On using the factor analysis to study the geodynamic processes of formation of the Greater Caucasus

The article describes the factor analysis procedure ensuring its correct usage for identifying the processes that cause formation of fold structures and the main layers of the continental crust in mobile belts. The proposed approach to this problem of geodynamics is specific: it aims at solving the inverse (rather than direct, which is common) problem of identifying the processes that led to the occurrence of a natural structure characterized by quantitative indicators varying within a certain range of values. The objectives of the study were to specify the number of main processes/factors, describe their nature and calculate their relative ‘loading’ values. The database included detailed structural profiles across the fold structure of the Greater Caucasus. A special method was applied to construct a balanced model of the sedimentary cover, considering ‘structural cells’ which are 5–7 km long along the profile. Each of the 78 ‘cells’ studied was characterized by six parameters: the depth of the basement top at three stages of development (pre-folded, post-folded, and post-mountain-building), the amount of shortening, the amplitude of neotectonic uplifting, and the difference between the depths of the basement at the first and final stages. The parameters, that are directly related to the evolution of the blocks of the continental crust in the study area, constituted the initial data array for the factor analysis. In the first step, the Kaiser criterion was used to determine the number of factors, and it was equal to two. This number was specified for the main study using the methods of principal components with rotation. Factor 1 (Isostasy) amounted to 46 % of loading value, with high loads of the parameter of the depth of the basement top at stages 1 and 3. Factor 2 (Shortening) amounted to 40 %, with high loads of the indicators of shortening values and the amplitude of neotectonic uplifting. Factor 1 is related to the process of ‘isostasy’: after folding and orogeny is complete, the basement top of the ‘structural cells’ tends to return to its depth which was obtained on the pre-folded stage. Factor 2 is related to the process of shortening of the structure. The Chiaur zone was chosen as an example to analyze the Alpine-type development of the structures using the isostatically balanced model. The analysis shows that this zone formed as the density of the crystalline crust gradually increased to the ‘mantle’ values. Geodynamic modeling still fails to properly take such transformations into account. In the discussion of the results, attention is drawn to the fact that the established process of ‘isostasy’ is natural, i.e. not pertaining only to a theoretical model. It is noted that a geodynamic model can be correctly constructed if it considers the impacts of both processes revealed in this study. The obtained results can be used for improving the geodynamic modeling of fold-thrust mobile belts.

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