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1.
沂沭断裂带内发育了大量的中生代火山岩，其成因研究对剖析断裂带活动规律具有重要意义。本文对断裂带北段潍坊、安丘、鄌郚地区中生代火山岩进行了详细的岩石学、锆石U-Pb年代学和主量元素、微量元素、Sr-Nd-Pb同位素分析。探讨了沂沭断裂带中生代火山岩成因及其形成的地球动力学过程。断裂带北段火山岩年龄集中在131~124Ma之间，喷发于早白垩世。岩石为一套高钾钙碱性火山岩，包括玄武安山岩、粗安岩、粗面岩、英安岩。火山岩富集Rb、Ba等大离子亲石元素，相对亏损Nb、Ta、Ti等高场强元素。稀土元素含量高（∑REE=140.5×10-6~433.1×10-6），富集轻稀土、亏损重稀土（∑LREE/∑HREE=9.8~31.0），无明显的Eu负异常。火山岩具有富集且变化范围较大的Sr-Nd-Pb同位素组成，（87Sr/86Sr）i=0.708054~0.711692，εNd（t）值为-15.3~-7.4，（206Pb/204Pb）i=17.213~17.962，（207Pb/204Pb）i=15.425~15.590，（208Pb/204Pb）i=37.597~38.365。研究表明，高钾钙碱性火山岩的源区与区域基性岩源区一致，均为富集岩石圈地幔。玄武安山岩、粗安岩、粗面岩经基性岩浆分离结晶作用形成，英安岩则遭受了华北下地壳强烈混染。三叠纪末期，由于扬子板块向华北克拉通俯冲，扬子地壳析出的流体/熔体交代了华北古老岩石圈地幔，形成富集岩石圈地幔。早白垩世，受古太平洋板块俯冲和后撤作用，富集岩石圈地幔部分熔融形成基性岩浆，岩浆在上升过程中发生分离结晶作用，受沂沭断裂深切作用影响，部分地区遭受华北下地壳混染，最终形成区内各类高钾钙碱性火山岩。  相似文献   

2.
本文对湘南宝山铅锌多金属矿区花岗闪长斑岩及其暗色包体进行了系统的锆石U-Pb年代学、岩石地球化学和Sr-Nd-Hf同位素研究,探讨其岩石成因和构造意义。LA-ICP-MS锆石U-Pb定年表明,宝山花岗闪长斑岩成岩年龄为156~158Ma,暗色包体的形成年龄为155.2±1.4Ma,与寄主岩的成岩年龄一致。宝山花岗闪长斑岩为准铝质花岗岩,富集K、Rb、U等大离子亲石元素,亏损Nb、Ti、P等元素,Nb/Ta平均比值为11.3,（87Sr/86Sr）i值为0.7095~0.7115,εNd（t）值为-7.3~-5.0,t2DM（Nd）值为1.35~1.54Ga,锆石εHf（t）值为-14.0~-9.0。暗色包体呈细粒结构,具浑圆的外形,与寄主花岗闪长斑岩接触界线清晰,具暗色的冷凝边,常见针状磷灰石。暗色包体具较低的SiO2含量（55.46%~57.30%）,较高的K2O含量（5.86%~6.90%）,富集Rb、Ba、Th、U等大离子亲石元素,亏损Nb、Ta、Ti等元素,Nb/Ta平均比值为15.3,（87Sr/86Sr）i值为0.7062~0.7063,εNd（t）值为-2.1~-1.9,锆石εHf（t）值为-12.1~-4.7。与寄主花岗闪长斑岩相比,暗色包体含有较高的Fe、Mg、V、Cr等相容元素。主微量元素和同位素特征表明,宝山花岗闪长斑岩是由来自经俯冲沉积物熔体交代过的富集岩石圈地幔且富水富钾的底侵基性岩浆与由其引起的下地壳部分熔融形成的长英质岩浆发生混合形成,暗色包体则是来自该底侵基性岩浆与少量长英质岩浆发生混合形成。Sr-Nd同位素模拟表明,宝山花岗闪长质岩浆由大约20%~30%的富集地幔物质和70%~80%的地壳物质组成。892±20Ma继承锆石核的εHf（t）值为+6.0,tDM（Hf）年龄为1.21Ga,与江南造山带东段新元古代岛弧岩浆的Hf同位素特征一致,推断在花岗闪长斑岩的源岩部分熔融过程中有新元古代岛弧岩浆岩物质的加入,新元古代岛弧岩浆带及扬子与华夏陆块弧陆碰撞带从萍乡向南延伸部分可能与郴州-临武断裂相接。在燕山早期（190~150Ma）,受古太平洋板块俯冲作用影响,南岭地区处于岩石圈伸展-减薄的构造环境,由于地幔玄武质岩浆底侵至古老地壳源区,诱发地壳发生部分熔融作用,伴随着壳幔岩浆混合作用,形成了该区众多花岗质岩石。  相似文献   

