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Geochemical research progress of accessory minerals
ZHOU Yao-qi, SHI Bing-jie, LI Su, LIU Qian, ZHANG Yun-cui
( School of Geosciences in China University of Petroleum, Qingdao 266580, China)
Abstract:
Accessory minerals are very sensitive to diagenetic environment of their host rocks, which will be inevitable to be embodied in the structural and geochemical characteristics of accessory minerals. Zircon, rutile, apatite were frequently reported on their crystal structure, trace element characteristics and isotopic chronology. This review will provide the previous outstanding works and try to predict the future of geochemical researches of accessory minerals. Content of U, Th, Zr, Hf and their ratios are relevant to genetic types of zircon, but paragenetic minerals of zircon and metamictization may have influence on these parameters, as well as the precision of U-Pb age. Rutile is characterized by high Nb and Ta, and the ratio of Nb/Ta of rutile varies in different igneous rocks. Cr-Nb diagram is useful in recognizing protoliths. The existence of Mn2+, Eu2+, Sm3+, Dy3+, Er3+ is the reason why apatite luminescence displays yellow, green or blue. Trace elements, such as REEs, in accessory minerals which were not or slightly affected by geological activities reserve substantial information from the diagenetic environment of their host rocks. Ti in zircon and Zr in rutile are function of temperature, and these make Ti-in-zircon and Zr-in-rutile thermometers. Inclusions in accessory minerals contain original materials from magma source and wall rocks, so they are significant for researches of rock formation and magma evolution. With high content of uranium, zircon, rutile and apatite are used in U-Pb geochronology; in addition, Sm-Nd and Lu-Hf become regular isotopic methods of geochronology. After the rapid development of thermochronology, different isotopic systems of high-, mid- and low-temperature can supplement each other. This application will present not only more accurate ages, but also completer p-T-t paths. In the future, changes of structure and chemical composition of less investigated accessory minerals in high-temperature metamorphism, in each stages of hydrocarbon accumulation and under microbiological activities may become research focuses. New isotopic systems, nanotechnology and the development of analytical instrument will bring vitality to researches of accessory minerals with no doubt.
Key words:  geochemistry  accessory minerals  zircon  rutile  apatite