The Tafuinsky granite massif, southern Primorye region: The structures and geodynamics of longitudinal compression

摘要

Detailed observations and mass angular measurements in relicts of the host protoskeleton, their foliation, the shadow banding, the contacts between granite and aplite varieties, and taxitic texture served as the basis for the graphical and statistical analyses of the structural patterns in the Ordovician Tafuinsky granite intrusion. They revealed pre- and syn-granite types of structural patterns that were formed under the external longitudinal compression. The first of them is characteristic of the trajectories of structural elements constituting the protoskeleton hosting the massif and the shadow banding in the granites oriented transversely to the compression. The second type corresponds to the two main phases of the massif formation: the granite and the aplite. It is formed by combinations of conjugate counter-dipping thrusts and shears that control the distribution of the granite and aplite substances. In addition, these combinations frequently produce pseudofolded structures distinctly reflected in the control over the aplite bodies. Such a structural style of syngranite deformations suggests that, by their formation dynamics, they are similar to their pregranite counterparts. Both the pre- and syn-granite structural patterns demonstrate that the activation of the external compression was of different-order and pulsed mode with a certain periodicity. Moreover, the long compression pulses distinctly correspond to the stages and phases in the massif formation, when the compression twice changed its orientation at their transitions in the clockwise manner with an angular step of 10°. The geodynamics of the main longitudinal compression and its structural derivatives are regarded as a principal factor that determined the position and architecture of the massif.