【摘要】：西秦嶺北緣分布有二疊紀(jì)甘家組和早三疊世隆務(wù)河組,其詳細(xì)的沉積地層劃分、沉積環(huán)境、沉積物源和原型盆地研究仍較為薄弱。本文以西秦嶺北緣循化道幃地區(qū)出露的二疊紀(jì)甘家組、早三疊世隆務(wù)河組為研究對(duì)象,在野外觀察、系統(tǒng)剖面測(cè)制、面積性地質(zhì)填圖基礎(chǔ)上,進(jìn)行詳細(xì)的巖石地層單位劃分,綜合巖石學(xué)、沉積學(xué)、碎屑骨架組分、砂巖巖石地球化學(xué)、碎屑鋯石U-Pb年齡信息分析,對(duì)沉積時(shí)代、沉積特征、沉積相與沉積環(huán)境、盆地充填序列、沉積物源、盆地構(gòu)造屬性及原型等進(jìn)行了論述,在此基礎(chǔ)上嘗試恢復(fù)了西秦嶺北緣晚古生代-早中生代構(gòu)造演化過(guò)程。取得了以下主要進(jìn)展和認(rèn)識(shí):1、西秦嶺北緣道幃地區(qū)晚古生代-早中生代沉積地層主要包括二疊紀(jì)甘家組和早三疊世隆務(wù)河組。甘家組由下到上可劃分為4段:一段(Pg~1)為粗碎屑巖夾板巖段,由扇三角洲平原沉積向上過(guò)渡為碳酸鹽巖臺(tái)地潮間帶沉積。二段(Pg~2)為細(xì)碎屑巖夾砂巖段,為淺海陸棚邊緣盆地沉積。三段(Pg~3)為生物礁灰?guī)r段,為淺海陸棚碳酸鹽巖臺(tái)地潮間帶沉積。四段(Pg~4)為細(xì)碎屑巖夾灰?guī)r段,為半深海—陸棚邊緣盆地沉積。隆務(wù)河組由下到上可劃分為5段:一段(T1l~1)為粗碎屑巖夾板巖段,屬濁積扇內(nèi)扇沉積。二段(T1l~2)為細(xì)碎屑巖夾薄層狀砂巖、灰?guī)r段,屬濁積扇中扇沉積(無(wú)水道部分)。三段(T1l~3)為薄層板巖、中-中薄層砂巖段,屬濁積扇中扇沉積(有水道部分)。四段(T1l~4)為板巖夾中-中厚層砂巖段(互層),為濁積扇中扇沉積,可能位于大陸斜坡中下部。五段(Tll5)為粉砂質(zhì)(泥質(zhì))板巖段,屬濁積扇外扇沉積,為濁積扇遠(yuǎn)端與深水盆地交接地帶。2、在甘家組一段的砂巖樣品中獲得的最小碎屑鋯石U-Pb年齡為299Ma,代表甘家組的沉積下限。結(jié)合古生物化石資料、地層疊覆關(guān)系將甘家組地層沉積時(shí)代厘定為二疊紀(jì)。隆務(wù)河組砂巖中最小碎屑鋯石U-Pb年齡為258Ma,為地層沉積下限,侵位于隆務(wù)河組的古夷閃長(zhǎng)巖結(jié)晶年齡為246.7±2.1Ma,為地層沉積上限,從而將隆務(wù)河組沉積時(shí)代限定在258~247Ma。綜合前人古生物化石資料,將研究區(qū)隆務(wù)河組沉積時(shí)代厘定為早三疊世。3、甘家組源巖風(fēng)化程度較低,屬第一次旋回沉積,主要物質(zhì)來(lái)源為祁連造山帶早古生代切割型巖漿弧,以酸性巖類為主,還有少量來(lái)自于祁連造山帶中元古代熱事件和新元古代響應(yīng)Rodinia超大陸匯聚、裂解的物質(zhì)記錄。沉積盆地原型為被動(dòng)大陸邊緣淺海陸棚。4、隆務(wù)河組為第一次旋回的沉積物,源區(qū)化學(xué)風(fēng)化較弱,古水流方向?yàn)镹WW-SEE方向,物源包括祁連造山帶的早古生代切割型巖漿弧、祁連造山帶南緣經(jīng)歷古特提斯洋初始裂解至俯沖過(guò)程中的系列記錄,以及祁連造山帶的變質(zhì)基底,特別是研究區(qū)出露的化隆巖群可能是其直接物源之一。源巖以酸性巖為主,還有少量基性巖,為兩種特征巖性的混合分布的區(qū)域,可能是受到基底隆升影響的結(jié)果。沉積盆地原型應(yīng)為弧后盆地。5、綜合本文資料、區(qū)域地質(zhì)資料及前人研究將西秦嶺北緣及鄰區(qū)晚古生代-早中生代的構(gòu)造演化過(guò)程劃分為三個(gè)階段:1)泥盆紀(jì)-中二疊世古特提斯洋裂解-拉張階段;2)中二疊世晚期-早三疊世洋殼北向俯沖,弧后裂谷盆地?cái)U(kuò)張階段;3)中晚三疊世弧后盆地關(guān)閉,碰撞及后碰撞階段。
[Abstract]:In the north margin of west Qinling, there are Permian Gan jia Formation and Early Triassic Longwu River Formation, and the detailed sedimentary stratum division, sedimentary environment, sediment source and prototype basin research are still relatively weak. Based on field observation, system profile measurement and area geological mapping, detailed rock formation unit division, comprehensive petrology and sedimentology are carried out on the basis of field observation, system profile measurement and area geological mapping. The sedimentary age, sedimentary characteristics, sedimentary facies and sedimentary environment, basin filling sequence, sediment source, basin structure attribute and prototype are discussed in this paper. On this basis, the evolution of late Paleozoic-early Mesozoic tectonic evolution in the northern margin of west Qinling is attempted. The following major progresses and understandings have been made: 1. The Late Paleozoic-Early Mesozoic sedimentary formation in the northern margin of the West Qinling Mountains mainly includes the Permian Gump Formation and the Early Triassic Longwu River Formation. The Ganjia Formation can be divided into 4 segments from below: one segment (Pg ~ 1) is the coarse clastic rock sandwiched slate section, and the transition from the fan delta plain to the carbonate platform. The second section (Pg ~ 2) is a fine clastic rock sandwiched sandstone section, which is deposited in the marginal basin of shallow sea continental shelf. Three sections (Pg ~ 3) are reef limestone sections, which are deposited in shallow sea shelf carbonate platform. The fourth section (Pg ~ 4) is a fine clastic rock sandwiched