【作者】 章凤奇；

【导师】 陈汉林； 董传万；

【作者基本信息】 浙江大学 ， 构造地质学， 2007， 博士

【摘要】 晚中生代东北亚地区发生了广泛的构造—岩浆事件，中国东北至蒙古东部发育了规模宏大的火山岩带和众多的断陷盆地群。火山岩是大地构造演化过程中岩浆作用的直接产物，是探讨地质事件和地球动力学演化的重要线索。本文利用松辽盆地北部近年来钻井获得的火山岩岩芯和露头资料，详细研究了早白垩世火山岩的发育特征及其地球动力学机理，取得如下认识：（1）松辽盆地北部早白垩世发育有一套以酸性流纹岩为主的中—酸性火山岩组合，火山活动具有多期性，早期主要以少量的中基性喷发开始，后期则大规模酸性火山喷发结束。露头区剖面揭示早白垩世火山岩主要有早、晚两期，早期是以流纹岩为主，晚期则以中基性的玄武质粗安岩为主，分别对应营城组一段和三段。（2）锆石SHRIMP年代学研究表明盆地北部早白垩世火山岩主体形成于108Ma～116Ma之间，且主要集中在111Ma～113Ma。断陷区兴城气田与升平气田早白垩世火山岩是同期火山喷发作用的产物，都属营城组三段范畴，时代上介于早白垩世晚期的Aptian期与Albian期界线附近。火山岩的年龄指示营城组顶界时代已经进入Albian期，因此认为营城组地层发育于早白垩世的Hauterivian期到Albian期。多组继承性岩浆锆石年龄的获得，指示东北地区古生代至中生代期间发生过多次构造热事件。（3）地球化学研究表明断陷区和露头区早白垩世火山岩基本上都属于高钾钙碱系列，准铝质的正常岩系或亚碱系列。火山岩稀土总量较高，轻稀土富集明显。酸性流纹岩类表现轻稀土分馏明显，而重稀土分馏不明显，富集Rb、Th、Zr等元素，强烈亏损Sr、Ba、P、Ti、Eu等元素，中基性安山岩类表现为轻重稀土分馏相当，除Sr显示亏损外其他元素亏损不明显，中酸性英安岩类特征介于两者之间；酸性火山岩类Eu和Ba的亏损表明的岩浆经历了强烈的斜长石的分异作用，P和Ti元素的亏损则与磷灰石和钛铁矿等分异作用有关。上述特征体现了早白垩世中—酸性火山岩的结晶分异演化过程。（4）Sr—Nd同位素分析表明松辽盆地北部早白垩世火山岩具有明显的低Sr高Nd特征。升平和兴城气田中—酸性火山岩由同源岩浆结晶分异演化而来，是同期火山喷发的产物。露头区与断陷区早白垩世火山岩源区性质相似，正的ε_Nd值和低的锶同位素初始比值指示它们来源于亏损型地幔源区，同时岩浆演化过程又受到地壳物质不同程度的混染。钕模式年龄指示其源区地壳形成于新元古代。（5）东北亚地区晚中生代火山作用具有时空分带性和迁移性，晚侏罗世主要与鄂霍次克洋的关闭有关，而早白垩世和晚白垩世分别受控于古太平洋板块的俯冲拆沉和后撤作用。松辽盆地北部早白垩世火山岩具有A型流纹岩特征，形成于造山期后板内伸展构造背景，是东北亚地区岩石圈减薄作用的直接产物。大兴安岭及其以西岩石圈主要表现为伸展减薄，减薄幅度小，而以东的松辽盆地经历了岩石圈的伸展减薄和热—化学侵蚀减薄，减薄幅度显著。岩石圈减薄的不均一性是导致大兴安岭两侧盆地演化差异性的根本原因。更多还原

【Abstract】 Late Mesozoic tectonic-magmatism event is widespread throughout northeastern Asia, which is characterized with large-scale volcanic belts and many faulted-depressions from NE China to mid-eastern Mongolia. As the direct product of magmatism during the process of tectonic evolution, volcanic rocks are the important clue in discussing the geological events and geodynamic evolution. This dissertation is focused on the study about the characteristics and geodynamic mechanism of the volcanic rocks from the northern Songliao Basin and its basin-margin outcrop. The main conclusions are as follows:（1） A suite of volcanic intermediate rocks to acidites, mainly acidic eruptive rocks, was widely distributed in the northern Songliao Basin during the early Cretaceous. The volcanic activities began with a small amount of intermediate rocks and finished with massive acidites. Outcrop section study shows that the early Cretaceous volcanism erupted in two stages, which are corresponding with 1^st member and 3^rd member of Yingcheng Formation respectively. The first stage is characterized with rhyolites and the second with Basaltic trachyandesites.（2） Geochronological study through zircon SHRIMP of the volcanic rocks displays that the main volcanic eruption occured between 108 Ma～116 Ma in the northern Songliao Basin, and mainly concentrated between 111 Ma～113 Ma.The volcanic rocks in both Shengping gas-field and Xingcheng gas-field formed synchronously, which sustained from the Aptian to the early Albian in the early Cretaceous. The volcanic strata in those two fields are thought to be divided into 3^rd member of Yingcheng Formation. Based on former studies and the SHRIMP-age of the volcanic rocks, the geological time of Yingcheng Formation is considered from Hauterivian to Albian in the the early Cretaceous. Several inheritable magmatic zircons appearing different ages implied that NE China experienced multiple tectonic-thermal events in Mesozoic.（3） Geochemical study shows that the early Cretacesous volcanic rocks belonged to subalkaline and para-pelite, as high∑REE and richer in LREE than HREE. The rhyolites are rich in such elements as Rb, Th, Zr, etc., and have obvious negative anomalies of Sr, Ba, P, Ti, Eu, etc., while the andesites have a notable loss of those elements, and the characteristics of dacites are between them. The loss of Eu, Ba, P and Ti in rhyolites indicates that the melts like intermediate intermediate rocks experienced a plagioclase-apatite-tutabuiferite predominant fractionation. All the above geochemical results imply that an evolved affinity existed between the intermediate and acidic rocks.（4） Sr and Nd isotopic analysis exhibits that the early Cretaceous rocks in the Songliao Basin have the low content of Sr and high content of Nd data. The positiveε_Nd and low value of the initial ⁸⁷Sr/⁸⁶Sr ratio indicate they were derived from a similar mantle source and contaminated by the crust in different level during the period of ascending and evolving. The model ages of Nd suggest that the source crust of the volcanic rock was formed in Neo-Proterozoic Era.（5） Late Mesozoic volcanism shows a characteristic of belt-spreading and migrating with the temporal and spatial variation in the northeastern Asia. It is suggested that the late Jurassic volcanism might have a relationship with the closure of the Okhotsk Ocean and the Cretaceous volcanic activities was quite possible to be controlled by the delamination and roll-back of the paleo-Pacific subduction. The early Cretaceous volcanic rocks characterized with A-type rhyolites and developed under a post-orogenic and within-plate tectonic environment. Those are attributed to lithospheric thinning during the late Mesozoic. The lithosphere of the Daxing’an ranges and its westward part are believed to have mainly experienced an extensional lithospheric thinning and subsequently their thickness reduced just a little in scale. However, the part to east of the Daxing’an Ranges, especially under the Songliao Basin, is thought to have undergone both extensional and thermal-chemical erosion lithospheric thinning, and its thickness decreased dramatically. Inhomogeneous lithospheric thinning may be the vital reason for the different evolution of basins which locate in the two sides of Daxing’an Ranges.更多还原