Mineralogical and textural studies on basalts in parts of malwa plateau

Abstract

Malwa plateau is composed mainly of basalt traps. The basalt flows are of uniform character and the total thickness varies from 50 m to 135 m. A number of flows have been identified, indicating breaks in the continuity of the eruptions. The breaks were of shorter nature as evidenced by the presence of thin discontinuous bands of intertrappean sediments. The trap maintains a uniform horizontal attitude with well developed joints and is sometimes scoriaceous. Petrographically, these basalts are divisible into porphyritic, massive and vesicular types. The rock types are composed essentially of plagioclase, pyroxene, iron ore and glass. Stray occurrences of olivine have been noted from the lower section of the flows. The plagioclase ranges in composition between An 59 and An 68 and the pyroxene is diopsidic augite. The rocks are fine grained, aphanitic showing porphyritic, glomeroporphyritic, intergranular, micro-ophitic and flow textures.

It is concluded that the lava flowed out quietly, in some cases through fissures, and that the area is away from the main centres of differentiation.