3.
岩基后成矿作用:来自小兴安岭鹿鸣超大型钼矿的证据   总被引：7，自引：3，他引：4  
小兴安岭鹿鸣钼矿是新近发现的斑岩型超大型钼矿.尽管近年有一些新年龄和新资料发表,但是关于矿区的成岩、成矿事件的时代和成因仍有很大争议.本文采用LA ICP-MS锆石U-Pb、辉钼矿Re-Os以及黑云母40Ar-39Ar等测年方法分别对矿区的花岗斑岩、辉钼矿、以及二长花岗岩(下文称鹿鸣花岗岩)中的黑云母开展年代学研究.结果显示矿区花岗斑岩形成于174.0±2Ma(MSWD=3.2);辉钼矿等时线年龄为177.8±2.3Ma(MSWD=0.078),辉钼矿模式年龄加权平均值为177.5±1.2Ma(MSWD=0.058).黑云母40Ar-39Ar 900~1400℃坪年龄为175.9±1.1Ma,表明鹿鸣花岗岩形成于约176Ma(之前).因此结合野外、岩相学、前人结果等,认为鹿鸣花岗岩岩基成岩在前(>176Ma),花岗斑岩成岩在后(约174Ma左右),成矿应当在花岗斑岩成岩近同时或稍后,为早侏罗世末期.花岗斑岩含有浸染状硫化物,表明花岗斑岩体是致矿侵入体,鹿鸣(二长)花岗岩岩基仅仅是钼矿的围岩.岩石地球化学特征,尤其是MgO含量较高,高Sr低Y等特征,以及构造环境判别显示鹿鸣花岗岩岩基和花岗斑岩形成于与俯冲有关的火山弧环境.在早侏罗世早-中期,该区在北部蒙古-鄂霍茨克海和东部的饶河、伊佐那崎洋联合汇聚下形成俯冲带之上的加厚地壳,此时与地幔楔发生过反应的幔源岩浆底侵产生广泛的壳幔相互作用,形成鹿鸣花岗岩的岩基.随后加厚下地壳拆沉导致鹿鸣花岗岩岩基快速隆升,在地壳浅部,与来自于深部的花岗斑岩岩浆(+钼矿和深部流体)相遇,后者侵入到鹿鸣花岗岩岩基中,形成了斑岩及辉钼矿矿床.据此,提出鹿鸣钼矿属于岩基后成矿作用的产物.  相似文献   

4.
中新世是青藏高原隆升、增厚的重要时期,并且在这一时期内拉萨地块广泛发育碰撞后岩浆岩。本文对南拉萨地块米拉山地区的钙碱性钾质火山岩进行了锆石U-Pb年代学、Lu-Hf同位素和全岩主量、微量元素的测定与系统研究。米拉山中新世火山岩为粗面英安岩、英安岩和流纹岩（SiO2=59.89%~71.78%）。锆石U-Pb定年结果为16.1±0.2Ma~20.4±0.3Ma,表明其喷发时代为中新世。岩石具有较高的Al2O3含量（13.54%~16.31%）,低MgO（0.46%~1.95%）、高Sr（388×10-6~804×10-6）、低Y（6.55×10-6~11.20×10-6）和Yb（0.70×10-6~1.07×10-6）的特征,具有较高的Sr/Y值（51~80）、低相容元素（Cr=4.26×10-6~32.53×10-6,Ni=4.16×10-6~25.75×10-6）和弱Eu负异常。岩石具有轻稀土元素和Rb、Th、U、K等元素富集、重稀土元素和高场强元素Nb、Ta、Ti亏损的特征。米拉山中新世火山岩显示出埃达克质岩石的地球化学特征,可能来自于的镁铁质加厚下地壳的部分熔融,推测下地壳源区是石榴石角闪岩。锆石εHf（t）值为+2.2~+7.8,表明源区为新生地壳物质,有俯冲板片熔体加入。米拉山中新世火山岩的喷发时代与米拉山断裂活动时间一致,二者可能同为拉萨地块岩石圈拆沉的结果。  相似文献   

