Progress in high-precision potassium isotope research, such as the Purple Mountain Observatory

[ Instrument Network Instrument Development ] On August 15, "Geochimica et Cosmochimica Acta" officially published the latest achievements in high-precision potassium isotope research, such as the Purple Mountain Observatory of the Chinese Academy of Sciences. The study found that during the formation process of the glass vermiculite, the potassium isotope differentiation did not occur during the impact evaporative cooling of the upper continental crust into glass vermiculite, which has a mechanism for revealing the general volatile element loss mechanism of the inner solar system. Important scientific significance.

With the revolutionary development of isotope mass spectrometry technology at the turn of the century, especially the advent of multi-receiver plasma mass spectrometry (MC-ICP-MS), a new sub-discipline of non-traditional stable isotope geochemistry emerged and flourished rapidly. Development has become one of the biggest highlights in the field of geochemistry in the first decade of this century. In recent years, the accuracy of potassium isotope analysis of MC-ICP-MS has increased by an order of magnitude (from 0.5 ‰ to 0.05 ‰) compared to conventional SIMS and TIMS, thus revealing some previously unresolved potassium isotope differences. In particular, the comparative analysis of the Apollo moonstone samples shows that the moon's potassium isotope is 0.4 比 heavier than the Earth, which provides strong evidence for the Moon's high-energy high-angle momentum impact origin theory.

Comparison of the degree of differentiation of K, Zn and Cu isotopes in total silicate earth (BSE), Chondrite and Tektite

Tektite is a vitreous formed by the instantaneous melting and cooling of surface rocks under high temperature and high pressure reduction conditions when the asteroids hit the earth. The size of the glass is generally about mm/cm. Researchers at the Purple Mountain Observatory collaborated with the University of Washington, St. Louis, Harvard University and other teams to analyze the potassium isotope and zinc isotope of the Australian and Asian glass meteorites using Neptune MC-ICP-MS (Fig. 1). The results show that glass vermiculite and whole rock silicic acid There is no significant difference between the salt and the earth, indicating that the potassium isotope is not differentiated during the impact melting evaporation of the upper continental crust into glass meteorite. The zinc isotope varies greatly even in a cross section. Further thermochemical simulation calculations show that the pro-copper elements copper and zinc are easily lost during evaporation, resulting in large isotope differentiation, while the lithophile element potassium has a pole. A low activity coefficient is more likely to remain in the silicate melt.

High-precision potassium isotope analysis is becoming a hotspot in the field of non-traditional stable isotope research. The new technique is used to re-detect the potassium isotope composition of chondrite, lunar meteorite, martian meteorite and HED vermiculite, revealing the formation and distribution of volatile matter in asteroids and planets. The role of heterogeneity is very necessary and urgent, which helps to clarify the mechanism of loss of general volatile elements in solar system celestial bodies. In addition, this work can be directly applied to the Moonstone/Moon soil samples recovered from the Moon on the Luzhou No. 5 in the future, and the scientific evidence of the large collision theory of the Moon can also be given. At the same time, relevant research also provides a theoretical basis for future asteroid exploration in China.

The first author of the research work is Jiang Yun, an associate researcher at the Purple Mountain Observatory.

The work was mainly supported by the National Natural Science Foundation of China (Fund No. 41573059, 41873076, 41773059, 11761131008), the Key Laboratory of Planetary Sciences of the Chinese Academy of Sciences and the Purple Planet Observatory Asteroid Foundation.