Debate over defining the Aravallis could reshape legal protection across north India
Experts warn height-based criteria ignore the range’s ancient geological continuity
The Aravalli system is one of the world’s oldest surviving mountain belts
Mineral wealth and mining pressures lie at the heart of the controversy
Recent environmental concerns surrounding the Aravalli mountain range, especially following attempts to formally define it through an expert committee process, have brought the range back into sharp focus. The way the Aravallis are defined determines which landscapes receive legal protection and which may be opened to mining or development.
To understand why this definition matters, it is essential to first understand what the Aravalli actually is from a geological perspective.
The Aravalli Supergroup is one of the oldest geological formations in India and among the oldest mountain systems in the world. Its complex history provides crucial insight into the early evolution of the Earth’s crust. The range stretches across north-western India, primarily through Rajasthan and Gujarat, although its eastern boundary remains imprecisely defined.
Geologically, the Aravallis preserve a record of an ancient geological time known as the Precambrian era. This includes:
Archaean Eon (3.5 to 2.5 billion years ago): The oldest rocks belong to the Banded Gneissic Complex (BGC). These rocks form the foundation of the range.
Proterozoic Eon (2.5 billion to 541 million years ago): Younger rocks were deposited over the older Archaean rocks.
As a result, the Aravallis comprise igneous rocks (formed from magma), sedimentary rocks (formed from deposited material), and metamorphic rocks (altered by heat and pressure). Many of these formations host economically valuable mineral deposits.
The Aravalli Craton covers more than 100,000 square kilometres, spanning Rajasthan, parts of Gujarat and Madhya Pradesh, and extending into Delhi and Haryana. It includes the Mewar Craton in the east and the Marwar Craton in the west, separated by the Phulad Lineament.
The eastern boundary is marked by the Great Boundary Fault (GBF), separating the orogenic belt from the Vindhyan Basin. To the south lies the SONATA (Son–Narmada–Tapti) Lineament. To the north, geological continuity likely extends beneath the Himalayas via the Delhi–Haridwar Ridge, while sparse western outcrops extend into Pakistan’s Thar Desert.
Unlike many ancient cratonic regions, the Aravalli system lacks extensive greenstone or volcanic-domaniated belts. Instead, it consists largely of quartzites, marbles, pelites, greywackes and volcanics, forming the Proterozoic Aravalli-Delhi orogen. This orogenic belt comprises two major fold belts, Aravalli and Delhi, resting unconformably on the Archaean BGC basement.
The region also hosts India’s largest felsic province, the Malani Igneous Suite, dated to around 750 million years ago and ranked as the third largest in the world.
Understanding the Aravalli as a cratonic and fold-belt system clarifies why a narrow height-based classification is scientifically problematic. The range is defined by tectonic boundaries, fault systems and lithological discontinuity. So, whether a particular ridge rises 100 metres above its immediate surroundings is not an adequate measure to define it.
Once believed to rival the Himalayas in height, the Aravallis are now classified as residual or relict mountains, reduced by billions of years of weathering and erosion. While largely stable, they remain tectonically influenced by far-field stresses from the India-Eurasia collision, evidenced by minor seismic activity and geomorphic indicators of uplift in regions such as Udaipur.
The urgency of the definitional debate becomes clearer when viewed in light of the region’s mineral wealth and development pressures. The Aravalli range plays a crucial climatic role in northern India, acting as a barrier against desertification and supporting groundwater recharge systems.
It contains around 70 identified mineral deposits, of which approximately 65 are commercially extracted.
These include:
Metallic minerals: Lead, zinc and silver (notably at Zawar in Udaipur), and copper at Khetri.
Strategic and critical minerals: Lithium, tungsten, rare earth elements, graphite, molybdenum and nickel.
Atomic minerals: Uranium and thorium.
Building and industrial stones: Makrana marble, granite, quartzite, sandstone and limestone.
Other industrial minerals: Mica, feldspar, rock phosphate, talc and asbestos.
The way the Aravalli is legally defined determines which landscapes remain protected and which may be opened to extraction and infrastructure expansion. Continuous mining and infrastructure projects involving controlled/uncontrolled blasting can induce fractures in the rock mass, potentially destabilising slopes and altering groundwater systems.
The Aravallis are an integrated, ancient mountain system expressed today in subdued topography. A definition that ignores their geological continuity risks fragmenting protection across a landscape that functions as a single structural and ecological unit.
RM Ananya Vasudev is geologist and disaster management expert. Views expressed are the author’s own and don’t necessarily reflect those of Down To Earth