[S-CG50] 地球惑星科学におけるレオロジーと破壊・摩擦の物理

[SCG50-10] 放射光を用いた高時空間分解能での深部岩石ダイナミクスその場観察手法の検討

★招待講演

*久保 友明¹、本田 陸人¹、後藤 佑太¹、坪川 祐美子¹、辻野 典秀²、肥後 祐司²、柴崎 裕樹³ (1.九州大学、2.高輝度センター、3.高エネ研)

Reaction-deformation coupling in deep rocks are potentially important processes to understand the plate-tectonic mantle convection in the Earth. Recent developments of high-pressure deformation techniques with D-DIA and D-111 type multi-anvil devices enable us to conduct in-situ observations of the coupling processes up to lower mantle pressures combined with synchrotron radiation at PF-AR NE7A and SPring-8 BL04B1 beamlines. We briefly report some experimental results on the reaction-induced shear instability and rheological weakening related to the deep slab processes (e.g., Honda+ and Goto+, this meeting). In these studies, the stress-strain and transformation-time curves were simultaneously obtained to reveal "bulk rock dynamics". The weak point of this method is that the spatial and temporal resolutions for in-situ X-ray observations are low (~10^2 µm and ~10^2 sec, respectively). To overcome these limitations, we are planning to introduce some strategies developed in materials science into the MA-type high-pressure deformation techniques to observe "grain-scale dynamics" on sub-second time scales. One is an in-situ observation of individual-grain behaviors by utilizing Mode I 3D-XRD method (e.g., Poulsen, 2012). Statistical information of the dynamics of grains such as time evolution of the number of grains can be obtained by taking 2D-XRD patterns with oscillating the sample (i.e., the apparatus) by a few degrees. By using an high-angular resolution 2D detector with a camera length of ~3m, in-situ obs. of grain dynamics down to sub-micron scales can be expected (e.g., Jakobsen+, 2006). This would be a powerful tool for detecting the grain-size evolution in deep rocks during transformation, dynamic recrystallization, and shear localization controlled by grain nucleation and growth processes. Another is to utilize a high-flux and high-energy X-ray beam from ID beamline for MA high-pressure deformation study. Recent preliminary experiments conducted at SPring-8 BL05XU beamline revealed a new dehydration mechanism of antigorite in time scales of ~10^-1 sec at high pressures. Combining these new methods with MA-type deformation techniques enable us to conduct in-situ observation of both bulk-rock and grain-scale dynamics at high spatiotemporal resolution. We will briefly present recent attempts and some preliminary results obtained.