北祁连造山带东段老虎山石英闪长岩成因及其地质意义     

张海瑞  赵姣龙  于汇洋 《高校地质学报》1997,25(5):641

以北祁连造山带东段老虎山石英闪长岩体为研究对象，进行了锆石U-Pb年龄及全岩元素与Sr-Nd同位素组成的系统 测定，据此探讨了岩石的成因及其对北祁连构造演化的启示。锆石LA-ICP-MS U-Pb定年结果表明，石英闪长岩体的形成 年龄为440 Ma。岩石具有亚碱、准铝以及贫钙、镁、铁的特征，碱铝指数（AKI值） 均低于0.85，铝饱和指数（A/NKC 值） 多小于1.0，属钙碱性I型花岗岩类岩石。在稀土和微量元素组成上，岩石富集轻稀土和大离子亲石元素（如Rb、Cs、 Th和U），亏损高场强元素（如Nb和Ta），显示弧岩浆岩的地球化学特征。岩体具有相对均一的Sr-Nd同位素组成，初始Sr同 位素值为0.7058~0.7071，εNd(t)值为-1.06~-0.31。综合分析表明，老虎山石英闪长岩应起源于玄武质下地壳物质的部分熔 融，并在成岩过程中有少量幔源物质的混入。对区内火成岩地质地球化学特征与产出背景的全面分析，表明受北祁连洋俯 冲及随后岛弧与祁连—柴达木陆块碰撞拼贴影响，弧后盆地的北向俯冲消减作用可能是诱发民乐窑沟和老虎山弧岩浆岩以 及导致毛藏寺—老虎山花岗岩带内埃达克质岩石侵位的基本动力机制。  相似文献   

西昆仑山阿卡孜岩体锆石SHRIMP定年及其地球化学特征   总被引：12，自引：3，他引：12  

张传林  王中刚  沈加林  毕华  郭坤一  王爱国 《岩石学报》2003,19(3):523-529

西昆仑山阿卡孜岩体是该区已知的最古老侵入体。岩体侵入于太古代赫罗斯坦群(TTG岩系)中。获得最新的单颗粒锆石SHRIMP年龄为2426±46Ma。岩石地球化学研究表明,岩石具有高碱度富K特征;∑REE为409.94×10~(-6)～787.76×10~(-6),δEu为0.48～0.73;微量元素显示富集大离子元素。综合分析该岩体地质地球化学特征,认为该岩体形成于晚太古代～古元古代初期碰撞后拉张背景,是TTG岩系(赫罗斯坦群)重熔的结果。这对研究西昆仑山早前寒武纪陆壳增生及构造演化提供了重要的地质资料。  相似文献   

安徽安庆月山岩体的磁组构及古地磁特征   总被引：3，自引：0，他引：3  

阎桂林  张鸣 《地球科学》1990,15(6):667-673

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河北阜平地区太古宙变质深成岩与金矿的关系初探          下载免费PDF全文

夏国礼  张家奇  杨进京 《地质与勘探》2007,43(4):46-50

区内变质深成岩由阜平岩群变质表壳岩经深部重熔作用形成,典型特征是低钾富钠,具有TTG岩石特点.经对变质深成岩成矿元素的研究表明:①Au元素丰度值很高(平均2.10×10-6),远远高于世界中性-中酸性侵入岩及地壳中Au元素的丰度值;②Au元素浓集克拉克值(488.37)远远大于1,呈非常强的富集状态;③Au元素在变质深成岩中的变异系数(0.65)几乎是区内变质表壳岩中Au元素的2倍,有利于Au元素的聚集成矿.故变质深成岩应是成矿物质的主要提供者.  相似文献   

Magmatic structures in the Krkonoše–Jizera Plutonic Complex,Bohemian Massif: evidence for localized multiphase flow and small-scale thermal–mechanical instabilities in a granitic magma chamber     

