本文選題：物源分析 + 鋯石U-Pb年代學(xué)�。� 參考：《中國地質(zhì)大學(xué)》2015年博士論文

【摘要】：下江群是分布在江南造山帶西段(黔東南地區(qū))的一套前寒武紀淺變質(zhì)陸源碎屑巖夾火山碎屑巖組合。其地層時代歸屬與劃分,特別是區(qū)域地層對比一直未能得到很好解決；此外,下江群的沉積演化、盆地性質(zhì)以及盆地動力學(xué)機制長期存在較大爭議。本文主要運用造山帶沉積地質(zhì)學(xué)的研究思路和方法,對黔東南地區(qū)下江群開展沉積地質(zhì)學(xué)、碎屑巖全巖地球化學(xué)、砂巖碎屑組分、碎屑鋯石微量元素和U-Pb年代學(xué)等多方面研究,獲得了如下主要認識：(1)下江群是一套具復(fù)理石特征的陸源碎屑巖夾火山碎屑巖建造。巖性主要以粉砂質(zhì)板巖、變余粉砂巖、變余粉-細砂巖、凝灰質(zhì)板巖、凝灰質(zhì)變余粉砂巖和沉凝灰?guī)r等為主。沉積構(gòu)造有水平層理、平行層理、粒序?qū)永�、交錯層理、塊狀層理、均質(zhì)層理、脈狀和透鏡狀層理等。事件沉積有滑塌滑移事件沉積和濁流事件沉積。屬于濱海-淺海-半深海沉積體系。(2)運用LA-ICP MS測年技術(shù),測得江南造山帶西段四堡群河村組頂部的碎屑巖和下江群中烏葉組第一段頂部的含凝灰質(zhì)碎屑巖、清水江組底部與中部的沉凝灰?guī)r、平略組中上部的含凝灰質(zhì)碎屑巖及隆里組中下部的碎屑巖中鋯石最小年齡組的加權(quán)平均年齡分別為819.8±6.4 Ma和779.5±4.7 Ma、764.0±6.3 Ma 與(756.8±7.6 Ma、756±13 Ma)、733.9±8.8 Ma及725±10 Ma。以這些年齡數(shù)據(jù)約束下江群地層沉積時限約為815～720 Ma。其中,甲路組一段沉積時限約為815～805 Ma；甲路組二段沉積時限約為805～800 Ma；烏葉組一段沉積時限約為800～780 Ma；烏葉組第二段至番召組沉積時限約為780～770 Ma；清水江組沉積時限約為770～745 Ma；平略和隆里組沉積時限約為745～720 Ma。結(jié)合江南造山帶地區(qū)報道的地層年齡或與地層具明顯先后關(guān)系的巖漿巖年齡,開展了下江群時期的地層劃分與對比。本文年齡數(shù)據(jù)表明下江群屬于新元古代,顯示江南造山帶基底的構(gòu)造背景與屬性與“格林威爾運動”無關(guān)。(3)通過對下江群的沉積相和沉積環(huán)境分析,認為下江期沉積演化經(jīng)歷了以下幾個階段：①剝蝕夷平和填平階段(甲路組一段)；②盆地初始伸展階段(弧后伸展)(甲路組二段)；③盆地持續(xù)伸展階段(弧后伸展)(烏葉組和番召組時期)；④盆地差異性隆升階段(清水江組時期)；⑤盆地萎縮和快速消亡階段(平略組至隆里組時期)。(4)下江群的砂巖碎屑顆粒組成統(tǒng)計顯示,砂巖整體分選磨圓較差-中等,少數(shù)分選磨圓較好,含較多的巖屑和長石顆粒以及凝灰質(zhì)雜基,部分發(fā)生硅化、絹云母化和泥化等淺變質(zhì)作用,見云母類、鋯石等副礦物。長石風(fēng)化蝕變明顯,火山灰具有蝕變微晶和霏晶結(jié)構(gòu)。主要組分石英總量(7.7%～89.3%)、單晶石英(5.5%～78.9%)、多晶石英(2.1%-38.6%)、長石總量(2.1%～34.3%)、斜長石類(2.1%～27.0%)、堿性長石類(1.1%-36.8%)、巖屑總量(4.9%～78.6%)、沉積巖屑+變質(zhì)巖屑(4.4%～73.1%)和火山巖屑(0.0%～65.9%)。Q-F-L、Q-M-Lt和Qp-Lv-Ls圖解顯示下江群砂巖物源較為復(fù)雜,主要來自再旋回造山帶物源及巖漿弧物源。表明物源區(qū)主要為與弧有關(guān)的再旋回造山帶。圖解中具有明顯弧造山帶物源,顯示下江群時期江南造山帶西段存在巖漿弧,結(jié)合區(qū)域資料認為該島弧在廣西龍勝一帶,下江群處于弧后盆地沉積環(huán)境。(5)全巖地球化學(xué)研究中,主量元素含量及比值、稀土微量元素含量及比值、稀土元素配分模式和主量、微量元素判別圖解等多種、多重參數(shù)判別結(jié)果表明,下江群的碎屑沉積物形成于活動大陸邊緣環(huán)境。(6)作者將下江群和四堡群中碎屑巖和沉凝灰?guī)r樣品所有年齡數(shù)據(jù)劃分為723Ma-745 Ma、745 Ma-775 Ma、775 Ma-815 Ma、815 Ma-825 Ma、825 Ma-875 Ma和875Ma等6個年齡組段,進行鋯石微量元素圖解判別。六個組別的投圖結(jié)果基本相似。在Th/U-Nb/Hf 和 Th/Nb-Hf/Th圖解上幾乎全部落入巖漿弧/造山帶環(huán)境,而遠離板內(nèi)/非造山帶環(huán)境。在Hf-Th/Yb、Hf-U/Yb、Y-Th/Yb和 Y-U/Yb圖解上落入大陸花崗質(zhì)巖石的鋯石區(qū)域,其中有1/2左右數(shù)據(jù)點落入大陸地殼鋯石和大洋地殼鋯石的混合區(qū),個別落入大洋地殼鋯石區(qū)域。由此認為江南造山帶西段新元古代鋯石可能形成于島弧俯沖環(huán)境,而非板內(nèi)環(huán)境,其島弧俯沖環(huán)境至少持續(xù)到新元古代時期下江群(760Ma±)。(7)揚子地塊東南緣(江南造山帶)東段的雙橋山群,西段的梵凈山群、冷家溪群和四堡群的碎屑鋯石具有相似的年齡譜峰值。揚子地塊東南緣西段的下江群、丹洲群以及板溪群和東段的下江期碎屑鋯石年齡譜峰值也具有相似性,區(qū)別在于兩個較老的年齡峰值存在差異,表明它們的物源區(qū)總體相似但存在一定的差異性。而四堡群及其相當層位與下江群及其相當層位的碎屑鋯石年離譜峰值比較,顯示四堡群的1600 Ma和1950 Ma年齡峰值更為明顯,而下江群的2500 Ma和2000 Ma峰值較為明顯,反映物源區(qū)的變化或是物源區(qū)剝蝕層位的變化。二者與華夏地塊巖漿巖和揚子地塊內(nèi)部巖漿巖年齡譜峰值存在明顯差異,而與揚子地塊周緣巖漿巖年齡譜峰值相似,揭示物源區(qū)主要是揚子地塊周緣增生帶。而大量同沉積碎屑鋯石的出現(xiàn)反映來自活動的火山物質(zhì)。來自揚子地塊內(nèi)部物源信息弱,沒有來自華夏地塊物源信息,暗示華夏地塊與揚子地塊新元古代四堡期和下江群尚未完全拼貼一體,二者之間存在深海(海溝)相隔。江南造山帶西段下江期可能處于“溝—弧—盆”體系。(8)清水江組是下江期物源轉(zhuǎn)換的關(guān)鍵時期。下江群早期(甲路組至清水江組)與下江群晚期(平略組和隆里組)物源的碎屑鋯石年離譜比較,前者具相對較多的老鋯石年齡,后者則幾乎未見老鋯石年齡,暗示下江群早期物源可能主要來自揚子地塊周緣四堡群及其相當層位的沉積區(qū)和揚子地塊基底,而晚期物源轉(zhuǎn)變?yōu)橄陆涸缙诔练e物,較少有來自四堡期的物源。另外,清水江組的沉凝灰?guī)r年齡770～745 Ma與區(qū)域上廣西龍勝、湖南古丈的枕狀玄武巖和基性巖漿巖年齡(760 Ma)在誤差范圍內(nèi)一致,暗示清水江組的源區(qū)可能來自廣西龍勝和湖南古丈一帶。