Tectonic evolution of the Anuy metamorphic rocks (Sikhote Alin, Russia) and their place in the Mesozoic geodynamic framework of East Asia

Abstract

In Sikhote Alin, the Anuy river provides a representative cross-section of the pre-Eocene structure of the area east of the central Sikhote Alin fault. The Mesozoic rocks are divided into the following groups, from bottom to top: Anuy metamorphic rocks; the Tithonian-Berriasian (Samarkinsk) accretionary complex; Early Cretaceous (Zhuravlevsk-Tumnin) turbidite; and mid-Cretaceous Al-rich (Khungariisk) granitoids. The Anuy metamorphic rocks have a postfolial NE-SW-trending antiformal structure. From bottom to top, they consist of: (1) low-grade schist and sandstone; (2) gneiss and micaschist; (3) migmatite; and (4) ophiolitic nappe. East-west-trending stretching lineation, isoclinal folds and top-to-the-east shear criteria are found in the ophiolite and migmatite units. These structures are related to ophiolitic thrusting that likely occurred in Early Cretaceous times. 40 Ar 39 Ar dating of migmatite and metagabbro indicates mid-Cretaceous ages (about 110 Ma) close to those of the Khungariisk granites. The main deformation, coeval to a high-temperature metamorphism, is characterized by NE-SW-trending stretching lineation with divergent senses of shear. 40 Ar 39 Ar dating of biotite and muscovite from several lithologies give Late Cretaceous to Paleogene ages (73-58 Ma). This tectono-thermal event is related to NE-SW-trending strike-slip faulting along the central Sikhote Alin fault system. The unroofing of the Anuy metamorphic rocks is likely related to granite emplacement. The collision of the Anuy microcontinent with Asia can be compared to that of the southern Japan microcontinent.