limestone section, which is deposited in the marginal basin of the semi-deep sea basin. The Longwu River Formation can be divided into 5 sections from below: one section (T1L ~ 1) is coarse clastic rock and slate section, which belongs to fan deposit in turbidite fan. The second stage (T1l ~ 2) is thin layer sandstone and limestone section of fine clastic rock, and belongs to fan deposit in turbidite fan (no water channel part). Three sections (T1l ~ 3) are thin layer slate, middle-middle layer sandstone section, and belongs to the fan deposit in the turbidite fan (with water channel section). The fourth section (T1l ~ 4) is the middle-middle thick layer sandstone section (mutual layer) in the slate clip, which is fan-deposited in the turbidite fan and may be located on the continental slope. The fifth section (Tll5) is a silt (mud) slate section, which belongs to the turbidite fan outside fan deposit, which is the transition zone of the turbidite fan far end and the deep water basin. 2. The minimum debris flow rate U-Pb obtained in the sandstone sample of the Ganjiagang Formation is 299Ma, representing the lower limit of the deposition of the Ganjia Formation. In this paper, the stratigraphic sedimentary age of Ganjia Formation is determined to be Permian in combination with terrestrial fossil data. The average age of U-Pb in the sandstone of Longmenhe Formation is 258Ma, which is the lower limit of the formation, and the crystallization age of the Paleogene in Longwu River Formation is 246. 7Mt. 2.1Ma, which is the upper limit of the formation, so that the sedimentary age of Longwu River is limited to 258 ~ 247Ma. The sedimentary age of Longwu River Formation in the study area is determined as early Triassic. The weathering degree of the source rocks in the Ganjiashan Formation is lower than that of the first cycle. There is also a small amount of the material records from the middle and late PROTEROZOIC THERMAL events in Qilianshan Belt and the new PROTEROZOIC-response Rodinia supercontinent. The sedimentary basin prototype is passive continental margin shallow sea shelf. 4, Longwu River Formation is the first cycle sediment, the source area chemical weathering is weak, the paleocurrent direction is NWW-SEE direction, and the object source includes the Early Paleozoic cutting type magma arc of Qilianshan belt. It is probably one of the source sources of the metamorphic basement of Qilianshan Belt and the metamorphic basement of Qilianshan belt, especially in the research area. The source rocks are dominated by marble, and a small amount of basic rocks, which are the mixed distribution of the two characteristic lithologies, may be the result of the influence of the uplift of the substrate. The sedimentary basin archetype should be an arc-back basin. 5. According to the data of this paper, the regional geological data and the previous studies, the tectonic evolution of the Late Paleozoic-Early Mesozoic in the northern margin of the West Qinling and the adjacent region is divided into three stages: 1) Triassic-Middle Permian Gutertitian lysis-tension stage; 2) Middle Permian late-Early Triassic oceanic crust north-to-dive, post-arc rift basin expansion stage; 3) middle-late Triassic arc back basin closing, collision and post-collision stage.
【學(xué)位授予單位】：長(zhǎng)安大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：P512.2;P534

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本文編號(hào)：2305616