【作者】 陈飞；

【导师】 和钟铧；

【作者基本信息】 吉林大学 ， 矿物学、岩石学、矿床学， 2016， 硕士

【摘要】 本文以内蒙古塔尔气地区花岗斑岩为研究对象,在野外地质调查的基础上,对塔尔气地区花岗斑岩进行了锆石U-Pb年龄和Hf同位素和稀土及微量元素的测定,进而确定研究区花岗斑岩的形成时代,并进一步讨论研究区花岗斑岩岩浆源区性质、岩石成因以及这些花岗斑岩所代表的构造背景。对采自研究区不同花岗斑岩岩体的三组样品进行了LA-ICPMS锆石U-Pb同位素分析,测年结果显示这些花岗斑岩形成于早白垩世阶段,分别为早白垩世早期阶段(136.5±1.3 Ma)和早白垩世晚期阶段(127.2±1.5 Ma、126.4±1.3 Ma)。研究区花岗斑岩主量元素表现出高硅、富碱,弱过铝质(A/CNK=1.0~1.29),高演化的特征,属于高钾钙碱性系列。稀土配分形式为典型的酸性火成岩的配分形式,整体表现为左高右低的形态,显示本区花岗斑岩轻稀土含量较高,重稀土含量相对较低,铕亏损显著,表明代表花岗斑岩的岩浆经历了斜长石的分离结晶或者是源区物质中有大量的斜长石残留。在微量元素Spider图解可以看出研究区花岗斑岩岩浆相对富集钾、铷、钍、铀,亏损钡、锶、铌、钽、钛,类似于大兴安岭地区低锶I型花岗岩。在花岗岩成因判别图中落入高分异的I型花岗岩区域,表明研究区花岗斑岩属于高分异的低锶I型花岗斑岩。在与同期白音高老组火山岩对比中发现本区至少有一部分花岗斑岩和白音高老组火山岩是同源同期的岩浆活动的产物。锆石Hf同位素组成特征显示大部分的花岗斑岩具有较高的εHf(t)值(+7.2~+7.3),二阶段模式年龄为851 Ma~569 Ma,仅有两颗锆石的εHf(t)值为负值-15.3和-15.6,二阶段模式年龄为2184 Ma和2162 Ma,暗示其可能起源于新元古代-早古生代期间从亏损地幔增生的地壳物质的部分熔融,同时可能有其它老的地壳物质的加入。结合构造判别图解和大兴安岭地区晚中生代的构造背景,本区花岗斑岩可能形成于古太平洋板块向欧亚板块下俯冲的伸展构造背景,同时可能受蒙古-鄂霍茨克构造体系的影响。更多还原

【Abstract】 This paper summarizes the characteristics of zircon U-Pb ages, the Hf isotope,geochemistry of the granitic porphyry in Taerqi, Inner Mongolia and determine the formation age of the granitic porphyry,discuss its petrogenesis and tectonic setting.The LA-ICP-MS zircon U-Pb dating results of the three samples indicate that granitic porphyry formed in early cretaceous,respectively early Early Cretaceous(136.5±1.3Ma) and late Early Cretaceous(127.2±1.5Ma,126.4±1.3Ma).The analysis of geo-chemical data show that granitic porphyry is characterized by high silicon, alkali-rich, show metaluminous to weakly peraluminous attribute(A/CNK=1.0~1.29) and high differential degree, Which belongs to high-k calc-alkaline series. Granitic porphyry has rich LREE with steep right_dipping REE distribution curves, LREE and HREE fractionation is obvious, HREE fractionation is not that obvious which is mild concave. The samples show strong depletion of Eu which indicate that Magma source area has residual plagioclase or experienced separation of plagioclase crystallization during magma evolution.In a Spider diagram of trace element can be seen in the study area with rich granitic porphyry magma K, Rb, Th, U, depleted of Ba, Si, Nb, Ta, Ti, similar to the low strontium I type granite in greate Xi`an Range.The samples fall into high differentiation I-type granite area in the granite genesis discriminant diagram,show that they are belong to low strontium I type granitic porphyry of high differentiation. We found that at least some of granitic porphyry have the same period and source with Baiyingaolao Formation in this area.Zircon characteristics of Hf isotopic compositions suggest that most of the granitic porphyry have high εHf(t) =(+7.2~+7.3) and TDM2= 851Ma~569Ma, Only two of the zircon εHf(t) < 0(-15.3 and-15.6) and older two-phase model age(2184 Ma,2162 Ma),which implies these granitic porphyry might be the partial meltdown of the crustal substance from depleted mantle during Neoproterozoic-Early Palaeozoic, at the same time may have old crustal materia’s participation.Combining with tectonic discrimination diagrams and regional tectonic settings, granitic porphyry in this area could be formed in the Extensional Setting of subduction of the Paleo-Pacific plate to the Eurasian plate, At the same time may affected by Mongolia-Okhotsk ocean tectonic system.更多还原