【作者】 周漪；

【导师】 葛文春；

【作者基本信息】 吉林大学 ， 地球化学， 2012， 硕士

【摘要】 随着地球化学的发展，近20年来中外学者对中国东部地区中-新生代玄武岩的研究愈加深入，并取得了丰富的科研成果。中国东部新生代发生大量火山活动，在东北、华北等地区形成了巨量的火山岩。而其中新生代大陆裂谷型汉诺坝玄武岩是多年来中外学者共同关心的热点之一。赤峰新生代玄武岩区，大地构造位置处于华北克拉通与兴蒙造山带的交界处，为华北克拉通北缘呈东西向展布的早古生代的增生造山带。赤峰新生代玄武岩区属于广义的汉诺坝玄武岩，前人的研究大量的数据都是来自狭义的汉诺坝玄武岩，忽略了内蒙古及周边地区广泛意义上汉诺坝玄武岩的研究，尤其是赤峰地区大面积的分布的新生代玄武岩的研究，那么这些玄武质岩石的成因、源区性质及动力学背景如何？赤峰新生代玄武岩的形成与邻近地区新生代玄武岩之间的演化有何关系？并且内蒙古东部地区新生代玄武岩和汉诺坝玄武岩的研究基础良好，而赤峰汉诺坝玄武岩与前人研究相比差距明显。所以基于以上的想法，本文选择位于内蒙古赤峰市之北，行政区划属内蒙古自治区赤峰市克什克腾旗和翁牛特旗管辖，东经118°00′—118°30′，北纬42°50′－43°10′范围内的汉诺坝玄武岩作为研究对象，通过详细的野外路线地质调查，系统采集样品，对玄武岩进行了岩石学和地球化学以及全岩的Sr-Nd-Hf同位素的研究，确定了赤峰汉诺坝玄武岩成因，探讨了玄武岩岩浆源区性质，然后通过对比周边新生代玄武岩探讨了华北北缘岩石圈地幔组成。1、赤峰新生代汉诺坝玄武岩岩石学特征赤峰地区汉诺坝玄武岩主要岩石组合类型是伊丁石化橄榄玄武岩、伊丁石化橄榄辉石玄武岩和辉石玄武岩等。所采集的岩石手标本颜色一般为灰黑色-黑色、灰紫色，斑状结构或显微斑状结构，基质为隐晶质结构，致密块状、气孔杏仁状构造。斑晶由橄榄石组成，偶见有少量的斜长石和辉石。薄片镜下观察可见其橄榄石斑晶呈他形粒状，常见有熔蚀现象，并多已发生伊丁石化、皂石化等蚀变。辉石斑晶多为半自形粒状，也有熔蚀现象。偶见具有环带的自形辉石斑晶。斜长石斑晶比较发育，自形-办自形柱状呈聚片双晶发育。基质多为显微晶质-隐晶质，由细小的橄榄石、斜长石、辉石、不透明矿物以及火山玻璃等组成。2、赤峰新生代汉诺坝玄武岩地球化学及Sr-Nd-Hf同位素特征赤峰新生代汉诺坝玄武岩通过主量元素换算成CIPW投图，分成两组：1组橄榄拉斑玄武岩和2组石英拉斑玄武岩。两组玄武岩具有比较相似的主量元素特征， SiO₂含量为46%～52%；Na₂O+K₂O含量为3.1%～5.3%，大部分在4.0%～5.0%之间，MgO含量相对较高且变化范围较大（4.14%-10.57%），Mg#值为49.1～62.1，暗示部分样品可能接近于原生岩浆。Harker图解显示，MgO-SiO₂、Al₂O₃、CaO、 Fe₂O₃有大致的相关性，而在MgO-K₂O、TiO₂、P₂O₅则表现出了不同的趋势，反映了两组玄武岩并没有明显的结晶分异演化趋势。赤峰新生代汉诺坝玄武岩稀土显示均有轻稀土富集的特征，明显Eu的正异常。石英拉斑玄武岩则具有低的稀土元素含量∑REE=44.4～145.6μg/g，平均为70.5μg/g，轻、重稀土分异（La/Yb）_N=3.2～10.3，平均为5.2；橄榄拉斑玄武岩具有高的稀土元素含量∑REE=63.2～136.5μg/g，平均为85.7μg/g，轻、重稀土分异（La/Yb）_N=5.1～7.5，平均为6.7。从整体上看研究区赤峰汉诺坝玄武岩中从橄榄拉斑玄武岩到石英拉斑玄武岩显示了一种轻稀土元素含量降低，重稀土元素含量增高的趋势；微量元素则显示具有相对一致的微量元素配分型式，配分曲线呈右倾型，富集Rb、Ba、Sr等大离子亲石元素，具有明显的Nb、Ta的正异常，与洋岛玄武岩的分配模式相似。我们挑选了7个样品进行Sr-Nd-Hf分析测试。所测样品具有高的¹⁴³Nd/¹⁴⁴Nd比值范围在0.512822-0.512934之间，而(⁸⁷Sr/⁸⁶Sr)i比值范围在0.703695-0.704315之间，εNd（t）值在3.59-5.77之间变化。样品的Lu-Hf同位素结果表明赤峰汉诺坝玄武岩具有类似的Hf同位素组成，并与Nd同位素有很好的正相关关系。样品¹⁷⁶Hf/¹⁷⁷Hf初始比值也比较集中，其范围在0.282969-0.283063，εHf（t）值从+6.89-+10.3。3、赤峰新生代汉诺坝玄武岩的成因赤峰汉诺坝玄武岩具有原生岩浆属性，其Nb/U和La/Nb比值都在OIB范围以内，微量元素蛛网图中显示明显Nb和Ta正异常，Sr-Nd-Hf同位素具有OIB特征，表明赤峰汉诺坝玄武岩具有软流圈来源的性质，并且没有受到明显的地壳混染。La-La/Sm图解中显示明显的正相关说明部分熔融作用是玄武岩成分变化主要影响因素， Ni-Mg^#和CaO/Al₂O₃-CaO的投图中呈现出正相关系说明在玄武岩浆形成后上升过程中，经历了单斜辉石与橄榄石的分离结晶。4、赤峰新生代汉诺坝玄武岩岩浆源区及性质赤峰汉诺坝玄武岩具有高Rb/Nb和Ba/Th比值类似EMⅠ型的洋岛玄武的特征，而在Zr/Nb-Ba/Nb投图中也落入EMⅠ型的洋岛玄武附近，暗示了其成岩过程中可能有来自岩石圈地幔的贡献。Sr-Nd-Hf同位素的研究表明两类玄武岩在EMI与DMM两个地幔端元之间呈连续变化的特征，且变化趋势相同，这暗示我们两者之间的地球化学差异可能是EMI与DMM地幔熔体参与混合的比例不同所致。根据CIPW标准矿物模拟计算玄武岩的起源深度：橄榄拉斑玄武岩的形成深度大约在70km左右，而石英拉斑玄武岩的形成深度大约在60km左右5、赤峰新生代汉诺坝玄武岩形成的深部过程赤峰汉诺坝玄武岩1组和2组玄武岩具有相同或相似的源区组成，但并不是单一岩浆的产物，根据模拟可能代表了一个熔融柱在不同压力下形成的岩浆的产物或称为变压熔融柱产物，然而由于赤峰汉诺坝玄武岩需要岩石圈-软流圈相互作用，我们采用了Perry et al（1987）提出的所谓“布丁”模型来解释其深部动力学。最后从岩石学，地球化学及Sr-Nd-Hf同位素角度，通过对比赤峰汉诺坝玄武岩与周边新生代玄武岩区，我们得到如下结论：赤峰-汉诺坝-集宁-天和永一线即华北北缘新生代玄武岩区源区组分应该是DMM-EMⅠ混合产物，形成不同的玄武岩的原因是地幔两个端元组分混合的比例不同所致，并且岩石圈减薄强度自西向东呈增强的趋势；而内蒙古阿巴嘎-外蒙古达里冈爱新生代玄武岩区源区组分是DMM-EMⅡ混合产物，这可能意味着赤峰和阿巴嘎之间，以西拉木伦河断裂为界，两侧的岩石圈地幔属性不同。更多还原

