The Neoproterozoic rocks of the Nakora Ring Complex (NRC) consist of three phases (Extrusive, Intrusive and Dyke) that are based on the detailed geological mapping (contact relationship, mode of occurrence, position o...The Neoproterozoic rocks of the Nakora Ring Complex (NRC) consist of three phases (Extrusive, Intrusive and Dyke) that are based on the detailed geological mapping (contact relationship, mode of occurrence, position of xenolith, flows, dykes and veins) and their stratigraphic position. NRC consists mainly of acid volcanic rocks besides minor amount of basic rocks with intermediate calc-alkaline to tholeiitic affinities and occurs in the form of ring structures. The Nakora basaltic rocks show LREE enriched nature and they have consistent negative Nb, Ta, Sr and Zr anomalies. The HREE pattern is showing parallel arrangement with HREE pattern of other basic rocks. The Nakora acid volcanic rocks exhibit high LREE enrichment than the HREE with negative Ba, Sr, Eu and Ti anomalies in primitive mantle normalized multi-element diagrams. All the samples show negative Ba, Sr, Eu and Ti anomalies. The diminution in amounts of Sr and Eu is apparently related to the fractionation of feldspars or their retention in the refractory minerals resistant to melting in the lower crust. As compared to trachytes, the rhyolites show high SiO<sub>2</sub>, high Al<sub>2</sub>O<sub>3</sub>, low total alkalis, low total iron, low TiO<sub>2</sub>, high CaO and high MgO. The petro-mineralogical and geo-chemical data specifies that the NRC rocks are generated from a co-magmatic source through a co-genetic process in a rift tectonic context. Petrogenetic modeling indicates that both the basic rocks and acid volcanic rocks of Nakora may have been derived from rocks akin to Bhilwara mafic metavolcanic/mixed Nakora gabbros and Siwana rhyolite/banded gneiss from Kolar Schist Belt by different degrees of partial melting respectively.展开更多
文摘The Neoproterozoic rocks of the Nakora Ring Complex (NRC) consist of three phases (Extrusive, Intrusive and Dyke) that are based on the detailed geological mapping (contact relationship, mode of occurrence, position of xenolith, flows, dykes and veins) and their stratigraphic position. NRC consists mainly of acid volcanic rocks besides minor amount of basic rocks with intermediate calc-alkaline to tholeiitic affinities and occurs in the form of ring structures. The Nakora basaltic rocks show LREE enriched nature and they have consistent negative Nb, Ta, Sr and Zr anomalies. The HREE pattern is showing parallel arrangement with HREE pattern of other basic rocks. The Nakora acid volcanic rocks exhibit high LREE enrichment than the HREE with negative Ba, Sr, Eu and Ti anomalies in primitive mantle normalized multi-element diagrams. All the samples show negative Ba, Sr, Eu and Ti anomalies. The diminution in amounts of Sr and Eu is apparently related to the fractionation of feldspars or their retention in the refractory minerals resistant to melting in the lower crust. As compared to trachytes, the rhyolites show high SiO<sub>2</sub>, high Al<sub>2</sub>O<sub>3</sub>, low total alkalis, low total iron, low TiO<sub>2</sub>, high CaO and high MgO. The petro-mineralogical and geo-chemical data specifies that the NRC rocks are generated from a co-magmatic source through a co-genetic process in a rift tectonic context. Petrogenetic modeling indicates that both the basic rocks and acid volcanic rocks of Nakora may have been derived from rocks akin to Bhilwara mafic metavolcanic/mixed Nakora gabbros and Siwana rhyolite/banded gneiss from Kolar Schist Belt by different degrees of partial melting respectively.
