大兴安岭中段五岔沟地区满克头鄂博组火山岩的成因及其构造意义

发布时间：2018-06-05 02:13

本文选题：大兴安岭中段 + 满克头鄂博组　；参考：《吉林大学》2017年硕士论文

【摘要】：本文对大兴安岭中段五岔沟地区满克头鄂博组火山岩进行了LA-ICP-MS锆石U-Pb年代学、全岩地球化学和锆石原位Lu-Hf同位素的测试分析,以便探讨其形成时代、岩石成因、源区性质等方面问题,为更进一步认识大兴安岭晚中生代大规模岩浆活动及其地球动力学背景提供依据。从岩相学来说,五岔沟地区满克头鄂博组火山岩岩石组合为流纹岩、流纹质凝灰岩和少量英安岩。所测四件火山岩样品的锆石呈自形-半自形,发育清晰的振荡生长环带,结合其较高的Th/U比值(0.40~1.54),暗示其典型岩浆成因的特征。LA-ICP-MS锆石U-Pb定年结果表明,五岔沟地区满克头鄂博组火山岩形成于早白垩世早期(143~139Ma)。岩石地球化学方面,满克头鄂博组火山岩具有高硅(SiO2=66.70~79.91 wt.%),富碱(Na2O+K2O=5.93~9.72 wt.%),贫镁(MgO=0.08~1.15wt.%)、铁(TFeO=0.68~4.50 wt.%)、钙(CaO=0.10~2.56 wt.%)的特征,总体为高钾钙碱性准铝质至弱过铝质岩石。这些火山岩富集大离子亲石元素(如Rb、Th、U等)和轻稀土元素,亏损高场强元素(如Nb、Ta、Ti等)和重稀土元素,具有高分异I型火山岩的特征。此外,满克头鄂博组火山岩锆石具有较高的176Hf/177Hf比值(0.282900~0.283093),正的εHf(t)值(+7.48~+14.19),年轻的二阶段Hf模式年龄(954~344Ma),表明满克头鄂博组火山岩源于新元古代—显生宙期间从亏损地幔中新增生地壳物质的部分熔融。在本文研究基础上,并结合东北地区中生代火山岩的时空分布规律,认为早白垩世期间大兴安岭地区可能受蒙古-鄂霍茨克洋闭合和古太平洋俯冲的双重影响,此时处于蒙古-鄂霍茨克构造域向古太平洋构造域转化的关键时期,在早白垩世早期主要受蒙古-鄂霍茨克洋闭合后岩石圈伸展作用的影响,在早白垩世早期之后主要受古太平洋俯冲的控制。
[Abstract]:In this paper, the LA-ICP-MS zircon U-Pb chronology, whole rock geochemistry and zircon in situ Lu-Hf isotopes of the volcanic rocks of the Mankitou Ebo formation in the Wuchagou formation of the central Daxinganling region have been measured and analyzed in order to discuss the formation age and petrogenesis of the volcanic rocks. The characteristics of the source region provide a basis for further understanding of the late Mesozoic magmatic activities and their geodynamic background in the Daxinganling Mountains. In terms of petrography, the volcanic rock assemblage of Mancitou Obo formation in Wuchaigou area is composed of rhyolite, streamline tuff and a small amount of dolomite. The zircon of the four volcanic rock samples showed a self-shape and semi-automorphism with a distinct oscillatory growth ring and a high Th/U ratio of 0.400.401.54, indicating the characteristics of its typical magmatic genesis. LA-ICP-MS zircon U-Pb dating results show that, The volcanic rocks of the Mankitou Ebo formation in Wuchaigou area were formed in early Cretaceous of the early Cretaceous. In terms of rock geochemistry, the volcanic rocks of the Orbo formation in Mankitou have the characteristics of high SiO2SiO66.7079.91wt., alkali-rich Na2O K2O=5.93~9.72 wt., magnesium-poor MgO0.081.15wt., TFeOO 0.68,4.50wt.batt, calcium CaO0.10n2.56wt.), which are generally high potassium calc-alkaline quasaluminite to weakly peraluminous rocks. These volcanic rocks are rich in large ion lithophile elements (such as RbPU, etc.) and light rare earth elements, depleted in high field strength elements (such as NbPU, Ti, etc.) and heavy rare earth elements, and are characterized by high differentiation I type volcanic rocks. In addition, The zircon of the volcanic rocks in Mankitou Ebo formation has a high 176Hf/177Hf ratio of 0.282900 (0.283093) and a positive 蔚 Hfft (7.48 ~ 14.19). The age of the young two-stage HF model is 954 ~ 344 Ma, which indicates that the volcanic rocks of the Orbo formation originated from the Neoproterozoic to Phanerozoic period and were newly added from the depleted mantle during the Neoproterozoic to Phanerozoic period. Partial melting of raw crust material. On the basis of this study and the temporal and spatial distribution of Mesozoic volcanic rocks in Northeast China, it is considered that the Daxinganling area during the early Cretaceous was affected by the closure of Mongolia-Okhotsk Ocean and the subduction of the Paleo-Pacific Ocean. At this time, it is in the key period of the transformation from Mongolia-Okhotsk tectonic domain to paleo-Pacific tectonic domain. In the early Cretaceous, it was mainly influenced by the lithospheric extension after the closure of the Mongolia-Okhotsk Ocean. After the early Cretaceous, it was mainly controlled by the paleo-Pacific subduction.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P588.14

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