【作者】 李舢；

【导师】 王涛；

【作者基本信息】 中国地质科学院 ， 矿物学、岩石学、矿床学， 2009， 硕士

【摘要】 北山造山带位于新疆-甘肃-内蒙古交界地区,西邻东天山,东接阿拉善,是中亚造山带南缘增生造山作用和岩浆活动的关键地区之一。在区域地质演化上,早中生代是中亚造山带重要的转折时期,岩浆活动比较明显,因此花岗岩的研究将为中亚造山带岩浆演化和增生造山作用提供新的资料及有价值的参考。本文在前人工作基础上,通过对区内有迹象为早中生代花岗岩的野外特征、岩石学、锆石U-Pb、地球化学及Sr-Nd-Hf同位素研究,并综合分析中亚造山带中南段早中生代花岗岩时空分布特点,得出以下几点认识：1.经过8件样品锆石U-Pb年龄测试,准确厘定了两个中生代花岗岩体(花牛山岩体和大豁落山南岩体)。对花牛山岩体首次进行SHRIMP锆石U-Pb定年,13个点获得了很好的年龄结果为221±3Ma,代表该岩体的形成年龄。采用LA-ICP-MS锆石U-Pb方法对大豁落山南岩体进行年龄测定,19个点206Pb/238U加权平均年龄为238+1Ma,代表岩石的形成年龄。在北山地区众多岩体定年中只厘定了两个中生代岩体,确认了北山地区也存在早中生代花岗岩。然而,早中生代花岗岩分布的规模可能很有限。2.花牛山岩体为准铝质-弱过铝质的高钾钙碱性-碱性花岗岩过渡的特点,具有I型-A型过渡特点的高分异钙碱性花岗岩及A型花岗岩,为A型和钙碱性花岗岩的过渡类型。大豁落山南岩体为后碰撞或后造山高钾钙碱性I型花岗岩。这为I型、I型-A型、A型花岗岩的组合系列及钙碱性.碱性岩浆的连续过渡提供了一个佐证。3.花牛山岩体具有较高的碱性含量(AR=2.94～4.49,σ=1.94～6.37)、TFeO/MgO值(2.8-9.3)、10000×Ga/Al值(2.48-2.93)和分异指数(DI=86.2-95.5),相对富集轻稀土元素(LREE)、大离子亲石元素(Rb、Th、K),而强烈亏损Ba、Sr、P、Ti、Eu元素及弱亏损Ta、Nb元素。该岩体的εNd(t)值为-1.5--2.1,TDM值为0.90～1.04Ga,εHf(t)值为2.94～5.63, TDM2 (Hf)为896.8-1068.8Ma,显示该岩体可能源于幔源岩浆(可能受到陆壳物质的混合)底侵而导致的上覆年轻地壳(可能为洋壳和岛弧建造组成)的部分熔融,并发生了较强的结晶分异作用。大豁落山南岩体具有低硅(SiO2=62.62%～70.52%)、低碱(AR=2.33-2.81,σ=2.65-3.13)、高镁铁质组分,相对明显富集Rb、Th等大离子亲石元素及REE、Zr、Hf等高场强元素,强烈亏损Ba、Ta、Nb、Sr、P、Ti元素的特点,无Eu的负异常或具有弱的Eu负异常,类似后碰撞花岗岩的特点。该岩体εNd(t)为-1.1,TDM为0.99Ga,其成因与花牛山岩体相似,但结晶分异作用较弱。4.结合区域地质演化,岩体特征及地球化学综合分析,认为北山造山带早中生代花岗岩可能形成于造山作用演化晚期阶段,为后碰撞或后造山构造背景。这对于进一步认识北山造山带增生造山作用及构造演化具有重要的参考意义。5.中亚造山带中南段早中生代花岗岩出露在很多岩浆带。依据花岗岩的锆石U-Pb年龄,北蒙古-西外贝加尔带出露210-230 Ma花岗岩；中蒙古带出露241～253Ma,227-230Ma和207-217Ma花岗岩；阿尔泰带出露244～251Ma,225-232Ma,210-221Ma,196-202Ma和182Ma花岗岩;东天山带出露246～253Ma,230-241Ma和209-222Ma花岗岩；北山带出露237～239Ma,220-229Ma花岗岩；内蒙古-吉林带出露234～238Ma,222-230Ma和204Ma花岗岩；华北地块北缘出露234-251Ma,220-229Ma和203-209Ma花岗岩。其中233-240Ma花岗岩出露在东天山、北山、内蒙古-吉林带和华北地块北缘,219-232Ma花岗岩在全区均有出露,210-218Ma花岗岩出露在阿尔泰和中蒙古带。更多还原

