Postcollisional granitoids and aptian-albian extension in tectonic evolution of Chukotka mesozoides, Northeast Russia

New U–Pb SIMS zircon datings from granitoid plutons and dikes of Western Chukotka together with earlier obtained data confirm that postcollisional granitoid magmatism and dike intrusion occurred in Aptian–Albian (117–105 m.y.) and fix change of tectonic regime from collision to extension in tectonic evolution of Chukotka Mesozoides. These events may be related to continuing expansion of Amerasian basin since Jurassic and forma- tion in Aptian—Albian time of both oceanic Makarov, Podvodnikov basins and Anakhurgen, Nutesyn and Kameshkov basins in continental framework of Eastern Arctic. Synchronism of tectonic events of extension and spreading in the Canada Basin and collisional events, deformations and reorganization of structural style and sedimentary environment in the South-Anyui suture is noted. This may be regarded as confirmation of rotation hypothesis of Amerasian Basin formation.

The features of the Paleozoic-Mesozoic complexes of Kiber Cape (Chukotka, Arctic Russia): a structural-deforma-tion analysis

Three major regional deformation stages of Central Chukotka tectonic evolution were determined in Paleozoic-Mesozoic deposits of Kiber Cape. The research was based on a structural analysis of the linear and planar elements. Ellesmerian (Late Devonian) structural parageneses were masked during (at least) two phases of young Mesozoic-Cenozoic deformations: syncollisional North-North-East - South-South-West and North-West - South-East regional compressions and post-collisional extension of various directions, followed the compressions. The structural data comparison was made for Kiber Cape region, South-Anyui suture and Western Chukotka sector. It was emphasized that these regional units have similar structure styles and coeval phases of the tectonic transformations.

South Anyui suture: tectono-stratigraphy, deformations, and principal tectonic events

Geochronologic and structural data from the terranes of the South Anyui suture zone record a protracted deformational history before, during and after an Early Cretaceous collision of the passive margin of the Chukotka-Arctic Alaska continental block with the active continental margin of the North Asian continent. Preceding this collision, the island arc complexes of the Yarakvaam terrane on the northern margin of the North Asian craton record Early Carboniferous to Neocomian ages in ophiolite, sedimentary, and volcanic rocks. Triassic to Jurassic amphibolites constrain the timing of subduction and intraoceanic deformation along this margin. The protracted (Neocomian to Aptian) collision of the Chukotka passive margin with the North Asian continent is preserved in a range of structural styles including first north verging folding, then south verging folding, and finally late collisional dextral strike slip motions which likely record a change from orthogonal collision to oblique collision. Due to this collision, the southern passive margin of Chukotka was overthrust by tectonic nappes composed of tectono-stratigraphic complexes of the South Anyui terrane. Greenschists with ages of 115–119 Ma are related to the last stages of this collision. The postcollisional orogenic stage (Albian to Cenomanian) is characterized by sinistral strike slip faults and an extensional environment.