基于扩散速率计的古元古代变质-构造过程研究：以胶北麻粒岩地体为例

变质作用速率，即变质岩石的埋藏、升温、抬升、冷却速率，对定量探讨变质-构造过程及其动力学机制具有重要意义。古元古代是早期板块构造建立的关键期，广泛发育高温-高压、高温-超高温麻粒岩。目前，对古元古代这两类麻粒岩的变质作用速率研究均基于传统年代学方法，该方法时间分辨率有限，很难定量刻画细致的、持续时间<20Myr的古元古代变质-构造过程。近年来，扩散速率计日趋成熟，可用于限定古老变质岩石的细致变质作用速率。为此，本项目拟以胶北地体的古元古代高温-高压、高温-超高温麻粒岩为研究对象，通过详细的野外考察厘清二者的接触关系，通过精细的变质作用和年代学研究确定变质P-T轨迹、变质时代。在此基础之上，利用扩散速率计对石榴子石等矿物进行元素扩散模拟，以限定两类麻粒岩的细致变质作用速率，如抬升/冷却的阶段性及速率，并探讨其热源机制和构造过程。本项目有望从变质作用速率的角度，提高对早期板块构造过程的认识。

Metamorphic rates refer to the rates of burial, heating, uplift and cooling of metamorphic rocks, and are of great significance to quantitatively decipher the metamorphic-tectonic processes and associated geodynamics. Paleoproterozoic is a critical era for the establishment of Early Plate Tectonics, which is characterized by widely development of high-temperature, high-pressure (HT-HP) and high-temperature, ultrahigh-temperature (HT-UHT) granulites. Extant studies on the metamorphic rates of these Paleoproterozoic granulites are based on traditional radiometric geochronology. However, current radiometric geochronology has inherent uncertainties that increase with the ages of rocks and limit the temporal resolution of the method. Hence, it is difficult for radiometric geochronology to identify and quantitatively characterize detailed metamorphic-tectonic processes with a duration scale less than 20 Myr from Paleoproterozoic rocks. In recent years, the diffusion geospeedometry has been progressively updated, and can be applied to refine the detailed metamorphic rates from ancient metamorphic rocks. Therefore, this project will focus on Paleoproterozoic HT-HP and HT-UHT granulites from the Jiaobei terrane. Their contact relationship, metamorphic P-T paths and ages will be determined by field, metamorphic and geochronological studies. On the basis of these studies, diffusion geospeedometry based on multicomponent diffusion in garnet and other minerals will be employed to constrain the detailed metamorphic rates of these two granulites, such as exhumation and cooling stages and related rates. The metamorphic rates defined will then be used to decode the heat source mechanism and tectonic processes. This project is expected to improve the understanding of the Early Plate Tectonics processes from the perspective of metamorphic rates.