The Institute actively encourages technicians to constantly develop new and innovative analytical methods. Using modern equipment and instruments, the technicians have made considerable progress in the development of innovative analytical methods and new technical investigations, which have, in turn, been widely applied by scientists around the world.
1. Minim and in situ micro-analytical methods
The MC-ICPMS Laboratory has developed a series of in situ micro-analytical methods. The method of in situ simultaneous determination of trace elements (i.e. the U-Pb and Lu-Hf isotopes in zircon and baddeleyite) has been widely used in studies related to Earth sciences, which includes fields such as petrogenesis and evolution of the continental crust and orogenic belts. In situ Sr-Nd isotopic analysis of single minerals, such as plagioclase, calcite, titanite, apatite, perovskite and monazite, give the MC-ICPMS laboratory unique abilities. In particular, the method of in situ simultaneous determination of trace elements, U-Pb and Sr/Nd isotopes in perovskite provides a new method for the resolution of the difficult issues concerning the age and petrogenesis of kimberlites.
The MC-ICPMS Laboratory has studied loparite, eudialyte and zirconolite from around the world, and made the discovery that eudialyte is not only suitable for U-Pb dating, but also for in situ Sr-Nd-Hf isotopic analysis. Eudialyte is the only mineral that may be used for in situ simultaneous determination of trace elements (i.e., U-Pb and Sr-Nd-Hf isotopes), and has been widely applied in the Earth sciences.
By using the multi-collection techniques of SIMS, Pb-Pb dating precision has been improved five-fold. The multi-collector SIMS is capable of direct determination of zircon Pb/Pb ages as young as those of the Mesozoic age. Moreover, this method may also be used for the dating of accessory minerals of a younger age in thin sections without external standardization.
Using the Gaussian illumination mode of the primary beam, the Institute has achieved the precise U-Pb zircon dating at a scale of <5 microns. This technique has been applied to fine-grained accessory minerals found in meteorite.
By introducing the “oxygen flooding” technique, the secondary ion yield was enhanced by a factor of 7, and the optical axis effect of baddeleyite U-Pb dating was also reduced. The possibility of young baddeleyite dating by SIMS has become a reality, and therefore, the technical problems of basic and ultrabasic rock dating have been solved.
2. The study of reference materials for in situ isotopic ratio measurement
Reference materials form the basis of in situ analysis. As analysis and testing in China are always carried out based on international reference materials, Chinese geologists have depended on international reference materials for many years. This situation has become one of the main obstacles to the development of in situ techniques. Penglai Zircon and M257 Zircon have been used as the first working references for Hf-O isotopes in China and Li isotopes in the world, respectively. This laboratory continuously makes breakthroughs in reference materials for isotope microanalysis in China.
3. Analytical methods of stable isotopes
The institute has established oxygen isotopic analyses methods for zircon, apatite, quartz and olivine, as well as a lithium isotopic analysis method for olivine. In situ oxygen isotopic analyses of olivine may be performed in thin sections, which provides important information concerning mantle metasomatism. The development of oxygen isotopic analysis for apatite has opened up a new research domain of Earth thermometers using conodont oxygen isotopes, which is becoming a strong technical support for the research of the paleo-ocean environment. The MAT series of stable isotope ratio mass spectrometers have combined with Flash HT elemental analyzers and Finnigan Gas Bench II, enabling online analyses of trace amounts of stable isotopes from carbonate and silicate minerals to fluid inclusions.
4. Analytical methods of solid isotopes
High sensitivity methods for Sm-Nd isotopic analysis by using tungsten filaments with silica-gel or tantalum fluoride as an ion emitter have been successfully established by the Institute, and these methods have been used for garnet Sm-Nd dating, meteorite dating and the constraint of the petro-genesis on highly depleted ultramafic rocks. An analytical procedure for the simultaneous determination of the concentrations of Re, Os, Ir, Ru, Pt, Pd and Os isotopic composition has been successfully established and this method has been used in mantle geochemistry and petrogenesis of ophiolite. Successful development has also become reality for Ultra-high Precision 142Nd/144Nd measurement method and may be applied to constrain early crust-mantle differentiation of silicate earth and planetary differentiation.