Ductile deformation mechanisms in micritic limestones naturally deformed at low temperatures (150–350°C)
Ductile deformation mechanisms in micritic limestones naturally deformed at low temperatures (150–350°C)
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低温（150–350°C）下自然变形的泥晶灰岩的延性变形机制
DOI：
10.1144/gsl.sp.1990.054.01.23
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发表时间：
1990
期刊：
影响因子：
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通讯作者：
M. Burkhard
中科院分区：
文献类型：
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作者：
M. Burkhard
摘要本文研究了瑞士西部海尔维推覆体中泥晶灰岩样品的变形显微结构，这些样品在150-350°C温度范围内变形。有限应变是用Rf/φ-ε和中心-中心技术测定的，在褶皱推覆体内部的样品中，应变在Rs = 2到10之间变化;在来自逆冲面的样品中，应变要高得多。通过图像分析对每个样品的三个切片和每个切片200至500个颗粒的光学显微照片进行定量。从成岩作用到锚带（3-6 µm），粒度相当恒定，仅在表带（6-10µm）内增加。晶粒形状优选取向是弱的，总是比应变比Rs小得多。长轴取向反映了有限应变取向。圆度测量与具有相对简单边界的颗粒一致，通常在120°三重结中相遇，与温度、有限应变或晶粒尺寸无关。在低温（高达300°C）微晶中，尽管存在大的有限应变，但没有检测到晶体学择优取向。在一个极细粒（< 1 µm）低温（T < 180°C）断层岩中发现了强c轴择优取向。一定程度的择优取向普遍存在于粗粒浅成（T > 300°C）石灰岩中，这些石灰岩都显示出孪晶。推测晶界滑动（GBS）是200-300°C之间中度变形泥晶（Rs < 10）的主要韧性变形机制。随着温度的升高，通过动态晶界迁移再结晶导致晶粒粗化，导致晶粒尺寸在300°C以上净增加。这有利于孪生而不是GBS，这反过来又导致明显的c轴织物。
Abstract Deformation microstructures have been examined in a series of micritic limestone samples from the Helvetic nappes of western Switzerland, deformed at temperatures ranging from 150–350°C. Finite strain has been determined with Rf/φ-ϑ and centre—centre techniques applied to pellets and varies between Rs = 2 to 10 in samples in fold nappe interiors; much higher strains occur in samples from thrust planes. Optical micrographs from three ultrathin sections per sample and 200 to 500 grains per section were quantified by image analysis. Grain size is fairly constant from diagenesis through to anchizone (3–6 µm) and increases only within the epizone (6–10µm). Grain shape preferred orientations are weak and invariably much smaller than strain ratios Rs. Long axis orientations reflect the finite strain orientation. Roundness measurements are consistent with grains having relatively simple boundaries, frequently meeting in 120° triple junctions independently of temperature, finite strain or grain size. No crystallographic preferred orientation could be detected in the low temperature (up to 300°C) micrites despite large finite strains. Strong c-axis preferred orientation is found in one extremely finegrained (< 1 µm) low temperature (T < 180°C) faultrock. Some degree of preferred orientation is widespread in the coarser grained epizonal (T > 300°C) limestones which all show twinning. Grain Boundary Sliding (GBS) is inferred to be the dominant ductile deformation mechanism in moderately deformed micrites (Rs < 10) between 200–300°C. Coarsening of grains with increasing temperature by dynamic grain boundary migration recrystallization leads to a net increase in grain size above 300°C. This favours twinning instead of GBS, which in turn leads to pronounced c-axis fabrics.