TRACING THE CRYPTIC SOLONKER SUTURE ZONE IN EAST ASIA: CONSTRAINTS FROM INTEGRATED SEDIMENTARY PROVENANCE ANALYSES

The Central Asian Orogenic Belt formed by accretion subsequent to the contraction of the Palaeo-Asian Ocean (PAO), and terminated along the Solonker Suture Zone in E Asia. Since typical regional collisional features are absent, its tectonic evolution still remains speculative. Integrated sedimentary provenance analyses across the accretionary collision zone between the Mongolian Arcs and the North China Craton (NCC) place new constraints on the events that led to final suturing.

An investigation on the geochronological and geochemical variability in Permian strata along a SE-NW transect revealed distinct differences across the Solonker Suture Zone: northern basins carry a broad Mesoproterozoic to latest Precambrian age signature, and their provenance terranes are of mixed juvenile to crustal magmatic origin. In contrast, southern basins contain detritus from the NCC, and their sources are of dominantly crustal contaminated magmatic origin. Provenance analysis suggests, that in the Early Palaeozoic (ca. 429 Ma) the PAO was consumed along the Uliastai Arc and the NCC, initiating the formation of the Northern and Southern Accretionary Orogens, respectively. By the end of the Middle Carboniferous the Mongolian Arcs consolidated after accretion of the Uliastai Arc. In the Late Carboniferous (ca. 314 Ma) the Hegenshan back-arc basin opened, detaching the Northern Accretionary Orogen. While subduction continued there, it may have temporarily ceased along the Southern Accretionary Orogen after accretion of a microcontinent (ca. 300 Ma). During the Middle Permian back-arc basin closure led to the formation and obduction of the Hegenshan SSZ Ophiolite. Eventually, the PAO closed after wedge-wedge collision, which would not involve continental deep subduction, thus, leading to cryptic suturing from the Late Permian to Early Triassic. Statistical analyses on the heterogeneity and similarity of the age probability density functions require a complex Permian palaeo-geographic setting, involving a variety of arc basins, which received sediments dependent on the contemporary arc geometry.

Early stages of the sequence likely resembled a Pacific-type scenario, including Japan-type back-arc basin opening, whereas the late stages were similar to the archipelago-type setting of present-day SE Asia.