Jiří Žák  Josef Klomínský 《Journal of Volcanology and Geothermal Research》2007

The present paper examines magmatic structures in the Jizera and Liberec granites of the Krkonoše–Jizera Plutonic Complex, Bohemian Massif. The magmatic structures are here interpreted to preserve direct field evidence for highly localized magma flow and other processes in crystal-rich mushes, and to capture the evolution of physical processes in an ancient granitic magma chamber. We propose that after chamber-wide mixing and hybridization, as suggested by recent petrological studies, laminar magma flow became highly localized to weaker channel-like domains within the higher-strength crystal framework. Mafic schlieren formed at flow rims, and their formation presumably involved gravitational settling and velocity gradient flow sorting coupled with interstitial melt escape. Local thermal or compositional convection may have resulted in the formation of vertical schlieren tubes and ladder dikes whereas subhorizontal tubes or channels formed during flow driven by lateral gradients in magma pressure. After the cessation or deceleration of channel flow, gravity-driven processes (settling of crystals and enclaves, gravitational differentiation, development of downward dripping instabilities), accompanied by compaction, filter pressing and melt segregation, dominated in the crystal mush within the flow channels. Subsequently, magmatic folds developed in schlieren layers and the magma chamber recorded complex, late magmatic strains at high magma crystallinities. Late-stage magma pulsing into localized submagmatic cracks represents the latest events of magmatic history of the chamber prior to its final crystallization. We emphasize that the most favorable environments for the formation and preservation of magmatic structures, such as those hosted in the Jizera and Liberec granites, are slowly cooling crystal-rich mushes. Therefore, where preserved in plutons, these structures may lend strong support for a “mush model” of magmatic systems.  相似文献   

Advective heat transfer and fabric development in a shallow crustal intrusive granite — the case of Proterozoic Vellaturu granite,south India     

Dilip Saha  Sukanya Chakraborti 《Journal of Earth System Science》2007,116(5):433-450

Syntectonic plutons emplaced in shallow crust often contain intermediate-to low-temperature deformation microstructures but lack a high-temperature, subsolidus deformation fabric, although the relict magmatic fabric is preserved. The Proterozoic Vellaturu granite emplaced at the eastern margin of the northern Nallamalai fold belt, south India during the late phase of regional deformation has a common occurrence of intermediate-to low-temperature deformation fabric, superimposed over magmatic fabric with an internally complex pattern. But high-T subsolidus deformation microstructure and fabric are absent in this pluton. The main crystal plastic deformation and fluid enhanced reaction softening was concentrated along the margin of the granite body. Resulting granite mylonites show Y-maximum c-axis fabric in completely recrystallized quartz ribbonds, dynamic recrystallization of perthites, and myrmekite indicative of fabric development under intermediate temperature (∼ 500–400°C). The weakly-deformed interior shows myrmekite, feldspar microfracturing and limited bulging recrystallization of quartz. The abundance of prism subgrain boundaries is indicative of continuing deformation through low-temperature (∼ 300°C). The relative rates of cooling influenced by advective heat transfer and deformation of the pluton seem to control the overall subsolidus fabric development. The rapid advective heat transfer from the interior in the early stages of subsolidus cooling was followed by slow cooling through intermediate temperature window as a well-developed phyllosilicate rich mylonitic skin around the granite body slowed down conductive heat loss. Low-T crystal plastic deformation of quartz was effected at a late stage of cooling and deformation of the shallow crustal granite body emplaced within the greenschist facies Nallamlai rocks.  相似文献   

