The final collision of the CAOB:Constraint from the zircon U-Pb dating of the Linxi Formation,Inner Mongolia

The Linxi Formation occupies an extensive area in the eastern Inner Mongolia in the Central Asian Orogenic Belt （CAOB）. The Linxi Formation is composed of slate, siltstone, sandstone and plant, lamellibranch microfossils in the associated strata. Major and trace element data （including REE） for sandstones from the formation indicate that these rocks have a greywacke protolith and have been deposited during a strong tectonic activity. LA-ICPMS U-Pb dating of detrital zircons yield ages of 1801 to 238 Ma for four samples from the Linxi Formation. 425-585 Ma, together with the ~500 Ma age for the metamorphism event previously determined for Northeast China, indicates that their provenance is the metamorphic rocks of Pan-African age that have a tectonic affinity to NE China. A few older zircons with U-Pb ages at 1689-1801 Ma, 1307 1414 Ma, 593-978 Ma are also present, revealing the Neoproterozoic history of NE China. The youngest population shows a peak at ca. 252 Ma, suggesting that the main deposition of the Linxi Formation was at late Permain. Moreover, the ca. 250 Ma zircon grains of all four samples yield weighted mean ^206pb/^238U ages of 250 ± 3 Ma, 248 ± 3 Ma, 249 ± 3 Ma, and 250 ± 2 Ma, respectively. These ages, together with the youngest zircon age in the sample ZJB-28 （ca. 238 Ma）, suggest that the deposition of the Linxi Formation extended to the early Triassic. Combining with previous results, we suggest that the final collision of the Central Asian Orogenic Belt （CAOB） in the southern of Linxi Formation, which located in the Solonker-Xra Moron-Changchun suture, and the timing for final collision should be at early Triassic.

Tectonic Evolution of the Northern Continental Margin of North China Platform in Middle Proterozoic

An orogenic belt developed in late middle Proterozoic in the northern margin of North China Plate extends from Inner Mongolia to Western Liaoning Province and Eastern Jilin Province.It is over 2000km long. The orogenic belt was formed by collision between North China Platform and Siberia Platform during the Rodinian Super-Continent period. From sedimentary formation, magmatic activity and crustal tectonic deformation, it is suggested that along the tectonic belt the paleocontinental margin experienced four stages of tectonic evolution in middle Proterozoic, they are: continental margin rift, passive continental margin, active continental margin and collisional orogenic stages.

Tectonic Framework and Evolution of the Dabie Mountains in Anhui, Eastern China

The Dabie Mountains are believed to be a collisional orogenic belt between the Yangtze amd Sino-Koreancontinental plates. It is composed of the foreland fold-thrust zone, the subducting cover and basement of theYangtze continental plate, the coesite- and diamond-bearing ultra-high pressure metamorphic zone and themeta-ophiolitic melange zone in the subducting basement, the fore-arc flysch nappe and the back thrust zoneoccurring respectively on the southern and northern margins of the Sino-Korean continental plate and the in-herited basin with molassic deposits on the northern margin. When the palaeo-Dabie oceanic plate subductednorthward in the Early Palaeozoic, volcanic arc and back arc basin probably formed on the southern margin ofthe Sino-Korean continental plate. The Sm / Nd isotopic dating of the strata and eclogite which were drawn in-to the foreland fold-thrust zone indicates that the intense collision of the two continental plates took place inthe Early Mesozoic.

Accretionary complex:Geological records from oceanic subduction to continental deep subduction

Accretionary complex was usually formed by offscraping of the subducting crustal material over the trench and thus often referred to as subduction zone mélange.The structure,composition and forming process of accretionary wedges can provide important insights into the evolution history of ocean basin,ocean-continent material cycle,continental accretion and thus contribute to understanding of the origin of plates and the growth of continents.Accretionary complex is characterized by a block-in-matrix structure associated with imbricate thrusts and isoclinal folds,diversified metamorphic types and intense water-rock interactions,which are distinct to the traditional stratigraphy.Since the proposal of the concept of accretionary wedge over a hundred years ago,great progress has been made in a variety of research focuses,such as the identification of the distribution of accretionary complexes,their compositions and formation mechanisms,the affinities of the matrix and igneous rocks,the recognition of the Ocean Plate Stratigraphy(OPS),the reconstruction of oceanic basin,the dynamic background of the tectonic evolution,the relationship between subduction zone and orogenic belt and,in particular,the accretionary complexes in continental subduction zones.These studies have significantly improved our understanding of the plate tectonic theory.Challenges remain in the identification of ancient accretionary complexes,the detailed analysis of accretionary complex zones,the accretion characteristics during continental collision,and the geochemical tracing of water-rock interaction during the accretion.China contains representative orogenic belts and accretionary complex zones in the world,and its geological records provide the best opportunity to make new breakthroughs in understanding of the plate tectonics.