本文選題：大同火山 + 沉積地層��； 參考：《上海師范大學(xué)》2017年碩士論文

【摘要】：大同火山群位于山(西)陜(西)地塹系最北端的大同盆地中。第四紀(jì)時(shí)期,大同火山群火山多次噴發(fā),在盆地內(nèi)堆積了大量的火山噴發(fā)物。自上世紀(jì)30年代開(kāi)始,中外學(xué)者對(duì)大同火山展開(kāi)了大量的科研工作,在大同火山的地質(zhì)構(gòu)造背景、火山活動(dòng)類型、巖漿化學(xué)成分、火山深度動(dòng)力學(xué)機(jī)制及活動(dòng)年代等方面都取得了眾多研究成果。然而,由于野外采樣困難,火山活躍期次較多等因素的影響,使得目前的火山活動(dòng)年代數(shù)據(jù)無(wú)法形成有效的比對(duì),更不能反映大同火山活動(dòng)的階段性歷史特征,因此人們對(duì)于大同火山的活動(dòng)期次及年代問(wèn)題一直爭(zhēng)論不斷。野外調(diào)查發(fā)現(xiàn):火山錐體坡麓附近和泥河灣古湖湖相沉積層與湖岸之上黃土—古土壤沉積層中夾有多層火山碎屑層。(1)在肖家窯火山坡麓位置存在有多套傾角不同的火山碎屑層。且位于底部的火山碎屑層傾角大于其上部碎屑層的傾角。(2)陳莊湖相沉積層和黑山黃土—古土壤沉積層中發(fā)現(xiàn)有多層疑似火山灰物質(zhì)沉積的延續(xù)良好的薄層灰黑色特征沉積層。這些沉積現(xiàn)象表明:大同火山在地質(zhì)歷史時(shí)期存在多個(gè)活躍期。區(qū)域的湖相沉積和黃土—古土壤沉積都詳細(xì)的記錄了當(dāng)時(shí)的火山活動(dòng)信息。為從沉積地層中獲得更為詳細(xì)的火山活動(dòng)信息、建立沉積剖面的年代框架、判斷沉積剖面中所夾火山物質(zhì)沉積層位的沉積年代。本文對(duì)火山群周邊受火山活動(dòng)影響的湖相沉積層和黃土—古土壤沉積層進(jìn)行了仔細(xì)的野外物理形態(tài)描述和高精度的采樣。我們選取陳莊剖面作為湖相沉積的典型剖面、黑山剖面作為黃土沉積的典型剖面。野外考察中都發(fā)現(xiàn)這兩剖面中存有明顯的火山活動(dòng)記錄信息,實(shí)驗(yàn)室分析表明這兩個(gè)剖面都有多個(gè)層位在沉積過(guò)程中受到了區(qū)域火山活動(dòng)的影響。在湖相沉積剖面中出現(xiàn)四層磁化率、Ti元素含量、Fe元素含量和平均粒度組成同步異常變大的沉積層位;在黃土—古土壤沉積剖面中出現(xiàn)三層磁化率、Ti元素含量或Fe元素含量同步異常變大的沉積層位。這些異常變大的現(xiàn)象表明沉積時(shí)受到區(qū)域環(huán)境突變的影響。在大同盆地中則是受到火山活動(dòng)導(dǎo)致的區(qū)域沉積環(huán)境突變。利用古地磁定年法和黃土古土壤定年法建立不同沉積剖面的年代框架,判斷湖相沉積層中四個(gè)火山物質(zhì)沉積層的沉積年代分別為:早于0.90MaB.P.、約0.51MaB.P.、約0.32MaB.P.和約0.09MaB.P.;黃土—古土壤沉積層中三個(gè)火山物質(zhì)沉積層的沉積年代分別為約0.32MaB.P.、0.19MaB.P.和約0.09MaB.P.。通過(guò)沉積層沉積年代比對(duì)認(rèn)為大同火山群共存在五個(gè)活躍期,分別為早于0.90M aB.P.、約0.51MaB.P.、約0.32MaB.P.、0.19MaB.P.和約0.09MaB.P.
[Abstract]:Datong Volcano Group is located in the Datong basin at the northernmost end of the Shanshan (West) Shaanxi (West) graben system. During the Quaternary period, the Datong volcanic group erupted many times and accumulated a lot of volcanic eruptions in the basin. Since the 1930s, Chinese and foreign scholars have carried out a great deal of scientific research on Datong volcano. In the geological tectonic background, volcanic activity type, magmatic chemical composition of Datong volcano, Many achievements have been made in the dynamic mechanism and age of volcanic depth. However, due to the difficulty of sampling in the field and the influence of many factors such as the secondary active period of volcanism, the current dating data of volcanic activity can not form an effective comparison, let alone reflect the historical characteristics of the stages of the volcanic activity in Datong. As a result, there has been a constant debate about the active periods and chronologies of Datong Volcano. Field investigation shows that there are multiple layers of volcanic clastic layer located in the loess paleosol sediment layer near the slope of the volcanic pyramidal body and above the lacustrine facies of the ancient lake in Nihewan) and there are several sets of volcanic clastic layers with different dip angles at the foothills of the Xiaojiayao fire slope. Moreover, the dip angle of the volcanic clastic layer located at the bottom is greater than that of the upper clastic layer. The Chenzhuang lacustrine sedimentary layer and the Montenegrin loess-paleosol sedimentary layer are found to have several layers of thin-layer gray-black sedimentary layers with good continuity of suspected volcanic ash deposition. These sedimentary phenomena indicate that there are many active periods in the geological history of Datong volcano. Regional lacustrine deposits and loess-paleosol deposits both recorded the volcanic activity in detail at that time. In order to obtain more detailed volcanic activity information from sedimentary strata, the chronological framework of sedimentary profiles is established, and the sedimentary ages of sedimentary layers of volcanic material in sedimentary profiles are determined. In this paper, the lacustrine sediments and loess-paleosol sediments around the volcanoes affected by volcanic activity were carefully described in the field and sampled with high accuracy. We select Chenzhuang section as typical section of lacustrine facies and Montenegro section as typical section of loess deposit. During the field investigation, it is found that there are obvious records of volcanic activity in the two profiles, and laboratory analysis shows that there are many layers affected by the regional volcanic activity in the sedimentary process of the two profiles. In the lacustrine sedimentary profile, there are four layers of magnetic susceptibility and Ti content, Fe content and average particle size composition. In the loess paleosol sedimentary profile, the three layers of magnetic susceptibility and the content of Ti element or Fe element become larger and larger synchronously. These abnormal phenomena indicate that the deposition is affected by the abrupt change of regional environment. In the Datong basin, the regional sedimentary environment changes due to volcanic activity. Paleomagnetic dating method and loess paleosol dating method were used to establish the chronological framework of different sedimentary profiles. The sedimentary ages of the four volcanic sediments in the lacustrine sediments were determined to be earlier than 0.90 MaB.P., about 0.51MaB.P.and about 0.32MaB.Prespectively. The sedimentary age of the three volcanic sediments in the Loess paleosol sedimentary layer is about 0.32 MaB.P./ 0.19 MaB.P. And about 0.09 MaB.P. Five active periods of the Datong volcanic group, which are earlier than 0.90 Ma B.P., 0.51MaB.P., 0.32 MaB.P.and 0.19 MaB.Prespectively, are considered to exist in Datong volcanic group by comparison of sedimentary ages. And about 0.09 MaB.P.
【學(xué)位授予單位】：上海師范大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：P318.44;P317

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