西准噶尔额敏东部志留系的厘定及其构造演化

发布时间：2018-02-01 16:25

  本文关键词： 志留系 恰尔尕也组 沙尔布尔组 厘定 地层划分与对比 岩石地球化学 额敏 西准噶尔　出处：《长安大学》2015年硕士论文　论文类型：学位论文

【摘要】：志留纪是西准噶尔北部洋盆、岛弧等发展建造的重要阶段,这一时期西准北部经历了洋盆的相互俯冲和岛弧的活动过程,横跨东哈萨克斯坦至新疆北部的博什库尔-成吉斯岩浆弧的岛弧建造就起始于该时期。由于基础地质研究的薄弱,造成了该区域对志留系认识的差异。本文对西准噶尔额敏县东部最新厘定的志留纪地层及火山岩进行了详细的研究并进行了地层的划分与对比,结合现有和前人研究资料,探讨了早-中志留世恰尔尕也组(S1-2q)和中志留世沙尔布尔组(S2s)的基本地质特征、岩性组合、沉积环境,并对火山岩进行了岩石学、岩相学、岩石地球化学、LA-ICP-MS锆石U-Pb测年、构造环境研究,并在此基础上对研究区志留纪构造演化进行探讨。研究区恰尔尕也组(S1-2q)以近缘岛弧碎屑岩-火山碎屑岩为主,综合分析判断其属于河口三角洲相沉积,并可进一步划分为三段,下段主要为中-粗粒碎屑岩夹少量细碎屑岩(含珊瑚、腕足等化石)及火山熔岩,中段主要为火山灰(凝灰质)碎屑岩,上段主要为粗碎屑岩。该组在沉积过程中伴随有一定程度的火山作用且距离火山口很近。沙尔布尔组(S2s)主要有火山熔岩和火山碎屑岩组成,火山岩主要为灰紫色辉石安山岩、灰绿色安山岩。对辉石安山岩进行LA-ICP-MS锆石U-Pb测年获得年龄为428.7±2.7Ma,时代属于中志留温洛克世。火山岩地球化学特征显示岩石以富Sr、Ba为特征且具有较高的Mg#、Sr/Y和Ba/La值,大离子亲石元素(LILE)相对富集,高场强元素(HFSE)相对亏损,其中Nb、Ta、Ti强烈亏损,具有轻微的负铕异常,岩石地球化学特征与日本中新世Setouchi火山岩带赞岐岩类相似。综合岩石地球化学特征所反映的构造信息、沙尔布尔组沉积特征及研究区所处的区域地质背景,认为其形成环境为岛弧火山活动。综合来看,研究区志留系很好的记录了西准噶尔北部在早古生代后期的大洋发展阶段;志留纪地层的岩石组合、沉积环境、古生物特征以及火山岩也对研究西准北部在早古生代后期至晚古生代早期的构造演化发展史具有重要意义。
[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 卤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.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P534.43;P548

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