◎ Liu Xiaohui
In the small geological museum of the 7th Geological Brigade of the Zhejiang Institute of Geology (hereinafter referred to as the "Zhejiang 7th Team"), there are two of the oldest ancient zircon in Asia.
"These two zircons more than 4 billion years old record the earliest known metamorphic event on Earth, providing a scientific basis for the long-disputed existence of the ancient Chinese continent. Wang Zhiguo, the captain of the Zhejiang Seventh Team, proudly introduced the great geological significance of the two zircons, "This is the treasure of our town hall!"
In May 2019, Zhejiang No. 7 Team organized a "Symposium on the Creation of Geology in Baishanzu National Park" in Lishui. Eight months later, the two chapters of geology and hydrology of the "Scientific Investigation and Compliance Certification Report of the Candidate Area of Baishanzu National Park" and the "Special Report on the Geology of the Candidate Area of Baishanzu National Park" were submitted. In the geological research part, they collected and sorted out the scientific research results of Xing Guangfu's team from the Nanjing Geological Survey Center of the China Geological Survey on Lishui Longquan zircon, and recommended it to the Baishanzu National Park Creation Office, which was finally refined into one of the eight advantages of Baishanzu National Park - the oldest zircon discovery site in Asia so far.
Zircon and ancient Chinese land
The geological characteristics of the early formation of the earth are the frontier research of the international geoscience community, mainly through the search and study of ancient rocks and minerals (zircon) in the Plutozoic (4.5 billion ~ 3.8 billion years ago).
Zircon, also known as zircon, is a common mineral found in continental crustal rocks and one of the oldest minerals formed on Earth. Because of its good stability, it is called the most important dating mineral in isotope geochronology.
The Plutozoic era is very old, and the initial rocks of the earth's formation have undergone meteorite impacts, crustal recirculation, remelting, and even recirculation to the mantle, and have almost disappeared. There are very few Plutozoic rocks exposed on Earth, while zircon is not easily changed during erosion or transportation, and can even be preserved in mantle conditions. Therefore, zircon is the only mineral preserved in the early Earth, especially the Plutozoic zircon, which preserves environmental information about the formation of the earth's crust and provides a valuable window for the study of the history of early terrestrial magma on Earth.
The geological concept of the Chinese paleocontinent was put forward by Gullips, which refers to the paleoland located east of the Huaxia Trough and above sea level during the Sinian to Jurassic periods, mainly the distribution range of the Precambrian metamorphic basement in China (Zhejiang-Fujian region) is called the Huaxia paleocontinent. The Longquan rock group in the Longquan area of southern Zhejiang is a typical representative. The proposal of the ancient continent of China has had a great and far-reaching impact on the study of regional geology and geological structure in China.
In 2014, a team of researchers from the Nanjing Geological Survey Center of the China Geological Survey discovered two Plutozoic detrital zircon for the first time in the mica quartz schist of the Longquanyan Group of the Huaxia Massif in Lishui, Zhejiang. Through high-precision dating studies, one of them is the oldest zircon in Asia, with a core formed by granitic magma crystallization and an age of 4.127 billion years, and the other zircon records the earliest metamorphic event of the earth, and the mantle is formed by metamorphism with an age of 4.07 billion years, which is the earliest metamorphic zircon found on the earth. Both zircons have extremely high crystallization temperature and abnormally high oxygen fugacity, which are obviously different from those of their contemporaries in other parts of the world, which proves the diversity of the Crustal properties and tectonic environment of the Plutozoic, and provides new and important information for understanding the early continental evolution of the Earth. The research results have been published in international core journals and have received wide attention.
In July 2015, the fourth issue of Acta Geologica Sinica also published an article entitled "The Oldest Zircon in Asia Found in the Huaxia Massif", which discussed this discovery in detail, showing the diversity of crustal properties and tectonic environment during the Plutozoic, and providing important new information for understanding the early continental evolution process of the earth.
In other words, the oldest zircon found in Asia in Lishui Baishanzu National Park in Zhejiang Province provides a scientific basis for the long-disputed existence of ancient Chinese continents.
The data show that in recent years, in addition to the Huaxia land massif, various types of Plutozoic rocks or zircon have been found in the North China land block, the Yangtze land mass, the Tibet mass, and the East Junggar Orogenic Belt in Central Asia, reflecting that there may be multiple ancient source areas 4 billion years ago in the world, and also indicating that different land blocks in the mainland may have similar early geological evolution histories.