5.
武丽艳  胡瑞忠  齐有强  朱经经 《岩石学报》2013,29(12):4151-4166
浸铜湖斑岩铜（钼）矿床位于福建紫金山矿田的北东侧,本文分析了出露于该矿床的石英正长斑岩的主量元素、稀土和微量元素组成,Nd同位素组成,并对其进行锆石LA-ICP-MS U-Pb定年。研究结果显示,岩石SiO2含量变化于57.59%~71.19%,岩石全碱含量为7.73%~10.01%,里特曼指数σ为 2.21~6.05,铝饱和指数A/CNK为1.24~1.53,为过铝质、高钾钙碱性系列。稀土元素总量为152×10-6~212×10-6,具有弱Eu负异常（Eu/Eu*=0.71~0.97）,（La/Yb）N为16.62~33.49,表现出轻稀土富集,重稀土亏损。微量元素具有亏损Nb、Ta、P、Ti等高场强元素,富集大离子亲石元素的特点,显示弧岩浆作用特点。岩石具有低的εNd（t）值和低的Nd模式年龄,分别为-6.60~-4.37和1.25~1.43Ga,显示壳-幔相互作用特征。对石英正长斑岩两个样品的锆石进行激光探针等离子体质谱（LA-ICP-MS）U-Pb微区测定,结果分别为95.3±0.9Ma和96.7±0.9Ma,为晚白垩世早期岩浆活动产物。结合已有的研究成果,本文认为石英正长斑岩形成于拉张的构造背景之下,由受到俯冲组分改造或影响的岩石圈地幔物质与中、下地壳物质部分熔融形成的花岗质岩浆混合形成。  相似文献   

6.
曲林岩体位于冈底斯带中段的南缘，为渐新世-中新世复合岩体，主体为粗粒花岗斑岩，被后期煌斑质、花岗闪长质和花岗质岩脉切割，是多期岩浆作用的产物，出露面积约8km2。花岗斑岩两组样品（T0849-PG和T0849-G）的锆石U-Pb定年结果分别为29.7±0.1Ma和30.0±0.2Ma。花岗斑岩为高钾，准铝质，低MgO，高度富集轻稀土元素（LREE）和大离子亲石元素（LILE），亏损重稀土元素（HREE）和高场强元素（HFSE）。此外具有高Sr、Sr/Y、（La/Yb）N；低Y和Yb，弱Eu负异常等特征。岩体内发育一系列近南北向展布的花岗闪长玢岩脉，其中两组样品的锆石U-Pb定年结果分别为15.5±0.1Ma（T0848-PY）和14.4±0.1Ma（T0850）。两条花岗闪长玢岩脉具有与岩体主体相似的稀土和微量元素分布模式，同样富集轻稀土及大离子亲石元素，亏损重稀土及高场强元素。花岗斑岩的87Sr/86Sr（i）=0.706102~0.706202，εNd（t）=-0.6~+0.6，锆石εHf（t）=+4.9~+7.9；花岗闪长玢岩脉的87Sr/86Sr（i）=0.705429~0.705474，εNd（t）=-1.4~-0.2，锆石εHf（t）=+2.6~+7.6。本文数据和文献数据结果表明：曲林花岗斑岩与花岗闪长玢岩脉均来源于加厚南拉萨下地壳的部分熔融，很可能与增厚的深部岩石圈的拆沉或俯冲印度岩石圈的撕裂诱发软流圈上涌有关。  相似文献   

