三维韧性剪切变形构造组构样式探讨

Fabric Patterns in Three-Dimensional Deformations of Ductile Shear

结合三维变形理论,在Transpression变形模型基础上,提出了“剪切方向物质挤出模型”,并从三维有限应变角度定量探讨剪切方向物质(体积)挤出对剪切带宏观组构样式、转变的影响及其与运动学涡度的关系。变形过程中剪切方向物质挤出对韧性剪切带构造组构样式影响显著在减薄型三维变形中,当竖直(z)方向体积挤出量小于剪切运动(x)方向挤出量(两者比值a<1或a=1)时,发生“拉长-减薄剪切变形”,剪切带发育稳定的竖直面理和水平线理,运动学涡度数(ωk)对面理和线理组合不产生影响;当a>1时,发生“加宽-减薄剪切变形”,剪切带组构样式取决于2个因素运动学涡度数(ωk)和剪切带收缩量(k),可能的组构组合类型为“竖直面理和水平线理”或“竖直面理和竖直线理”。根据剪切方向物质挤出模型,得到结论同一运动性质的韧性剪切带可形成不同取向的拉伸线理;拉伸线理方向不一定和变形的简单剪切组分方向一致。

A new model, assuming ＂material extrusion along the simple-shearing direction during deformation＂, based on three- dimensional deformation theory and transpression model, investigates the relationships between ＂material extrusion along shear direction＂ and emerging combinations of foliation-lineation orientations, switches of foliation or lineation orientations and three- dimensional kinematic vorticity in terms of finite strains. The analysis shows that the material extrusion along shear direction will work on structural fabric patterns in tectonites. In thinning deformation, if material extrusion along vertical direction （z） is less than that along shear direction （x） （ a≤ 1 ） , the vertical foliation-horizontal lineation develops for the lengthening / thinning shear deformation, and the combining-patterns of foliation-lineation are independent of kinematic vorticity number （ωk） . However, in case of a 〉 1, i.e. widening / thinning shear deformation, structural fabric patterns of shear zone are determined by two factors, namely, kinematic vorticity number （ ωk） and shortening （k） parallel to y-axis. The implications of this study are differential orientations of stretching lineations might be formed in the same transport direction of a shear zone, particularly in high-strain zones, the orientation of stretching lineations is not necessarily shear-parallel to the simple-shear component during the three-dimensional deformation.