实验探究位错蠕变机制下水对幔源单斜辉石流变性质的影响

As one of the major constituent minerals of the Earth's lower crust, upper mantle and other terrestrial planets, clinopyroxene plays an important role in determining the flow behavior of Earth’s Interior and other terrestrial planets. Published experimental studies about the rheological properties of clinopyroxene usually use crust-derived clinopyroxene rather than mantle-derived clinopyroxene as samples. However, there are difference between clinopyroxene from lower crust and upper mantle in chemical composition, especially in iron content. Previous studies indicated that chemical composition would have significant influence on the rheological properties of some silicate minerals. Therefore, it is critical to explore the rheological properties of mantle-derived clinopyroxene in order to accurately understand the flow behavior of clinopyroxene within Earth's upper mantle. Water dissolved as hydrogen in nominally anhydrous minerals is a common phenomenon, and the introduction of water usually dramatically affects the rheological properties of nominally anhydrous silicate minerals. Some studies further suggested that water-weakening effect on the nominally anhydrous minerals of Earth’s upper mantle plays an important role in the formation of asthenosphere, so experimental investigation of the effect of water on the rheological properties of nominally anhydrous minerals would contribute to clarify Earth’s interior structure of spheres, and thus help to understand geodynamic process within Earth’s interior. This project plans to conduct a series of high-temperature and high-pressure experiments on mantle-derived clinopyroxene both under anhydrous and hydrous conditions, thus to investigate the effect of water on the rheological properties of mantle-derived clinopyroxene. The result of this study will provide better constrain on the flow behavior of upper mantle, especially in the hydrous and clinopyroxene-rich regions.

单斜辉石作为下地壳、上地幔及其他类地行星的重要组成矿物之一，它的流变性质无疑会影响地球壳幔和其他类地行星中发生的动力学过程。水在地球内部普遍存在，且分布具有区域不均一性，它的存在会显著弱化硅酸盐名义无水矿物的流变强度。以往对单斜辉石流变性质的研究多采用下地壳来源的单斜辉石作为对象，而关于上地幔来源的单斜辉石的研究却极度匮乏，特别是水对幔源单斜辉石流变性质影响的研究则更是一片空白。已有的研究结果表明化学成分对矿物流变性质影响显著，而壳源和幔源单斜辉石的化学成分存在明显差异。因此，本项目拟在Paterson高温高压流变仪上对幔源单斜辉石进行含水和不含水体系高温高压变形实验，量化其位错蠕变域的流变参数，探究水和化学成分对上地幔单斜辉石流变性质的影响。研究结果将有助于准确阐释上地幔单斜辉石的流变行为及其对上地幔流变性质的制约关系，进而为剖析不同构造背景下上地幔复杂的动力学过程提供新的实验约束。

单斜辉石作为下地壳、上地幔及其他类地行星的重要组成矿物之一，它的流变性质无疑会影响地球壳幔和其他类地行星中发生的动力学过程。以往对单斜辉石流变性质的研究多采用下地壳来源的单斜辉石作为对象，而关于上地幔来源的单斜辉石的研究却极度匮乏。因此，本项目以幔源单斜辉石为研究对象，在 Paterson 高温高压流变仪上进行一系列轴向压缩实验，重点探讨温度、应力、应变速率对幔源单斜辉石多晶集合体位错蠕变和显微构造发育的影响，丰富单斜辉石的力学数据。. 本研究利用Paterson流变仪对不含水条件下的单斜辉石进行围压为300 MPa，温度为1323–1473 K的高温高压变形模拟实验。然后，对实验过程中获取的力学数据进行分析，我们厘定了不含水条件下单斜辉石位错蠕变的幂律流变方程，其中n = 4.91，Q = 340 kJ/mol，A = 2.05×10-5 s–1 MPa–4.91。另外利用透射电镜，我们在变形后的样品中观察到了大量的螺旋位错和刃位错，这与力学数据的拟合结果一致，表明实验过程中主导单斜辉石变形的是位错蠕变。. 在上地幔内存在一些辉石富集的区域，如被熔体交代的俯冲带上覆地幔楔、克拉通或造山带内部拆沉的下地壳及大火成岩省的源区母岩等，我们研究获得的流变方程，将有助于准确阐释这些构造的运动学和动力学成因机制，为物理模拟和数值模拟提供实验数据和理论支持。.