Attractor structures of riftogenesis as an attribute of the cenozoic stage in evolution of the lithosphere within the Baikal rift system

Abstract

In accordance with the principle of actualism, theresults of studying the modern geodynamics and tectonophysics of the Baikal rift system (BRS) have beenapplied for development and broadening of ideasabout the Cenozoic Stage of the lithosphere in theregion. Identification of three attractor structures ofriftogenesis (ASR) has allowed the theory of moderngeodynamics and tectonophysics of the BRS to bedeveloped: the regional energy sources for geodynamical and seismic reconstructions have been includedinto the pattern, and their nature and effects have beendescribed in the first approximation. Within theframework of the theory of dissipative dynamical systems of selforganization and nonlinear media, theASRs have been considered as an attribute of Cenozoic geodynamics of the BRS lithosphere: they formednonlinearity and instability of geodynamical and tectonophysical processes in this period of time. Threestages of volcanic activation of the BRS lithosphere areexplained by sequential origination and developmentof three ASRs: firstly, in the South Baikal Depression(Late Cretaceous–Paleocene), then in the KhubsugulDepression (Eocene–Oligocene), and finally in theMuya Depression (postOligocene). The start of theCenozoic riftogenic stage of the Baikal Depressionabout 70 Ma BP is explained by appearance of theASR is the South Baikal Depression. Two stages of rifting, an increase in the rate of rift processes in the BRS,and propagation of riftogenesis southwestwards andnortheastwards from the South Baikal Depression areattributed to the appearance and gradual twolateralevolution of the ASRs in the Khubsugul (southwesternflank) and Muya (northeastern flank) depressions.In the hierarcy of natural systems, intracontinentalrift systems, which consist of deeplaid fault zones andzones functioning in a relatively narrow thermodynamical regime, are classified as mesosystems [1].N.A. Logachev et al. [2, 3] found the main features ofthe Cenozoic riftogenesis dynamics of the intracontinental BRS: evolution of the process southwestwardsand northeastwards from the South Baikal Depression, which is the historical core of the BRS, tookplace during two stages, namely, slow and rapid rifting.Such systems that change in space and time are identified as dynamic [4], and it follows from the theorythat dissipative dynamical systems in geological–geophysical media should have spatiotemporal attractors;in the lithosphere of a rift system, these attractors areto be classified as attractors of riftogenesis (spacedomains and time periods where normal faultrelatedearthquakes, which are typical for this mode, dominate). It has been found that temporal attractors of riftogenesis in the BRS lithosphere correspond to assemblage structure within the framework of the evolutional scenario with bifurcation of triple equilibrium[5]. The detailed study and generalization of theseparameters of seismic sources enabled the identification of three ASRs in the lithosphere of the region:South Baikal, Khubsugul, and Muya depressions [6](Fig. 1). ASRs are the main peculiarity of regionallithosphere since they form nonlinearity and instability of modern geodynamical and tectonophysical processes in the BRS lithosphere.In the present paper, the ASRs are considered as anattribute of Cenozoic nonlinear geodynamics of theBRS lithosphere. Their inclusion in the history ofregional Cenozoic geodynamics allows us to supplement the available description [2, 3, 7] with modernconcepts about the origin and evolution of riftogenesisin the BRS lithosphere within the framework of theselforganization theory for dissipative systems andnonlinear media. We lean upon the actualism principle here; it is not understood as a statement about similarity between present and past geological–geophysical processes, but as a statement that systems preserve