Geochemical and Sm–Nd isotopic study of titanite from granitoid rocks of the eastern Dharwar craton,southern India |
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Authors: | R Anand S Balakrishnan |
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Institution: | (1) National Geophysical Research Institute (Council of Scientific and Industrial Research), Uppal Road, Hyderabad, 500606, India;(2) Department of Applied Geology, Curtin University, Bentley, 6845, Western Australia;(3) John de Laeter Centre, Curtin University, Bentley, 6845, Western Australia;(4) Centre for Exploration Targeting, School of Earth and Environment, The University of Western Australia, 6009 Crawley, Western Australia |
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Abstract: | Titanite occurs as an accessory phase in a variety of igneous rocks, and is known to concentrate geologically important elements
such as U, Th, rare earth element (REE), Y and Nb. The differences in the abundances of the REEs contained in titanite from
granitoid rocks could reflect its response to changes in petrogenetic variables such as temperature of crystallization, pressure,
composition, etc. Widespread migmatization in the granodiorite gneisses occurring to the east of Kolar and Ramagiri schist
belts of the eastern Dharwar craton resulted in the enrichment of the REEs in titanite relative to their respective host rocks.
A compositional influence on the partitioning of REEs between titanite and the host rock/magma is also noticed. The relative
enrichment of REEs in titanite from quartz monzodiorite is lower than that found in the granodioritic gneiss. Depletion of
REE and HFSE (high field-strength elements) abundances in granitic magmas that have equilibrated with titanite during fractional
crystallization or partial melting has been modelled. As little as 1% of titanite present in residual phases during partial
melting or in residual melts during fractional crystallization can significantly lower the abundances of trace elements such
as Nb, Y, Zr and REE which implies the significance of this accessory mineral as a controlling factor in trace element distribution
in granitoid rocks. Sm–Nd isotope studies on titanite, hornblende and whole rock yield isochron ages comparable to the precise
U–Pb titanite ages, invoking the usefulness of Sm–Nd isochron ages involving minerals like titanite. |
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