7.
甲玛超大型铜多金属矿床位于冈底斯成矿带东段，矿体主要包括矽卡岩型、斑岩型、角岩型和独立金矿体4种类型。矿床中酸性侵入体中广泛发育岩浆黑云母，部分岩体较发育角闪石。本文在全面开展矿区地质调查和详细的钻孔岩芯编录的基础上，对含矿二长花岗斑岩和含矿花岗闪长斑岩中的岩浆黑云母以及含矿花岗闪长斑岩中的角闪石开展了矿物学及矿物化学研究，以揭示其成岩成矿意义。研究结果表明，二长花岗斑岩和花岗闪长斑岩中的岩浆黑云母为镁质黑云母，具有富镁高钛、高铝低硅、富钾贫钠的特点。与花岗闪长斑岩相比，二长花岗斑岩中的岩浆黑云母具有较低的TiO2、FeOT、MgO、MnO、Na2O、BaO含量，较高的Al2O3和SiO2含量。花岗闪长斑岩中的角闪石属于阳起石，具有高硅低铝钛、富镁钙贫钠钾等特征。黑云母和角闪石温度计计算结果显示，含矿二长花岗斑岩中黑云母结晶温度为740.1~783.8℃，平均为762.4℃；含矿花岗闪长斑岩中黑云母结晶温度为750.3~766.9℃，平均为757.2℃；含矿花岗闪长斑岩中角闪石结晶温度为654.1~698.9℃，平均为680.3℃。黑云母和角闪石矿物化学特征指示，二长花岗斑岩和花岗闪长斑岩为造山带钙碱性岩系、Ⅰ型花岗岩，具有壳幔混源的特征。二长花岗斑岩和花岗闪长斑岩具有较高的氧逸度（NNO以上）及水含量，有利于铜、钼等成矿物质进入成矿流体中。  相似文献   

8.
胶东早白垩世高镁闪长岩类的发现及其构造背景   总被引：3，自引：2，他引：1  
胶东地区发育大规模早白垩世壳幔混合源花岗岩类，但一直未发现与花岗岩类相关的独立的幔源侵入体，给深入理解早白垩世壳幔演化带来了困惑。胶东的柳林庄和夏河城岩体以往被认为是三叠纪闪长岩类，本文在详细的野外地质工作基础上，通过年代学、岩石地球化学、同位素地球化学分析，发现这2个岩体为早白垩世高镁闪长岩。样品的SiO2含量在53.29%~62.54%之间，MgO含量为3.60%~8.10%，Mg#主要介于0.47~0.68之间；富集Ba、Rb、K等大离子亲石元素，亏损Nb、Ta、Zr等高场强元素；初始87Sr/86Sr值为0.7082~0.7083，与地幔平均值接近；εNd（t=113Ma）值很低（-20.5~-16.8），与胶东地区的基性脉岩同位素组成一致。2个岩体相比而言，柳林庄岩体富K2O、Fe2O3T，REE、LILE、HFSE含量较高，而MgO、Ni和Cr含量偏低。3件样品的锆石LA-ICP-MS U-Pb同位素加权平均年龄值分别为120.1±1.6Ma、118.3±1.7Ma和122.3±4.0Ma，与壳幔混合源的伟德山型花岗岩及胶东金矿的成岩、成矿时代一致，指示他们形成于统一的地球动力学背景。高镁闪长岩的地球化学特征介于高镁埃达克岩与赞岐岩及埃达克岩与Piip型高镁安山岩之间，指示其形成于古太平洋板块俯冲的地幔楔环境，为富集岩石圈地幔部分熔融的产物。夏河城岩体的岩浆直接来源于含角闪石的富集岩石圈地幔源区，而柳林庄岩体岩浆源区为含金云母的岩石圈地幔并且在岩浆上侵过程中混染了部分地壳物质。  相似文献   

9.
刘学龙  李文昌  尹光侯  张娜 《岩石学报》2013,29(9):3049-3064
普朗斑岩型铜矿床位于西南三江构造火成岩带义敦岛弧南端,是晚三叠世甘孜-理塘洋壳向德格-中甸陆块俯冲的产物,是我国近年来印支期新发现的超大型铜多金属矿床。与成矿关系密切的斑岩体的岩石类型主要为石英闪长玢岩和石英二长斑岩,通过系统的锆石U-Pb测年方法获得,含矿石英闪长玢岩的形成年龄为219.6±3.5Ma,石英二长斑岩的形成年龄为212.8±1.9Ma。岩石地球化学特征表明,SiO2含量为61.99%~70.58%,Al2O3含量为10.84%~14.96%,MgO含量为1.5%~3.96%,A/CNK值为0.80~1.08,为准铝质-弱过铝质。岩石轻稀土较富集,轻重稀土分馏明显((La/Yb)N=11.41~16.48),δEu(0.76~0.9)值无明显异常。微量元素表现出具较高的Sr(244×10-6~845×10-6)、Ba(543×10-6~2237×10-6)含量,Y、Yb含量较低(Y=6.83×10-6~17.65×10-6,Yb=0.97×10-6~1.09×10-6)指示岩石类型为造山带钙碱性花岗岩系列,具I型花岗岩的特点。利用黑云母和角闪石地质温压计估算出岩浆的结晶温度为750~800℃,岩体侵位的压力为0.77×108~0.9×108 Pa,相应的岩体侵位深度在2.55~2.97km,氧逸度为10-9~10-12bar,反映了成矿斑岩体形成于高温、高氧逸度的环境,岩浆侵位具浅成-超浅成侵位的特点。结合本区岩石地球化学、矿物学及同位素年代学的研究,推测普朗成矿斑岩体深部仍存在类似的斑岩型Cu(Au)矿化,具有良好的找矿前景。  相似文献   

