【作者】 张超；

【导师】 刘永江； 徐仲元；

【作者基本信息】 吉林大学 ， 构造地质学， 2014， 博士

【摘要】 延边地区处于华北板块北缘东段，地处兴蒙造山带与龙岗地块的交接部位，是研究古亚洲洋构造域和古太平洋构造域转换的理想地区。目前关于延边地区中生代的构造演化存在较大的争议，主要是对于古亚洲洋在延边地区最终闭合时间和位置以及古太平洋构造域开始对吉黑东部作用的时间没有统一的认识。这些存在的问题限制了对延边地区中生代以来构造演化的认识。因此本文对延边和龙地区中生代岩浆岩和青龙村群新东村组变质岩进行详细的岩相学、年代学和岩石地球化学研究，同时对出露在研究区内中生代岩体中的韧性剪切带进行了应力分析。综合区域上岩浆岩分布特点和色洛河群分布特征，探讨延边地区中生代期间的构造演化。LA-ICP-MS锆石U-Pb结果表明延边和龙地区岩浆活动主要集中在以下三个时间段：早三叠世（智新岩体、勇新岩体）、早-中侏罗世（石国水库岩体、月山洞岩体、沙松顶岩体、高岭岩体）和早白垩世（柳洞岩体和泉水村组火山岩）。早三叠世岩浆岩主要分布在古洞河断裂东北侧，呈北西向展布，其主要由智新角闪辉长岩体和勇新花岗质岩体组成，两者构成了类双峰式岩石组合。智新岩体角闪辉长岩锆石U-Pb年龄为251.05±0.95Ma。岩石具有低硅富镁的特点，同时富集大离子亲石元素和轻稀土元素，亏损Nb、Ta等高场强元素，具有俯冲环境下形成的基性岩浆岩特点；其具有低Isr值和正εNd值特点表明其岩浆源区为受俯冲流体交代作用的亏损地幔楔。勇新花岗质岩石以含石榴石二长花岗岩和黑云母二长花岗岩为主，岩体遭受了韧性变形作用；二长花岗岩锆石U-Pb年龄为238.5±2.8Ma和243.2±1.1Ma；样品含有少量的石榴石，岩石地球化学特征上具有高硅高铝的特点，同时富集大离子亲石元素（Cs、Rb、K）和高场强元素Zr，亏损Ba、Sr等大离子亲石元素和Nb、Ta、P和Ti等高场强元素，具有壳源花岗岩的特征；其Al2O3、CaO、MgO、P2O5、FeOt和TiO2与SiO2含量呈明显的负相关，表明其岩浆演化过程中经历了分离结晶的作用；二长花岗岩具有相对较高的Isr值和变化的εNd值，表明岩浆应起源于中-新元古代新增生的基性下地壳的部分熔融，同时岩浆源区应受到了俯冲流体交代的作用。早三叠世类双峰式岩浆岩组合可能形成于古亚洲洋俯冲闭合过程中板片断离引起的伸展环境下。早-中侏罗世岩浆岩在研究区大面积分布，岩性包括花岗闪长岩、二长花岗岩、黑云母闪长岩和橄榄辉长岩。早侏罗世石国水库花岗闪长岩的锆石U-Pb年龄为193.06±0.8Ma，具有高硅富铝低镁的特点，且富集大离子亲石元素（Cs、K、Th），亏损高场强元素（Nb、Ta、P、Ti），具有活动大陆边缘岩浆岩的特点；所有样品的Al2O3、FeOt、MgO、TiO2、P2O5、和CaO与SiO2呈较好的线性关系，暗示原始岩浆经历了明显的分离结晶作用；同时样品具有与大陆下地壳一致的Isr值和负的εNd值，表明石国水库岩体岩浆起源于地壳物质的部分熔融，并受到了古老地壳物质的混染作用。高岭岩体主要由似斑状花岗闪长岩和似斑状二长花岗岩组成，锆石U-Pb年龄结果为180.47±0.741Ma、172.25±0.97Ma和170.9±0.68Ma。高岭岩体花岗质岩石与埃达克岩类似，具有较高的SiO2含量、Al2O3含量、Sr含量和较低的Y和Yb含量，并强烈富集轻稀土元素，亏损重稀土元素，同时富集大离子亲石元素和亏损高场强元素Nb、Ta。多数样品具有较低的Isr值和负的εNd值，表明高岭岩体原始岩浆起源于加厚下地壳基性物质的部分熔融，并受到了古老地壳物质的混染。早侏罗世沙松顶橄榄辉长岩和月山洞黑云母闪长岩锆石U-Pb年龄分别为175.6±1.1Ma和178.4±1.2Ma。两者均具有较低的SiO2含量和较高的MgO含量，两者的Rb/Sr比值和Nb/Ta比值与地幔平均值一致，暗示其幔源岩浆的特点。同时两者均富集大离子亲石元素，亏损Nb、Ta高场强元素，且P2O5和TiO2含量较低，因此具有拉斑玄武岩特征的橄榄辉长岩和具有钙碱性特征的黑云母闪长岩形成于俯冲流体交代作用下的地幔楔的部分熔融。早白垩世柳洞岩体二长花岗岩锆石U-Pb年龄为118.58±0.87Ma和118.52±0.67Ma。所有样品富硅、富碱、富铝和低钛，稀土元素总量相对较低，轻重稀土元素分异较强，富集Ba、Rb、U、K等大离子亲石元素，相对亏损Nb、Ta、P、Ti等元素，与壳源形成的花岗岩类似。Isr值和εNd(118Ma)值分别为0.7041~0.70596和2.0~2.7，其Isr在下地壳Isr的范围内，原始岩浆应起源于新元古代增生的亏损下地壳基性物质的熔融。早白垩世泉水村组流纹质火山岩具有钙碱性火山岩的特点，形成于活动大陆边缘的环境下。样品富硅、富铝、低镁、低钛，强烈亏损高场强元素、富集大离子亲石元素，同时具有较低的Sc、Ni、V和Co，表明该火山岩原始岩浆起源于地壳部分的熔融。研究区内早三叠世岩浆活动与古亚洲洋的俯冲有关，而早侏罗-早白垩世岩浆活动则形成于古太平洋板块俯冲的构造环境下。此外，所有岩浆岩均具有与兴蒙造山带一致的Sr-Nd特征，表明在中-新元古代期间，研究区内存在地壳增生事件。新东村组浅变质主要由大理岩、二云母片岩和少量火山岩组成，其岩石组合与海相地层特点类似。岩石地球化学特征上也表现出了浅海盆环境下海相地层的特点，其最年轻的碎屑锆石年龄为242Ma，与邻区同时期的海相地层共同形成于中三叠世之前的残留海盆环境中。新东村组变质岩的存在说明242Ma之前古亚洲洋在延边地区并没有完全闭合。研究区内韧性剪切带形成于中-晚三叠世期间，对其进行应力作用分析表明该韧性剪切带受到了来自北北东向应力挤压作用，可能与古亚洲洋的闭合有关。在上述研究的基础上，本文总结了延边-绥芬河地区的岩浆活动规律：晚二叠世-早三叠世岩浆活动主要分布在汪清-珲春一线附近及其南侧，华北板块北缘处于古亚洲洋持续俯冲闭合的构造环境中；中三叠世晚期-晚三叠世进入了陆-陆碰撞向伸展垮塌的转换阶段，并发育了一系列的碱性-基性岩浆岩带。早侏罗世吉黑东部进入了古太平洋构造域的俯冲作用下，并发育大面积的与俯冲有关的岩浆岩。晚侏罗世-早白垩世早期古太平洋板块存在俯冲作用间歇期，早白垩世晚期古太平洋板块再次对延边地区开始俯冲作用。综上所述，延边地区早三叠世-中三叠世早期处于古亚洲洋持续闭合过程中，古亚洲洋在中三叠世早期最终沿延边地区的汪清-珲春一线闭合，中三叠世晚期-晚三叠世早期，延边地区处于陆-陆碰撞向伸展垮塌转换的构造环境中，从早侏罗世（~200Ma）开始，延边地区完全进入了古太平洋板块俯冲作用的构造体制下。更多还原

