Evidence for the Contrasting Magmatic Conditions in the Petrogenesis of A‑type Granites of Phenai Mata Igneous Complex: Implications for Felsic Magmatism in the Deccan Large Igneous Province

Abstract

We report contrasting magmatic conditions in the generation
of anorogenic (A-type) felsic rocks from the Phenai Mata hill of Deccan
Large Igneous Province. The felsic units in the present study area can
be classified as granite, monzonite, quartz monzonite and granodiorite.
The field as well as the geochemical evidences collectively indicate the
mixing and mingling of contrasting magma compositions which were
widely involved in the genesis of these anorogenic intrusions. Based on
the anorogenic granite classification diagrams, it has been observed
that the granite shows A1 type character whereas the monzonite, quartz
monzonite and granodiorite exhibit A2 type characters. Both A1 and A2
type intrusions were compared with the associated basaltic andesites in
the variation diagrams and found that the A1 type rocks exhibit a welldefined
trend pointing towards a fractional crystallization process. The
A2 type rocks do not exhibit any particular geochemical relation with the
mafic rocks. Moreover, the A2 type rocks are characterized by negative
Nb and Ta anomalies in the normalized diagrams indicating the involvement
of crustal components. From the field and geochemical evidence,
it can be presumed that the A1 type rocks represent the fractional crystallization
sequence from a basaltic magma, whereas the A2 rocks might
have been produced by the melting of the pre-existing crust or by the
assimilation of crustal components into the mafic magma during ascent.
These contrasting magmas along with the mafic magma variably interacted
in the shallow crustal levels to form present-day field features in
the Phenai Mata Igneous complex.