赤峰下马架—刘家营子流纹岩年代学与地球化学特征

发布时间：2018-12-09 07:57

【摘要】：万合永火山盆地位于大兴安岭南段最南端,华北北缘增生带北侧,紧邻西拉沐伦断裂带。盆地基底受古生代近东西向古亚洲洋构造域控制明显,盖层受晚中生代北东向环太平洋构造域影响,因此在其构造活动史上必然受古亚洲构造域和太平洋构造域的双重影响。盆地区内广泛发育晚中生代火山岩,以出露过铝质高钾钙碱性流纹岩组合为特征,呈北东向展布。本文在充分收集整理前人资料的基础上,主要以万合永火山盆地下马架-刘家营子流纹岩为研究对象,利用SHRIMP锆石U-Pb同位素测年技术确定流纹岩的形成时代;通过实测野外地质剖面,查明了岩石组合特征,确定了流纹岩的地层时代归属;最后通过岩石学、岩石地球化学分析,并结合已有区域资料,讨论了流纹岩的岩石成因、物质来源与其形成的构造背景。研究区内主要出露一套中酸性火山岩、火山碎屑岩组合,以盆地内出露的一套紫红色的碎屑岩组合为标志,同时结合下马架-刘家营子流纹岩的年龄数据,将盆地内原属于满克头鄂博组火山岩中的这套紫红色碎屑岩组合划归为土城子组,将其之下的一套中酸性火山岩组合划归入新民组,将其之下的中酸性火山岩组合划归入兴安群。下马架-刘家营子流纹岩SHRIMP锆石U-Pb年龄显示为159.6±1.5Ma,表明晚中生代时期研究区内存在火山-岩浆事件,岩浆活动时间为晚侏罗世。岩石地球化学资料显示,万合永火山盆地钙碱性流纹岩以高硅高钾、贫钙镁为特征,在火山岩TAS图解,流纹岩显示为亚碱性系列。流纹岩分异指数DI值介于89.83~96.32之间,表明在其岩浆演化过程中经历了较高程度的分离结晶作用。稀土元素总量较高,ΣREE值为264.44×10-6~540.98×10-6,轻、重稀土元素分馏较为明显,(La/Yb)N值为5.34~14.46,轻稀土元素明显富集,ΣLREE/ΣHRE值为7.83~10.33,重稀土较为平坦,稀土元素球粒陨石标准化配分模式图显示为典型的轻稀土右倾型,具有强烈的负Eu异常,正Ce异常不明显。微量元素分析显示,流纹岩明显的富集Rb、Zr、Th、Ga、Y等而亏损Ba、Sr、Ti、P等元素,与大兴安岭地区低Ba-Sr流纹岩地球化学特征一致。下马架-刘家营子流纹岩在K2O+Na2O、K2O/Mg O、Zr、Nb-10000Ga/Al以及Fe OT/Mg O、(K2O+Na2O)/Ca O-Zr+Nb+Ce+Y图解上,全部落入到A型花岗岩区域。其Rb/Sr、Ti/Zr、Ti/Y与Th/La比值分别为1.52~10.00、0.01~0.03、0.28~0.39、0.18~1.45,都在壳源岩浆范围内;在Ce/Nb-Th/Nb图解上,样品落入大陆地壳范围内,说明其物质来源与地壳物质相关。在R1-R2以及Nb-Y-3Ga、Nb-Y-Ce图解上,样品落入到后造山花岗岩区域;在Y-Nb与(Y+Nb)-Rb图解上,样品全部落入到板内花岗岩区,表明其应该形成于板块内部造山后的伸展拉张构造环境。综上所述,下马架-刘家营子流纹岩应归属于新民组,形成于晚侏罗世,其物质来源为地壳物质的部分熔融,应该形成于板块内部造山后伸展拉张的构造环境,可能与蒙古-鄂霍茨克洋的演化有关。
[Abstract]:The Wanheyong volcanic basin is located at the southernmost end of the southern part of the Daxinganling Mountains, north of the North China North margin accretive belt, adjacent to the Xilamulun fault zone. The basement of the basin is obviously controlled by the Paleozoic near east-west direction paleo-ocean tectonic domain, and the cover is influenced by the late Mesozoic north-east circumferential Pacific tectonic domain. Therefore, the tectonic activity of the basin is bound to be influenced by the paleo-Asian tectonic domain and the Pacific tectonic domain in the history of its tectonic activity. The late Mesozoic volcanic rocks are widely developed in the basin area, characterized by the outcropping of aluminous high-potassium calc-alkaline rhyolite assemblages, which are distributed in the north to east direction. On the basis of collecting and sorting out the previous data, this paper mainly takes the Xiamajiayingzi rhyolite in the Wanheyong volcanic basin as the research object, and uses the SHRIMP zircon U-Pb isotope dating technique to determine the age of the rhyolite formation. The characteristics of rock assemblage and stratigraphic age of rhyolite are determined by field geological profile. Finally, the petrogenesis, material source and tectonic setting of rhyolite are discussed through petrology, petrogeochemical analysis and regional data. In the study area, a set of intermediate-acid volcanic rocks and volcanic clastic assemblages, marked by a set of purplish red clastic assemblages from the basin, and age data of Xiamaka-Liujiayingzi rhyolite, The fuchsia