Rethinking the complex geology of the Himalayas

On any world map, one feature immediately stands out: the vast Tibetan Plateau, often called “the roof of the world.” Rising more than 4,500 meters above sea level and stretching across two million square kilometers, it dominates every other highland on Earth. For decades, geologists have explained its formation with a familiar story. India collided with Asia about 50 million years ago, and the force of that slow-motion crash lifted Tibet skyward. But what if that story, taught in geology textbooks and repeated in countless documentaries, is only partly true? That’s the bold claim made by Yong-Fei Zheng, a geologist at the University of Science and Technology of China, whose paper was published in [Earth-Science Reviews]. Zheng argues that two of the most widely accepted ideas about the India-Asia collision don’t actually hold up when you look closely at the evidence. And if he’s right, it changes how we understand the Himalayas and also reshapes how scientists think about mountain building, plate tectonics, and the deep workings of our planet. Since the 1970s, Earth science students have been taught two core assumptions about the India-Asia collision. The collision has been ongoing throughout the entire Cenozoic Era (the past 65 million years). The Indian continent has been steadily sliding, or “underthrusting,” beneath Tibet, like one bumper of a car crumpling under another. These assumptions seemed to explain the rise of the Tibetan Plateau and the Himalayan peaks, including Everest. They also fit nicely with the then-new theory of plate tectonics, which emphasizes the role of subduction (one slab of crust sinking beneath another), as the engine of mountain building. But Zheng points out something surprising: these ideas were accepted long before there was strong evidence for them. And over the decades, new data have raised more problems than they solved. So, what really happened? Zheng’s review of geological, geophysical, and geochemical data suggests that the actual collision between India and Asia was surprisingly short-lived. The crunch began when the Neo-Tethys Ocean, once separating India from Asia, finally disappeared. India’s northern edge scraped into Asia around 55–45 million years ago, producing what geologists call “soft collision.” Imagine a car bumper grazing another before hitting harder. Soon after, a “hard collision” followed, where continental crust shortened and rocks were shoved up into thrust belts, creating the beginnings of the Himalayas. But by about 45 million years ago, the main collisional phase was already over. India did not keep burrowing far under Tibet as many had assumed. Instead, the geological evidence points to only shallow subduction no more than 200–300 kilometers deep beneath the Yarlung-Zangpo Suture, the geological scar that still marks where the two continents met. India didn’t wedge its way under Tibet for tens of millions of years. The big impact was quick, geologically speaking. If the collision was short-lived, what explains Tibet’s enormous uplift? What caused the “roof of the world” to rise thousands of meters skyward, mostly in the past 30 million years? Zheng’s answer shifts the focus from crustal collision to mantle dynamics. Deep beneath our feet, Earth’s rigid outer shell (the lithosphere) floats on a softer, hotter layer called the asthenosphere. After the early collision, Zheng argues, pieces of the dense lithospheric mantle beneath Tibet began to “founder”, that is, break off and sink into the deeper mantle. This allowed hot, buoyant asthenosphere to well upward, heating the crust, melting rocks, and causing dramatic uplift. It’s a bit like removing heavy weights from a raft, the raft bobs higher in the water. In this case, Tibet rose as the heavy mantle roots peeled away. This process also explains other puzzling geological signs: young granitic rocks formed by crustal melting, metamorphic “core complexes” that domed upward, and changes in the style of faulting from compression to extension. These events mostly happened 30 to 10 million years ago, well after the supposed long-lived collision. Another key point Zheng makes is that Tibet is not one single, uniform block of crust. Instead, it’s a mosaic of ancient terranes. It's small continental fragments and island arcs that were stitched onto Asia long before India arrived. These sutures and weak zones were later reactivated during the short-lived collision and again during post-collisional mantle upwellings. So, the Himalaya-Tibet region isn’t a single mountain belt created by one collision. It’s more like a collage, assembled over hundreds of millions of years and remodeled again and again by shifting tectonic forces. The implications of these findings are significant. For one, the India-Asia collision has long been treated as the archetype of continental collision. Geologists use it to interpret mountain belts around the world, from the ancient Appalachians in North America to the Alps in Europe. If our model of the Himalayas is off, then much of our global tectonic thinking may need to be revisited. It also changes how we think about plate tectonics itself. The traditional view sees continents as stiff bulldozers pushing and shoving each other indefinitely. Zheng’s work highlights that mantle processes, what happens beneath the crust, in the unseen depths of Earth, can be just as important in raising mountains and shaping continents. Finally, Zheng's work also has practical implications. The Himalayas are still seismically active, home to devastating earthquakes. Understanding whether the collision is “ongoing” or whether mantle upwellings are now the dominant process could influence how geologists' model seismic hazards in the region. Of course, these two assumptions have been baked into decades of research, from paleomagnetic studies to seismic imaging. Therefore, some geophysicists still interpret deep anomalies under Tibet as evidence of India plunging northward. Others, however, see the same anomalies as fragments of foundered lithosphere, just as Zheng suggests. What makes Zheng’s work stand out is its synthetic approach. Rather than relying on one type of data, he brings together geology, geophysics, and geochemistry, showing how multiple strands point to the same conclusion. It’s humbling to realize that even the tallest mountains on Earth don’t have a simple origin story. The Himalayas, it seems, are less a monument to a single titanic collision than the product of multiple phases of assembly, collision, and deep mantle dynamics. And the Everest is the result of the restless, invisible flow of Earth’s mantle, reshaping the surface in ways we’re only beginning to understand. If you want to learn more, the original article titled "A revisit to continental collision between India and Asia" on [Earth-Science Reviews] at [https://doi.org/10.1016/j.earscirev.2025.105087](https://doi.org/10.1016/j.earscirev.2025.105087). [Earth-Science Reviews]: https://doi.org/10.1016/j.earscirev.2025.105087

Article tags