Studies on deformation mechanisms of regional metamorphic rocks by means of microfabric analyses

本研究的主要目的是通过x射线织构角仪进行定量组构分析，了解岩石塑性变形的过程和机制。首先，我们设计并开发了一个计算机程序，通过对变形岩石中的云母、绿泥石、角闪石、橄榄石和石英进行多次试验，进行测量和数据处理。我们建立了一种高度可靠的方法，它比现有的方法提供了更多的应计值，并且只需要现有仪器测量时间的一半到三分之一。测量结果以首选取向的类型和程度定量表示。主要结果如下：1. 板岩的变形机制在低温条件下以压力溶解为主，在高温条件下以择优再结晶为主。应变椭球呈扁圆形，与S型织物相关。2. 位错蠕变和优先再结晶是高P/T三巴川变质岩的主要变形机制。应变椭球体一般呈长形。3. 低P/T Ryoke变质岩的变形机制以扩散蠕变为主。应变椭球体一般呈长形。4. 超镁铁质构造岩的变形可能是由橄榄石的织构模式引起的位错蠕变，为了解上地幔的变形机制提供了线索。将来，应该对从更广泛的地区收集的岩石进行测量，并建立应变量与织物类型之间的关系。对比研究世界各主要造山带的变形机制，对于认识地壳深部和上地幔的塑性变形机制也具有重要意义。

The main purpose of this study is to know processes and mechanisms of plastic deformation of rocks by means of quantitative fabric analyses that are carried out by the x-ray texture goniometer. First, we devised and developed a computer program for measurement and data-processing through many trial experiments on micas, chlorite, hornblende, olivine, and quartz in deformed rocks. We established a highly reliable method which gives more accruate values than those from current methods, and only takes a half to one third of measuring time on a current apparatus. Results of measurement are represented quantitatively in terms of types and degrees of preferred orientation. Main results are as follows. 1. As deformation mechanisms for slates, pressure solution is dominant at a lower temperature condition, while preferred recrystallization is dominant at a higher temperature condition. The strain ellipsoids are oblate and are correlative to S fabric. 2. As deformation mechanisms for the high P/T Sambagawa metamorphic rocks, dislocation creep together with preferred recrystallization is dominant. The strain ellipsoids are generally prolate. 3. As deformational mechanism for low P/T Ryoke metamorphic rocks, diffusion creep is dominant. The strain ellipsoids are generally prolate. 4. The deformation of ultramafic tectonites, which may give a clue to know the deformational mechanism in the upper mantle, is inferred to be due to dislocation creep from the fabric pattern of olivine. In future, measurements should be carried for rocks collected from wider areas, and the relationship between amounts of strain and fabric types should be established. Comparative studies on deformation mechanisms among main orogenic belts in the world are also important to know the machanisms of plastic deformation in the deeper crust and upper mantle.