10.
江西省都昌县阳储岭钨钼矿床位于江南造山带东段，为准确厘定阳储岭钨钼矿床的成岩成矿时代，本次在详实的野外地质调查基础上，对阳储岭成矿花岗闪长斑进行锆石U-Pb定年工作，同时开展辉钼矿Re-Os同位素定年研究。LA-ICP-MS锆石U-Pb年龄为（145.08±0.35）Ma（MSWD=0.51，n=7）；辉钼矿Re-Os模式年龄为（143.3±2.0）Ma~（145.5±2.2）Ma，等时线年龄为（145.4±1.0）Ma。阳储岭成矿花岗闪长斑岩锆石U-Pb年龄与辉钼矿Re-Os等时线年龄基本一致，表明阳储岭钨钼矿床成岩成矿时代约为145 Ma。辉钼矿中Re含量为16.62×10-6~87.76×10-6，平均值为44.68×10-6，与壳幔混源岩浆热液矿床中Re的含量相似，指示阳储岭钨钼矿床成矿物质来源于壳幔混源。  相似文献   

11.
西准噶尔夏尔莆岩体岩浆混合的锆石U-Pb年代学证据   总被引：1，自引：1，他引：0  
尽管岩相学标志是识别岩浆混合的最直接、最重要的证据,但其寄主岩石、幔源包体及基性岩墙群的精确同位素定年则是对岩浆混合证据的重要补充。夏尔莆岩体由寄主岩石、微细粒镁铁质包体和中基性岩墙群组成,高精度LA-ICP-MS锆石U-Pb测年表明三者的年龄分别为297.6±2.5Ma、298.2±8.0Ma、298.9±5.0Ma,在误差范围内一致,说明三者是同一岩浆事件的产物,为夏尔莆岩体岩浆混合成因提供了年代学证据。夏尔莆岩体的岩浆混合成因的确立证实了早二叠世西准噶尔地壳深部发生过强烈的壳幔岩浆混合作用,并导致了该地区一次重要的地壳垂向生长事件,而岩体中大量的微细粒镁铁质包体和中基性墙群正是这次生长事件的物质记录者。  相似文献   

12.
选择3个典型岩体,即位于西南天山东段的拜城县英买来岩体和位于西段阔克萨岭区的川乌鲁岩体、巴雷公岩体（为了对比,也选择了位于塔里木盆地西北缘的麻扎山岩体）,进行了岩石学和地球化学研究。结果表明,这些岩体具有不同的特点。英买来岩体为黑云母花岗岩和二云母花岗岩,具有高的SiO2含量,弱过铝,高的Sr同位素初始值（约0.710）和负的εNd(t)值（-4～-6）,属于S—A型之间的过渡类型。麻扎山岩体由正长岩组成,属于碱性岩,微量元素标准化图解和其他岩体明显不同的是没有明显的Nb和Ta的负异常。川乌鲁岩体是一个由3个不同期次岩石组成的杂岩体,主体为正长岩-二长岩,地球化学特征显示是由基性岩浆和酸性岩浆不同程度混合形成的。位于同一构造区的巴雷公岩体则与川乌鲁岩体中的花岗斑岩的地球化学特征相似。综合岩石学和地球化学特征推测,南天山东段的英买来岩体是地壳熔融的结果,没有任何地幔物质加入的地球化学信息,西段的阔克萨岭地区酸性岩浆的形成则可能是来自于幔源底侵的基性岩浆导致薄的地壳发生熔融的结果。麻扎山岩体则完全是不同构造背景的产物,有可能与发生在塔里木盆地的二叠纪大规模的岩浆活动有关。因此,二叠纪岩浆活动的性质主要受地壳成分和结构的控制。  相似文献   