【Abstract】 The Beishan orogen is located in the joint areas among the Xinjiang, Gansu and Inner Mongolia Provinces. To its west is the east Tianshan mountain is to west and east is Alashan mountain. This orogen is key areas of the accretionary-collision and magmation in the southern of Central Asian Orogenic Belt. Regional geology show that the early Mesozoic is important period in the Central Asian Orogenic Belt. the study of granite could provide the new data for magmation evolvement and accretionary-collision process in the Central Asian Orogenic Belt.Combined investigations of field observations, petrology, zircon U-Pb, geochemistry, Sr-Nd-Hf isotopes, and spatio-temporal distribution of early Mesozoic granitoids in central and south CAOB, and taking available previous data into account, following results is achieved:1. Two granitic plutons(Huaniushan and Dahuoluoshan pluton) were confirmed as Mesozoic plutons by zircon U-Pb dating. The Huaniushan pluton SHRIMP zircon U-Pb dating yeilded an age of 221±3Ma, which is interpreted as the emplacement age. And the Dahuoluoshan pluton obtained 238±1Ma by LA-ICP-MS zircon U-Pb dating.2. The Huaniushan granitic pluton appears transitions from high K calc-alkaline of metaluminous-weakly peraluminous to alkali, and their rock type changes from I-type to A-type, showing the granitoids have I-A type feature. The Dahuoluoshan pluton belongs to high K calc-alkaline I-type.3. The Huaniushan granitic pluton is characterized by high alkali(AR=2.94～4.49,σ=1.94～6.37) content, high FeOT/MgO(2.8～9.3), high 10000xGa/Al(2.48～2.93) and differentiation index(DI=86.2～95.5) values. The granites shows a little rich of LREE and large iron lithophile elements(Rb, Th, K), an intense depletion in Ba, Sr, P, Ti and Eu, and a low depletion in Ta and Nb. The value ofεNd(t) is -1.5 to-2.1 and TDM 0.90 to 1.04Ga, andεHf(t) is 2.94 to 5.63 and TDM2(Hf) 896.8 to 1068.8Ma, indicating that the granitoids was probably formed by partial melting of younger continental crust, due to underplating mantle-derived magma(maybe contaminated by continental crust). And crystallization differentiation is obvious in the formation of the Huaniushan granitic pluton. During the formation of the Huaniushan granitic pluton, there is a strong crystallization differentiation.The Dahuoluoshan granitic pluton is characterized by low Si(SiO2=62.62%-70.52%), low alkali (AR=3.99～5.05, NK/A>0.85) content, high mafic content. The granites show a rich of REE, Rb, Th, Zr, Hf, an intense depletion in Ba, Ta, Nb, Sr, P and Ti, and unconspicuous to no negative anomaly of Eu, showing post-collision feature. The values ofεNd(t) (-1.1) and TDM(0.99Ga) is similar to that of the Huaniushan pluton, suggesting that they have the similar origin. But, there is a weak crystallization differentiation.4. Based on all above features and the areal geologic evolvement, the early Mesozoic granitic plutons are interpreted as post-orogenic or late stage orogenic pluton and provide important information on the accretionary orogeny and tectonic evolution in Beishan orogen.5. Early Mesozoic granite occur in many magma belts. According to zircon U-Pb ages, the ages of granitic plutons outcropped in North Mongolia belt range during 210-230Ma, Central Mongolia 241-253Ma,227-230Ma and 207-217Ma, Altai 244-251Ma,225-232Ma,210-221Ma,196-202Ma and 182Ma, East Tianshan 246-253Ma,230-241 Ma and 209-222Ma, Beishan 237-239Ma,220-229Ma, Inner Mongolia-Jilin 234-238Ma,222-230Ma and 204Ma, northern North China block 234-251Ma,220-229Ma and 203-209 Ma. In summary, the granitic plutons with ages between 233Ma and 240Ma outcropped in the belts of East Tianshan, Beishan, Inner Mongolia-Jilin and northern North China block, otherwise those with ages 219-232Ma in all belts and 210-218Ma in Altai and Central Mongolia.更多还原