【Abstract】 Yanbian Area, which is at the eastern segment of the northern margin of the NCC, islocated between XingMeng Organic Belt and Longgang block. Because the final closuretime and location of Paleo-Asian Ocean and the subduction time of Paleo-Pacific areuncertain, the Mesozoic tectonic evolution of Yanbian Area is distuped all the time. Theproblems mentioned above limit the understanding of the Mesozoic tectonic evolution inYanbian Area. However, the study about Mesozoic igneous rocks and metamorphic rocksof Xindongcun formation in Qinglongcun group is done in this paper. All the work includein petrology, Geochronology and Geochemistry. Besides these, the characteristics ofductile shear zone are also analyzed. Combined with the distributed features of igneousrocks and Seluohe Group in the regional area, the Mesozoic tectonic evolution in YanbianArea is further discussed.The results of LA-ICP-MS Zircon dating indicate the magmatic activities in Helongarea of Yanbian are divided into three stages:(1) the early Triassic magmatic eventsincluding Zhixin pluton and Yongxin pluton;(2) the early-middle Jurassic magmatic eventsincluding Shiguoshuiku Pluton, Yueshandong Pluton, Shasongding Pluton and GaolingPluton;(3) the early Cretaceous magmatic events including Liudong Pluton and volcanicrocks in Quanshuicun Formation.The early Triassic magmatic events are composed of Zhixin pluton and Yongxinpluton and have characteristics of the similar bimodal igneous rocks. They are to thenortheast of Gudonghe Fault and spread in the north-eastern direction. The analyses ofZircons from Zhixin pluton yield weighted mean206Pb/238U age of251.05±0.95Ma whileThe analyses of Zircons from Yongxin pluton yield weighted mean206Pb/238U ages of238.5±2.8Ma and243.2±1.1Ma，which suggesting they are formed in the early Triassic.Geochemically, the amphibole gabbro of Zhixin pluton is low in SiO2and MgO, and theyare strongly enriched in large ion lithophile elements and depleted in high field strengthelements (e.g., Nb, Ta), the petrogeochemical features are consistent with the ones of basicigneous rocks formed in the subduction environment. Furthermore the rocks have low Isr and positive εNd, indicating that the magma source is from the mantle wedge influencedby the fluid. The granitic rocks in Yongxin pluton are composed of garnet monzograniteand biotite monzogranite, and the granitic rocks are deformed highly. Petrogeochemically,the granitic rocks are in high SiO2and Al2O3, and are also strongly enriched in large ionlithophile elements(e. g. Cs, Rb, K) and Zr (HFSE). They are depleted in high fieldstrength elements (Nb, Ta, P and Ti) and Ba, Sr (LILE). The petrogeochemical fetures arelikely to the granites whose magma sources are from crustal material. In the harkerdiagram, they have negative correlation between the major elements (Al2O3, CaO, MgO,P2O5, FeOt, TiO2) and SiO2, which indicate the magma experienced the fractionalcrystallization during the magma evolution. Compared to the basic rocks of Zhixin pluton,the granitic rocks have higher Isr and different εNd, the magma source of granitc rockswas also influenced by the fluid, and it was derived from