大别硬玉石英岩中金红石原位高温高压下晶体结构和OH的研究

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

本文通过金刚石对顶砧与拉曼光谱、红外光谱联用技术,原位模拟了金红石在高温高压下晶体结构及其OH的变化,从而了解俯冲带流体中金红石在地质过程中的行为及作用。实验证明,金红石在压力的作用下经历两次相变,分别为金红石型TiO_(2)结构→斜锆石型TiO_(2)结构(P=23.43GPa)→萤石型TiO_(2)结构(P=34.98GPa),其结构在经历过超深俯冲后、折返过程中则以ɑ-PbO_(2)型TiO_(2)结构稳定存在。并且金红石晶体中的OH红外特征峰强度随着压力的增加而降低,从而显示在加压过程中金红石中OH含量降低,但直至地球深部超过600km(37.28GPa,约1200km),其晶体中的OH也并未完全脱去。在高温高压实验中,金红石样品从常温常压条件加压、加温至P=4.01~4.08GPa和T=700℃时,金红石晶体的有序度、OH含量随着温度增加而降低,但至实验最高温压,晶体内部仍保留OH,其结构也稳定存在,因此金红石可以将水携带至深部约120km处。在降至常温常压的过程中,金红石中OH含量虽然增加,但并未恢复至实验开始时的含量,因此经历过快速俯冲、折返后的金红石中的OH含量无法代表金红石形成时的OH含量。

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 TiO_(2)→baddeleyite phase of TiO_(2) structure(P=23.43GPa)→fluorite of TiO_(2) structure(P=34.98GPa).The structure of TiO_(2) is stable as ɑ-PbO_(2) of TiO_(2) 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(37.28GPa),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=4.01~4.08GPa and T=700℃.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.