13.
The Middle Miocene Tsushima granite pluton is composed of leucocratic granites, gray granites and numerous mafic microgranular enclaves (MME). The granites have a metaluminous to slightly peraluminous composition and belong to the calc‐alkaline series, as do many other coeval granites of southwestern Japan, all of which formed in relation to the opening of the Sea of Japan. The Tsushima granites are unique in that they occur in the back‐arc area of the innermost Inner Zone of Southwest Japan, contain numerous miarolitic cavities, and show shallow crystallization (2–6 km deep), based on hornblende geobarometry. The leucocratic granite has higher initial 87Sr/86Sr ratios (0.7065–0.7085) and lower εNd(t) (?7.70 to ?4.35) than the MME of basaltic–dacitic composition (0.7044–0.7061 and ?0.53 to ?5.24), whereas most gray granites have intermediate chemical and Sr–Nd isotopic compositions (0.7061–0.7072 and ?3.75 to ?6.17). Field, petrological, and geochemical data demonstrate that the Tsushima granites formed by the mingling and mixing of mafic and felsic magmas. The Sr–Nd–Pb isotope data strongly suggest that the mafic magma was derived from two mantle components with depleted mantle material and enriched mantle I (EMI) compositions, whereas the felsic magma formed by mixing of upper mantle magma of EMI composition with metabasic rocks in the overlying lower crust. Element data points deviating from the simple mixing line of the two magmas may indicate fractional crystallization of the felsic magma or chemical modification by hydrothermal fluid. The miarolitic cavities and enrichment of alkali elements in the MME suggest rapid cooling of the mingled magma accompanied by elemental transport by hydrothermal fluid. The inferred genesis of this magma–fluid system is as follows: (i) the mafic and felsic magmas were generated in the mantle and lower crust, respectively, by a large heat supply and pressure decrease under back‐arc conditions induced by mantle upwelling and crustal thinning; (ii) they mingled and crystallized rapidly at shallow depths in the upper crust without interaction during the ascent of the magmas from the middle to the upper crust, which (iii) led to fluid generation in the shallow crust. The upper mantle in southwest Japan thus has an EMI‐like composition, which plays an important role in the genesis of igneous rocks there.  相似文献   

14.
余石山铌钽矿区位于北阿尔金-柴北缘-祁连的交汇部位，该区域构造演化复杂.为了揭示矿区内二长花岗岩的成因和形成环境，运用岩石学、岩石地球化学、锆石U-Pb年代学、锆石Lu-Hf同位素等理论及技术方法对该二长花岗岩进行了系统的研究.该二长花岗岩的详细定名为中细粒似斑状黑云二长花岗岩，暗色矿物以黑云母、角闪石为主.地球化学特征表明，余石山的二长花岗岩属于钾玄质准铝质-弱过铝质系列，富集Rb、Th、K等大离子亲石元素，相对亏损Nb、Sr、P、Ti等高场强元素，稀土元素配分曲线具有明显的负Eu异常，δEu的平均值为0.57，（La/Yb）N的平均值为11.09，说明该二长花岗岩体岩浆部分熔融程度较高.根据岩石学及地球化学特征可判断该岩体为I型花岗岩.锆石LA-ICP-MS U-Pb定年显示，该二长花岗岩的结晶年龄为481.3±1.7 Ma，形成于早奥陶世.锆石Lu-Hf同位素分析表明，锆石εHf（t）的值为+0.4~+11.8，均为正值，二阶段模式年龄的范围为675~1 308 Ma，指示其源岩主要为元古代新生地壳物质.该二长花岗岩的形成与早奥陶世时期北阿尔金洋壳俯冲中南祁连陆壳密切相关，在中南祁连陆壳边缘的余石山地区（弧后），由于洋壳俯冲导致了陆壳的伸展从而产生了裂隙，俯冲产生的熔融岩浆通过裂隙上侵而形成了该二长花岗岩岩体.   相似文献   

