摘要
通过沉积地层、地貌、构造形变等的综合研究，对祁连山西段及酒西盆地区第四纪构造运动的期次和阶段进行了划分。上新世晚期以来，这一地区至少经历过６次显著的构造变动或构造事件，其中以玉门、酒泉和白杨河运动最为强烈。针对上述构造事件进行了古地磁、孢粉、红外释光和热释光等方法的综合研究和年龄测定，论述了各阶段构造运动的方式、性质和其它有关特征。
Flanked by the Jiuxi basin with several kilometers Denozoic deposits, west Qilianshan mountain is located in the junction of the Qinghai-Xizang plateau, Tarim basin and Alashan block. It is one of the regions characterized by strongly active folding and faulting with NW～NWW trend, where surface thrusts, blind thrusts and active folds are the main structural style.At least six tectonic events have been identified according to the neotectonic records, including the unconformities and deformation of strata, sedimentary facies transitions, geomorphic evolution, and so on in west Qilianshan mountain and Jiuxi basin since the late Pliocene, and the first, fourth, and sixth events were the strongest. Detailed lithostratigraphies, magnetic-polarity stratigraphies, spore-pollen stratigraphies, IL and IRSL dates were determined at several typical profiles in order to provide refined temporal constraints on these events.Following the first tectonic event in the late Pliocene, extensive molasse sediments (Yumen formation) began to aggrade in the Jiuxi basin at about 2.5～2.4Ma B.P.Since then, over 1 000m of sediments have accumulated along the southern margin of the basin. The following five separate tectonic events occurred at about 2.14～2.12,1.67, 0.85～0.73, 0.249 and 0.119Ma B. P. respectively. Widespread basin sedimentation was terminated by accelerated uplift of north Qilianshan mountain and Jiuxi basin after about 0.119 Ma B.P.The first tectonic event is represented by strongly uplifting and thrusting of north Qilainshan mountain, the replacement of the fine-clastic river-lake facies of the Pliocene Niugetao formation with the conglomeratic facies of molasse deposits of the Early Pleistocene Yumen formation and local disconformities between them. The second is characterized by the syntectonic intraformational unconformities at the bottom of Yumen formation, northward thrusting of the Miaobei thrust faults, and folding of the Laojunmiao anticline. The third is represented by the unconformities between the Lower and the Upper Yumen formation and folding of the Laojunmiao anticline. The fourth is characterized by strongly uplifting; folding and thrusting of north Qilianshan mountain and the Cenozoic sediments including Yumen formation in the pediment,and the angular unconformities between the tower and the Middle Pleistocene deposits.The fifth is represented by southWard thrusting of the Bainan thrust faults and initially folding of the Baiyanghe anticline. The sixth is characterized by thrusting of the northern Qilianshan faults, Miaobei thrust faults, Bainan thrust faults and Xinminpu thrust fault, folding and faulting of the Middle Pleistocene Jiuquan formation, and initial aggradation of the Laojunmiao piggy-back basin. Tectonic deformation has continued to the present time and is evidenced by warped and faulted stream terrace surfaces,and tilted flood deposits. On the basis of luminescence dating, these terraces were incised, abandoned and uplifted at about 90 000, 70 000, 44 000, 29 000, 20 000, 13 000 and 5 600 a B.P. respectively.In combination with drillhole data and reflection seismic studies, a hand-balanced cross section (NE20°) across west Qilianshan mountain and Jiuxi basin was made,the total crustal shortening and the rates of uplift at different period were discussed.
出处
《第四纪研究》
CAS
CSCD
1996年第3期263-271,共9页
Quaternary Sciences
基金
国家自然科学基金
关键词
祁连山
第四纪
年龄测定
酒西盆地
构造运动
west Qilianshan mountain, Quaternary tectonic event, dating of the event