冀北小张家口超基性岩体的锆石U-Pb年龄和Hf同位素组成   总被引：6，自引：5，他引：6  

田伟 陈斌刘超群  张华锋 《岩石学报》2007,23(3):583-590

采用离子探针(SHRIMPⅡ)测得小张家口基性-超基性岩体中的锆石主要有220±5Ma和491±7Ma两组年龄,以及一个很老的继承锆石年龄2453Ma。年龄为220±5Ma的一组锆石(A组)具有典型的岩浆型振荡环带,这组年龄应代表该岩体的侵位年龄。A组锆石的~(176)H/~(177)Hf比值从0.282557到0.282690,ε_(Hf)(220Ma)=-2.9～ 1.66。年龄为491±7Ma的一组锆石(B组)具有变质成因的蝴蝶结构(Butterfly structure)和熔蚀边,属于继承锆石。B组锆石的~(176)Hf/~(177)Hf比值从0.282239到0.282483,ε_(Hf)(491Ma)=-8.6～0.06。~(207)Pb/~(206)Pb年龄为2453Ma的锆石应该是岩浆侵位时从华北克拉通古元古代基底中捕获的锆石。A组锆石的Hf同位素数据表明,220Ma左右由于华北北缘岩石圈伸展,导致软流圈地幔上涌,亏损的软流圈地幔流/熔体与富集的岩石圈地幔相互作用并混合,这种混合地幔源区发生部分熔融而形成小张家口基性-超基性岩体。B组锆石可能是小张家口岩体在岩浆侵位过程中捕获的来源于富集地幔或大陆下地壳的锆石。  相似文献   

浙江沐尘石英二长岩体的岩石地球化学特征及构造意义   总被引：5，自引：0，他引：5  

卢成忠 《地球化学》2007,36(5):457-466

出露于江山-绍兴断裂带西南段东南侧的沐尘岩体,以发育暗色包体和环斑长石为特征,具有显著的岩浆混合作用.寄主岩为二长岩-石英二长岩组合,包体岩石为二长闪长岩.二长岩组合.造岩矿物有钾长石、斜长石、石英、普通角闪石和黑云母.岩石富碱(Na2O K2O=6.58%～10.42%,平均8.41%)、高钾(K2O/Na2O=0.72～1.45,平均1.16)、贫钛(TiO2=0.37%～1.22%,平均0.76%)、富集大离子亲石元素和轻稀土元素,具有钾玄质系列的岩石地球化学特征.该岩体侵位于后碰撞弧构造环境,是早白垩世早期该区重要的构造.岩浆热事件的产物.  相似文献   

姑婆山复式岩体的基本特征及其与成矿作用的关系   总被引：5，自引：0，他引：5  

王建辉  蒋柏昌  孔祥伟  唐奎保 《矿产与地质》2006,20(1):47-53

姑婆山复式岩体由晚侏罗世里松岩体、姑婆山岩体及早白垩世新路岩体组成。复式岩体为壳幔混合源成因。据岩石地球化学判断和分析,姑婆山岩体和新路岩体为含锡岩体;整个姑婆山复式岩体为含钨岩体,里松岩体和姑婆山岩体为含稀有、稀土岩体。上述矿产的形成与岩石中挥发份F、B及放射性U、T h等元素的高含量有关。  相似文献   

内蒙古沙麦岩体：正εNd（t）值的过铝质花岗岩   总被引：1，自引：0，他引：1  

胡朋  聂凤军赫英 刘妍 《岩石学报》2006,22(11):2781-2790

内蒙古沙麦岩体位于大兴安岭中段西坡,是二连浩特-东乌珠穆沁旗花岗岩带的重要组成部分。岩体中脉岩和围岩捕虏体较为发育,岩性组合主要为中细粒黑云母花岗岩和细粒似斑状花岗岩。在化学成分上,沙麦岩体以铝弱过饱和,富硅,全碱含量中等和低磷为特点,标准矿物中刚玉分子大于1%,可归为过铝质 S 型花岗岩。在稀土元素和微量元素组成上,岩体富 Rb、Th、U、Ta,贫 Ba、Sr、P、Ti,Rb/Sr 比值高,K/Rb 比值低,Eu 负异常明显。在 Nd 同位素组成上,岩体 Nd 同位素组成变化较大,除一件样品ε_(Nd)(t)值为负值以外,普遍以具正ε_(Nd)(t)值为特点,T_(2DM)值介于275.79～1048.41Ma 之间。研究结果表明,沙麦岩体形成于晚中生代后造山的岩石圈伸展环境中,是幔源基性岩浆底侵及其诱发的壳-幔混合岩浆,同化中上地壳泥质围岩并经高程度分离结晶的产物。  相似文献