Hidden mantle layer found beneath Himalayas, revises 100-year-old theory

A new study has challenged a century-old theory about the structure of the Himalayas.

For decades, geologists believed the mountain range was supported by a double-thick crust.

In 1924, Swiss geologist Émile Argand mapped two continental crust layers 45–50 miles deep beneath the Himalayas. His model suggested the Indian plate slid far under Asia, creating 70–80 km of crust to hold up the towering peaks.

But recent computer simulations reveal a different picture.

They suggest blobs of mantle rock have wedged between India’s crust and Asia’s crust. This means a dense mantle layer lies beneath the Himalayas, adding rigidity to the mountain roots and helping them stay buoyant.

The new research, published in the journal Tectonics, highlights flaws in Argand’s model.

According to scientists, at depths of about 40 km, rocks behave more like “yogurt,” becoming ductile rather than rigid. This undermines the idea of simply stacking crust layers to support the range.

Geoscientists had long observed anomalies that Argand’s model could not explain. The mantle-sandwich model now offers a solution. Study co-author Simone Pilia said observations that once “seemed to be enigmatic” finally make sense under the crust–mantle–crust structure.

The discovery carries major implications for tectonics and seismic risk. The thick Tibetan crust is now understood to float on a stronger base, changing how scientists view stress buildup along the India-Asia fault zone. While the Himalayas continue to rise about 1 cm each year due to plate collision, the process also fuels powerful earthquakes.

The Himalayan belt is one of the most earthquake-prone regions in the world. Experts say understanding the true structure of the crust and mantle is critical for building accurate models of tectonic forces and seismic hazards in the area.