Researchers have found where the Indian Plate stops under Tibet by examining the chemistry of over 200 geothermal springs, contradicting certain long-debated notions regarding the process of continental collision.
The Indian and Asian continental plates collided – and continue to collide now – to construct the world’s biggest and tallest geologic features, the Himalayan Mountains and the Tibetan Plateau.
Despite the significance of these landforms, which impact global climate via air circulation and seasonal monsoons, specialists have suggested contradictory hypotheses regarding how tectonic plates under the earth’s crust built the famous behemoths. Scientists have now delineated the border between the Indian and Asian tectonic plates using geochemical data from 225 hot springs, revealing information on processes that occur deep under the surface. The results, which have implications for mineral formation, are published in the current edition of the Proceedings of the National Academy of Sciences.
“A major issue among geologists is whether or not continental collision resembles oceanic collision,” said lead research author Simon Klemperer, a geophysics professor at Stanford’s School of Earth, Energy, and Environmental Sciences (Stanford Earth). “Seismology wasn’t giving us the answer because there were too few measurements; that’s why I took up geochemistry as a whole new approach to measure things.”
Klemperer has spent the greater part of a decade traveling to Tibet and India to gather samples to back up his idea that chemicals bubbling to the surface may be utilized to comprehend what’s going on 50 miles below. He and his colleagues tracked down distant geothermal springs for hundreds of miles over the mountains and plains in the western United States, about the distance from Canada to Mexico.
The research authors identified which springs came from each continental plate by using the noble gas helium, which does not react with other substances. One helium isotope signature showed that the gas originated in the heated mantle (the Asian plate), while another indicated that it originated in the much cooler Indian plate. According to the findings, the cooler plate can only be found in the south, under the Himalayas, while farther north, India is no longer contacting Tibet above it, separated by a wedge of hot mantle. The findings suggest that an earlier hypothesis that the Indian plate rests flat under Tibet is no longer valid.
“It’s incredible that we now have this extremely well-defined barrier only a few kilometers broad at the surface above a 100-kilometer-deep plate boundary,” Klemperer said.
Collision vs. subduction
When a colder, heavier plate dives beneath a continental plate and sinks, material in the subsurface gets recycled into the Earth’s mantle. The process happens in areas renowned for frequent earthquakes and active volcanoes, such as the Ring of Fire.
Researchers suggested that sinking of ocean crust brought the two continents closer together until they clashed, sealing the subduction zone and allowing mountain formation to begin. This evidence of the continental border under Tibet raises the likelihood that the continental crust is releasing fluids and melting, as would occur during oceanic subduction.
“This suggests that we shouldn’t think about continental collision and oceanic subduction as two distinct phenomena; rather, we should think of them as the same process with somewhat different flavors since geometrically, they appear the same,” Klemperer said.
Changes in the tectonic seafloor
Plate tectonics theory revolutionized Earth sciences in the 1960s by describing how continental plates slide away and into one other, triggering mountain formation, volcanic eruptions, and earthquakes. However, scientists know very little about why plates move the way they do.
According to Klemperer, the new discoveries add a crucial layer of knowledge, with implications for what governs the convection that drives plate tectonics. Despite the fact that it is a continental collision, the Indian plate descending into the mantle helps govern the pattern of convection; it alters our understanding of how elements and rock types are transported and re-distributed on Earth, he added.
Klemperer and his colleagues previously studied the Himalaya collision zone using seismic data and discovered that when the Indian tectonic plate advances from the south, the thickest and strongest component of the plate falls under the Tibetan plateau, causing rips in the Indian plate. Those tears were in the same place as helium fluxes in hot springs.
“We’re viewing the same processes through various glasses, and we need to find out how to integrate them together,” Klemperer continued.
Implications for minerals
Civilizations have known about rich mineral reserves in regions like the Andes Mountains, which are part of the Ring of Fire, since the Spaniards invaded South America in quest of gold. Southern Tibet has lately been identified as a mining area rich in gold, copper, lead, zinc, and other resources that are difficult to explain using simply the conventional ideas of continental collision.
“The biggest copper concentrations occur in granites created by melting of the hot mantle wedge — that shouldn’t happen in continental collision if the previous model holds true, but we know it occurred because we have all these minerals in Tibet,” Klemperer said. “Our findings provide insight into the large-scale tectonics of continental collision and imply that mineral deposits in continental-collision settings may be similar to those seen in oceanic subduction environments.”
The Himalayas and Tibet, being the only current continental collision on our planet, also provide insight into how other mountain ranges have originated in the past and may develop in the future.
“Australia is just about to crash with the Indonesian block — that’s the beginning of a continental collision,” Klemperer added. “Tibet is the type-example to be solved, and we hope it’s an analog for how this occurs everywhere else on Earth.”
Klemperer is also a courtesy professor of geological sciences. Tianze Liu, a Stanford PhD student who worked on the research, is a co-author on the paper. The Chinese Academy of Sciences, The Ohio State University, the University of New Mexico, and the Scripps Institution of Oceanography are among the other co-authors.