partial melting of mafic rocks inlower crust. However, the similar bimodal igneous rocks in early Triassic were formed inan extensional environmentThe magmatic activities in the early to middle Jurassic are distributed widely,including granodiorite, monogranite, biotite diorite and peridotite gabbro. The analyses ofZircons from grandonite of Shiguoshuiku pluton yield weighted mean206Pb/238U age of193.06±0.8Ma. Petrogeochemical, the granitic rocks are in high SiO2and Al2O3, andhave low MgO contents. In the other hand, they are also strongly enriched in large ionlithophile elements(e.g. Cs, K, Th) and depleted in high field strength elements(Nb, Ta, Pand Ti). The characteristics of geochemistry are constant with igneous rocks formed in theactive continental margin. Besides these, the major contents (Al2O3, FeOt, MgO, TiO2,P2O5and CaO)are in negative linear relationship with SiO2, indicating the evolution ofmagma is dominated by the fractional crystallization. The Isr andεNdvalues of thesamples are similar to ones of crust, these features indicate the magma source were frompartial melting of mafic rocks in lower crust, and affected by the ancient crust materials.The Gaoling pluton is composed of porphyritic granodiorite and porphyriticmonogranite, The analyses of Zircons from porphyritic granodiorite yield weighted mean206Pb/238U age of180.47±0.74Ma, while The analyses of Zircons from porphyriticmonogranite yield weighted mean206Pb/238U age of72.25±0.97Ma and170.9±0.68Ma,respectively. Similar to geochemistrical characteristics of adakite rocks, all the sampleshave high SiO2and Al2O3contents, high Sr contents and low Y and Yb contents. They are also strongly enriched in light REE and depleted in heavy REE, while are enriched in largeion lithophile elements and depleted in high field strength elements. These rocks have lowIsr and negativeεNdvalues, the geochemical data indicate that the Gaoling pluton magmawas derived mainly from partial melting of mafic rocks in thickened lower crust whichlikely affected by Neoproterozoic accretion material and also was influenced by the ancientcrust.The analyses of Zircons from grabbro of Shasongding pluton and diorite ofYueshandong pluton yield weighted mean206Pb/238U age of175.6±1.1Ma and178.4±1.2Ma, respectively. Both of them are low in SiO2and high in MgO, the values of Rb/Srand Nb/Ta are consistent with the average values of mantle, indicating that their magmasource are from Mantle. Besides these, both of them are enriched in large ion lithophileelements and depleted in high field strength elements (Nb, Ta). With the low P2O5contentsand TiO2, the magma source of tholeiitic grabbro and cal-alkaline diorite are from themantle wedge affected by the fluid.The analyses of Zircons from monogranite of Liudong pluton yield weighted mean206Pb/238U age of118.58±0.87Ma and118.52±0.67Ma, respectively. All of the samplesare high in SiO2, Alk and Al2O3and low in TiO2and∑REE, They are also stronglyenriched in light REE and