滇西双江县勐库地区临沧花岗岩中暗色包体锆石U-Pb年代学及其地质意义

位于三江南段双江勐库地区的临沧花岗岩,主体岩性为黑云母二长花岗岩,其次为黑云母花岗闪长岩和碱长花岗岩。通过野外地质调查,在勐库热水塘附近黑云二长花岗岩中发现了与其紧密共生的暗色镁铁质微粒包体(MME)-闪长岩。本文对暗色闪长岩包体进行了岩相学观察、LA-ICP-MS锆石U-Pb定年和全岩主量元素分析。暗色闪长岩包体LA-ICP-MS锆石U-Pb年龄为230.9±1.2Ma,与中细粒黑云二长花岗岩LA-ICP-MS锆石U-Pb年龄(229.2±0.8Ma)基本一致。岩石地球化学特征表明,黑云二长花岗岩富K₂O和Na₂O,Na₂O > K₂O,富Al₂O₃,铝饱和指数A/CNK平均为1.17;闪长岩K₂O和Na₂O含量中等,Na₂O > K₂O,富Al₂O₃和MgO,铝饱和指数A/CNK平均为0.77。二者稀土配分曲线为右倾的轻稀土富集型,二者均富集大离子亲石元素而亏损高场强元素Nb、Ta等,均具有相对较高的Mg^#(黑云二长花岗岩30.50~61.41;闪长岩58.58~67.34)。中细粒黑云二长花岗岩Cr、Ni含量(平均值分别为46.96×10^-6和11.21×10^-6)小于闪长岩Cr、Ni含量(平均值分别为197.62×10^-6和75.68×10^-6)。综合研究表明,该地区花岗质岩浆的形成很可能与地幔流体作用引发的地壳部分熔融与壳幔岩浆混合作用密切相关,形成于陆陆碰撞-后碰撞的构造背景,暗示保山地块与思茅地块在230Ma已经进入了陆陆碰撞-后碰撞的地质时期。     

甘肃北山旧井岩体BS03号钻孔岩石地球化学特征

文章对旧井岩体BS03号钻孔的岩石学、岩石化学以及同位素地球化学特征等进行了研究。结果表明:BS03号钻孔所见的主要岩石类型为似斑状二长花岗岩,其次为英云闪长岩、石英闪长岩及中粗粒花岗岩、伟晶岩、细晶岩等。似斑状二长花岗岩、黑云母花岗岩以及英云闪长岩的铝碱指数(ASI)为1.0左右,均为准铝质;而石英闪长岩的铝碱指数(ASI)仅为0.66~0.68,表现为明显的铝不饱和。上述各类岩石均表现为I型花岗岩的稀土配分曲线特征,且其稀土配分曲线总体较为相似,说明它们之间具有一定的成因联系。Nd、Sr同位素地质特征揭示:该区花岗岩的成岩物质来源于下地壳,并可能有上地幔物质的介入。     

福建同安二长花岗岩风化壳中的粘土矿物

二长花岗岩风化壳自下而上划分为原生带、微风化带、弱风化带和强风化带。风化壳中粘土矿物主要为埃洛石,其次为高岭石及少量伊利石。微风化带下部以高岭石为主,往上埃洛石逐渐占优势,并于弱风化带中、上部和强风化带中局部富集,这与当时地下水活动状态有关。高岭石结晶程度随风化程度的增强而提高。在弱酸性介质条件下及水分丰富、溶出条件强烈时,从长石解理面上和长石的“溶蚀”空隙中可以直接形成高岭石或埃洛石,而过渡阶段的伊利石很不发育或不存在。     

Field evidence,mineral chemical and geochemical constraints on mafic-felsic magma interactions in a vertically zoned magma chamber from the Chotanagpur Granite Gneiss Complex of Eastern India

