【作者】 孙明道；

【导师】 陈汉林； Simon A.Wilde；

【作者基本信息】 浙江大学 ， 构造地质学， 2013， 博士

【摘要】 佳木斯地块位于中国东北，构造上处于华北克拉通和西伯利亚克拉通之间，作为环太平洋构造带的拼贴地块，在早中生代与西部的松辽地块发生陆陆碰撞，成为欧亚大陆的一部分，并开始受到古太平洋板块俯冲的影响。在古太平洋板块俯冲引起的弧后区域构造伸展的背景下，佳木斯地块以及整个欧亚大陆东部广泛分布晚中生代至新生代的岩浆岩。研究这些岩浆岩的年代及岩石学成因，对了解区域晚中生代大地构造演化有着重要意义。本论文在中国东北佳木斯地块及邻区选取典型的白垩纪火山岩或次火山岩剖面进行系统的野外地质、岩相学、锆石SHRIMP U-Pb年代学、地球化学、Sr-Nd同位素及锆石Lu-Hf同位素、锆石O同位素研究，精细确定了佳木斯地块晚中生代岩浆活动的年代，反演各岩浆岩的源区性质以及成因机制；并在此基础上，综合区域地质背景及洋壳俯冲的最新研究结果，通过与大兴安岭、松辽盆地及欧亚大陆东缘其他地区的岩浆岩年代学、地球化学特征的对比，归纳了中国东北地区晚中生代岩浆作用的空间迁移规律，并提出岩浆及构造解释模型。论文主要成果如下：1.佳木斯地块晚中生代岩浆活动集中发生在白垩纪中期104﹣100Ma。其中，穆棱地区伊林组流纹岩和乌拉嘎花岗斑岩锆石SHRIMP年龄均为104±1Ma；鹤岗松木河组玄武岩的年龄约为102﹣101Ma；桦南复合岩墙和其围岩、佳木斯双峰式岩墙均形成于100±2Ma。2.佳木斯地块晚中生代岩浆岩地球化学整体上属于高钾钙碱性系列，并具有双峰式特征，富集轻稀土元素和大离子亲石元素，亏损高场强元素，形成于活动大陆边缘板内伸展的构造背景，具有多样的岩石成因类型。3.穆棱地区伊林组流纹岩高Sr，高La/Yb，低Yb，高Mg#（⁰.57），属于高镁埃达克岩。正的εNd（t）=+0.75、较低的锆石δ¹⁸O=5.6﹣6.7、εHf（t）=5.8﹣12.7表明，其形成于受俯冲洋壳脱水交代的地幔橄榄岩的部分熔融。负Eu异常和Ba异常说明源区残留矿物含斜长石，熔融压力相对较小。部分样品Sr含量、Sr同位素比值、Mg#变化范围较大，可能受岩浆-地表水相互作用影响。乌拉嘎金矿岩体有两种花岗斑岩，一种为角闪花岗斑岩，侵入早白垩世宁远村组地层之中，高Sr、La/Yb，低Y、Yb，高Mg#（0.57），亦属于高镁埃达克岩，εNd（t）值为+0.5，与伊林组流纹岩接近。不同的是，锆石δ¹⁸O较高（⁸.0），Y含量更低（7.5﹣8.3ppm），表明其形成于俯冲洋壳的部分熔融并接受了很少程度的地幔的交代混染，源区残留矿物可能为石榴子石、角闪石和金红石，熔融压力相对较大。另一种花岗斑岩和前者相比，虽位于同一个岩体，但无角闪石、黑云母，侵入到麻山群副变质岩之中，相近的log （Na₂O/MgO）值，但高的铝饱和指数特征表明，其不是源自角闪花岗斑岩的结晶分异，而是属于S型花岗岩类，形成于埃达克质岩浆侵位引发上地壳围岩部分熔融形成的。4.松木河组玄武岩具有较高的SiO₂（52.09﹣53.22%），Na₂O含量为4.25﹣4.36%，K₂O含量为1.32﹣1.35%，在TAS图解中位于玄武质碱性安山岩范围。高铝（17.97﹣19.04%）、低镁（3.00﹣3.98%）、低Mg#（0.42﹣0.45）的特征表明岩浆经历过较高程度的结晶分异或地壳混染；没有Eu负异常（Eu/Eu*=0.98﹣1.00），在球粒陨石标准化蛛网图中，除Nb, Ta, P, Ti and Y元素亏损、Pb元素的富集，其他元素按相容性排序递减，以及正的εNd（t）值（+2.9﹣+3.0），表明基性岩浆没有经历显著的地壳混染，源区为亏损地幔。偏高的(⁸⁷Sr/⁸⁶Sr)i值（0.70565﹣0.70571）表明地幔源区受到俯冲洋壳中受海水蚀变的玄武岩的影响。在构造判别图中，松木河组玄武岩位于活动大陆边缘弧后板内伸展环境下，代表了佳木斯地块中白垩世玄武质岩浆活动的开始及岩石圈进一步的伸展。5.桦南复合岩墙位于佳木斯地块的中部，由各3米宽的安山斑岩的边部和5米宽的流纹斑岩的核部组成，其围岩为含安山岩包体的花岗斑岩。安山岩包体大多呈浑圆状；部分成次棱角状并具暗色矿物反应边，但岩石成分与浑圆状包体相同，它们都形成于因基性岩浆与酸性岩浆温差过大导致的基性岩浆在酸性岩浆中的淬冷作用。复合岩墙安山斑岩、流纹斑岩的锆石中含大量流体包裹体以及针状磷灰石，表明其岩浆也经历了快速的冷却。复合岩墙核部的流纹斑岩与含安山岩包体的花岗斑岩围岩地球化学特征相似，表现为高SiO₂、低MgO和Fe2O3、高Al2O3、LILE和LREE富集、HFSE亏损、Eu、Ba、U、Sr负异常等特征，源区为中上部地壳；安山岩包体无Eu负异常、低硅高镁铁，原始岩浆可能为玄武质；复合岩墙边部安山斑岩的中心位置的SiO₂含量相对最低，εNd（t）最高，最能代表原始玄武质岩浆的成分，可能来自于富集岩石圈地幔；距流纹斑岩岩墙及酸性围岩越近，SiO₂含量增加，εNd（t）值降低，表明受到越多酸性岩浆的混染。桦南复合岩墙及其含安山岩包体花岗斑岩围岩显示了玄武质岩浆和地壳组分不同程度的相互作用，标志着中白垩世100Ma玄武质岩浆的底侵以及快速的构造伸展。6.佳木斯双峰式岩墙位于佳木斯地快的西部，岩墙由流纹岩岩墙和辉绿岩岩墙组成。流纹岩SiO₂含量为74.99﹣76.09%，Na₂O含量为2.55﹣4.92%，K₂O含量为2.72﹣6.30%，富集大离子亲石元素和轻稀土元素，高场强元素Nb、Ta、P、Ti亏损，具有显著的Eu、Sr、Ba负异常，εNd（t）=0.49﹣1.66，低Mg#（0.01﹣0.17），具有铁质花岗岩（A型花岗岩）的特征，⁸⁷Sr/⁸⁶Sr比值分为两组（0.7045和0.7061），表明铁质流纹岩分别来源于玄武岩的结晶分异和地壳的减压部分熔融。辉绿岩SiO₂含量为47.10﹣53.49%，Na₂O含量为2.44﹣4.58%，K₂O含量为0.74﹣2.89%，在TAS图解中分别位于玄武岩和安山岩范围，属钙碱性系列。较高的Mg#（0.57﹣0.67）、没有或有较弱的Eu负异常（Eu/Eu*=0.85﹣1.02），εNd（t）值为–1⁺4，表明辉绿岩来自软流圈地幔与岩石圈地幔不同程度的相互作用。大离子亲石元素富集、高场强元素亏损，偏高的(⁸⁷Sr/⁸⁶Sr)i表明源区受到俯冲洋壳中的受海水蚀变的玄武岩或受俯冲作用卷入到地幔深部的陆源沉积物的影响。佳木斯双峰式岩墙辉绿岩及铁质流纹岩标志着区域地壳发生了强烈的减薄与地幔物质上涌，标志着区域构造伸展。7.佳木斯地区多样的岩浆类型包括高镁埃达克岩、铁质流纹岩、玄武岩及丰富的玄武质岩浆-壳源酸性岩浆混合及双峰式岩浆作用等等现象，这些现象揭示了洋壳俯冲至地幔转换带脱水、部分熔融；脱水形成的流体及部分熔融形成的熔体交代岩石圈地幔；洋壳脱水引发软流圈地幔及岩石圈地幔的部分熔融、基性岩浆上涌；基性岩浆侵入上地壳引发沉积地壳的部分熔融、形成S型酸性岩浆，基性岩浆与S型酸性岩浆不同程度的混合、混染；基性岩浆底侵到减薄的地壳下部，形成铁质（A型）流纹岩等等过程，这些过程形成的岩浆能够上升到地表或近地表，指示了岩石圈的快速伸展、减薄，与俯冲洋壳后撤引发区域构造伸展有关。