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Exhumation processes of the Sambagawa metamorphic rocks, as inferred from quartz microstructures and mineral radiometric ages

从石英微观结构和矿物辐射年龄推断三巴川变质岩的折返过程

基本信息

批准号：
14340151
负责人：
TAKESHITA Toru
金额：
$ 6.21万
依托单位：
HIROSHIMA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

项目摘要

The results obtained in this research have been summarized below.(1)We have set up an automated measurement system of c-axis orientation of deformed quartz, using a Zeiss petrographic microscope, digital camera and Macintosh personal computer. This was made possible by Prof.R.Heilbronner, who stayed at Hiroshima University for 1 month in 2003, and investigated a lot of microstructures in quartz schists from the Sambagawa belt, central Shikoku with this method. The results will be submitted for a special volume of Tectonophysics.(2)The boundary and difference in the nature of terrane between the Sambagawa and Northern Chichibu belt have not been clear. In this study, we have found that the Kiyomizu Tectonic Line is the boundary fault between the two tectonic belts, which are completely different in both lithology and geologic structure.(3)We have conducted detailed geological survey and microstructural analyses of deformed quartz schist. As a result, it has become clear that an extensive folding and faulting occurred, and existing well-defined quartz c-axis fabrics were destroyed by solution-reprecipitation of quartz assisted by micro-faulting during the final exhumation stages under low temperatures in this area.(4)I hired Dr.N.Shigematsu as a research associate for three month in 2004. He was engaged in deformation experiments of K-feldspar single crystals, using a modified Griggs apparatus installed at Hiroshima University. We have found that K-feldspar single crystals deformed by mechanical twinning and intracrystalline slip, but also sometimes failed by faulting at the physical conditions (T=800゜C, strain rate=10^<-5>/s), suggesting that the experimental conditions can be correlated with those of the brittle-ductile transition. Also, these experimental conditions can be correlated with the temperature conditions of ca.400゜C at natural strain rate, which interprets that feldspars start to plastically deform around these temperatures in nature.

本研究取得的成果总结如下：(1)利用蔡司岩相显微镜、数码相机和Macintosh个人电脑，建立了变形石英c轴取向自动测量系统。 2003年，R.Heilbronner教授在广岛大学停留了1个月，用这种方法研究了四国中部三波川带石英片岩的大量微观结构，使这一成果成为可能。研究结果将提交给构造物理学专卷。(2)三波川带和北秩父带地体性质的界限和差异尚不明确。本研究发现清水构造线是两条构造带之间的边界断层，这两条构造带的岩性和地质结构都完全不同。(3)对变形石英片岩进行了详细的地质调查和微观结构分析。结果表明，在该地区低温下的最终折返阶段，发生了广泛的折叠和断层，并且在微断层辅助下的石英溶液再沉淀作用下，现有的清晰石英c轴织物被破坏。（4）我于2004年聘请N.Shigematsu博士为研究员三个月。他从事钾长石单晶，使用广岛大学安装的改良格里格斯装置。我们发现钾长石单晶会因机械孪晶和晶内滑移而变形，但有时也会在物理条件（T=800゜C，应变速率=10^<-5>/s）下因断层而失效，这表明实验条件可以与脆塑转变的条件相关。此外，这些实验条件可以与自然应变率下约 400゜C 的温度条件相关，这解释了长石在自然界中在这些温度附近开始塑性变形。