The Tectonic Feature And Its Petroleum Exploration Meaning In The Western Part Of The Northern Junggar Basin

By the comprehensive analyzed method of the regional geology, well-log geology and seismic profiles, this paper firstly studied the rock-stratigraphic units, the important tectonic events and its related attributes in the western part of the northern Junggar basin and its adjacent large area. Then, the structure deformation characters and the related key tectonic events in the Hashan area of the western part of the northern Junggar basin were deeply researched and well revealed. Also, according to the structure styles and the tectonic features, the Hashan favorable areas for future petroleum exploration were discussed. The main results could be concluded as follows.Firstly, the regional rock-stratigraphic units and the geotectonic framework were studied. It was revealed that the western part of the northern Junggar basin was situated in the metamorphism and deformation activity region which were controlled by the effects of the paleo-oceanic subduction to collision orogeny and the post-collision transition during the early to middle Yanshanian around Dalabute-Kelamaili faulted belt, as well as the effects of intra-continental compressive strike-slip process of after the Yanshanian. Also, the reunderstanding for several rock-stratigraphic units of the Upper-Paleozoic, which were disputed for years, showed that the Shiqiantan group should belong to the Upper Carboniferous, the Halaalate group and Aladeyikesai group should be attached to the Upper Carboniferous, the Haerjiawu Upper and Kalagang Upper should be attached to the Lower Permian, and the Kujiertai group and Zaheba group should be attached to the Middle Permian.Secondly, base on the age data Stat of greenstone, granite and apatite fission track, the regional unconformity event and the peak-age event were studied. It was revealed that the prominent unconformity events of the Early-Middle Devonian were ubiquitous in the region of interest and its adjacent area, which were corresponded with the peak value age event of the collision and Late collision granite about 310Ma±and 290Ma±. The unconformity events of the Late Devonian and the late Indo Chinese epoch mainly occurred at the Late Permian and the Late Triassic. The unconformity events of the Yanshanian mainly occurred at the Late Jurassic, which was contrasted with the peak value age event of the apatite fission track about 160～130Ma±. According to the statistics of the apatite fission track age, the event of the Xishanian as the form of uplifting activities mainly occurred at the age among 100～50Ma with the peak age of 70 Ma±.Thirdly, the synthetic structural analysis of the seismic profiles were deeply studied by the ground geology and the log geology, it was revealed that the tectonic deformation character of the Hashan is mainly the unsymmetric flower structure which displays the superimposition of structure as the previous overthrust and the strike-slip thrust at the later. The structure styles are, the semi-symmetry flower structure of bedrock sliping-napping and the sliver thrusting nappe in the east part of the Hashan and the semi-symmetry flower structure of the striking-sliping extrusion and the reverse thrusting nappe in the west.Fourthly, According to the structure deformation characters, deformation sequences, the unconformity event and the peak value age event of the Ha mountain region, it was revealed that the early overthrust structure deformation event as the form of collision orogeny mainly occurred at the Carboniferous in the Ha mountain region. Then, it had undergone the compression strike-slip thrust which were multiple cycles and weakened for the deformation strength from the late Devonian to the middle Yanshanian at least. After the Xishanian, it mainly represented the character of the uplift and denudation.Finally, based on structure analysis, oil and gas exploration trends in region of interest were discussed, it revealed that the Permian source rocks in Mahu depression should be emphasized, on the other hand, the favorable constructive combinations of considerable potential source rock of the Hujierte group of the Devonian, the Shiqiantan group of the Carboniferous, the Haerjiawu group of the Lower Permian and the Zaheba group of the middle Permian, and the potential of the Jurassic hydrocarbon source rock should also be emphasized in the weak deformation areas of the Hashan region. It also revealed that the coincidence zone of the deformation band structural trap as the form of fold-thrust structural trap and unconformity trap of the Hashan margin may be the most practical favourable exploration area, and the east part has weaker intensity of the fault activity, late reformation and better favourable factors of conservation conditions than the west.