鞍山附近“樱桃园组”的构造样式及其时代讨论

本文区分了“樱桃园组”岩石在元古主构造旋回的三幕变形,详细描述了各幕SFL组合和按区段进行了投影。主变形幕D₁的构造最发育,F₁控制着本区的岩性分布。构造序列及样式变化显示由高塑性向脆性的变形格式。本组与下伏的太古鞍山群变粒岩在构造序列、样式和变质相上都有显著差异,过去许多地质学家把二者混划为一个单位,统名“鞍山群”,属太古宙。但本组与上覆的辽河群(上元古)的构造样式和变质相却相似,故其时代相当于早元古Ferrian期。

TECTONIC STYLE OF THE"YINGTAOYUAN FORMATION" NEAR ANSHAN, LIAONING PROVINCE, WITH FURTHER DISCUSSION ON THE CHRONOLOGICAL PROBLEM OF THIS FORMATION

Based on applying the techniques of structural analysis to rocks involved in the so-called "Yingtaoyuan Formation" near Anshan city, Liaoning province, structural sequence and thus the tectonic style of this formation have been discerned and clarified. Rocks belonging to the "Yingtaoyuan Formation" have undergone at least three phases of deformation during Proterzoic time. The first phase of deformation produced folds ranging in size from intrafolial to regional scale and generally exhibiting tightly appressed to isoclinal forms of nearly N-S trend. F₁ folds have a best development and exercise the major control on the disposition of rock units within entire area. S₁, a newly formed planar element which is an axial plane to F₁ folds, is defined by the preferred orientation of platy minerals such as,mica and chlorite in pelitic rocks and by parallel banding in ore-bearing quartzite. It shows transposition relationship with preexisting So, the origional bedding of rocks. Linear structures including boudins, mullions and Si/So intersections are found in various rock types. Mullions are always occurred in the hinge protions of folds(particularly in antiform)and this may be taken as an indication to identify folds in thick-bedded and even massive rocks. Structures by which the second phase deformation was denoted are S₂, F₂ and L₂. S₂ is a set of typical crenulation cleavage that overprinted on an anisotropic background of rocks which already contained earlier structures S₀, S₁ and F₁ etc.. It is an axial plane to F₂ folds, a series of folds of mainly mesoscopic in size except those distributed in the Yanqianshan domain. Fine wrinkles, the surface expression of S₂/S₁ intersections, labelled L₂, are widely distributed on S₁(≈S₀)surface within pelitic rocks and run parallel to axial trends of folds nearby. Third phase deformation is marked by the spasmodically developed kink-bands. All of these indicate a general evolution tendency of decrease in both metamorphic temperature and plasticity of rocks during this tectonic cycle. On the basis of considering the geometrical homogeneity of the S₁ fabric, 9 domains were divided throughout the area occupied by this formation. Data obtained from field survey have been plotted on equal-area stereogram(lower hemisphere)for each domain. Preferred orientation and trend determination of the ambiguous fabric patterns are determined by means of computer treatment using the eigenvalue method. By comparing the structural sequence and tectonic style in the "Yingtaoyuan Formation" to those in the underlying granulite association of the Archean Anshan Group, it is obvious that a great difference exists between these two rock units and that it is improper to regard the "Yingtaoyuan Formation" as one unit of the Archean Anshan Group as was proposed previously by many geologists. However, there is a great resemblance between this formation and the overlying Liaohe Group(Upper Proterozoic)in two aspects, i.e. the structural sequence and the metamorphic facies, so it is reasonable to correlate the time of this formation to Ferrian of Early Proterozoic.