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 well-defined 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.