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Geochemical studies of monazites from coastal sands of Kandivalasa–Dibbalapalem coast, Andhra Pradesh

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Abstract

The present study deals with the geochemical and geochronological studies of monazite from Kandivalasa–Dibbalapalem coast, north Andhra Pradesh. The average concentration of ThO2 and UO2 from beach sands is 11.38 and 0.40 wt.% and from dune sands is 11.94 and 0.63 wt.%. The average REE from beach and dune sands is 58.64 and 57.94 wt.% and they are rich in La, Ce, and Nd. The most common characteristic feature to all monazite shows that the total REE content exceeds that of the actinides (Thru). Monazite that formed after the garnet break down contains significantly higher amounts of Y and HREE in fine sediments. The chondrite-normalized REE distribution patterns of monazite show uniformly enriched light rare earth element (∑LREE) which could be due to the preferential incorporation of lighter lanthanides and positive europium anomalies indicate that monazite was formed from magma/anatectic melt with high oxygen fugacity. Back-scattered electron (BSE) images of monazite showing compositional zoning and the bright outermost rim which is attributed to the influence by variations of LREE, HREE, U, Th, Pb and Y concentrations. The primary controlling factor, radiation damaged monazite yields in most cases significantly, with a strong dependence on the degree of metamictization based on the BSE intensity. The geochemical dating (U–Th–Pb) of monazite ranging age from 487 to 977 Ma from grain interior, can signify the age of Grenvillean evolution. This interpretation changes the existing tectonothermal history of the northern Eastern Ghats Belt. Our data show that the two adjacent crustal domains of the Eastern Ghats Belt show distinctly contrasting Neoproterozoic histories.

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Acknowledgements

The authors are thankful to Head, Department of Geology, Andhra University for providing the necessary facilities and for their constant encouragement to carry our work and also Geological Survey of India (GSI), Hyderabad and Indian School of Mines (ISM), Dhanbad for extending the lab facilities (EPMA) to carry out geochemical analysis. The first author wishes to thank Department of Science and Technology (DST), Government of India, New Delhi for providing the financial assistance to execute this research work through the INSPIRE Fellowship program in the form of SRF and also thankful to Principal, Maharaja College (A), Vizianagaram for their constant encouragement to publish this work and also the authors extend the word thankful to Dr. N V Chalapathi Rao, Editor-in-Chief, JESS for his valuable suggestions and help to publish this work.

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Ganapathi Rao, P., Bangaku Naidu, K., Reddy, K.S.N. et al. Geochemical studies of monazites from coastal sands of Kandivalasa–Dibbalapalem coast, Andhra Pradesh. J Earth Syst Sci 129, 143 (2020). https://doi.org/10.1007/s12040-020-01387-z

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