15.
栖霞牙山花岗岩体形成于中生代早白垩世（118 Ma），其岩石类型以花岗岩和花岗闪长岩为主，岩体中发育大量的暗色闪长质微粒包体。通过对牙山花岗岩及其暗色包体地球化学特征研究表明，包体围岩w（SiO2）=65.5%~68.82%，铝饱和度（A/CNK）为0.89~1.03<1.1，为准铝质钙碱性Ⅰ型花岗岩；暗色包体具有较低w（SiO2）值（54.82%~60.89%）、高w（TFe2O3）值（6.11%~8.15%）、高w（MgO）值（3.57%~5.19%）的特征。稀土元素配分模式图显示二者皆为轻稀土富集的右倾型曲线，微量元素蛛网图中二者均表现为富集Ba、K等大离子亲石元素，亏损Ta、Nb、Ti等高场强元素，具有大陆地壳的特征。暗色包体与寄主岩石的Sr同位素初始比值（87Sr/86Sr）i分别为0.709 29~0.709 58和0.709 21~0.709 71，应为同源岩浆的产物。两阶段Nd模式年龄（T2DM）分为2 291 Ma-2 391 Ma和2 208 Ma-2 353 Ma，表明可能是古元古界陆壳物质部分熔融的产物。Pb同位素特征显示牙山岩体的原始岩浆以下地壳为主，w（Nb）/w（Ta）值介于下地壳与原始地幔之间，表明可能受到幔源物质的影响，包体中大量磷灰石呈针状结晶状态，进一步暗示存在岩浆混合作用。综上并结合区域构造背景认为，牙山岩体为早白垩世中晚期起源于火山弧环境的壳源特征花岗岩，形成过程中存在幔源物质的加入，它的形成与太平洋板块的俯冲作用密切相关。  相似文献   

16.
The Yingchengzi gold deposit, located 10 km west of Shalan at the eastern margin of the Zhangguangcai Range, is the only high commercially valuable gold deposit in southern Heilongjiang Province, NE China. This study investigates the chronology and geodynamic mechanisms of igneous activity and metallogenesis within the Yingchengzi gold deposit. New zircon U–Pb data, fluid inclusion 40Ar/39Ar dating, whole‐rock geochemistry and Sr–Nd isotopic analysis is presented for the Yingchengzi deposit to constrain its petrogenesis and mineralization. Zircon U–Pb dating of the granite and diabase–porphyrite rocks of the igneous complex yields mean ages of 471.7 ± 5.5 and 434 ± 15 Ma respectively. All samples are high‐K calc‐alkaline or shoshonite rocks, are enriched in light rare earth elements and large ion lithophile elements, and are depleted in high field strength elements, consistent with the geochemical characteristics of arc‐type magmas. The Sr–Nd isotope characteristics indicate that the granite formed by partial melting of the lower crust, including interaction with slab‐derived fluids from an underplated basaltic magma. The primary magma of the diabase–porphyrite was likely derived from the metasomatized mantle wedge by subducted slab‐derived fluids. Both types of intrusive rocks were closely related to subduction of the ocean plate located between the Songnen–Zhangguangcai Range and Jiamusi massifs. However, fluid inclusion 40Ar/39Ar dating indicates that the Yingchengzi gold deposit formed at ~249 Ma, implying that the mineralization is unrelated to both the granite (~472 Ma) and diabase–porphyrite (~434 Ma) intrusions. Considering the tectonic evolution of the study area and adjacent regions, we propose that the Yingchengzi gold deposit was formed in a late Palaeozoic–Early Triassic continental collision regime following the closure of the Paleo‐Asian Ocean. In addition, the Yingchengzi deposit could be classified as a typical orogenic‐type gold deposit occuring in convergent plate margins in collisional orogens, and unlikely an intrusion‐related gold deposit as reported by previous studies. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

