Earth's geographical surfaces have been formed over millions of years, and various current theories aim to explain their formation. The most popular theory, called the "plate tectonics theory," states that Earth's outermost layer is a dynamic system consisting of slowly moving plates, also known as "tectonic" plates. As theses plates move, they come close to each other and collide, or drift away from or slide past the other, causing tension or rupture along their boundaries. If two colliding plates face enormous compression force along the rupture line, a slab of the earth would uplift. The uplifted piece of land gives rise to geographical structures such as mountains or plateaus on the landscape of the earth.
The Tibetan Plateau, the highest plateau in the world, is believed to have been formed through one such tectonic process, when the Indian and Eurasian continental plates collided with each other. Interestingly, the landscape of this enigmatic plateau consists of various unusual geological structures that have baffled geologists globally. For example, many independent geological units of different structures and ages are placed next to each other in a way that cannot be explained by a single tectonic event as per the existing theory. Intrigued by this, in a new study published in Earth Science Frontiers, a group of scientists at the China University of Geosciences, led by Dr Liu Demin, investigated in detail the geological structures of the southern Tibetan Plateau. Talking about their motivation, Dr Demin says, "The southern Tibetan Plateau has a complicated geological structure, which cannot be explained by the existing 'plate tectonics' theory. Our study uses a new idea to explain some unusual tectonic structures that are part of the southern Tibetan Plateau."
To begin with, the scientists analyzed ancient tectonic ruptures in the form of "boundaries" between the distinct geological regions. The "South Tibet detachment system" (STDS) is one such boundary that runs parallel to the Himalayan range for more than 2,000 km. The researchers analyzed the geological data of STDS and other structures in the region, such as the Rongbu Temple normal fault and the Main Central Thrust (MCT), to trace the possible chain of events related to the evolution of these boundaries. They speculated that instead of a single "collision-compression" process (as per the existing theory), these boundaries were created in different periods altogether, through a series of tectonic events that date back to the early Cenozoic era (a geological era that extends from 66 million years ago to the present day) and occurred in multiple stages.
According to this model, called the "opening-closing" theory, the upper layer or "crust" of a prehistoric ocean called the "Neo-Tethys" ocean expanded or "opened," and a part of the oceanic crust moved under the other, resembling a "closing" movement. The continental plates too followed a similar process of "opening and closing" as they moved towards and away from each other. This chain of events gave rise to the structures of the Tibetan Plateau. Using this model, the scientists were able to deduce that the Rongbu Temple normal fault and the MCT were formed earlier than the STDS was. Further, they revealed that two tectonic units, klippes and windows, in the Chomolungma region were actually the result of gravitational gliding (as opposed to compression, as previously believed) and thus should be characterized as extensions and slips, respectively. Dr Demin further explains, "Thermal energy and gravitational potential energy in the deep earth played a key role during this opening-closing evolutionary process."
The geology of Earth's surfaces has changed over millions of years through continuous evolutionary processes. In this study, scientists unraveled part of the mystery surrounding the complex geological structures of the southern Tibetan Plateau. Dr Demin concludes, "A deeper understanding of the 'opening-closing' process requires us to focus more on the detailed geological record for evidence of continuous rather than temporal processes.'' The research team now plans to study the differences between the opening-closing view and the plate tectonic theory in detail, to shed further light on the genesis of the Tibetan plateau.
Authors: Liu Demin, Yang Weiran, Guo Tieying, RU Jiangtao, Xiong Aimin
Title of original paper: Discussion on the Cenozoic tectonic evolution and dynamics of southern Tibet
Journal: Earth Science Frontiers
Affiliations: School of Earth Sciences, China University of Geosciences, Wuhan, China
About Earth Science Frontiers
Earth Science Frontiers is a bimonthly peer reviewed scholarly journal co-sponsored by the China University of Geosciences (Beijing) and Peking University. It was first published in 1994, and academician Wang Chengshan is the current Editor-in-Chief. Each issue of the journal is centered on a specific geoscience topic and managed by experts in that field as Guest Editors. Each issue also contains a number of articles on self-select subjects. Articles published on Earth Science Frontiers cover all disciplines of earth sciences with emphasis on frontier and innovative basic research. At the same time, the journal also publishes research findings that may be considered contentious. Over the years, Earth Science Frontiers has won several publisher awards, including "The Internationally Most Influential Journal in Chinese Language" and "The Top 100 Outstanding Chinese Scholarly Journals." In 2019, Earth Science Frontiers was selected among top-tier journals to join a national action plan for achieving excellence in science and technology research publishing in China.
About Dr Liu Demin
Dr Liu Demin is Associate Professor at the School of Earth Sciences, China University of Geosciences, Wuhan. His research is focused on the geodynamics of continental and geothermal geology. He has published seven research papers in reputed international journals.