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      https://www.ias.ac.in/article/fulltext/jess/129/0143

    • Keywords

       

      EPMA; rare earth elements; U–Pb–Th; detrital monazite; BSE; Neoproterozoic ages.

    • Abstract

       

      The present study deals with the geochemical and geochronological studies of monazite from Kandivalasa–Dibbalapalem coast, north Andhra Pradesh. The average concentration of ThO$_2$ and UO$_2$ 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 ($\sum$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.

    • Author Affiliations

       

      GANAPATHI RAO P1 BANGAKU NAIDU K2 REDDY K S N3 RAVI SEKHAR CH3 MURALI KRISHNA K N4 ANJI REDDY M2

      1. Department of Geology, M.R. College(A), Vizianagaram, Andhra Pradesh 535 002, India.
      2. Center for Environment, Jawaharlal Nehru Technological University Hyderabad, Telangana 500 085, India.
      3. Department of Geology, Andhra University, Visakhapatnam, Andhra Pradesh 530 003, India.
      4. Department of Civil Engineering, NRI Institute of Technology, Guntur, Andhra Pradesh 522 005, India.
    • Dates

       
  • Journal of Earth System Science | News

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