Mylonitization in the Lethakane shear zone, eastern Botswana
Mylonitization in the Lethakane shear zone, eastern Botswana
复制标题
博茨瓦纳东部莱塔卡内剪切带的糜棱岩化
DOI：
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发表时间：
1977
影响因子：
2.7
通讯作者：
J. Wakefield
中科院分区：
文献类型：
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作者：
J. Wakefield
Lethakane剪切带是一条平移韧性剪切带，右旋位移为c。50 km，发育于博茨瓦纳东部林波波造山带低角闪岩-绿片岩相条件下。剪切带内存在三种不同的次级构造：糜棱岩面理（Sa）、应变滑移或断裂劈理（Sb）和次级剪切带（Sc）。非穿透构造Sb和Sc具有横向运动方向，并以共轭组形式出现，方向与剪切带边缘近平行和近垂直。渗透组构Sa仅限于含石英岩石，与小剪切带的S形关系与Ramsay和Graham（1970）描述的韧性剪切带中的渗透性相同。这种关系证实了约翰逊（1967）首先提出的观点，即糜棱岩面理确定了有限应变椭球的XY平面，因此与弹性相似。Sa对含石英岩石的限制表明，在低角闪岩相条件下，石英的韧性行为和长石的脆性行为之间的对比是控制Lethakane剪切带变形过程的重要因素。
The Lethakane shear zone is a transcurrent ductile shear zone with a dextral displacement of c. 50 km which developed under low amphibolite-to greenschist-facies conditions in the Limpopo orogenic belt of eastern Botswana. Three distinct minor structures occur within the shear zone: mylonitic foliation (Sa), strain-slip or fracture cleavage (Sb) and minor shear zones (Sc). The non-penetrative structures Sb and Sc have transcurrent movement senses and occur in conjugate sets orientated sub-parallel and sub-perpendicular to the shear zone margins. The penetrative fabric Sa is restricted to quartz-bearing rocks and has the same sigmoidal relationship to minor shear zones as that described for schistosity in ductile shear zones by Ramsay & Graham (1970). This relationship confirms the view, first proposed by Johnson (1967), that mylonitic foliation defines the XY plane of the finite strain ellipsoid and is thus analogous to schistosity. The restriction of Sa to quartz-bearing rocks indicates that, under low amphibolite-facies conditions, the contrast between the ductile behaviour of quartz and the brittle behaviour of feldspars is the essential factor controlling deformation processes in the Lethakane shear zone.