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Structural Characteristics And The Evolution In Western Ordos Basin

Posted on:2004-01-04Degree:DoctorType:Dissertation
Country:ChinaCandidate:H G ZhaoFull Text:PDF
GTID:1100360092498611Subject:Mineral prospecting and exploration
Abstract/Summary:PDF Full Text Request
The structure phenomena in Ordos basin are complicated and different in various areas. The views to Mesozoic structure attribute and its evolution differ between scholars, especially much diversity on the structure attribute in Late Mesozoic. Based on extensively gathering and sysmatically analyzing much geophysics, sedimentary, structure and petrological materials in research field and taking two field geological explorations from south to north in western Odors basin margin, the paper studied large numbers of seismic sections and newly-finished profiles in former seismic blanked area of western margin as well as up-to-date gravity and magmatic fruits, put views on the regional geotectonic background and basin-mountain coupling and made through research on the structure features and attribute together with the result of fission track testing.Through the regional background analysis in which western structures developed, it suggested that there did not exist a united and steady block to the west of Ordos basin. Alashan Block neighboring on the north of the western margin was largely influenced by the action of Qilian and Tianshan-Xingmeng folded belt which is respectively to the south and north of Alashan Block, was narrow in the steady block and was limited by the Longshou Mountain-Zhongwei strike fracture in the south area. These all formed the regional background of western margin of Ordos basin in which there were extremely difference in south and north area and developed special structures in the middle area. Great many Mesozoic basins in which Mesozoic sediments had certain depth and Early-Mid Jurassic strata were broadly distributed are found nearby western Ordoa basin. So it can be concluded that there did not exsit regional compressional folded-uplifted area which was eroded widely in Mesozoic in the west neighouring district.The tholeiite with Late Trassic age has been found in Helanshan area on the north part of western margin of Ordos basin. Late Triassic to Mid Jurassic strata in which owns the good coal of Van'an Formation distributes widely with huge thickness in Helan Mountain. Structure characteristics show that Helan Mountain was in extensional environment in Late Triassic and no obvious compressional evidence in Early-Mid Jurassic. The present thrust nappe structure formed in late Jurassic according to comprehensive analysis of sedimentary, structure and fission track tesing result. The main uplift age is in Eocene and isochronous to that of the formation of Yinchuan graben. Liupan mountainous area deposited and toke sediments in huge district in which Late Triassic has huge thickness, which is similar to that of Ordos basin and the water is connected. Therefore, Liupanshan area during Late Triassic to Mid-Jurassic is not a compressional orogen.Comprehensively studied the features in present geomorphography, surface geology, sedimentary environment and structural distributed direction and seismic, gravity and magmatic data, the paper proposes the new view that there still lies evident structure difference in western margin of Ordos basin from south to north. The western margin can be divided by Qingtongxia-Wuzhong and Zhongwei-Zhongning fracture with east-west tending into three districts, north, middle and south distict.The north district includes Zhuozishan and Yinchuan graben and Hengshanbu part by the boundary of Zhengyiguan fault. Hengshanbu part have three secondary parts which are Tiekesumiao, eastern Taole and south of Selunkademiao. The Zhouzishan part of is charactered by thrust nappe which is composed by faultsthrust from west to east, anticlines and synclines, involving much of Proterzoic, Palozoic and very limited Mesozoic in which a suite of conglomerate is found in the front of thrust fractures in Late-Jurassic. It is concluded that the thrust structure formed in Late-Jurassic. Faults with high angles appeared in Hengshanbu structure part which is also developed in Late-Jurassic deduced by strata contact relationship.Middle district includes two parts which...
Keywords/Search Tags:western Ordos basin, structure characteristics, Mesozoic, structure attribute, evolution fission track, late reformation
PDF Full Text Request
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