The Earth’s interior is a complex system comprised of various layers, each playing a vital role in shaping the planet. Among these layers, the lower mantle is of particular importance due to its substantial volume and mass. To gain a comprehensive understanding of the Earth’s formation, evolution, and dynamics, it is crucial to delve into the material composition and thermal state of the lower mantle.
Previous studies have identified variations in seismic wave velocities within the lower mantle, particularly under Africa and the Pacific. However, the cause and implications of these anomalies have remained elusive. Overcoming the challenges of measuring mineral elasticity under the extreme conditions of the lower mantle has proven to be a significant obstacle. To address these challenges, a team of researchers led by Professor Wu Zhongqing developed an innovative computational method.
Professor Zhongqing’s team combined seismic tomography with mineral elasticity to determine the composition and spatial distribution of materials and temperatures in the lower mantle. They devised a computational method that proved to be more efficient than conventional approaches. This method allowed them to study the elastic properties of key minerals in the lower mantle and obtain results consistent with experimental data obtained at lower temperatures and pressures.
By integrating their computed elastic data with a three-dimensional tomographic imaging model, the research team successfully inverted the mineral composition and temperature distribution of the lower mantle. Through the use of a Markov chain Monte Carlo method, they also obtained a three-dimensional density model. These findings shed light on the temperature distribution, revealing a Gaussian pattern within a depth range of 1,600 kilometers. However, as the depth increases, the distribution gradually widens. Notably, at the very bottom of the lower mantle, the temperature distribution deviates from the Gaussian pattern, indicating strong lateral heterogeneity.
Further analysis of the data emphasized the impact of thermal anomalies and chemical composition on velocity anomalies within the lower mantle. The researchers discovered that thermal anomalies primarily contribute to velocity anomalies in the upper portion, while variations in chemical composition predominantly influence velocity anomalies in the deepest part of the mantle. The study also highlighted the higher densities of large-scale low shear wave velocity provinces (LLSVPs) at the bottom of the lower mantle compared to the surrounding mantle. These LLSVPs display lower densities above a depth of approximately 2,700 kilometers, suggesting a distinct composition.
The elevated temperatures and enriched concentrations of iron and bridgmanite within LLSVPs suggest that these regions may have originated from primordial basal magma oceans during the early stages of the Earth’s development. This finding has significant implications for understanding the formation, evolution, and dynamics of the Earth. By gaining insights into the mysteries of the lower mantle, scientists can continue to unravel the complex processes that have shaped our planet throughout its history.
The groundbreaking research conducted by Professor Wu Zhongqing and his team has brought us one step closer to comprehending the composition and thermal state of the Earth’s lower mantle. This newfound knowledge significantly advances our understanding of the planet’s deep structure. With further exploration and analysis of the lower mantle, scientists can continue to unlock the secrets of the Earth, ultimately enhancing our understanding of the formation, evolution, and dynamics of our remarkable planet.
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