depleted in heavy REE, and are enriched in large ion lithophileelements (Ba, Rb, U, K) and depleted in high field strength elements (Nb, Ta, P, Ti). Thecharacteristics mentioned above are similar to the ones of crust. And the Isr andεNd(118Ma)values are also in the range of ones of low crust. All of the characteristics indicate themagma source of Liudong pluton is from partial melting of depleted low crust mafic rocks.The cal-alkaline volcanic rocks in Quanshuicun formation are formed in activecontinent margin. All the sample are high in SiO2and Al2O3and low in MgO, TiO2, Sc, Ni,V and Co. The samples are also enriched in large ion lithophile elements and depleted inhigh field strength elements. The characteristics of volcanic rocks indicate the primarymagma is from partial melting of low crust mafic rocks.The early Triassic igneous activities are related to the subduction of paleo-asianocean, and the igneous activities in early Jurassic to early Cretaceous are formed in thesubduction environment of Paleo-pacific ocean. The features of Sr-Nd in the study area aresimilar to the ones in the XingMeng Organic Belt, suggesting the existence ofNeoproterozoic crustal growth event. The metamorphic rocks in Xindongcun Group are composed of marble,muscovite-biotite schistis and small amount of volcanic rocks. Its rock association issimilar to the marine stratum, and the geochemistrical features are also similar to the onesof marine stratum formed in the neritic environment. The youngest detailed zircon age is242Ma, sugguesting the paleo-asian ocean is still being before242Ma in the study area.The deformation age of ductile shear zone is between240Ma and200Ma, and theresults of stress analysis indicate the formation of ductile shear zone is related to theNNE-direction compressive stress under the environment of paleo-asian ocean subduction.Based on the study above, we also analyze the characteristics of magmatic activitiesin Yanbian-Suifenhe area. And we find the magmatic activities are mainly distributed to thesouth Wangqing-Hunchun area, suggesting the paleo-asian ocean final suture is nearWangqing-Hunchun. And after~240Ma, the pale-asian ocean disappeared, and the tectonicsetting became the setting of continental collision and collapse which resulted analkaline-basic magmatic zone were formed in the Yanbian-suifenhe area. But during theJurassic period, the Yanbian-Suifenhe area is completely controlled by the subduction ofpale-pacific ocean, and magmatic rocks with charateristics of subduction were formed ineastern Jinlin and Heilongjiang area. During the150Ma-130Ma, the subduction ofpaleo-pacific ocean was weak and in the Late cretaceous, the subducion of paleo-pacificocean once began.Above all, the tectonic of Yanbian area was controlled by the subdution of paleo-asianocean before the middle Traissic, and the final sutre is located from Wangqing to Hunchun.The eastern of Jinlin and Heilongjiang area is affected by the paleo-pacific ocean from~200Ma.更多还原