clastic rock assemblage, which belongs to the volcanic rocks of the Mankitou Obo formation in the basin, is classified as Tuchengzi formation, and a set of intermediate-acid volcanic rock assemblages under the assemblage are classified into the Xinmin formation. The intermediate-acid volcanic rock assemblage under it is classified into the Xingan Group. The SHRIMP zircon U-Pb age of Xiamajiayingzi rhyolite is 159.6 卤1.5 Ma, indicating that there were volcanic-magmatic events in the study area during the late Mesozoic, and the magmatic activity occurred in the late Jurassic. The petrogeochemical data show that the calc-alkaline rhyolite in Wanheyong volcanic basin is characterized by high silicon and high potassium and poor calcium and magnesium. In the TAS diagram of volcanic rocks the rhyolite is subalkaline series. The DI value of the rhyolite differentiation index is between 89.83 and 96.32, which indicates that the rhyolite experienced a high degree of separation and crystallization in the process of magmatic evolution. The total amount of rare earth elements is relatively high, 危 REE value is 264.44 脳 10-6, 540.98 脳 10-6, light, heavy rare earth element fractionation is obvious, (La/Yb) N value is 5.34 ~ 14.46, light rare earth element is obviously enriched, 危 LREE/ 危 HRE value is 7.83 ~ 10.33, The normalized partition pattern of chondrites of rare earth elements shows a typical light rare earth right-dip type with strong negative Eu anomalies and no significant positive Ce anomalies. Trace element analysis shows that rhyolite is obviously enriched in Rb,Zr,Th,Ga,Y and depleted in elements such as Ba,Sr,Ti,P, which is consistent with the geochemical characteristics of low Ba-Sr rhyolite in Daxinganling area. The Liujiayingzi rhyolite all fell into the A-type granite area on the K _ 2O Na2O,K2O/Mg, ZrNb-10000Ga / Al and Fe OT/Mg O, (K _ 2O Na2O) / Ca O-Zr Nb Ce Y diagrams. The ratio of Rb/Sr,Ti/Zr,Ti/Y to Th/La is 1.52U 10.00 0. 01 ~ 0. 03U 0.28 ~ 0. 39 ~ 0. 18 ~ 1. 45, which are within the range of crust-derived magma. In the Ce/Nb-Th/Nb diagram, the samples fall into the continental crust, indicating that the source of the material is related to the crustal material. In the R1-R2 and Nb-Y-3Ga,Nb-Y-Ce diagrams, the samples fall into the post-orogenic granite area. On the Y-Nb and (Y Nb) Rb diagrams, all samples fall into the intraplate granite area, indicating that they should be formed in the extensional and extensional tectonic environment after orogeny within the plate. In conclusion, the rhyolite belongs to the Xinmin formation, formed in the late Jurassic, and originated from the partial melting of the crustal material, and should be formed in the tectonic environment of extension and extension after orogeny within the plate. It may be related to the evolution of Mongol-Okhotsk Ocean.
【学位授予单位】：东华理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.141

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