【作者】 史兴俊；

【导师】 张招崇； 王涛；

【作者基本信息】 中国地质大学(北京) ， 矿物学、岩石学、矿床学， 2012， 硕士

【摘要】 阿拉善地块位于华北地台西部，花岗岩广泛分布，近年来在阿拉善北缘发现了一些花岗岩多形成于晚古生代，这与以往的认识有所不同。本论文在野外地质填图的基础上对阿拉善北部庆格勒地区的花岗岩开展详细的岩石学、年代学、地球化学、全岩Sr-Nd和锆石Hf同位素综合研究，并探讨了其岩石成因。LA-ICP-MS锆石U-Pb定年表明，德尔和通特岩体形成于321±1Ma，早石炭世晚期；哈里努登岩体形成于284±2Ma，属早二叠世，而不是过去认为的志留纪；哈沙图岩体形成于275±1Ma，属早二叠世。结合前人研究成果，阿拉善北缘的花岗岩形成于早石炭世晚期-早二叠世，且多集中于早二叠世，该期花岗岩构成了阿拉善北缘雅布赖-诺尔公-红古尔玉林岩浆岩带的主体。庆格勒地区晚古生代花岗岩主要岩石类型为黑云母二长花岗岩、花岗闪长岩和钾长花岗岩，弱变形，为准铝质-弱过铝质，钙碱性-高钾钙碱性系列，部分达到钾玄岩系列。不含白云母、堇青石等矿物，暗色矿物主要为黑云母及少量角闪石，表明主要为I型花岗岩。这些花岗岩稀土元素总量较低，其中哈沙图岩体轻重稀土分馏不明显（LREE/HREE=1.0¹.7, La/Yb_N=1.3².8），在球粒陨石标准化图解上呈海鸥型，有较明显的铕负异常（δEu=0.07⁰.20），表明其源区有斜长石残留。哈里努登、德尔和通特、牙马图岩体则相对富集轻稀土（La/Yb_N=4.1⁵2.8），球粒陨石标准化图解上呈右倾型，具有较明显的铕正异常或无异常，而且明显高Sr(149.9×10^-6749.4×10^-6)低Y和Yb(Y≤20×10^-6), Yb≤2×10^-6)，显示出类似埃达克质岩石的地球化学特征。Sr-Nd同位素组成显示这些岩体具有低的(⁸⁷Sr/⁸⁶Sr)i值（0.70635⁰.71770），和绝对值较大的负εNd（t）值（-16.4^-8.7），T_DM2为1751²399Ma。锆石Hf同位素分析表明，庆格勒地区花岗岩锆石普遍具有很低的εHf（t）值，εHf（t）值变化范围较大，在-20^-4之间，同时具有较老的二阶段模式年龄，集中于1.5Ga².2Ga。揭示源区主要为古老的地壳物质，可能有少量的幔源物质贡献，证明阿拉善北部存在着古老基底。阿拉善北部陆缘弧可能是在晚古生代期间由古亚洲洋向阿拉善陆块俯冲所形成的，该区花岗岩具有弧花岗岩的特征，部分显示出高分异I型花岗岩特点，表明该区二叠纪是挤压环境向拉张转变的过渡时期。更多还原

【Abstract】 The Alax block located in the west of North China platform, contains lots ofgranites with different epochs.Recent research have showed that there are somePermian granites in the northern margin of Alax, which is different from the previousperspective. This paper made detailed studies on zircon U-Pb chronology,petrology,geochemistry, Sr,Nd and Hf isotopic compositions of the granitoids in theQinggele area. The following achievements and conclusions have been made.LA-ICP-MS U-Pb dating of zircons from the Halinudeng pluton yields an age of284±2Ma,indicating that the formation of this plution is Early Permian.Zircon U-Pbdating yield a206Pb/208Pb age of275±1Ma of Hashatu granitoid and a206Pb/208Pb ageof321±1Ma of Deerhetongte granitoid.Combining other people’s research, the lateCarboniferous-middle Permian granites constituted main body of the northern Alaxmagmatic activity.The main rock types of the northern Alax magmatic rock include biotitemonzogranites, biotite-plagioclase granite and granodiorite. Geochemicalcharacteristics indicate that they are metaluminous-weakly peraluminous(A/CNK=0.98~1.08), calc-alkaline to high-K calc-alkaline rocks (Na~2O=2.5%~4.4%，K~2O=2.1%~7.3%),and the Derhetongte pluton is proved alkaline series.The mineralof the granites did not include cordierite and muscovite, and the main dark mineral isbiotite, as the characteristic of I-type granite.All the rocks have lower REE contents(12~198×10-6),and the Hashatu graniteshow relatively flat REE patterns, without significant fractionations of REEs(LREE/HREE=1.0~1.7, La/YbN=1.3~2.8).It has strength Eu deplete,chondrite-normalized REE pattern is―sea-gull‖type, which means plagioclase left inthe magma chamber.While the other granites is enriched in LREEs(La/YbN=4.1~52.8)， and the chondrite-normalized REE pattern show theright-inclined feature, with significantly positive Eu anomalies (δEu=0.8~1.9),whichmay reflect little plagioclase left in the magma chamber.Besides, most of the granitesare high-Sr (149.9×10-6~749.4×10-6) and low-Yb (Y≤18×10-6, Yb≤1.9×10-6), similarly to the adakites.The granites in Qinggele area has low initial Sr isotopic radios of0.70635~0.71770and variable εNd(t) of-8.7~-16.4,the two-stage Nd depleted-mantlemodel ages(TDM2) range from1.7Ga~2.3Ga.The measurement of zircon Hf isotopic inthe granite exhibits wide range of εHf(t) values (-20~-4),and the relatively old mantlemodel ages(1.5Ga~2.2Ga).The Sr-Nd-Hf isotopic compositions suggest that thegranites were derived from the partial melting of ancient crust probably with littleadditions of mantle material and the northern margin of Alax has old metamorphicbasement.The late Early Carboniferous to Early Permian intrusive rocks are interpreted assubduction related magmatic rocks emplaced in an Andean-style continental marginarc during the southward subduction of the Paleo-Asian oceanic plate beneath theAlax block. The arc-related granite occurred at the structural transition fromcollisional compression to extension tectonic.更多还原