western Ghats stratigraphy. Broad chemical and isotopic similarities of several Pachmarhi intrusions to the northern and northeastern Deccan lavas indicate petrogenetic relationships. Distances these lava flows would have had to cover, if they originated in the Pachmarhi area, range from 150 to 350 km. The Pachmarhi data enlarge the hitherto known chemical and isotopic range of the Deccan flood basalt magmas. This study highlights the problems and ambiguities in dyke-sill-flow correlations even with extensive geochemical fingerprinting.
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