The Structural Feature And Tectonic Evolution About Hai Laer Basin

Hailaer basin is a Mesozoic extensional and compressional basin consisted of many small and medium size fault groups which is locate Paleozoic collision of Iner Mongolia–Daxing'anling orogenic belt between Sino-korea plate and Siberia plate in western part of northeast of China. It. Appearance likes lozenge. The basin's total area is about 70208 km2, and about 44210km2 in our country. It can be devided into three depressions and two uplifts including 16 sags. They are in different direction and time , The factors influencing the basin is not only on basin's size, depth and direction, but also the sedimentary strata lithology, organic matter content, organic capacity, oil-genesis oil-migration, oil accumulation and so on .Hailaer basin's base is consisted of Prepaleozoic plutonic metamorphic rock, Light metamorphic rock, not metamorphic rock and magmatic rock. There are Mesozoic Cretaceous and Cenozoic Tertiary, Quaternary. The thickness of strata is 6000m in all.On the base of the exploratory data and the preceded reasches, it is necessary to study the structure features of Hailaer basin further. This thesis guided by geodynamics studies of the secondary structure unit, especially focus on the Urxun and Beier sag, adopting from macro scope to micro scope, and to macro scope again, gains the conclusion of the structure evolution feature all over the basin. The thesis can put the theory into practice well.The thesis discusses the relationship between faults and folds in work area, points out the forming time and process of the structure develompent and gains five new understandings.1. The paper depicts the Hailaer basin's nature detailed and clearly, and point out that the basin is a Mesozoic extensional and compressional basin with consisted of medium, small fault depresses . Hailaer basin began to form at the early stage of Cretaceous, it was extensional fault basin from Xing'anling group to Nantun formation, formed extensional sedimentary sequence, and it was compressive basin in Damoguaihe formation period, formed positive Converse compressive sedimentary sequence. In Yimin formation period, it was the same as Xinganling group-Nantun formation period, and at last stage of Yimin formation period- earlier stage of Qingyuangan formation period. it was compressive basin formed compressive sedimentary sequence.2. Hailaer basin is consisted of 4 structure layers with different composition. Basement rock sequence structure layers of the basin formed by Paleozoic orogenic belt; lower sedimentary cover structure layer consisted of lower Cretaceous Xinganling group–Nantun formation volcano rock- detritus rock ; middle at bottom sedimentary cover structure layer consisted of lower Cretaceous Damoguaihe formation formed in earlier compression period; middle at upper sedimentary cover structure layer consisted of upper Cretaceous Yimin formation formed in later extension period; upper sedimentary cover structure layer consisted of upper Cretaceous, Tertiary, and Quaternary .3. The thesis defines the period and mechanism of Hailaer basin's tectonics, it discusses types of the inverse structure and action in detail first, and points out the basin inversion time .The structures of the basin spread four directions. That is North–east direction, north- east east direction, south-north direction, and north-west direction. The north-east structure is tensional, the south-north and north-east east structure is tensor-shear. The structures are all in same stress field formed in Cretaceous extension period, superimposed on Paleozoic era light metamorphic rock, not metamorphic rock and Proterozoic era granite–gneiss, granite. The basin was stretched in north-west and south-east direction in earlier Cretaceous Xinganling group -Nantun formation period, and compressed in north-west and south-east direction in Damoguaihe formation period, The earlier structures all inversed, formed a lot of inversed structure, the structure correlation fold formed in the basin and cover in the same time. The basin was extended in north-west and south-east east direction in Yimin formation period. Controlling fault existed in the basin act again, some new shovel-like faults and negative flower shape structure in north-west direction appeared. The basin was compressed in north-west and south-east east direction form last Yimin formation period to earlier Qingyuangang formation period, inversion structure and structure correlation fold formed . The extension and compression action last long geologic time in Hailaer basin. The structures formed in deferent time consisted the basins structure framework. The whole basin evolution consist of two extension-compression cycles.4. Study shows that Hailaer basin sediment action controlled by structure all the time.Not only semi-graben in extension structure system and positive inversion structure, but also structure correlation fold in compression structure system, the sedimentary layers thickness and sedimentary centre of them are all controlled by the subsidence and elevation of the structure. That the structure elevation rate was faster than the layers sedimentary rate caused the regional angular discordance in Hailaer basin.5. The formation of Hailaer basin is affected by the collision of the Pacific plate and the Eurasian plate.The change of underthrust angle of the Pacific plate affects the change of extension and compression stress field. The change of the Pacific plate underthrust in direction affects the change of extension and compression in direction .