Geochemistry data of trachyandesite of Ulindakonda vent agglomerate of Gadwal greenstone belt of eastern Dharwar Craton, India

Abstract

Ulindakonda vent agglomerate of Neo-archean Gadwal Greenstone Belt in the Eastern Dharwar Craton (EDC), is located partly in the Kurnool district of Andhra Pradesh and partly in Jogulamba Gadwal district of Telangana state, India. Trachyandesite occurs as matrix of the agglomerate and at some places it exhibits massive and interbedded nature with granodiorite that mainly occurs as sub-rounded clasts in the agglomerate reflecting magma mixing and mingling. The rock is dotted with small dark specks of a ferromagnesian mineral which often shows a well-developed cleavage surface. The size of grains ranges from medium to fine-grained. Petrographically it is dominated by feldspars and mafic minerals like hornblende and biotite as accessory minerals and quartz in minor amounts. Further, titanite, allanite, carbonate and epidote occur as phenocrysts. Consertal texture is seen between amphibole and quartz, sieve texture also observed in plagioclase feldspar. The percentage of SiO2 ranges from 49.84 to 62.92%, TiO2 grades from 0.51 to 2.46%, Al2O3 varies from 11.43 to 15.99%, FeOT ranges from 5.88 to 18.28%, MnO grades from 0.07 to 0.14%, MgO varies from 1.27 to 4.95%, CaO shows variation from 2.58 to 7.62%, Na2O grades from 2.56 to 4.84%, K2O shows variation from 1.66 to 4.87%, P2O5 varies from 0.30 to 0.80% and LOI grades from 0.67 to 1.93%. In the primitive mantle-normalized spidergrams, all the samples of trachyandesitic matrix are depleted in high field strength elements (HFSE; Nb, Ti, Zr, Hf and Ta) but are enriched in large ion lithophile elements (LILE; Cs, Rb, Ba, Sr, U, K and Pb). The chondrite normalized REE pattern of trachyandesitic matrix show moderately fractionated LREE (La/SmN= 2.44-4.45, La/YbN= 5.85-23.29) with negligible negative Eu anomaly (0.71-0.91) and flat HREE (Gd/YbN=1.99-3.30) showing the normalized values are >10. The Ulindakonda trachyandesitic samples are plotted in the field of calc-alkaline basalts (CAB) and in the island/ volcanic arc in the tectonic discrimination diagram.