發(fā)布時間：2018-02-01 16:25

  本文關(guān)鍵詞： 志留系 恰爾尕也組 沙爾布爾組 厘定 地層劃分與對比 巖石地球化學(xué) 額敏 西準(zhǔn)噶爾　出處：《長安大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

【摘要】：志留紀(jì)是西準(zhǔn)噶爾北部洋盆、島弧等發(fā)展建造的重要階段,這一時期西準(zhǔn)北部經(jīng)歷了洋盆的相互俯沖和島弧的活動過程,橫跨東哈薩克斯坦至新疆北部的博什庫爾-成吉斯巖漿弧的島弧建造就起始于該時期。由于基礎(chǔ)地質(zhì)研究的薄弱,造成了該區(qū)域?qū)χ玖粝嫡J(rèn)識的差異。本文對西準(zhǔn)噶爾額敏縣東部最新厘定的志留紀(jì)地層及火山巖進(jìn)行了詳細(xì)的研究并進(jìn)行了地層的劃分與對比,結(jié)合現(xiàn)有和前人研究資料,探討了早-中志留世恰爾尕也組(S1-2q)和中志留世沙爾布爾組(S2s)的基本地質(zhì)特征、巖性組合、沉積環(huán)境,并對火山巖進(jìn)行了巖石學(xué)、巖相學(xué)、巖石地球化學(xué)、LA-ICP-MS鋯石U-Pb測年、構(gòu)造環(huán)境研究,并在此基礎(chǔ)上對研究區(qū)志留紀(jì)構(gòu)造演化進(jìn)行探討。研究區(qū)恰爾尕也組(S1-2q)以近緣島弧碎屑巖-火山碎屑巖為主,綜合分析判斷其屬于河口三角洲相沉積,并可進(jìn)一步劃分為三段,下段主要為中-粗粒碎屑巖夾少量細(xì)碎屑巖(含珊瑚、腕足等化石)及火山熔巖,中段主要為火山灰(凝灰質(zhì))碎屑巖,上段主要為粗碎屑巖。該組在沉積過程中伴隨有一定程度的火山作用且距離火山口很近。沙爾布爾組(S2s)主要有火山熔巖和火山碎屑巖組成,火山巖主要為灰紫色輝石安山巖、灰綠色安山巖。對輝石安山巖進(jìn)行LA-ICP-MS鋯石U-Pb測年獲得年齡為428.7±2.7Ma,時代屬于中志留溫洛克世�；鹕綆r地球化學(xué)特征顯示巖石以富Sr、Ba為特征且具有較高的Mg#、Sr/Y和Ba/La值,大離子親石元素(LILE)相對富集,高場強元素(HFSE)相對虧損,其中Nb、Ta、Ti強烈虧損,具有輕微的負(fù)銪異常,巖石地球化學(xué)特征與日本中新世Setouchi火山巖帶贊岐巖類相似。綜合巖石地球化學(xué)特征所反映的構(gòu)造信息、沙爾布爾組沉積特征及研究區(qū)所處的區(qū)域地質(zhì)背景,認(rèn)為其形成環(huán)境為島弧火山活動。綜合來看,研究區(qū)志留系很好的記錄了西準(zhǔn)噶爾北部在早古生代后期的大洋發(fā)展階段;志留紀(jì)地層的巖石組合、沉積環(huán)境、古生物特征以及火山巖也對研究西準(zhǔn)北部在早古生代后期至晚古生代早期的構(gòu)造演化發(fā)展史具有重要意義。
[Abstract]:Silurian is an important stage of the development and construction of the ocean basin and island arc in the northern part of West Junggar. During this period, the northern part of the west Junggar experienced the process of the subduction of the ocean basin and the activity of the island arc. The island arc formation of the Boshkur-Chenggis magmatic arc spanning East Kazakhstan to the north of Xinjiang began during this period due to the weakness of basic geological research. This paper makes a detailed study on the newly determined Silurian strata and volcanic rocks in the eastern part of Ermin County, West Junggar, and makes stratigraphic division and correlation. Based on the existing and previous research data, the basic geological characteristics, lithologic assemblages and sedimentary environment of the early and Middle Silurian Chargari formation (S1-2q) and the Middle Silurian Shahlbur formation (S2s) are discussed. The petrology, lithofacies and geochemistry of volcanic rocks have been studied by zircon U-Pb dating of LA-ICP-MS. On this basis, the Silurian tectonic evolution of the study area is discussed. In the study area, the Kargari formation S1-2qis mainly composed of island-arc clastic rocks and volcanic clastic rocks. It belongs to estuarine delta facies deposit and can be further divided into three sections. The lower part is mainly medium-coarse clastic rock with a small amount of fine clastic rock (including coral, brachiopod and other fossils) and volcanic lava. The middle part is mainly volcanic ash (tuff) clastic rock. The upper member is mainly composed of coarse clastic rocks. The sedimentary process of this group is accompanied by volcanism and is very close to the crater. The S2s of the Schalbur formation are mainly composed of volcanic lava and pyroclastic rocks. The volcanic rocks are mainly grayish purple pyroxene andesite and gray-green andesite. The LA-ICP-MS zircon U-Pb dating of pyroxene andesite is 428.7 鹵2.7 Ma. The age belongs to the Middle Silurian Wenlock epoch. The geochemical characteristics of the volcanic rocks show that the rocks are rich in Sr ~ (2 +) Ba and have high values of mg #N Sr ~ (-) Y and Ba/La. The large ion lithophile element (LILE) is relatively enriched, and the high field strength element (HFSE) is relatively depleted, among which NbTa-Ta-Ti is strongly depleted and has a slight negative europium anomaly. The petrogeochemical characteristics are similar to those of the Zambic rocks in the Miocene Setouchi volcanic belt in Japan. The sedimentary characteristics of the Schalbur formation and the regional geological background in which the study area is located, it is considered that the formation environment is island arc volcanic activity. The Silurian in the study area recorded the stage of oceanic development in the northern part of West Junggar in the late early Paleozoic. The lithological assemblages, sedimentary environments, paleobiological characteristics and volcanic rocks of Silurian strata are also of great significance in studying the history of tectonic evolution from the late early Paleozoic to the early Paleozoic in the northern part of the west.
【學(xué)位授予單位】：長安大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：P534.43;P548

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