揚子地塊北緣、西緣及雪峰山地區(qū)的770～745 Ma的巖漿活動明顯,但是由于揚子地塊相隔,它們無法為南緣提供物源(如果提供物源必然有更多的揚子地塊內(nèi)部物源信息)。在揚子地塊北緣、西緣及雪峰山地區(qū)的下江群地層與上覆南華系地層角度不整合關(guān)系,延至研究區(qū)已演變?yōu)槲⒔嵌炔徽稀叫胁徽稀辖佑|(北西向南東方向),反映雪峰造山運動的核心區(qū)域不在揚子地塊南東緣的黔東南地區(qū)。雪峰運動使得廣西龍勝一帶的火山弧消亡。(9)建立了江南造山帶西段下江期的俯沖(弧-陸)—伸展動力學(xué)模式。(a)870-830Ma時期：江南造山帶西段處于溝—弧—盆體系,沉積了梵凈山/四堡群的一套具復(fù)理石建造的碎屑巖。(b)830～815 Ma時期：由于揚子地塊與華夏地塊之間的洋—陸匯聚導(dǎo)致四堡火山弧的消失,發(fā)生強烈的擠壓造山作用(武陵運動),江南褶皺帶雛形最終形成。晚期發(fā)生造山后的垮塌。(c)815～770 Ma時期：江南造山帶西段持續(xù)發(fā)生擠壓縮短,廣西龍勝一帶島弧環(huán)境逐漸發(fā)育并最終成熟。黔東南至桂北地區(qū)處于弧后伸展環(huán)境,沉積了下江群下部的甲路—番召組地層。(d)770-745 Ma時期：揚子地塊周緣發(fā)生強烈俯沖匯聚——弧-陸造山作用(雪峰運動)。但其匯聚強度存在差異,在揚子地塊西緣與北部規(guī)模大、活動強烈；而揚子?xùn)|南緣江南造山帶西段規(guī)模較小。(e)745～720 Ma時期：經(jīng)雪峰運動以后,華夏地塊與揚子地塊可能已經(jīng)完全拼貼一體。
[Abstract]:The lower river group is a set of pyroclastic rock assemblage of the Precambrian shallow metamorphic terrigenous clastic rocks distributed in the western part of the Jiangnan orogenic belt (Qiandongnan area). Its stratigraphic age and division, especially the regional stratigraphic contrast has not been well solved. In addition, the sedimentary evolution of the lower river group, the nature of the basin and the mechanism of the basin dynamics are long term. In this paper, we mainly use the research ideas and methods of the sedimentary geology of the orogenic belt to study the sedimentary geology, the whole rock geochemistry of the detrital rock, the sandstone debris composition, the trace elements of the detrital zircon and U-Pb chronology in the Qiandongnan area: (1) the lower river group is a set of complex sets. The lithic rocks are characterized by terrigenous clastic rocks. The lithology is mainly composed of silty slate, residual siltstone, residual powder - fine sandstone, tuffaceous slate, tuffaceous siltstone and tuff. The sedimentary structures have horizontal bedding, parallel bedding, granular bedding, interlaced bedding, homogeneous bedding, pulse and lenticular Stratification and so on. The sedimentary and turbidity current deposits are deposited in the coastal - shallow sea - semi deep sea. (2) using LA-ICP MS dating technique, the clastic rocks at the top of the four Fort Group and the top of the first section of the first section of the Wu Ye formation in the lower Jiangnan group of the Jiangnan orogenic belt, and the bottom and the middle of the Qingshui River group, are measured. The weighted average age of the minimum age group of zircon in the middle and upper part of the middle and lower part of the Luli group is 819.8 + 6.4 Ma and 779.5 + 4.7 Ma respectively, 764 + 6.3 Ma and (756.8 + 7.6 Ma, 756 + 13 Ma), 733.9 + 8.8 Ma and 725 + 764 Ma. under these age data constraints. The limit is about 815~720 Ma., and the time limit for the first section of the Jia Road Group is about 815~805 Ma, the two section of the two section of the Jia Road Group is about 805~800 Ma, the time limit for the first section of the Wu leaf group is about 800~780 Ma, the sedimentary time of the second to the summon group in the Wu Ye formation is about 780~770 Ma, and the sedimentation time of the Qingshui River group is about 770~745 Ma; The sedimentary time is about 745~720 Ma. combined