本文選題：賀蘭造山帶　切入點：前寒武系　出處：《西北大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：賀蘭山位于南北構(gòu)造帶的北段,東與鄂爾多斯盆地相鄰,西北部緊臨阿拉善地塊,南接走廊過渡帶,總體呈北北東向展布。由于其所處的特殊的大地構(gòu)造位置,使之成為地質(zhì)工作者研究構(gòu)造變形、巖漿活動以及變質(zhì)作用的理想場所。本文以賀蘭山地區(qū)前寒武系作為研究對象,以露頭構(gòu)造解析為基礎(chǔ),結(jié)合構(gòu)造—熱年代學(xué)和顯微構(gòu)造分析,重點對前寒武紀地質(zhì)體記錄的構(gòu)造變形進行詳細研究,恢復(fù)建立構(gòu)造變形序列。認為:(1)賀蘭山北段前寒武系構(gòu)造活動具有多期次的特點,D1為固態(tài)流變與順層韌性剪切變形,主要表現(xiàn)為固態(tài)流變褶皺和順層韌性剪切帶。D2為區(qū)域性右行走滑韌性剪切變形,是賀蘭山北段前寒武系最為重要構(gòu)造形跡,強韌性剪切變形,指向構(gòu)造均指示右行走滑剪切。D3為北西—南東向高角度逆沖韌性剪切變形,表現(xiàn)為普遍存在、稀疏發(fā)育且規(guī)模不大的韌性剪切帶,為自南西向北東高角度左行逆沖韌性剪切變形。D4是伸展拉張構(gòu)造變形,韌脆性變形,醒目之處是輝綠巖的構(gòu)造侵位。D5為自北東向南西的逆沖推覆作用,斷層分枝復(fù)合,巖體被切割呈大小不一的菱形塊體。常見石英脈沿斷面貫入,并在局部發(fā)生片理化且褶皺,反映出遞進變形的特征。D6是共軛剪切構(gòu)造變形,表現(xiàn)為兩組產(chǎn)狀近直交的密集且透入性強的破劈理帶,近直立,是研究區(qū)最晚一期構(gòu)造變形,是塑造現(xiàn)今地貌的主要因素;(2)上述各期變形作用對應(yīng)不同的溫壓條件。在區(qū)域性右行走滑韌性剪切變形(D2)過程中,石英多晶條帶、石英新晶呈長矩形、長石亞顆粒旋轉(zhuǎn)重結(jié)晶呈鑲嵌狀集合體等,反映出高角閃巖相-麻粒巖相的變質(zhì)變形條件;高角度逆沖韌性剪切變形(D3)階段,礦物顆粒強細�；�、發(fā)育機械雙晶、核幔構(gòu)造、亞顆粒旋轉(zhuǎn)重結(jié)晶、顯微分層等現(xiàn)象,變質(zhì)程度弱于前者,反映出高綠片巖相-低角閃巖相溫壓條件;在伸展拉張構(gòu)造變形(D4)過程中,出現(xiàn)脆韌性破碎、膨凸重結(jié)晶等現(xiàn)象,為綠片巖相變形變質(zhì)環(huán)境;(3)通過構(gòu)造—熱年代學(xué)的分析研究所厘定的六期構(gòu)造變形中,第二期(D2)區(qū)域性右行走滑韌性剪切變形時間在2.0Ga前后;第三期(D3)北西—南東向高角度逆沖韌性剪切變形時間在400Ma左右;第四期(D4)伸展拉張構(gòu)造變形的時間約在200Ma;170Ma可能是第五期(D5)逆沖推覆作用的起始時間,且一直持續(xù)至新生代;研究區(qū)最后一次變形(D6)發(fā)生在新生代,約20Ma以來。
[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.
【學(xué)位授予單位】：西北大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：P542
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本文編號：1621478