Flow laws and fabric transitions in wet quartzite
Flow laws and fabric transitions in wet quartzite
复制标题
湿石英岩中的流动规律和织物转变
DOI：
10.1016/j.epsl.2018.10.017
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发表时间：
2019
影响因子：
5.3
通讯作者：
W. Behr
中科院分区：
文献类型：
--
作者：
L. Tokle;G. Hirth;W. Behr
我们根据21个不同的实验研究数据，研究了在700-1200℃温度范围内加水变形的石英岩的流动规律，发现了两种明显的趋势：一种是幂函数应力指数n=4±0.3，另一种是在较高应力和较低温度下，应力指数n=2.7±0.3。应力指数的变化表明位错蠕变的限速过程发生了转变。发生n变化的变形条件也与观察到在一般剪切变形的样品的c轴组构发生明显变化的条件相关。在低应力时，石英织物由Y-max定义(其中c轴平行于应变椭圆的Y方向)，这表明在棱镜系统上很容易滑动。在更高的应力下，石英布在底部系统上很容易打滑。应力指数与c轴组构之间的相关性表明，流动规律的转变是主导滑移系和限制变形的滑移系相伴切换的结果。另一方面，最近对实验和自然样品的研究提供了石英集合体中位错调节的晶界滑动(DisGBS)的证据；在n=4和n=2.7流动定律之间的转变附近变形的样品的微观结构和力学数据表明了这一过程，为提出的类似于冰和橄榄石的流变学模型提供了证据。这些新的约束流动定律的外推描述了Y-max和基底&a>；组构在地壳中保存的估计的变形条件。这些结果为应用石英岩流动规律研究大陆地壳的流变性提供了进一步的支持，并促进了对石英集合体中蠕变的粒度相关性的更多分析。
We investigated quartzite flow laws based on data from 21 different experimental studies on samples deformed with added water at temperatures from 700 to 1200° C. Two clear trends emerge: one with a power-law stress exponent of n= 4±0.3 and the other, at higher stresses and lower temperatures, with a stress exponent of n= 2.7±0.3. The change in stress exponent indicates a transition in the rate-limiting process of dislocation creep. The deformation conditions where the change in n occurs also correlate with conditions where a distinctive change in the c-axis fabric is observed for samples deformed in general shear. At low stresses, quartz fabrics are defined by a Y-max (where c-axes align parallel to the Y direction of the strain ellipse), suggesting easy slip on the prism< a> system. At higher stresses quartz fabrics indicate easy slip on the basal< a> system. The correlation between the stress exponents and c-axis fabrics suggests that the flow law transition results from a concomitant switch in the dominant slip system and the slip system that rate-limits deformation. Alternatively, recent studies on both experimental and natural samples provide evidence for dislocation-accommodated grain boundary sliding (disGBS) in quartz aggregates; microstructures and mechanical data acquired on samples deformed at conditions near the transition between the n= 4 and n= 2.7 flows laws are indicative of this process, providing evidence for a rheological model similar to that proposed for ice and olivine. Extrapolation of these newly constrained flow laws delineates estimated deformation conditions where the Y-max and basal< a> fabrics are preserved in the crust. These results provide further support for the application of quartzite flow laws to investigate the rheology of the continental crust and motivate more analyses on the grain size dependence of creep in quartz aggregates.