8.对中国东北地区晚中生代岩浆岩年龄数据的整理表明，岩浆活动的开始时间具有由西向东由老变新的时空分布特征。大兴安岭的岩浆活动起始于160Ma，强烈活动至少持续至120Ma；松辽盆地的岩浆活动主要以营城组火山岩为代表，在120Ma-110Ma；佳木斯地块的岩浆活动则主要发生在110Ma-90Ma。这一规律可以用洋壳俯冲-堆积-后撤的模型来解释，即洋壳低角度俯冲至地幔转换带、俯冲洋壳在地幔转换带中堆积、堆积过程导致继续向地幔转换带俯冲堆积产生阻力、俯冲洋壳后撤，俯冲角度变大，在更换了堆积位置之后开始新的一轮循环。这一模型指出，在洋壳运动速率和方向不发生改变的情况下，通过俯冲-堆积-后撤，同样可以形成板内构造的幕式演化，这对中国东部其他地区的晚中生代板内幕式岩浆活动的解释仍具有借鉴意义。更多还原

【Abstract】 The Jiamusi Block of NE China is located between the North China and Siberiacratons. It collided with the Songliao Block to the west in the early Mesozoic as one of thecircum-pacific accreted blocks, and formed the unified Eurasian eastern boundary as aresult of subduction of the paleo-Pacific plate. Huge amounts of igneous rocks wereproduced in the whole of eastern Eurasia, including the Jiamusi Block, caused by back-arcintraplate extension triggered by paleo-pacific subduction. Study of the petrogenesis ofthese igneous rocks is important for understanding the nature of the late Mesozoicmagmatism and geodynamic evolution of the Jiamusi block and eastern China.For this research, typical late Mesozoic geological sections were selected from theJiamusi Block for field geology, petrographic study, zircon SHRIMP U-Pb geochronology,geochemistry, Sr-Nd isotope, zircon Lu-Hf isotope and zircon O-isotope study, in order toaccurately determine the age of the late Mesozoic igneous rocks and their petrogenesis.This study also summarizes previous research of subduction processes in the region andcompares the geochronological and geochemical results with the igneous rocks in the GreatXing’an Range, the Songliao Basin, and other areas of East Asia. Finally the temporalrelationship of the igneous rocks in NE China is discussed and illustrated by utilizingseveral models.The main achievements and conclusions of this thesis are as follows:（1） The late Mesozoic magmatism of the Jiamusi Block mainly occurred in themid-Cretaceous between104±1and100±2Ma. Zircon SHIRMP U-Pb dating shows thatthe Yilin Formation rhyolite and Wulaga granite porphyry have the same age of104±1Ma; the Hegang Songmuhe Formation basalt erupted between103±2and100±2Ma;and the Huanan composite dyke and its country rock and the Jiamusi bimodal dykes wereall emplaced at100±2Ma.（2） The mid-Cretaceous igneous rocks of the Jiamusi Block belong to the high-Kcalc-alkaline series, with a bimodal signature. They are all rich in LILE and HREE,depleted in HFSE, and formed in an active continental margin or intraplate tectonic setting.