Main Fault Systems of the Soviet Far East

The analysis of the distribution of thrusts, normal faults and strike-slip faults of various ages has allowed us to determine the character of lithospheric block displacements in the Soviet Far East. The early Mesozoic, late Mesozoic and Cainozoic kinematics were each essentially different. The Early Mesozoic Dzhagdinsk fault system appeared as a result of the collision of the Bureinsk--Khankaisk microcontinent with the Siberian continent. The largest faults of the system are neither longstanding nor deep but were formed during the latest stage of the structural evolution. The multistage formation of the faults of the Dzhagdinsk system is conditioned by its position at the margin of the continent. The late Mesozoic faults are mainly strike-slip faults caused by the subduction of the oceanic crust at an acute angle with respect to the strike of the active continental margin. The Cainozoic faults were formed under compression on the boundary between the Siberian platform and the Bureinsk massif, but under tension in the east of the region. The geology of the Malvern Hills has been the subject of controversy since the 1850s. Many of the problems have now been resolved by using a combination of techniques including mapping, seismic-reflection profiling, deep drilling and geochronology. The Malvern Lineament is a major north--south trending crustal structure with a complex history of tectonic activity. In early Palaeozoic times thrusting on the Malvern axis caused uplift of the area to the east of the axis and some thickening of sedimentary deposits to the west. The importance of the Llandovery unconformity along the western side of the Malvern Hills is stressed. In late Carboniferous times there was major thrusting in a westerly direction, probably associated with dextral transpression, and considerable uplift and erosion of the area to the east of the Malverns. In Permian and Triassic times an extensional lithospheric stress field was initiated. This resulted in reactivation of the earlier thrusts as major normal faults downthrowing to the east and with throws, locally, in excess of 2.5 km. These faults, which dip eastwards at between 35 and 50 degrees, are detectable on seismic-reflection profiles to a depth of about 5 km and controlled the development of the Worcester Basin, inverting the site of an older `high'.