内蒙古五十家子地区中生代花岗岩地质特征及形成构造背景

发布时间：2018-03-19 09:40

本文选题：大兴安岭中南段　切入点：晚中生代　出处：《吉林大学》2016年硕士论文　论文类型：学位论文

【摘要】：大兴安岭地区中生代岩浆活动十分强烈,构成了这一地区岩浆岩带主体。前人对大兴安岭花岗岩的研究比较集中在北部地区,对于大兴安岭中南部地区缺乏系统研究,对大兴安岭乃至整个中国东部中生代地质构造演化认识起着严重的制约作用。本文以大兴安岭中南段林西五十家子地区中生代花岗岩为研究对象,通过元素地球化学、岩石学以及同位素年代学,探讨以五十家子地区中生代花岗岩形成的地球动力学背景、岩体地质特征、以及花岗岩源岩的形成。林西五十家子地区中生代花岗岩体主要有三个:朝阳沟花岗岩体、胡都格绍荣花岗岩体以及巴彦琥硕花岗岩体。通过讨论五十家地区中生代花岗岩的岩石类型及成因,最后深入研究这一地区晚中生代的构造演化。1、从时间上看,锆石U-Pb定年结果显示朝阳沟花岗岩体年龄为126.2±2.5Ma、胡都格绍荣花岗岩体年龄为129.9±1.4Ma、巴彦琥硕岩体年龄为150±1Ma,形成于为晚侏罗世-早白垩世期间。大兴安岭地区中生代岩浆活动主要集中在侏罗纪和白垩纪两个时期。2、对朝阳沟、胡都格绍荣和巴彦琥硕花岗岩体的主量、微量以及稀有元素的地球化学特征进行对比发现,它们三者具有一定的相似性,都表现富硅、富碱、贫水等特征。在A/CNK-A/NK图解及SiO2-K2O图解中,三者都属于高钾钙碱性铝质岩石系列。尤其是在稀土元素的配分模式形态上、斜率以及倾斜方向上比较一致。轻稀土元素(LREE)较富集,重稀土元素(HREE)较亏损,存在明显的Eu负异常。Sr、Ba、P等元素强烈亏损,Rb、Th等元素的富集。说明三者之间具有较好的亲缘关系。3、通过对胡都格绍荣岩体和巴彦琥硕岩体进行Hf同位素分析,显示胡都格绍荣花岗岩体的锆石具有正的εHf(t)值(+2.2~+9.4),Hf两阶段模式(TDM2)年为1030~570Ma,平均808.7Ma;巴彦琥硕花岗岩体的具有正的εHf(t)值(6.1~12.3),对应二阶段模式年龄(TDM2)为415~810Ma,平均为666.9Ma。结合两者的Th/U、Nb/Ta比值特征,区内中生代花岗岩岩浆源区为新元古代亏损地幔物质,在后期侵位上涌过程中与年轻地壳发生混染熔融形成。4、区内的三个中生代岩体均为A型花岗岩,结合周围广泛出露的碱性岩石和中基性-酸性岩脉群,大兴安岭中南段地区在早白垩世应该处于伸展构造环境。晚侏罗世-早白垩世为大兴安岭地区由挤压向伸展转换的过渡期。区内晚侏罗世花岗岩受早期蒙古-鄂霍茨克构造作用影响,形成于挤压向伸展构造环境转换的过渡期;早白垩世花岗岩则受环太平洋西向俯冲构造作用,碰撞挤压使得加厚岩石圈发生拆沉熔融形成的,为伸展背景下产物。
[Abstract]:The Mesozoic magmatic activity in the Daxinganling area is very strong, forming the main body of the magmatic rock belt in this area. The previous studies of the granites in the Daxinganling Mountains are concentrated in the northern region, but there is no systematic study on the central and southern part of the Daxinganling Mountains. In this paper, the Mesozoic granites in Linxi 50 Jiazi area of the central and southern part of the Daxing'anling Mountains are taken as the objects of study, and through element geochemistry, the Mesozoic granites in the Mesozoic tectonic evolution of the Daxing'anling Mountains and the whole East of China are seriously restricted. Petrology and isotopic chronology, the geodynamic background and geological characteristics of the Mesozoic granites formed in the 50 Jiazi area are discussed. And the formation of granite source rocks. There are three main Mesozoic granitic bodies in the 50 Jiazi area, Linxi: Chaoyang ditch granitic body, The Huduge Shaorong granite body and the Bayan susuo granite body. By discussing the rock types and genesis of the Mesozoic granites in 50 regions, the tectonic evolution of the late Mesozoic in this area is studied in depth. The zircon U-Pb dating results show that the age of Chaoyang Gou granite body is 126.2 卤2.5 Ma., that of Huduge Shaorong granite body is 129.9 卤1.4 Ma. and that of Bayansuo granite body is 150 卤1 Ma. it was formed during the late Jurassic-early Cretaceous period. The Mesozoic magma in the Daxinganling area. The activities are mainly concentrated in the Jurassic and Cretaceous periods. The geochemical characteristics of the principal, trace and rare elements of the Hu Duge Shaorong and Bayan Shuo granites have been compared. It is found that the three have certain similarities, all of which are rich in silicon and alkali, In the A / CNK-A / NK diagram and the SiO2-K2O diagram, they all belong to the high-potassium calc-alkaline aluminous rock series, especially in the distribution pattern, slope and inclined direction of the rare earth elements. The heavy rare earth element (HREE) is relatively depleted, and there is obvious negative EU anomaly. SrPbBa-P and other elements are strongly depleted in the enrichment of RbTh and so on. It shows that there is a good genetic relationship between the three elements. The HF isotopic analysis of the Huduge Shaorong and Bayanhushuo rock bodies is carried out, and the results show that there is a good relationship between the three elements. The results show that the zircon of Huduge Shaorong granite body has positive 蔚 HfT) value (2.29.4Hf two-stage model TDM2) is 1030U 570Mawith an average of 808.7Ma.The value of positive 蔚 Hfttof the Bazugeshaorong granite body is 6.112.3, corresponding to the two-stage model age of TDM2 is 415U 810Ma, with an average of 666.9Ma. the average value of zircon from the Huduge Shaorong granite body is 66.9Ma. the mean value of the zircon from the Huduge Shaorong granite body is 6.112.3a, with an average of 666.9Ma. The characteristics of the ratio of Thr / U and NB / Ta, The Mesozoic granitic magma source area is a Neoproterozoic depleted mantle material. During the late emplacement upwelling process, the magma source of the Mesozoic granites mixed with the young crust formed .4. the three Mesozoic rocks in the area are all A-type granites. Combined with widely exposed alkaline rocks and intermediate-acid vein groups, The central and southern part of the Daxing'an Mountains should be in an extensional tectonic environment in the early Cretaceous. The late Jurassic-early Cretaceous is the transition period from compression to extension in the Daxinganling area. The late Jurassic granites in the region were subjected to early Mongolia-Hubei Province. The influence of Holtzke tectonism, The early Cretaceous granites were formed by the westward subduction structure of the circumferential Pacific Ocean, and the thicken lithosphere was formed by collision and extrusion, which is the product of extensional background.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P588.121;P548

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