Reconstruction of Tectonic Stresses by Different Methods of Jointing Analysis (as the Example of the Morskoi Fault Zone in Cisbaikalia)

Abstract

Abstract —Complex analysis of jointing in the Morskoi fault zone rocks (Cisbaikalia) has been carried out to compare two principally different methods of tectonophysical reconstruction of paleostress tectonic field, by geologic-structural data. A new approach to the paragenetic analysis of statistic measurements for ‘mute’ joints has been used; this approach makes it possible to reconstruct the stress state in the local rock exposure and to understand whether it belongs to the fault zone of a certain morphogenetic type and orientation. The second approach to reconstruct the stress filed is the Angelier–Delvaux kinematic analysis, which allows us to calculate the stress tensor and determine the stress regime, based on the analysis of strike-slip vectors on joints. Using the two methods we obtained the stress state solutions of local and regional levels for the study area. The paragenetic analysis gave twice as many local solutions for the same number of observation points. This is due to different environments of the formation of jointing sets and slickenlines in time (stages of fault zone evolution) and space (closeness to the fault plane). Most of the local solutions of the kinematic analysis coincide with the identical solutions of the paragenetic method on the stress state of the first or second orders. We obtained by an order of magnitude more ‘new’ (not repeated in the other method) paragenetic solutions than kinematic ones. At the next hierarchic level, the paragenetic analysis made it possible to reconstruct the stress field and fault zones of a higher rank. The results of both methods involve several stages of tectonic evolution of the rock massif. The identical regional stress fields reconstructed by different methods seem to belong to one stage. The studied fragment of the Morskoi fault, according to both methods, was activated in the three most intensively pronounced settings: compression, left-lateral strike-slip, and extension. Strike-slip stresses are concentrated closer to the fault plane. Moreover, we also revealed submeridional extension and NW compression. The results of the stress field reconstruction using the two methods are compatible and, in general, successfully complement and justify each other; however, the paragenetic method gives more numerous and variable solutions, resulting in the transition to the regional level and construction of the map for the study area fault zones. Complex application of both methods is recommended.