Petrogenesis of gabbro and orthopyroxene gabbro from the Phenai Mata Igneous Complex,Deccan volcanic province: Products of concurrent assimilation and fractional crystallization |
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Authors: | K R Hari N V Chalapathi Rao Vikas Swarnkar |
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Institution: | (1) Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2215, USA;(2) School of Earth Sciences, SRTM University, Nanded, 431606, Maharashtra, India;(3) Geochemistry Division, NGRI, Hyderabad, 500007, Andhra Pradesh, India;(4) Op. Andhra Pradesh, Geological Survey of India, Southern Region, Bandlaguda, Hyderabad, 500068, Andhra Pradesh, India |
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Abstract: | We report the occurrence of orthopyroxene gabbro from the Phenai Mata Igneous Complex (containing thoeliitic and alkaline
rocks) that occur within Deccan Traps. The P-T calculations based on two pyroxene thermometry vary from 8.5±1.0 kbar and 963±39
°C. These gabbroic rocks exhibit high Mg# (0.67 to 0.71). But their primary magma signature can be negated due to their high
SiO2 (> 50 wt %), low Ni (32–35 ppm) and Cr (105–182 ppm) contents. Further, simple fractional crystallization was not responsible
for the modification of the magma. Modeling carried out using trace element concentrations revealed that concurrent assimilation
and fractional crystallization (AFC) was responsible for the genesis of these rocks. Small pods of magma could have accumulated
in the crustal portions and concurrent assimilation and fractional crystallization have taken place in the generation of gabbro
and orthopyroxene gabbro in the present study area. |
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