with the age of the stratigraphic age reported in the Jiangnan orogenic belt or the magmatic age which has a distinct relationship with the strata. The stratigraphic division and comparison of the lower river group are carried out. The age data shows that the Jiangnan group belongs to the Neoproterozoic, which shows the tectonic background and attributes of the basement of the Jiangnan orogenic belt and the greenway. (3) through the analysis of the sedimentary facies and sedimentary environment of the lower river group, it is believed that the sedimentary evolution of the lower river period has experienced the following stages: (1) the stage of denudation and leveling and filling (a section of the Jia Lu Group); (2) the initial extension stage (back arc extension) of the basin (two sections of the Jia Lu formation); (3) the continuous extension of the basin (back arc extension) During the period of the Zhao group); (4) the basin difference uplift stage (Qingshui River Group); 5. Basin atrophy and rapid extinction phase (period of the plateau to the Longli formation). (4) the sandstone debris particle composition of the lower river group shows that the overall separation grinding circle of the sandstone is poor - medium, and a few separation grinding circles are better, with more debris and feldspar particles and tuff. Hetero base, partial silicification, sericite and argillaceous metamorphism, and other accessory minerals such as mica and zircon. The weathering alteration of the feldspar is obvious, the volcanic ash has altered microcrystalline and felsite structure. The main components of quartz (7.7% to 89.3%), single crystal quartz (5.5% to 78.9%), polycrystalline quartz (2.1%-38.6%), total feldspar (2.1% to 34.3%), and plagioclase (2.) 1% ~ 27%), basic feldspar (1.1%-36.8%), total rock mass (4.9% ~ 78.6%), sedimentary debris + metamorphic cuttings (4.4% ~ 73.1%) and volcanic debris (0% to 65.9%).Q-F-L, Q-M-Lt and Qp-Lv-Ls diagrams show that the source of the lower river group sandstone is more complex, mainly from the source of the re gyratory orogenic belt and the source of magma arc. It is indicated that the source area is mainly related to the arc. There is an obvious arc orogenic belt in the diagrammatic orogenic belt. It shows that there is a magma arc in the west section of the Jiangnan orogenic belt during the period of the lower Jiangnan group. The island arc is located in the Longsheng area of Guangxi, and the lower river group is in the sedimentary environment of the back arc basin. (5) the content and ratio of the main elements and the trace elements of the rare earth elements and the content of the rare earth elements in the whole rock geochemistry study. The ratio, rare-earth element distribution pattern, principal quantity, trace element discriminant diagram and so on, multiple parameter identification results show that the detrital sediments of the lower river group are formed on the active continental margin environment. (6) the author divides the data of all years of age of the lower river group and the four Fort group to 723Ma-745 Ma, 745 