【Abstract】 In the past20years, the development of geochemical makes scholars have evenmore depth-the study of the Cenozoic basalts in eastern China （East Asia）, and obtain awealth of scientific research. China ’s volcano activity, a lot of volcanic rock in thenortheast china, north china and other regions during the Cenozoic. The Cenozoiccontinental rift type Hannuoba basalt was for many years the Chinese and foreign scholarsfocus of common concern. Cenozoic basalts from Chifeng area, tectonic position located atthe juncture of North China Craton and the Da hinggan MTS.-Mongolia orogenic belt, asthe northern margin of the early Paleozoic North China Craton accretion-type Orogen.Chifeng Cenozoic basalts are belongs to the generalized Hannuoba basalt, Previous studiesof large amounts of data are from the narrow sense of the Hannuoba basalt, ignoring theInner Mongolia and the surrounding areas of broad sense of the Hannuoba basalt research,Especially in Chifeng Cenozoic basalt research.How the magmatism in the process of thesebasaltic rocks? What the magma source and Geodynamic environment of these basalticrocks? What is the relationship between the the Chifeng Cenozoic basalts and theneighboring regions of Cenozoic basalts? And the research base of the eastern InnerMongolia region of Cenozoic basalts and Hannuoba basalt, while the Chifeng Hannuobabasalt compared to the gap significantly. Based on the above idea, this paper choose inNorth of Chifeng City, Inner Mongolia, E118°00′—118°30′，N42°50′－43°10′Hannuobabasalt as the object of study. Through detailed field geological survey line,systematic sampling, on the petrology,geochemistry and whole rock Sr-Nd-Hf isotope research tomake sure the genesis and magma source of the chifeng hanhuoba basalt, then through thecontrast of the surrounding Cenozoic basalts to discuss on northern margin of North Chinalithosphere mantle composition.1、petrology of the Chifeng Cenozoic Hannuoba basaltPetrological characteristics show that there exist such basalt rock types asiddingsite olivine basalt, iddingsite olivine pyroxene basalt and pyroxene basalt. Thehand specimen colour is generally black, Porphyritic texture Matrix, is cryptocrystallinetexture, massive structure. Phenocrysts mainly about olivine, followed by small amountsof plagioclase