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莱萨堪(Lethakane)剪切带出现在博茨瓦那东部的林波波造山带内,是一个右旋位移大约50公里的横推韧性剪切带,发育在低级角闪岩到绿片岩相条件下。在剪切带内,又出现三个性质不同的次级构造:糜棱状叶理(Sa)、应变滑劈理或破劈理(Sb)以及次级剪切带(Sc)。非穿透构造 Sb 与 Sc 具有横推的动向,出现在与剪切带边缘呈近平行和近垂直定向共轭位置。穿透构造 Sa 组构局限在含石英的岩石中,就像 Ramsay 及Graham 所描述的韧性剪切带中片理那样,同次级剪切带(Sc)具有相同的 S 型关系。这种关系证实了 Johnson 首先提出来的见解,即糜棱状叶理限定在有限应变椭球状体的xy 面,并与片理一致。Sa 限制在含石英的岩石中表明在低级角闪岩相条件下。在莱萨堪剪切带,石英韧性状态和长石脆性状态之间的差异是控制形变过程的不可缺少的因素。莱萨堪剪切带(东27°45’,南21°50’,)是发育于博茨瓦纳东部林波波造山带最后一次构造事件期间的巨大韧性剪切带(图1)。这个剪切带作用于主要是花岗岩类成份的角闪岩和麻粒岩相的片麻岩。其构造年龄考虑用林波波带的矿物年龄2000±50百万年。区域变质作用的证据表明,剪切带是在绿帘石——角闪岩相条件下开始形成,并在变质作用程度退化到低级绿片岩相期间继续形成。韧性剪切带意义,特别是它们与片理和构造层的形成关系,最近为Ramsay和Graham、还有Vernon所强调。莱萨堪剪切带是由各种碎裂岩石类型组成,并在很好的限定构造系统内便能够调查研究糜棱岩化作用、压碎作用及剪切带形成。本文第一部份描述了剪切带与其有关的次级构造,然后讨论了与糜棱岩和剪切带形成有关的资料。本文所描述的糜棱状岩石的穿透构造指的是糜棱状叶理。使用糜棱岩化作用这个术语,是限于描述含糜棱化叶理的岩石形成过程。此外,除特别指出外,Higgins的命名法还将这些术语用于描述碎裂岩石及其构造方面。
The Lethakane shear zone appears in the Limpopo orogenic belt in the eastern part of Botswana and is a transverse thrust ductile shear zone with a right-lateral displacement of about 50 km developed from low-grade amphibolite to greenschist facies . Within the shear zone, there are three secondary structures of different nature: mylonite leaf (Sa), stratified slippery or broken (Sb) and secondary shear band (Sc). The non-penetrating structures Sb and Sc have a transverse thrusting behavior, appearing in near-parallel and near-perpendicular conjugation to the edge of the shear band. Penetration tectonics The Sa-structure is confined to quartz-bearing rocks, with the same S-type relationship as the secondary shear zone (Sc), as is the case in the ductile shear zones described by Ramsay and Graham. This relationship confirms the first suggestion made by Johnson that mylonitic foliage is confined to the xy plane of a finite strain ellipsoid and is consistent with the palliation. Sa is limited in quartz-bearing rocks to low-grade amphibolite facies. The difference between the Lisacan shear zone, the quartz ductile state and the feldspar brittle state is an indispensable factor in controlling the deformation process. The Leshancan shear zone (east 27 ° 45 ’, south 21 ° 50’) is a giant ductile shear zone developed during the last structural event of the Limpopo orogen in eastern Botswana (Figure 1). This shear zone acts on gneisses of the amphibolite and granulite facies, which are predominantly granitic components. Its age of formation is considered to be 2000 ± 50 million years of mineral age with the Limpopo zone. Evidence from regional metamorphism suggests that the shear zone started to form under the epidote-amphibolite facies and continued to form during the degenerated metamorphism to the lower greenschist facies. The significance of ductile shear zones, in particular their relationship to the mechanistic and tectonic layers, most recently by Ramsay and Graham, and Vernon. Leszcan shear zones are composed of various types of fractured rocks and are capable of investigating mylonitization, crushing and shear band formation within well-defined structural systems. The first part of this article describes the secondary structure to which the shear zone relates and then discusses the data related to the formation of mylonites and shear zones. The penetrating structure of the mylonitic rocks described herein refers to mylonitic foliage. The term mylonitization is used to describe rock formation with mylonized foliage. In addition, Higgins nomenclature has also used these terms to describe fractured rocks and their tectonic aspects, unless otherwise specified.