Ma-775 Ma, 775 Ma-815 M. A, 815 Ma-825 Ma, 825 Ma-875 Ma and 875Ma and other 6 age groups, determine the trace elements of zircon. The results of the six groups are basically similar. In the Th/U-Nb/Hf and Th/Nb-Hf/Th diagrams, almost all fall into the magma arc / orogenic environment, but far away from the inner / non orogenic belt. In Hf-Th/Yb, Hf-U/Yb, Y-Th/Yb, and Y-U/Yb diagrams. The zircon regions that fall into the continental granitic rocks include about 1/2 data points falling into the continental crust of zircon and the mixed region of the oceanic zircon and the zircon region of the oceanic crust. It is believed that the Neoproterozoic zircons in the western section of the southern orogenic belt may be formed in the island arc subduction environment, not the internal environment, and the island arc subduction environment at least holds. To the New Proterozoic era, the lower Jiang Group (760Ma +). (7) the Shuangqiao mountain group in the eastern section of the southeast of Yangtze block (Jiangnan orogenic belt), the detrital zircon of the van Jing mountain group, the Leng Jia Xi group and the four Fort Group in the western part of the Yangtze block, with similar age peaks. The lower river group, the Dan Zhou group, the Banxi group and the east segment of the lower Yangtze stage of the lower Yangtze River in the western section of the southeast margin of the Yangtze block. The peak values of the age spectrum are also similar, and the difference lies in the differences in the two older peaks, indicating that their source areas are generally similar, but there are some differences. The peak value of the four Fort Group and its equivalent level and the lower river group and its corresponding clastic zirconium peaks shows that the peak value of the 1600 Ma and 1950 Ma ages of the four Fort Group is more significant. It is obvious that the peak value of 2500 Ma and 2000 Ma in the lower river group is more obvious, reflecting the change of the source area or the variation of the erosion layer in the source area. The two are obviously different from the peak age spectrum of magmatic rocks in the magmatic rocks and the Yangtze massif, which are similar to the annual peak of the annual age spectrum of the magmatic rocks on the margin of the Yangtze block, which reveals that the main source area is the Yangtze. The presence of a large number of sedimentary clastic zircons shows that the occurrence of a large number of sedimentary clastic zircons reflects the active volcanic materials. The source information from the interior of the Yangtze block is weak and does not come from the source information of the Huaxia massif, suggesting that the Neoproterozoic four Fort period and the lower river group in the Neoproterozoic of the Huaxia and Yangzi massif have not yet been completely collaged, and the deep-sea (trench) facies exists between the two. The west section of the Jiangnan orogenic belt may be in the "gully arc basin" system. (8) the Qingshui River group is the key period of the transformation of the source of the next Jiang River. There is almost no old zircon