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https://www.ias.ac.in/article/fulltext/jess/127/06/0087

Bastipadu; tourmaline; borosilicate; schorl; leucogranite

Tourmaline bearing leucogranite occurs as a pluton with pegmatitic veins intruding the Archaean granodiorite in the Bastipadu area, Kurnool district of Andhra Pradesh. We present field and petrographic relations, mineral chemistry and geochemical data for the leucogranite. It is essentially a two-mica granite, composed of quartz, perthite, microcline, albite, tourmaline and muscovite alongwith minor biotite and titanite. The euhedral tourmalines are regularly distributed in the rock. The geochemical studies show that the leucogranite is calc-alkaline, peraluminous to metaluminous which formed in a syn-collisional to volcanic arc-related setting. It displays strong ‘S’ type signatures with high K/Na ratios, moderately fractionated light rare earth elements, relatively flat heavy rare earth elements with $\rm{[Ce/Yb]_{N}} \leq 27.8$ and a strong negative Eu anomaly. The geochemical characteristics indicate that the leucogranite melt might have been generated from partial melting of metasediments. Electron probe microanalyser data show the presence of alkali group tourmaline in leucogranite represented by schorl and dravite. Tourmaline compositions plot in the Li-poor granitoids and associated pegmatites and aplites and metapelites/metasammites fields. Partial melting of boron-enriched source rocks is linked with the development of tourmalines in the leucogranite.

Kiran Jyoti Mishra¹ Santanu Bhattacharjee¹ Reddy M S¹ Praveen M N¹ Bhimte A D¹ Mahanta N¹

1. Geological Survey of India, Southern Region, Hyderabad 500 068, India.

Published

5 August 2018

Manuscript received

17 October 2017

Manuscript revised

2 January 2018

Accepted

19 January 2018

Final version published online

10 August 2018