Stosunek B-lineacji do regionalnego, lokalnego i cząstkowego pola naprężeń i sił

Józef Oberc, Jerzy Kotowski

Abstract


Relation of B-lineation of the regional, local and partitive field of force and strain

According to the authors, the general direction of B-lineation (lineation of grains, crenulation, fold axes, boudinage, and others) is associated with the regional field of force, the effect of which is a branch of folded zone of the tectogene. Within the (regional field same local fields may appear, compardsing minor second- and third-irate fragments of the branch with different orientation, i.e. represented by different directions of B- lineation. If the latter is perpendicular, or nearly perpendicular, to the regional B-lineation, it is sometimes wrongly defined as A-lineation. The partitive field of force is examined here on the basis of mesoscopic tectonic structures. Strain has been related to the axes of the coordinate system of fields of different scale: regional (a, b, c), local (a’, b’, c’) and partitive (a’’ , b’’, c’’ ). As appears from the analysis, there are 9 fundamental cases of spatial orientation of fields and their interrelations. When considering the causes of dispersion of B-lineation associated with a single tectogenic phase, sedimentary crocks, epizonal and mesozonal metatmorphites have been discussed separately. In sedimentary rocks, B-lineation is represented by axes of (minor folds, boudinage, beta axes, and others. Local elevation and depressions, as well as the effect of resistance and folding massifs, changes in the structural plan during a single phase, considerable differences in (the value of the resultant forces, and, finally, competency are regarded as responsible for dispersion. Long duration of folding and the amplitude of horizontal displacements after the .Creation of B-lineation, due to (which B-lineation is further reoriented, as well as the depth of folding are of great importance for the dispersion. In epizonal rocks, the process of folding that began during diagenesis is continued. Due to greater load pressure, the new-formed types of B-ineation (recrystallization-lineation, crenulation, beta axes, etc.) show smaller dispersion than under the diagenebic conditions. Disharmonie folding caused by changes in competency and displacement rate, particularly in schists, as well as greater amplitudes of horizontal overthrusts are responsible for the dispersion of pre-existing lineation. In mesozonal rooks, especially in their deeper parts (Z-l zone), within thicker gneiss plates, some earlier deformations on a micro- and mesoscale and the associated lineations disappear, due to which their dispersion is lesser. An increase in the competency differences gives rise to new lineations in incompetent series. Their dispersion is not significant because, the field of force is uniform in deeper zones of folding. In conclusions, the problem of mutual relations between lineations and coordinate system has been discussed and new suggestions given. All the lineations, except for A-lineation, are considered as the b axis for the particular type of lineation and for the definite point of time at which it is formed. If the coordinate system changes from point to point in time, it is the ’’kinetic coordinate system” (Gzowsky, 1971). The static coordinate system refers to the present day spatial orientation of lineations. In structural analysis, only analogous lineations identified on the basis of their morphological and mineralogical features, their genesis and internal anatomy may be compared. In every point of the investigated series it (is necessary to determine the interrelation between time and space, which defines the extent of local and partitive fields as related to the regional field. The coordinate system for the regional field is rectangular and curviaxial, with the a axis horizontal. For local fields the system is rectangular and rectaxial, with the a axis horizontal or nearly horizontal only in the hinge zones; on the limbs the a axis is inclined concordantly with the dip of the folded surface. Similarly, for partitive fields the coordinate system is rectangular and rectaxial, with the a axis horizontal in the hinges of anticlines and/or synclines, and inclined on the limbs (diagonal coordinate system). The above principles are valid for folds with the b axis horizontal or nearly horizontal. For folds with inclined axes, appropriate corrections must be introduced in which the principles of perpendicularity of the axes in the point of their intersection will be observed.

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