and clinopyroxene.2、Geochemistry of Chifeng Cenozoic Hannuoba basalt and Sr-Nd-Hf isotope of WholerockMajor elements of Chifeng Cenozoic Hannuoba basalt are translated into CIPWand then divided into two groups.1group is olivine tholeiite and2group is quartz tholeiite.Two groups of basalt has quite similar to the major element characteristics. SiO₂contentsranging from46wt%to52wt%,Na₂O+K₂O ratios being between3.1%～5.3%.MgOcontents and Mg^#values ranging from4.14%to10.57%and from49.1to62.1,. In theHarker diagram,it can be seen that the contents of SiO₂、Al₂O₃、Na₂O decrease linearlyfollowing the increase of MgO contents,but contents of K₂O、TiO₂、P₂O₅No correlationlinearly following the increase of MgO contents showing No correlation with fractionalcrystallization..The Chifeng Cenozoic Hannuoba basalt rare display was light REE enrichmentcharacteristics,obvious Eu positive anomaly. Quartz tholeiite has a low content of rare earthelements The ΣREE=44.4¹45.6μg/g, an average of70.5μg/g, REE fractionation （La/Yb）_N=3.2to10.3, an average of5.2; olive tholeiitic basalt has a high content of rare earthelements the ΣREE=63.2¹36.5μg/g, the average is85.7μg/g, light, REE fractionation （La/Yb） N=5.1⁷.5, an average of6.7. From the olives tholeiite to quartz tholeiite ofthe Chifeng Hannuoba basalt shows a LREE contents lower but HREE content is slightlyhigher trend. The trace elements are displayed with a relatively consistent patterns, showssimilar right-dipping forms, enriched in large ion lithophile elements （LILE）such asRb,Ba,and Sr, Nb and Ta elements for the basalt show obvious positive anomalies in thespider diagram. Similar to the distribution patterns of oceanic island basaltsWe selected7samples for Sr-Nd-Hf analysis test. The Chifeng Cenozoic Hannuobabasalt have high¹⁴³Nd/¹⁴⁴Nd ratios（0.512822-0.512934） and (⁸⁷Sr/⁸⁶Sr)iratios（0.703695-0.704315）, ε_Nd（t） values（3.59-5.77）. Samples of Lu-Hf isotope results show thatChifeng Hannuoba basalt with similar Hf isotopic composition, And have a good positivecorrelation with Nd isotopes.176Hf/177Hf ratios,ranging from0.282969to0.283063,εHf（t） values（+6.89-+10.3）3、Petrogenesis of Chifeng Cenozoic Hannuoba basaltChifeng Hannuoba basalt has the primary magma attribute, its Nb/U and La/Nbratio in the OIB range, Nb and Ta elements for the basalt show obvious positive anomaliesin the spider diagram, Sr-Nd-Hf isotope with OIB characteristics, indicating that the theChifeng Hannuoba basalts from the sources of the asthenosphere. which reflects invisiblecrustal contamination and