Tectonic evolution of the Aravalli Mountains

The Aravalli Mountain Range is a northeast-southwest trending orogenic belt that is located in the northwestern part of India and is part of the Indian Shield that was formed from a series of cratonic collisions. The Aravalli Mountains consist of the Aravalli and Delhi fold belts, and are collectively known as the Aravalli-Delhi orogenic belt. The span of the whole mountain range is about 700 km in length. Unlike the much younger Himalayan section nearby, the Aravalli Mountains are much older that can be traced back to the Proterozoic Eon. The collision between the Bundelkhand craton and the Marwar craton is believed to be the primary mechanism for the development of the mountain range.

The precise evolutionary processes responsible for the Aravalli Mountain Range remains controversial today with diverse theories put forward for the tectonic history.

The Aravalli Mountain Range features horst-like structure and consists of a series of Proterozoic rocks that are intensely deformed and metamorphosed.

Three main subdivisions of rocks constitute the stratigraphy of the mountain range, with the Archean Bhilwara Gneissic Complex basement being the lowest strata, followed by the overlying lower Aravalli Supergroup and the upper Delhi Supergroup. The northern part of the mountain range only consists of the Delhi Supergroup, and this has given to its name of ‘North Delhi Belt. On the southern side, however, both the Aravalli and Delhi supergroups are present. The mountain range is bounded by the Eastern and Western marginal faults, where the former is also termed as the Great Boundary Fault.

Quartzites

The Bhilwara Gneissic Complex basement is about 2.5 Ga old. It is made up of a group of metamorphic and igneous rocks that are mainly amphibolite to granulite grade, tonalitic to granodioritic gneisses and intrusive granitoids with a minor amount of metasedimentary and metavolcanic rocks. The basement is categorized into two subdivisions: the Sandmata Complex and the Mangalwar Complex. The Sandmata Complex refers to gneisses and granitoids while the Mangalwar Complex refers to the metasedimentary and metavolcanic series which are considered to be metamorphosed older granite-greenstone belt.

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