The Nimchak granite pluton (NGP) of Chotanagpur Granite Gneiss Complex (CGGC), Eastern India, provides ample evidence of magma interaction in a plutonic regime for the first time in this part of the Indian shield. A number of outcrop level magmatic structures reported from many mafic-felsic mixing and mingling zones worldwide, such as synplutonic dykes, mafic magmatic enclaves and hybrid rocks extensively occur in our study domain. From field observations it appears that the Nimchak pluton was a vertically zoned magma chamber that was intruded by a number of mafic dykes during the whole crystallization history of the magma chamber leading to magma mixing and mingling scenario. The lower part of the pluton is occupied by coarse-grained granodiorite (64.84–66.61?wt.% SiO₂), while the upper part is occupied by fine-grained granite (69.80–70.57?wt.% SiO₂). Field relationships along with textural and geochemical signatures of the pluton suggest that it is a well-exposed felsic magma chamber that was zoned due to fractional crystallization. The intruding mafic magma interacted differently with the upper and lower granitoids. The lower granodiorite is characterized by mafic feeder dykes and larger mafic magmatic enclaves, whereas the enclaves occurring in the upper granite are comparatively smaller and the feeder dykes could not be traced here, except two late-stage mafic dykes. The mafic enclaves occurring in the upper granite show higher degrees of hybridization with respect to those occurring in the lower granite. Furthermore, enclaves are widely distributed in the upper granite, whereas enclaves in the lower granite occur adjacent to the main feeder dykes.Geochemical signatures confirm that the intermediate rocks occurring in the Nimchak pluton are mixing products formed due to the mixing of mafic and felsic magmas. A number of important physical properties of magmas like temperature, viscosity, glass transition temperature and fragility have been used in magma mixing models to evaluate the process of magma mixing. A geodynamic model of pluton construction and evolution is presented that shows episodic replenishments of mafic magma into the crystallizing felsic magma chamber from below. Data are consistent with a model whereby mafic magma ponded at the crust-mantle boundary and melted the overlying crust to form felsic (granitic) magma. The mafic magma episodically rose, injected and interacted with an overlying felsic magma chamber that was undergoing fractional crystallization forming hybrid intermediate rocks. The intrusion of mafic magma continued after complete solidification of the magma chamber as indicated by the presence of two late-stage mafic dykes.     

Igneous banding, schlieren and mafic enclaves in calc-alkaline granites: The Budduso pluton (Sardinia)

This study deals with the origin of igneous layering in plutons, and, especially, the extent layering is related to mafic–silicic magma interactions. The Budduso pluton (Sardinia) shows three main scales of organization.(i) Large scale lithological variations correspond to three main magmatic units, with differentiation increasing from the Outer (hornblende-bearing biotite granodiorite/monzogranite) to the Middle (biotite monzogranite) and the Inner (leucomonzogranite) units. The striking homogeneity of ⁸⁷Sr/⁸⁶Sr initial ratios (0.7090 ± 4) and ε_Nd(t) values (− 5.6 ± 0.1) strongly suggests that magma isotopic equilibration was achieved prior to emplacement, whereas mixing/mingling structures observed within the pluton reflect second-stage processes involving broadly cogenetic components.(ii) Metre to decametre-scale igneous layering may be isomodal or modally-graded, locally with cross-layering. Biotite and plagioclase compositions are similar in both biotite-rich and quartzofeldspathic layers, as are the trace-element patterns which differ only by relative abundances. This precludes an origin by fractional crystallization. A penetrative submagmatic fabric superimposed on the layering and corresponding mainly to flattening can be ascribed to interference between pluton growth and regional deformation.(iii) Composite layering and schlieren are commonly associated to mafic microgranular enclaves, locally within synmagmatic shear zones or disrupted synplutonic dykes. In that case, there is a progressive shift in biotite X_Fe values from the core of enclave ( 0.65) to the host monzogranite ( 0.72): schlieren in the monzogranite show biotite X_Fe values similar to that of the host rock, whereas schlieren close to mafic enclaves show lower X_Fe values ( 0.69) towards those of enclave rims.These features can be ascribed to three main processes: (i) assembly of differentiated (± mixed/mingled) magmatic pulses; (ii) local hydrodynamic sorting related to density currents in a mush, and segregation of residual melt; (iii) mechanical disruption and chemical hybridization of mafic magmas during ascent or within the pluton related to magma dynamics. None of these processes affect the whole pluton but they are limited to specific magmatic units. Therefore, pluton growth by incremental assembly of magma batches is not incompatible with magma chamber processes.     

