Geochemistry of Alirajpur Granitoids (Gujarat, India) and Their Genetic Relationship to the Precambrian Basement Underlying the Deccan Traps

Abstract

The granitic basement rocks of central and western India, which are overlain by the Deccan Traps, are important for understanding early Earth processes and crustal evolution. The Alirajpur region presents a unique opportunity to study the complete sequence of basement granites, overlain by the marine Turonian Bagh beds. These granitic basement rocks are mainly composed of orthoclase, quartz, plagioclase, and biotite as rock-forming minerals. Abundant zoned zircons are hosted within biotite and hornblende. The whole rock geochemistry is calc-alkaline with a prevalence of potassium over sodium. The Alirajpur granitoids exhibit low REE with positive Eu anomaly exhibiting typical lower crust signatures. A detailed petrological-geochemical comparison of the granitic basement rocks from the Koyna and Alirajpur basement, separated by ~500 km, indicates that they are genetically related and provide important clues about the extent of the Precambrian basement underlying the ~500 000 km² of Deccan Traps.