Mesozoic subduction-related accretion of micro-blocks in the East Asian Ocean-Continent Connection Zone

Abstract As part of the assessment and need to clarify the Mesozoic subduction-related accretion history of the East Asian Ocean-Continent Connection Zone (EAOCCZ), 27 micro-blocks were identified on the continental margin of Northeast Asia, of which 22 are related to the Paleo-Pacific Plate (PPP) subduction. Two new methodologies are proposed to fulfil this purpose, comprising the residual crustal anomaly extraction technique and the gravity line-drawing method. The residual crustal gravity anomaly fields were extracted by multi-scale moderate-wavelength gravity field separation to reveal basement structures of the EAOCCZ. Meanwhile, the linear tectonic framework of Northeast Asia is determined through a gravity line-drawing method based on the fourth-order detailed field of the complete Bouguer gravity anomaly, to identify the micro-block boundaries. As a result, the recognized micro-blocks are mainly distributed along the Mongol-Okhotsk Suture Zone, Northeast China, Russian Far East and Japan Island Arc. In addition, the Mesozoic strike-slip faults and the pull-apart basins in the Trans-Baikal are evidenced by the left-stepping horsetail-shaped structure on the magnetic lineations and the continuous gravity high on the residual crustal gravity field. The latter reveals regional crustal extension, which indicates a strong intracontinental sinistral strike-slip motion in the Early Cretaceous on the northern flank of the Mongol-Okhotsk Suture Zone. Affected by the change of motion of the Paleo-Pacific Plate in Mesozoic, the EAOCCZ experienced frontal accretion in the Jurassic and oblique accretion in the Cretaceous. The Cretaceous braided structures on the northeastern continental margins indicate at least two stages of strike-slip movements. The earlier stage is controlled by dextral strike-slip transpression of the arc slivers, from north to south, to form the oroclinal-bending structures; whereas the later stage is controlled by the sinistral strike-slip faulting, moving the Taukha Terrane from south to north. The crustal residual gravity anomaly field reveals the crustal structure of the Okhotsk Micro-plate, which shows the characteristics of a subduction-related accretionary continental margin. This accretionary margin has been located at the northern slope of the Kurile Basin, similar to the Sikhote-Alin and Kamchatka volcanic arcs, and has not yet completely collapsed. Crustal thinning has obviously occurred in the back-arc area, and some main depocenters developed in the northwest, controlled by the NNW-trending boundary faults.