（3） The Yilin Formation rhyolite is a high-Mg adakite, with geochemical signature ofhigh-Sr and La/Yb, low-Yb and Y, and high Mg#（⁰.57）. Positive εNd（t）（⁺0.75）, lowzircon δ¹⁸O （5.6-6.7） and positive εHf（t）（5.8-12.7） suggest that the source of the adakite ismantle peridotite metasomatized by slab derived melt/fluid. Negative Eu and Ba anomaliesindicate residual plagioclase in the source and low melting pressure. Some samples have low Sr contents and abnormal⁸⁷Sr/⁸⁶Sr values, possibly caused by magma-ground waterinteraction. The Wulaga pluton has two types of granite porphyry. One is hornblendegranite porphyry which invaded into the early Cretaceous Ningyuancun Formationsandstone and tuff. The geochemical features of high Sr （>300ppm）, low Y （⁸ppm）, highMg#（⁰.57）, positive εHf（t）（6.3-12.7） and εNd（t）（⁺0.5） show that the hornblende graniteporphyry is also a high-Mg adakite, similar to the Yilin Formation rhyolite. However, thecrustal zircon δ¹⁸O （⁸.0） and lower Y content （7.5-8.3ppm） suggest that it was derivedfrom the partial melting of a subducted slab but experienced minor mantle contamination,while the melting pressure was relatively high, with garnet, hornblende and rutile asresidual minerals. The other type of granite porphyry has only minor hornblende. Itinvaded into khondalitic rocks of the pan-African Mashan Complex. Higher aluminumsaturation index but consistent log （Na₂O/MgO） values compared with the hornblendegranite porphyry suggests that it was derived from partial melting of upper continentalcrust triggered by adakitic magma upwelling and emplacement.（4） The Hegang Songmuhe Formation basalt has relatively high SiO₂contents（52.1-53.2%）, with4.25-4.36%Na₂O and1.32-1.35%K₂O, putting it into the alkalinebasaltic andesite field in the TAS diagram. The high Al2O3（18.0-19.0%） and low MgO（3.0-4.0%） contents and Mg#of0.42-0.45are features indicative of magma thatexperienced high degrees of crystal fractionation. No Eu anomalies （Eu/Eu*=0.98-1.00）,high εNd（t） values （2.9-3.0）, and flat LILE patterns suggest that crustal contamination wasminor. High εNd（t） and relatively low (⁸⁷Sr/⁸⁶Sr)isuggest that the mantle source wasdepleted. The (⁸⁷Sr/⁸⁶Sr)iratios （0.70565-0.70571） are higher than expected for normalasthenosphere-derived basalt, indicating that the mantle source was affected by subductedoceanic crust basalt which was altered by sea water. In tectonic discrimination diagrams,the Songmuhe Formation basalt plots in the active continental margin and intraplate field.It represents the beginning of the mafic magmatism in the Jiamusi Block, and extention ofthe lithosphere in the mid-Cretaceous.（5） The Huanan composite dyke is located in the centre of the Jiamusi Block. Itconsists of two3m wide andesite porphyry margins and one5m wide rhyolite porphyryinterior. Zircons from the andesite and rhyolite porphyry have abundant acicular apatiteinclusions indicating fast cooling considering the crystalization temperature drop fromapatite to zircon. Both granite porphyry and rhyolite porphyry have high SiO₂and Al2O3,low MgO and Fe2O3, with enrichment of LILE and LREE, and depletion of HFSE, Eu, Ba, U, and Sr; their sources are most possibly upper continental crust. The andesite porphyrywas contaminated invarious degrees by the acidic magma. The Huanan composite dykeand its country rock represent interaction between basaltic magma and upper continentalcrust; it also represents evidence of extension of the Jiamusi Block in the mid-Cretaceous.