阿尔金造山带南缘岩浆混合作用:玉苏普阿勒克塔格岩体岩石学和地球化学证据

阿尔金造山带南缘玉苏普阿勒克塔格岩体中的似斑状中粗粒黑云钾长花岗岩发育有岩浆成因的暗色包体,并且该花岗岩被花岗细晶岩呈脉状侵入。该岩体含有丰富的岩浆混合作用特征: 如暗色包体中的碱性长石斑晶、针状磷灰石、长石的环斑结构、石英/斜长石主晶和榍石眼斑等。暗色包体、寄主花岗岩和花岗细晶岩代表了岩浆混合演化过程中不同端元比例混合的产物。地球化学特征上,钾长花岗岩和暗色包体的主要氧化物含量在Harker图解中多呈线性变化。暗色包体主要为闪长质,MgO、K₂O含量高,为钾玄岩系列,总体上高场强元素不亏损,显示了岩浆混合中的基性端元信息,可能为幔源熔体结晶分异或壳幔物质的混合产物。寄主花岗岩均为准铝质,富碱,为高钾钙碱性系列,亏损Nb、Ta、Sr、P、Ti等高场强元素,高K₂O/Na₂O,富集高不相容元素,Ga含量高,显示了A型花岗岩的特征,Th/U 和Nb/Ta比值分别介于为6.67~10.96、8.99~11.94,代表了下地壳源区。花岗细晶岩均为钠质、过铝质,TiO₂、MgO含量低, Na₂O和CaO含量高,具有混合岩浆侵位后分异的特征。岩相学和地球化学特征说明岩浆混合作用对于环斑结构花岗岩的形成起到重要作用。花岗细晶岩中环斑长石的斜长石外环与钾长石内核的厚度比大于钾长花岗岩中的环斑长石,指示混合岩浆在一定的减压条件下更有利于环斑结构的形成。玉苏普阿勒克塔格岩体中的钾玄质暗色包体、高钾钙碱性花岗岩和中钾钙碱性花岗细晶岩代表了岩浆演化不同阶段的产物,反映了一个幔源岩浆和下地壳不断相互作用,引起地壳连续伸展减薄的过程,指示阿尔金南缘在早古生代末期存在造山后伸展背景下的幔源岩浆底侵作用。同一岩体中两种不同时代岩性的环斑结构显示了该岩体形成历史中的一定时空演化关系,代表了伸展过程中不同阶段的产物。     

