In situ high temperature and high-pressure investigation of crystal structure and OH of rutile in jadeite quartzite from the Dabie Mountains, China

In this paper, the crystal structure and OH changes of rutile under high temperature and pressure were simulated in situ by means of diamond anvil cell combined with Raman spectroscopy and infrared spectroscopy, so as to understand the behavior and role of rutile in the subduction zone fluid during the geological process. The experimental results show that rutile underwent two phase transitions under the action of pressure, respectively: rutile type TiO2 -> baddeleyite phase of TiO2 structure (P =23. 43GPa) -> fluorite of TiO2 structure (P = 34. 98GPa). The structure of TiO2 is stable as alpha-PbO2 of TiO2 structure after the ultra -deep subduction and exhumation. And with the increase of pressure, the intensity of infrared characteristic peak of rutile will decrease, which leads to the decompression of OH content of rutile in the decrease of pressure process. But until it subducted to a depth of more than 600km (37. 28 GPa), the OH of rutile is not completely removed. In the high temperature and high-pressure experiments, the rutile sample is stable when it is pressurized from room temperature and pressure to P = 4. 01 similar to 4. 08 GPa and T = 700 degrees C. With the increase of temperature, the stability of rutile crystal increases and the content of OH decreases. However, the OH in rutile crystal does not completely remove at the highest temperature and pressure, therefore rutile can carry water to the depth of about 120km. Although the OH content of rutile increased during the process of falling to room temperature, it did not return to the content at the beginning of the experiment. Therefore, the OH content of the rutile after rapid subduction and exhumation cannot represent the initial OH content of the rutile formation.