Two ancient zircons in the Geological Museum of the Seventh Geological Brigade of Zhejiang Institute of Geology
The oldest zircon
Plutozoic zircon, often referred to as clastic zircon, is found in metasedimentary rocks in Brazil, western Tibet, North and South China, while the other, known as inherited zircon, is found in igneous rocks in Western Australia, North China, South China, northern Dabie Orogenic Belt, and eastern India.
In 2007, Academician Dorjee of the Chinese Academy of Engineering also introduced in his paper that 4.1 billion-year-old detrital zircon was found in the quartz schist of Pulan County, Tibet, which was the oldest single-grain detrital zircon age in China at that time, and belonged to magmatic zircon, which provided important age data for the study of the geological evolution of the Qinghai-Tibet Plateau.
According to research data by Long Yijie of the Institute of Geology and Geophysics of the Chinese Academy of Sciences, the oldest zircon in the world was discovered by geologists in the sandstone layer of the Jack Hill area of Western Australia. Scientists have tested that the miniature zircon crystals extracted from stones from a sheep farm in Western Australia have been 4.4 billion years old, making them one of the oldest parts of the earth's crust. Anthony Burnham of the Australian National University's Institute of Earth Sciences has since led a team to analyse the 4.4 billion-year-old tiny zircon mineral grains preserved in the sandstone rocks of Western Australia's Jack Ranges, which are also the oldest fragments found on Earth.
In this regard, the website of Russia's "Komsomolskaya Pravda" also reported in 2014 that the world's oldest zircon found on Australian farms proves that the earth's crust has been formed in the solar system 160 million years ago.
According to a report in the British journal Nature Geoscience, scientists used a new dating technique to determine the zircon crystals found in the rocks of a sheep farm in Western Australia in 2001, which has been controversial in age, and confirmed that it was indeed formed in the earliest days of the earth 4.4 billion years ago. The gemstone is only twice the diameter of a human hair, making it extremely small, but it is important for studying the formation of the earth and the age of life. The Earth itself was formed about 4.5 billion years ago, making this zircon sample the oldest material on Earth today. About 4.5 billion years ago, when the Earth was formed, its outer layers cooled and solidified, and the crust gradually formed from the original lava state. Researchers believe that the discovery of this zircon indicates that the earth has begun to cool and form the earth's crust within 100 million years after its formation, which may mean that the temperature of the early earth has been low enough to sustain the existence of the ocean and even life.
The colorful world of Zircon
Zircon is a gemstone with a refractive index second only to diamond and a high dispersion value in natural gemstones.
Zirconium gets its name from zircon, which is derived from the Persian word for "golden", which is said to be due to the striking color of some zircon jewelry.
In geology, zircon is a silicate mineral that is also found in metamorphic rocks and other sediments, and its chemical properties are very stable, so if you are lucky, you will also encounter gem-quality zircon in the gravel of rivers. Zircon is famous in southern Norway and the Russian Urals, while the world's most important gem-quality zircon is found in Laos, Cambodia, Myanmar, Thailand and other places.
In 1789, the German chemist Martin proved that zircon was not a diamond, clarifying the misconception that zircon was not a diamond.
By heating zircon with the reactive compound sodium hydroxide, he discovered that the two substances reacted to form an oxide. Martin believed that this oxide contained a new element within it, which he named zirconia, and this new element was named zirconium.
However, it was not possible to extract pure zirconium under the technical conditions at that time, because it was chemically similar to hafnium, and hafnium was often co-co-co-deposited with zirconium ore. It was not until 35 years later, in 1824, that the Swedish chemist Bechlias succeeded in producing pure zirconium by placing a mixture of potassium and potassium fluorozirconate in an iron pipe and heating it, and the purity of the black powdered zirconium obtained by the experiment reached 93%. Nearly 100 years later, higher purity zirconium was produced. Currently, most of the zirconium is extracted from zircon and zirconium dioxide.
As an important metal ore, zircon has a wide range of applications in industry and science. Due to its high melting point, high hardness, excellent heat resistance and corrosion resistance, zircon is widely used as a refractory material, playing an important role in metallurgy, glass manufacturing, ceramic industry, and atomic energy, and can be used to manufacture electronic components, semiconductor materials, and high-voltage capacitors. Zirconium exists in metal form and is mainly used in the chemical industry and nuclear reactor industry, as well as in other industries that require corrosion resistance, high temperature resistance, special fusion properties, or the absorption of special neutrons.
(Author's Affiliation: China Mining News)