【作者】 郭芳放；

【导师】 姜常义；

【作者基本信息】 长安大学 ， 矿物学、岩石学、矿床学， 2011， 硕士

【摘要】 中坡山北和红石山镁铁.超镁铁层状岩体中出露一系列与其有密切时、空联系的花岗岩脉,岩性主要为黑云母花岗岩脉、石英闪长玢岩、钾长花岗岩和花岗斑岩四种,前两种岩性分布于坡北岩体内,后两种岩性分布于红石山岩体内。黑云母花岗岩和钾长花岗岩同为过铝质,岩石化学属钾玄岩系列,稀土元素配分曲线为轻稀土元素富集型,并具有具明显的负Eu异常；富集大离子亲石元素,在多元素配分曲线上,Nb、K20表现为小的低谷,显著亏损P205、Ti02,均属A型花岗岩。黑云母花岗岩的εNd值为-4.54,ISr因低于0.7000而无使用意义,钾长花岗岩εNd值为.5.53,ISr为0.7090,在(207Pb/204Pb)i.(206Pb/204Pb)i相关图中,二者样品均落在EMⅡ和MORB之间。因此,它们应为古老地壳物质在幔源岩浆加热下部分熔融的产物,在形成过程中可能有少量幔源物质的加入。石英闪长玢岩中角闪石以褐色角闪石为主,Si/(Si+Ti+Al)小于0.765,属幔源角闪石,并与层状岩体中以斜长石为堆晶相的石英闪长岩地球化学特征相似,是较为少见的幔源M型花岗岩。在Haker图解中,石英闪长玢岩和石英闪长岩样品与镁铁.超镁铁岩石样品构成良好的分异演化趋势,说明二者均为镁铁质岩浆演化末期的产物。石英闪长玢岩的εNd值为.2.67和-2.61,而样品在(207Pb/204Pb)i.(206Pb/204Pb)i相关图中落在靠近BSE区域的位置,这可能是因为同化混染作用对Pb元素影响较小,而对Nd、Sr影响较大的缘故。花岗斑岩Si02含量较高,K20/Na2O比值均小于1,Ga/Al比值和Zr+Nb+Ce+Y值均低于A型花岗岩的下限值,且P205与Si02呈负相关关系,属Ⅰ型花岗岩。花岗斑岩的εNd值为.0.13-0.77,在Nd、Sr同位素相关图中,与红石山橄榄辉长岩样品和钾长花岗岩样品构成良好的演化趋势,且花岗斑岩样品在(207Pb/204Pb)i.(206Pb/204Pb)i相关图中落在MORB区域边缘,说明花岗斑岩应为幔源岩浆与其诱发的地壳物质部分熔融后形成的长英质岩浆均一混合的结果。综上所述,幔源岩浆不但可以提供花岗岩形成所需的热能,同时也可以在一定程度上为花岗岩提供物源,在同一环境、同一时间形成-M-A花岗岩共生组合。更多还原

【Abstract】 Numerous Permian granitic dykes are spatially and temporally associated with the Zhongposhanbei and Hongshishan mafic-ultramafic layered intrusions. There are four types of granitic dykes totally, including biotite granite, quartz diorite porphyrite, moyite and granite porphyry. The former two are distributed in the Pobei intrusion and the latter two in the Hongshishan intrusion.Both biotite granite and moyite belong to the shoshonite series, they are enriched in LREE and LILE, obviously depleted in Eu, P2O5 and TiO2, relatively depleted in Nb and K2O, and both of them are A-type granites. TheεNd and Isr values of the biotite granite and moyite range from -4.54 to -5.53, and 0.6999 to 0.7090 respectively, but Isr value of the biotite granite is lower than 0.7000, and thus has no geological meaning. All the samples are distributed between EMⅡand MORB field in the (207Pb/204Pb)i vs. (206Pb/204Pb)i diagram, hence they should be the products of partial melting of old crust heated by mantle derived magmas, and there might be some mantle derived materials involved in this process.Amphiboles in quartz diorite porphyrite are mainly brown amphiboles. These amphiboles have low Si/(Si+Ti+Al) values (lower than 0.765), indicating mantle origin. The geochemical characteristics of the quartz diorite porphyry are similar to the cumulus plagioclase bearing quartz diorite in the layered intrusion, and the quartz diorite should be M-type granite. Samples of quartz diorite porphyry, quartz diorite and mafic rocks compose a well fractionate trend on the Harker diagrams, which indicate that the quartz diorite porphyry and quartz diorite should be products formed at the end of the evolution of mafic magma. TheεNd values of the quartz diorite range from -2.67 to -2.61, indicating crustal contamination. But in the (207Pb/204Pb)i vs (206Pb/204Pb)i diagram, the samples lie near the BSE area, indicating insignificant involvement of crustal materials. This may be due to less effection of Pb isotopes than that of Nd and Sr isotopes in the process of crustal contamination.The granite porphyry belong to I-type granites evidenced by high SiO2 contents, low ratios (<1), low Ga/Al ratios and Zr+Nb+Ce+Y values and negative correlation between P2O5 and SiO2.TheεNd values of granite porphyry are 0.13～0.77, distributing near the MORB area, and composing a well fractionate trend in the Nd-Sr isotope diagram together with samples of olivine gabbro and moyite, which indicate that the granite porphyry may be generated by mixing of a mantle-derived magma and a felsic magma which originated from partial melting of ancient crust heated by underplating of mantle-derived magmas.In conclusion, the mantle-derived magma can not only provide the heat source for the granites, but also can provide materials for the granites to some extend, and thus I-M-A type granites can be formed in the same environment at the same time.更多还原