age, suggesting that the early provenance of the lower river group may mainly come from the four Fort Group, the sedimentary area and the basement of the Yangtze block on the margin of the Yangtze block, and the late provenance is transformed into the early sediments of the lower river group and less from the source of the four Fort period. In addition, the age of the sedimentary tuff in the Qingshui River group is 770~745 Ma and the region. The age of occipital basalt and basic magmatic rock (760 Ma) in Longsheng, Hunan and Guzhang, Hunan, is consistent with the error range, suggesting that the source area of the Qingshui River group may come from Guangxi Longsheng and Hunan Guzhang. The northern margin of the Yangtze block, the western margin and the 770~745 Ma of the Xuefeng mountain area are obviously active, but they are unable to be separated by the Yangtze block. In the northern margin of the Yangtze block, the lower river group in the western margin and the Xuefeng mountain area is unconformable with the angle of overlying the South China system, which has evolved into the micro angle unconformity, parallel unconformity, and integrated contact (North West to the east direction) in the northern margin of the Yangtze block. The core area reflecting the snow peak orogeny is not in the Qiandongnan area of the South East edge of the Yangtze block. The snow peak movement has led to the extinction of the volcanic arcs in Longsheng, Guangxi. (9) the subduction (arc land) extension dynamic model of the lower Yangtze River in the west of the Jiangnan orogenic belt was established. (a) 870-830Ma period: the western section of the Jiangnan orogenic belt is in a ditch arc basin system and sinks. A set of clastic rocks built in the van Jing Shan / four Fort Group. (b) 830~815 Ma period: since the oceanic and terrestrial convergence between the Yangzi block and the Huaxia block led to the disappearance of the four Fort volcanic arc, the strong extrusion orogeny (Wuling movement), the embryonic form of the Jiangnan fold belt finally formed. The late orogenic collapse. (c) 815 ~ 770 Ma period: the western section of the Jiangnan orogenic belt continued to be compressed and shortened, and the island arc environment in Longsheng, Guangxi was gradually developed and matured. The region of Qiandongnan to North Guangxi was in the post arc extension environment and deposited the formation of the Jia Lu and Sumi formation in the lower part of the lower river group. (d) the period of the strong subduction and convergence in the periphery of the Yang Zi block - arc land Orogeny (snow peak movement), but its convergence intensity is different, in the west margin of the Yangtze block and in the north, the activity is strong, while the west section of the southern orogenic belt on the southeast margin of the Yangtze is small. (E) 745~720 Ma period: after the snow peak movement, the Huaxia block and the Yangtze block can be completely collaged.
【學(xué)位授予單位】：中國地質(zhì)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：P535;P534.1

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