The western Koryak fold and thrust belt consists of a set of
tectonostratigraphic terranes that
contain units ranging from Lower Palaeozoic to Cenozoic. Three deformational
events have been identified
in the study area. The first event structures are folds, domes and shear
zones with related high-pressure/low-temperature metamorphism. These
structures are early Carboniferous and are only recognized in the
metamorphic terranes. The second event structures are imbricate fans of
thrusts and folds with southeast
vergence, broken formation and serpentinite mélange. These are
latest Jurassic to early Cretaceous (early
Albian) and occur throughout the study area. During this event, thrusting
was accompanied by dextral
strike-slip faulting. The second event structures are overlapped by the
Upper Albian sedimentary rocks with
an angular unconformity at the base. During metamorphism associated with
the first and second deformational
events, some of the rocks were metamorphosed to blueschist grade and
were affected by strain with
axial ratios of up to 15[ratio ]1. The third deformational event is
characterized by significant sinistral strike-slip
displacement at higher crustal levels. This resulted in a new set of
structures and rotation of pre-existing
structures. The age of the sinistral strike-slip faults is interpreted
to
be late Cretaceous to Cenozoic. The
kinematics of the second and third deformational events correspond to
assumed proto-Pacific plate motions based on palaeomagnetic data.