17.
《Gondwana Research》2014,26(4):1570-1598
Granitic rocks are commonly used as means to study chemical evolution of continental crust, particularly, their isotopic compositions, which reflect the relative contributions of mantle and crustal components in their genesis. New SIMS and K–Ar geochronology, isotope, geochemical, and mineral chemistry data are presented for the granitoid rocks located in and around Gabal Dara in the Northern Eastern Desert of Egypt. The granitoid suite comprises quartz diorites, Muscovite (Mus) trondhjemites, and granodiorites intruded by biotite-hornblende (BH) granites and alkali feldspar (AF) granites. Mus trondhjemite, granodiorite and BH granite exhibit I-type calc alkaline affinities. Mus trondhjemite and granodiorite show medium-K calc-alkaline and metaluminous/mildy peraluminous affinities, whereas BH granites have high-K calc-alkaline and metaluminous character. Concordant 206Pb/238U weighted mean ages together with geochemical peculiarities suggest that Mus trondhjemites (741 Ma) followed by granodiorites (720 Ma) are genetically unrelated, and formed in subduction-related regime by partial melting of lower oceanic crust together with a significant proportion of mantle melt. The genesis of Mus trondhjemites is correlated with the main event in the evolution of the Eastern Desert, called “~750 Ma crust forming event”.The field and geochemical criteria together with age data assign the high-K calc-alkaline BH granites (608–590 Ma) and alkaline AF granites (600–592 Ma) as post-collisional granites. The differences in geochemical traits, e.g. high-K calc-alkaline versus alkaline/peralkaline affinities respectively, suggest that BH granites and AF granites are genetically unrelated. The age overlap indicating coeval generation of calc-alkaline and alkaline melts, which in turn suggests that magma genesis was controlled by local composition of the source. The high-K calc-alkaline BH granites are most likely generated from lithospheric mantle melt which have been hybridized by crustal melts produced by underplating process. AF granites exhibit enrichment in K2O, Rb, Nb, Y, and Th, and depletion in Al2O3, TiO2, MgO, CaO, FeO, P2O5, Sr, and Ba as well as alkaline/peralkaline affinity. These geochemical criteria combined with the moderately fractionated rare earth elements pattern (LaN/YbN = 9–14) suggest that AF granite magma might have been generated by partial melting of Arabian–Nubian Shield (ANS) arc crust in response of upwelling of hot asthenospheric mantle melts, which became in direct contact with lower ANS continental crust material due to delamination. Furthermore, a minor role of crystal fractionation of plagioclase, amphibole, biotite, zircon, and titanomagnetite in the evolution of AF granites is also suggested. The low initial 87Sr/86Sr ratios (0.7033–0.7037) and positive εNd(T) values (+ 2.32 to + 4.71) clearly reflect a significant involvement of depleted mantle source in the generation of the post-collision granites and a juvenile nature for the ANS.  相似文献   

18.
Mesozoic granitic intrusions are widely distributed in the Nanling region,South China.Yanshanian granites are closely connected with the formation of tungsten deposits.The Xihuashan granite is a typica...  相似文献   

19.
浙闽沿海大面积出露的中生代酸性火山岩区有少量早白垩世玄武岩分布,它们具典型钾富集和铌等元素亏损特征,其同位素组成表现为较高ISr(0.7055-0.7106)、低的εNd(1.2--10.6,大多介于-3.2--10.6之间)及富放射性成因铅(206Pb/204Pb=18.355-18.726,207Pb/204Pb=15.455-15.799,208Pb/204Pb=38.530-39.319).这些特征表明玄武岩源区为一富集型的陆下岩石圈地幔,由古老的俯冲地壳物质再循环进入并交代地幔而形成。没有证据表明本区早白垩世基性和酸性岩浆之间发生过大规模的化学混合,但不排除同位素之间的交换以及局部的化学和机械混合。壳-幔混合与地壳混染仅在少数玄武岩的形成过程中起着较重要的作用。  相似文献   

20.
The Sharang porphyry Mo deposit is the first discovered Mo porphyry‐type deposit in the Gangdese Metallogenic Belt. The orebody is hosted by the Eocene multi‐stage composite intrusive complex which is emplaced in the Upper Permian Mengla Formation and cut by the Miocene dykes. Granite porphyry is recognized as the ore‐bearing porphyry in the complex, which consists of quartz diorite, quartz monzonite, granite, prophyritic granite and post‐mineral lamprophyre. Granodiorite porphyry and dacite porphyry intrude the granite porphyry. Geochemical data indicate that Sharang complex has a High‐K calc‐alkalinc to shoshonitic, metaluminous to slightly peraluminous composition. The Sharang complex rocks are enriched in large ion lithophile elements, depleted in high‐field strength elements, Nb, Sr, P and Ti. REE patterns show slight enrichments in light REE relative to heavy REE and weak negative Eu anomalies. All rocks in this complex have a wide range of initial 87Sr/86Sr ratios (0.705605～0.712496) and lower εNd(t) values (?0.61～?7.80). The geochemical data suggest highly oxidized‐evolved magma and old continental materials may have been the magma source for the Sharang intrusive complex that host porphyry Mo mineralization. Eocene pre‐ore and ore‐forming rocks at Sharang may have formed by partial melting of mantle wedge and by mixing with old continental crust at the lower crust level. In contrast the post‐ore rocks may have formed by partial melting of enriched lithospheric mantle.  相似文献   

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