represents the isotope composition of mantle source. La-La/Smdiagrams showed significantly positive correlation,which infer that partial melting is themain factors affecting the changes in basalt composition. The voted diagram of the Ni-Mg^#and CaO/Al₂O₃-CaO, showing a positive correlation illustrate that basaltic magmaExperienced clinopyroxene and olivine fractionation crystallization during magma ascent.4、Magma source and Source characteristics of Chifeng Cenozoic Hannuoba basaltChifeng Hannuoba basalt has a high Rb/Nb and Ba/Th ratio similar to EM I typeoceanic island basalt.. In the Zr/Nb-Ba/Nb Figure also fall into the EM I type of oceanicisland basalt. Implies that there exist a lot of lithospheric mantle material in the reservoir. Sr-Nd-Hf isotope studies have shown that two types of basalt was the continuous changesin the characteristics between EMI and DMM mantle end-members and have the samethrend. The difference between two type basalt may be just due to the EMI and DMM-typemantle melt in a mixture of different proportions. According to the CIPW standard mineralsimulated basalt depth of origin: olivine tholeiite formed about the depth of about70km,and quartz tholeiite formation depth at about60km.5、Deep process of Chifeng Cenozoic Hannuoba basaltThe two groups of the Chifeng Hannuoba basalts may be from the same or similarsource region, But not comagmatic products. According to the simulation may berepresented by a column under different pressure of molten magma product or pressuremelting column product. However, due to the Chifeng Hannuoba basalt need thelithosphere-asthenosphere interaction, we adopted the Perry, et al （1987） proposed theso-called "pudding" model to explain the deep dynamics mechanism. Finally from thepetrology, geochemistry and Sr-Nd-Hf isotopic Perspective. Through contrast ChifengHannuoba basalt and the surrounding area of Cenozoic basalts, we get the followingconclusions: line of Chifeng-Hannuoba-Jining-tianheyong source region component ofthe northern margin of the North China Cenozoic basalt area. should be a component ofDMM-EM I mixed product, form different basalt is the result of mantle two end-membermixing ratio induced by different, and lithospheric thinning intensity decrease from east toWest. Inner Mongolia Abaga-Mongolia Dariganga Cenozoic basalt area sourcecomponent is the DMM-EM II mixed product, which may mean that the Chifeng andAbaga between West LA, Mulun River fault as the boundary, on both sides of thelithospheric mantle with different attributes更多还原