Paleoproterozoic Extensional Structure and Its Controlling on Mineralization in the East of Liaoning Province

IntroductionThe area of eastern Liaoning is an importantmetal and nonmetal metallogenetic district in China,and the Liaohe group is one of the most importantstrata that hosts Pb, Zn, Au, B and Mg etcstratabound deposits. Up to now many geo1ogistssuch as Z…     

Pure shear to simple shear-dominated transpression during the Eburnean major D2 deformation,Daléma sedimentary basin,eastern Senegal

Field studies in the Palaeoproterozoïc Daléma basin, Kédougou-Kéniéba Inlier, reveal that the main tectonic feature comprises alternating large shear zones relatively well-separated by weakly deformed surrounding rock domains. Analysis of the various structures in relation to this major D₂ phase of Eburnean deformation indicates partitioning of sinistral transpressive deformation between domains of dominant transcurrent and dominant compressive deformation. Foliation is mostly oblique to subvertical and trending 0–30° N, but locally is subhorizontal in some thrust-motion shear zones. Foliation planes of shear zones contain a superimposed subhorizontal stretching lineation which in places cross-cuts a steeply plunging stretching lineation which is clearly expressed in the metasedimentary rocks of weakly deformed surrounding domains. In the weakly deformed domains, the subhorizontal lineation is absent, whereas the oblique to subvertical lineation is more fully developed. Finite strain analyses of samples from surrounding both weakly deformed and shearing domains, using finite strain ratio and the Fry method, indicate flattened ellipsoid fabrics. However, the orientation of the long axis (X) of the finite strain ellipsoid is horizontal in the shear zones and oblique within the weakly deformed domains. Exceptionally, samples from some thrust zones indicate a finite strain ellipsoid in triaxial constriction fabrics with a subhorizontal long axis (X). In addition, the analysis of the strain orientation starting from semi-ductile and brittle structures indicates that a WNE–ESE (130° N to 110° N) orientation of strain shortening axis occurred during the Eburnean D₂ deformation.     

辽东早元古造山带隆滑构造初析

辽东早元古代裂谷带内的隆滑构造是在吕梁造山前期伸展体制下的第一幕变形期间形成的。本区隆滑构造的内核隆起部位大致与中南岩基空间分布一致，由同构造侵位的二长花岗岩（辽吉花岗岩）组成，在裂谷带西区和东区，辽吉花岗岩皆顺基底与盖层之间的接合面呈席状侵位。由于辽吉花岗岩局部隆起，引起外壳内多层滑脱型韧性剪切带（简称韧变带）及流褶层的形成，在递进变形过程中流褶层会发生尖灭。因变形分解作用，在形成韧变带及流褶层的同时，也形成一些巨型透镜体，它们为弱变形域或未变形域，其内原生构造保存完整。对流褶层内流动褶皱的倒向及拉伸线理的统计，结果进一步表明中南岩基为辽河群内隆滑构造的隆起部位。现今东区和西区的穹形构造是初始席状侵位的叠加性构造，即在吕梁运动期间收缩体制下，辽吉花岗岩仍呈塑性并向背斜部位聚集，呈底辟式重就位；第三幕构造形迹横跨叠加于第二幕构造形迹之上，从而最终使辽吉花岗岩有规律地分布于穹形构造核部。     

古元古代拉伸构造模式──以胶北、辽东和吉南地区为例

对胶北．辽东和吉南地区古元古代层状岩系第一系构造变形作的详细研究和综合分析，并以此为典型实例，提出了古元古代拉伸构造模式，即隆起一顺层分层滑脱构造模式。该模式由核部隆起和上部盖居及两者之间的拆离型韧性剪切带三部分组成。核部隆起常由岩浆隆起或基底隆起构成，上部盖层内发育有顺层分层滑脱构造体系，由底部主滑脱面和内部次级滑脱面、低级滑脱面及其间的流褶居和片理化带构成，靠近核部隆起的盖居表现为正向滑脱，而滑脱前缘则表现为反向滑脱，具有滑覆特征。该模式一般发生在大规模收缩造山作用之前，由于区域拉伸作用，导致壳下地任上隆，形成岩桨隆起或基底隆起，使上覆盖层岩系重力失稳，发生滑脱，内部横向构造置换强烈，形成透入性片理，且平行区域地层层理     

Paleoproterozoic Extensional Structure and Its Controlling on Mineralization in the East of Liaoning Province

The palaeoproterozoic extensional structure in the east of Liaoning Province underwent sub - bedding ductile shear flowing deformation with metamorphism and magmatic emplacement. The reversal structure following the processes constructed the present framework of palaeoproterozoic orogenic belt. As a result of the ductile shearing along the layers, the gold in the Liaohe group was activated, migrated upward to the interface between the Dashiqiao rock formation, which was lower green schist facies and the Gaixian rock formation, so the gold deposit was formed in the space of brittle - ductile shear zone as ductile - shear - zone - typed stratabound gold deposit.