安徽铜陵地区幔源镁铁质团块研究及其地质意义

幔源岩石包体研究,是认识上地幔岩石圈物质组成、幔源岩浆演化及壳幔动力学过程的重要手段。铜陵地区小铜官山石英二长闪长岩中发育有微粒闪长质包体,并且这些微粒闪长质包体中不均匀地分布着镁铁质团块,三者的形成过程可视为铜陵地区岩浆演化的缩影,为了解本区深部岩浆作用过程提供了有力的证据。在前人研究的基础上,笔者借助电子探针、扫描电镜、电镜能谱和二次飞行时间离子探针(Tof-SIMS)对产于铜陵地区微粒闪长质包体中的镁铁质团块进行了详细的研究,首次获得了一套精确的矿物化学资料和元素分布图,总结了镁铁质团块的特征,并讨论了本区的深部岩浆作用过程。矿物学研究表明,镁铁质团块中的角闪石和辉石均已发生了不同程度的透闪石化和阳起石化蚀变,蚀变过程中,从镁钙闪石到镁角闪石,再到透闪石,随着Si的增加,角闪石呈现出Mg的富集和Ti、Al贫化的特点。团块中的富Cr磁铁矿、Ti磁铁矿和少量的铝直闪石指示了其具有深源性。Tof-SIMS元素分布图显示,透闪石主要由Al、Si、Ca、Sc、V、Cr、Mn、Cu和Sr元素组成,透辉石主要由Si、Mg、Ca、Cu和Rb组成。在铜陵地区,上地幔部分熔融形成一套玄武岩浆,受岩浆底侵作用影响,玄武岩浆上侵,进入下地壳深位岩浆房,与下地壳硅镁层发生同化混染作用,形成一套轻度演化的中基性(辉长质)玄武岩浆,镁铁质团块就是这类中基性玄武岩浆直接结晶形成的。后受构造作用影响,这类中基性玄武岩浆上侵到中地壳岩浆房(12~16 km),与中地壳的变质岩系发生同化混染和结晶分异作用形成一套中性闪长质岩浆,微粒闪长质包体就是这套闪长质岩浆发生结晶分异作用而形成的。镁铁质团块和微粒闪长质包体清楚地解释了铜陵地区深部岩浆作用过程,并有力地证明了铜陵地区中地壳的闪长质岩浆来源于下地壳的壳幔混源岩浆。     

City on edge: immigrant businesses and the right to urban space in inner-city Johannesburg

Paradoxically, Johannesburg is a quintessentially migrant city and also ranks among the least immigrant-friendly cities in the world. Over the past 20 years, inner-city Johannesburg has been vacated and then reconstituted as a hive of informal trade networks and migration circuits that extends well beyond national borders. Research on immigrants in Johannesburg has contributed significantly to understandings of xenophobic sentiments and immigrant identities, but there remains a large gap in knowledge about immigrant entrepreneurship, economic enclaves and economic mobility. Our research is based on extensive fieldwork, discussions with immigrant organizations and in-depth interviews with immigrants and South Africans engaged in business in three prominent inner-city immigrant business enclaves: Jeppe/Delvers, Eighth Avenue and Raleigh Street. Our research shows that these immigrant business zones each operate differently and vary in the degree to which they connect to urban and national economic grids; some retain stronger ties to transnational networks that link dispersed spaces to Johannesburg, creating specific local milieus. We advocate for a more geographically sensitive and nuanced understanding of immigrant entrepreneurs and a reconsideration of their rights to the city.     

西秦岭天水地区太白花岗岩体LA-ICP-MS锆石U-Pb年龄、地球化学特征及其地质意义

秦岭造山带南缘勉略构造带北侧发育有近东西向展布的印支期花岗岩带,位于甘肃徽县地区的太白岩体是该花岗岩类的一部分。LA-ICP-MS锆石U-Pb同位素年龄表明,太白岩体的形成时代为221.8Ma±1.5Ma,属于印支期晚期。主要岩石类型为灰白色—肉红色中细粒二长花岗岩和花岗闪长岩。地球化学特征表明,太白岩体属于准铝质—弱过铝质的高钾钙碱性系列;稀土元素总量ΣREE为79.0×10-6~194×10-6,稀土元素配分模式呈轻稀土元素强烈富集、重稀土元素相对亏损的右倾型,Eu负异常明显;高场强元素（HFSE）Nb、P、Ti、Y、Yb和大离子亲石元素Ba、Sr强烈亏损。太白岩体是以中基性岩石为主的壳源物质部分熔融形成的岩浆上升侵位形成的,且处于同碰撞（挤压环境）向后碰撞（伸展环境）转化阶段,为后造山期花岗岩,是扬子板块和华北板块全面碰撞导致增厚下地壳物质部分熔融的产物。     

铜陵地区中酸性侵入岩的懈体岩石学研究

铜陵地区中生代中酸性侵入岩中含有捕虏体、残余体和岩产乐包体三大类型，其中岩浆包体包堆积岩包体、堆积晶包体、混杂岩包体和冷凝边包体。各类石包体的岩石学、矿物学、地球化学特征均不相同，反映了它们成因上的差异。