（6） The Jiamusi bimodal dykes section is located in the west of the Jiamusi block. Itconsists of rhyolite and dolerite dykes. The rhyolite is characterized by enrichment in LILEand LREE, and depletion in HFSE. It shows a significant negative Eu anomaly, and hasεNd（t） values ranging from0.49to1.66and two groups of initial⁸⁷Sr/⁸⁶Sr ratios at0.7045and0.7061. The rhyolite displays the compositional signature of Peraluminous FerroanGranitoid （A-type）, indicating it was derived by either differentiation of basalt or lowpressure partial melting of continental crust. The dolerite is also characterized byenrichment in LILE and LREE, and depletion in HFSE. It has a weak negative Eu anomalyand has εNd（t）=–1.22to+3.26, and (⁸⁷Sr/⁸⁶Sr)i=0.7057–0.7074. The dolerite originatedfrom partial melting and mixing of both asthenospheric and lithospheric mantle which wasaffected by residual oceanic slab or sediment, and experienced different amounts oflithospheric and crustal assimilation and contamination. The Jiamusi bimodal dolerite andferroan （A-type） rhyolite dykes indicate lithospheric thinning, mantle upwelling andtectonic extention.（7） The igneous rocks of the Jiamusi Block therefore show a range of types, includinghigh-Mg adakite, ferroan rhyolite, basalt and rocks related to mixing between basalticmagma and crustal acid magma. These various types of rocks show a variety of processes,including: dehydration and partial melting of subducted slab; assimilation andcontamination of mantle peridotite by slab fluid and melt; partial melting of bothasthenospheric and lithospheric mantle triggered by fluid; and basalt upwelling andemplaced into the crust forming partial melting of upper continental crust; mixing andmingling of basaltic magma and crustal magma; basalt upwelling and underplating at thebottom of thinned crust forming ferroan （A-type） rhyolite. Magma formed by theseprocesses ascended to the surface or sub-surface, suggesting an extension and thinning ofthe lithosphere, which is most possibly related with oceanic plate subduction and roll back.（8） The late Mesozoic igneous rocks in NE China show an eastward temporalmigration, and can be divided into three separate areas, which are from west to east:（1）The Great Xing’an Range¹60-120Ma,（2） The Songliao Block¹20-110Ma,（3） TheJiamusi area¹10-90Ma. This temporal migration can be interpreted by the subduction– accumulation–rollback model of the paleo-Pacific plate. This model indicates that theepisodic evolution of intraplate structural and magmatism evolution can be interpreted bysubduction-accumulation-rollback of subducted slab, with or without the change of rateand direction of subduction. This model is possibly also helpful to interpret the lateMesozoic tectonic evolution of other areas of eastern China.更多还原