Estimating subduction boundary stresses and incorporation in next-generation modeling

本研究的目的是利用俯冲型变质带的岩石记录，特别是日本西南部发育较好的三川变质带的岩石记录，估计沿俯冲界面作用的剪切应力，并将这些结果纳入新的俯冲带热模型中。变质温度的精确测定是这项研究的重要组成部分。我们在这个问题上取得了重大进展。特别是，我们已经表明，在三巴川带的高品位变质岩中估计铁(II)/(III)比率的传统方法足以根据Mg-Fe阳离子交换测温法给出准确的温度估计。我们使用基于同步辐射的微XANES方法进行了大量实验，并得到了Moessbauer分析的支持。在获得可靠的结果之前，该方法仍有几个方面需要改进，但去年的结果显示，在某些高档样品中获得显着改进的温度估计的可能性相当大。我们在微观结构分析方面也取得了重大进展，这需要得出可靠的应力估计。研究进展包括：评价粒度测量中的切片效应；这是之前大多数研究都没有涉及到的。我们还探讨了在平面应力下测量自然试样变形到在单轴缩短下变形的实验室样品的方法的理论背景。

The purpose of this research is to use the rock record in subduction-type metamorphic belts, and in particular the well-developed and studied Sanbagawa belt of south west Japan, to estimate the shear stress acting along the subduction interface and incorporate these results in new thermal models of subduction zones. An important part of this study relies on accurate determination of the metamorphic temperature. We have made signifiant progress with this issue. In particular, we have shown that conventional methods for estimating Fe(II)/(III) ratios in the higher grade metamorphic rocks of the Sanbagawa belt are in sufficient to give accurate temperature estimates based on Mg-Fe cation exchange thermometry. We carried out numerous experiments using synchrotron radiation-based Micro XANES methods supported by Moessbauer analyses. There are still several aspects of the method that need to be refined before reliable results can be obtained, but the results of the previous year show considerable promise in the possibility to obtain significantly improved temperature estimates in some high-grade samples. We have also made significant progress in the analyses of microstructures required to derive reliable stress estimates. The progress includes evaluating the sectioning effect in measurements of grain size; something which is not incorporated in most previous studies. We also explored the theoretical background for approaches to use measurements of natural samples deformed under plane stress to laboratory examples deformed under uniaxial shortening.