贺兰山地区前寒武系构造变形研究

发布时间：2018-03-16 20:09

  本文选题：贺兰造山带　切入点：前寒武系　出处：《西北大学》2017年硕士论文　论文类型：学位论文

【摘要】：贺兰山位于南北构造带的北段,东与鄂尔多斯盆地相邻,西北部紧临阿拉善地块,南接走廊过渡带,总体呈北北东向展布。由于其所处的特殊的大地构造位置,使之成为地质工作者研究构造变形、岩浆活动以及变质作用的理想场所。本文以贺兰山地区前寒武系作为研究对象,以露头构造解析为基础,结合构造—热年代学和显微构造分析,重点对前寒武纪地质体记录的构造变形进行详细研究,恢复建立构造变形序列。认为:(1)贺兰山北段前寒武系构造活动具有多期次的特点,D1为固态流变与顺层韧性剪切变形,主要表现为固态流变褶皱和顺层韧性剪切带。D2为区域性右行走滑韧性剪切变形,是贺兰山北段前寒武系最为重要构造形迹,强韧性剪切变形,指向构造均指示右行走滑剪切。D3为北西—南东向高角度逆冲韧性剪切变形,表现为普遍存在、稀疏发育且规模不大的韧性剪切带,为自南西向北东高角度左行逆冲韧性剪切变形。D4是伸展拉张构造变形,韧脆性变形,醒目之处是辉绿岩的构造侵位。D5为自北东向南西的逆冲推覆作用,断层分枝复合,岩体被切割呈大小不一的菱形块体。常见石英脉沿断面贯入,并在局部发生片理化且褶皱,反映出递进变形的特征。D6是共轭剪切构造变形,表现为两组产状近直交的密集且透入性强的破劈理带,近直立,是研究区最晚一期构造变形,是塑造现今地貌的主要因素;(2)上述各期变形作用对应不同的温压条件。在区域性右行走滑韧性剪切变形(D2)过程中,石英多晶条带、石英新晶呈长矩形、长石亚颗粒旋转重结晶呈镶嵌状集合体等,反映出高角闪岩相-麻粒岩相的变质变形条件;高角度逆冲韧性剪切变形(D3)阶段,矿物颗粒强细粒化、发育机械双晶、核幔构造、亚颗粒旋转重结晶、显微分层等现象,变质程度弱于前者,反映出高绿片岩相-低角闪岩相温压条件;在伸展拉张构造变形(D4)过程中,出现脆韧性破碎、膨凸重结晶等现象,为绿片岩相变形变质环境;(3)通过构造—热年代学的分析研究所厘定的六期构造变形中,第二期(D2)区域性右行走滑韧性剪切变形时间在2.0Ga前后;第三期(D3)北西—南东向高角度逆冲韧性剪切变形时间在400Ma左右;第四期(D4)伸展拉张构造变形的时间约在200Ma;170Ma可能是第五期(D5)逆冲推覆作用的起始时间,且一直持续至新生代;研究区最后一次变形(D6)发生在新生代,约20Ma以来。
[Abstract]:Helan Mountain is located in the northern section of the north-south structural belt, adjacent to the Ordos basin in the east, adjacent to the Alashan block in the northwest, and adjacent to the corridor transitional zone in the south. It is an ideal place for geologists to study tectonic deformation, magmatic activity and metamorphism. In this paper, the Precambrian system in Helan Mountain area is taken as the research object, and the outcrop structure analysis is taken as the basis. Combined with tectonic-thermochronology and microstructural analysis, the tectonic deformation recorded from Precambrian geological bodies is studied in detail. It is considered that the Precambrian tectonic activity in the northern part of Helanshan is characterized by multiple stages of solid rheology and ductile shearing deformation. The main features are solid rheological fold and ductile shear zone. D2 is a regional right strike-slip ductile shear deformation, which is the most important structural trace of Precambrian in the northern part of Helanshan, with strong and tough shear deformation. The pointing tectonics indicate that the right strike-slip shear. D3 is a ductile shear deformation with a high angle from NW to SE, which is characterized by widespread, sparse and small ductile shear zone. D4 is extensional tectonic deformation, ductile ductile deformation, ductile ductile shear deformation, ductile ductile shear deformation. D4 is extensional tectonic deformation, ductile brittle deformation, notable tectonic emplacement of diabase. D5 is a thrusting nappe from NNE to west-south, fault branching is complex, The rock mass is cut into rhombic blocks of different sizes. The common quartz veins intersect along the cross section and occur locally in the sheet physicochemical and pleated, reflecting the progressive deformation characteristics. D6 is conjugate shear structural deformation. These two groups of closely intersected, dense and penetrating cleavage belts, which are nearly erect, are the latest tectonic deformation in the study area. It is the main factor to shape the present geomorphology, the deformation of each of the above periods corresponds to different temperature and pressure conditions. During the regional right strike-slip ductile shear deformation (D2), the quartz polycrystalline band and the new quartz crystal take on a long rectangle. The rotational recrystallization of feldspar subgrains shows the metamorphic deformation conditions of high amphibolite facies and granulite facies, and the high angle thrust ductile shear deformation stage, in which the mineral particles are strongly fine-grained, with mechanical bicrystals and core-mantle tectonics. The metamorphic degree of subgranular rotating recrystallization and microstratification is weaker than that of the former, which reflects the temperature and pressure conditions of the high greenschist facies and the low amphibolite facies, the brittle ductile fracture and the swelling and convex recrystallization during the extensional and extensional tectonic deformation. For the deformation-metamorphic environment of greenschist facies, the second phase of the six-stage tectonic deformation determined by the tectonic-thermochronological analysis shows that the time of regional right-strike-slip ductile shear deformation is about 2.0 Ga; In the third stage, the time of ductile shearing deformation in NW-SE high angle thrust is about 400Ma, and the time of extensional tectonic deformation in stage 4th is about 200 Ma-170 Ma, which may be the beginning time of 5th stage D5) thrusting and thrusting and thrusting and thrusting and thrusting and thrusting and thrusting and thrusting and thrusting and thrusting and thrusting and thrusting and thrusting and thrusting and thrusting. The last deformation of D6 in the study area occurred in the Cenozoic, since about 20 Ma.
【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P542
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本文编号：1621478