【摘要】：華南板塊由揚(yáng)子地塊和華夏地塊拼貼而成,二者的拼貼作用在揚(yáng)子?xùn)|南緣形成了一條呈弧形展布的江南造山帶,該造山帶形成和演化過(guò)程長(zhǎng)期受到地學(xué)界的關(guān)注。下江群分布于江南造山帶西段的湘黔桂地區(qū),角度不整合覆于梵凈山群之上,平行不整合于南華系之下,為一套巨厚的淺變質(zhì)陸源碎屑巖夾火山碎屑巖組合,對(duì)于該套地層的時(shí)代、盆地類型及構(gòu)造背景等問(wèn)題一直以來(lái)存在很多爭(zhēng)議,對(duì)其進(jìn)行詳細(xì)研究能有效探索江南造山帶西段的演化過(guò)程。本文以黔東南及其鄰區(qū)下江群為研究對(duì)象,在詳細(xì)野外地質(zhì)調(diào)查基礎(chǔ)之上,應(yīng)用沉積學(xué)、地球化學(xué)和同位素年代學(xué)等分析手段,對(duì)其進(jìn)行沉積相和物源屬性綜合研究,并結(jié)合區(qū)域研究成果系統(tǒng)分析下江群的盆地性質(zhì)及構(gòu)造背景。通過(guò)相標(biāo)志的識(shí)別和巖性橫向、垂向上的變化特征研究,發(fā)現(xiàn)研究區(qū)下江群為一套同期異相的沉積產(chǎn)物,梵凈山和芷江地區(qū)為濱岸-淺海陸棚環(huán)境,黔東南黎平-天柱地區(qū)為大陸斜坡環(huán)境,反映出盆地北高南低的古地理格局。鏡下鑒定顯示下江群砂巖巖石類型為巖屑長(zhǎng)石砂巖和長(zhǎng)石巖屑砂巖,碎屑成分主要為石英、長(zhǎng)石、長(zhǎng)英質(zhì)火山巖屑及少量沉積巖屑;稀土和微量元素特征表明下江群源巖為長(zhǎng)英質(zhì)巖漿巖;Dickinson物源判別圖解和微量元素投圖結(jié)果表明下江群物源區(qū)構(gòu)造背景主要為巖漿弧,底部層位物源區(qū)構(gòu)造背景為再旋回造山帶。這些特點(diǎn)暗示下江群物源可能來(lái)自巖漿弧的中酸性火山巖。梵凈山地區(qū)清水江組底部凝灰?guī)r測(cè)年結(jié)果為777±9Ma,下江群碎屑鋯石的年齡譜顯示其年齡值主要集中在810~760Ma,具有794Ma主峰值和2016Ma弱峰值;810~760Ma的鋯石自形程度好、發(fā)育振蕩環(huán)帶且Th/U比值大于0.4,具有巖漿成因的特征。通過(guò)與揚(yáng)子周緣和華夏地塊的鋯石年齡譜對(duì)比,發(fā)現(xiàn)下江群和揚(yáng)子北緣具有相似的年齡譜,結(jié)合向南的古流向及砂巖巖屑特征,認(rèn)為下江群的物源區(qū)應(yīng)為下伏梵凈山群和揚(yáng)子北緣的中酸性火山巖。巖石組合、沉積相帶展布和物源特征等表明下江群沉積盆地類型為楔頂盆地,其演化經(jīng)歷了緩慢沉降期(甲路組-烏葉組;橫路沖組-通塔灣組)、初始裂陷期(番召組-清水江組;五強(qiáng)溪組-多益塘組)和強(qiáng)烈裂陷期(平略組-隆里組;百合垅組-牛牯坪組)三個(gè)階段的充填過(guò)程。揚(yáng)子與華夏地塊俯沖造山作用可能一直持續(xù)到早古生代晚期。
[Abstract]:The South China plate is composed of Yangtze block and Huaxia block. The collage between them formed an arc-shaped Jiangnan orogenic belt on the southeast margin of Yangtze River. The formation and evolution of the orogenic belt has been paid close attention to by geoscientists for a long time. The Lower Yangtze Group is distributed in Hunan, Guizhou and Guangxi areas in the western section of the Jiangnan orogenic belt, with angle unconformity overlying the Fanjingshan Group and parallel unconformity under the South China series, which is a set of extremely thick continental clastic rocks with volcanic clastic rocks. There have been many controversies about the age of the strata, basin type and tectonic background, and detailed study of them can effectively explore the evolution process of the western section of the Jiangnan orogenic belt. Based on the detailed field geological survey, the sedimentary facies and provenance properties of the Lower Yangtze Group in the southeast of Guizhou and its adjacent areas are studied by means of sedimentology, geochemistry and isotopic chronology. The basin nature and tectonic setting of Xiajiang Group are systematically analyzed based on the regional research results. Based on the identification of facies markers and the study of lateral and vertical variation of lithology, it is found that the Xiajiang Group in the study area is a set of contemporaneous and heterogeneous sedimentary products, and the Fangjingshan and Zhijiang areas are shore-shallow-sea shelf environments. The Liping-Tianzhu area in the southeast of Guizhou is a continental slope environment, which reflects the paleogeographic pattern in the north, south and south of the basin. The results show that the rock types of the sandstone are lithic feldspathic sandstone and feldspathic sandstone, and the main clastic components are quartz, feldspar, felsic volcanic rock and a little sedimentary lithology. The characteristics of rare earth and trace elements show that the source rocks of the Lower Yangtze Group are derived from the Dickinson source of felsic magmatic rocks. The results show that the tectonic setting of the source area of the Lower Yangtze Group is mainly a magmatic arc, and the tectonic setting of the source area of the bottom layer is a re-cycle orogenic belt. These characteristics suggest that the provenance of the Lower Yangtze Group may come from the intermediate-acid volcanic rocks of magmatic arcs. The dating of tuff at the bottom of Qingshuijiang formation in Fanjingshan area is 777 鹵9 Ma.The age spectrum of detrital zircon from the Lower Yangtze Group shows that the age range is mainly 810 ~ 760 Ma, with a main peak value of 794 Ma and a weak peak value of 2016 Ma at 810 ~ 760 Ma. The oscillating ring zone and the ratio of Th- / U > 0.4 have the characteristics of magmatic genesis. By comparing the zircon age spectra with those of the Yangtze and Huaxia blocks, it is found that the lower Yangtze group and the northern Yangtze block have similar age spectra, combined with the southward paleodirection and sandstone lithic characteristics. It is considered that the source region of the Lower Yangtze Group should be the intermediate-acid volcanic rocks of the Lower Flavand Jingshan Group and the northern margin of Yangtze River. The rock assemblages, distribution of sedimentary facies and provenance characteristics indicate that the sedimentary basins of the Lower Yangtze Group are wedge-top basins, and their evolution has undergone a slow subsidence period (Jialu formation-Wuye formation); The filling process of three stages: Hengluchong formation-Tongtawan formation, initial rifting stage (Fanzhao formation-Qingshuijiang formation; Wuqiangxi formation-DuoYitang formation) and strong rifting stage (Pingliao formation-Longli formation; Lilong formation-Niu-Ping formation). The subduction orogeny of Yangtze and Cathaysian massif probably lasted until the late early Paleozoic.
【學(xué)位授予單位】：中國(guó)地質(zhì)大學(xué)(北京)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：P542.2

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